Development of novel force-limiting grasping forceps with a simple mechanism

Development of novel force-limiting grasping forceps with a simple mechanism Abstract OBJECTIVES In endoscopic surgery, fragile tissues may be damaged by the application of excessive force. Thus, we developed novel endoscopic forceps with a simple force-limiting mechanism. METHODS The novel forceps were constructed with a leaf spring, and the spring thickness determines grasping pressure. We established an evaluation system (maximum score is 11 points) for lung tissue damage leading to complications. We tested the conventional forceps (186.8 kPa) and 3 novel spring forceps with the following thicknesses: 1.3 mm (53.0 kPa), 2.2 mm (187.7 kPa) and 2.8 mm (369.2 kPa). After grasping, peripheral canine lung tissues were microscopically examined for acute- and late-phase damages. RESULTS In the acute phase (20 sites), the novel forceps caused capillary congestion and haemorrhage in the subpleural tissue, whereas the conventional forceps caused deep tissue and pleural damages. In the late phase (30 sites), both forceps caused fibroblast formation and interstitial thickening, which progressed to the deeper tissues as grasping pressure increased. In the acute phase, the median scores were 2.0 and 6.0 for the novel and conventional forceps, respectively (P = 0.003). In the late phase, the median scores were 2.0, 2.5 and 5.0 for 1.3-, 2.2- and 2.8-mm thick forceps, respectively, and 5.0 for the conventional forceps (P < 0.001). In both phases, the novel forceps with grasping pressure set below 187.7 kPa (2.2 mm) caused significantly less lung tissue damage than the conventional forceps. CONCLUSIONS The novel endoscopic forceps are able to regulate the tissue-grasping pressure and induce less damage in lung tissues than conventional forceps. Grasping forceps , Force-limiting mechanism , Lung tissue damage , Novel instrument INTRODUCTION The use of endoscopic and robot-assisted surgery has become increasingly common in recent years. While conventional open surgeries are conducted through direct visualization and manipulation of the surgical site, endoscopic surgeries are performed based on visual information via a monitor and weak haptic feedback through surgical tools [1]. Robot-assisted surgery is an advanced form of endoscopic surgery that is performed using only visual information displayed on a monitor, which deprives surgeons from any haptic feedback during the procedure. Due to the technical difficulties inherent in endoscopic and robot-assisted surgery, inexperienced surgeons may damage fragile tissues through the application of excessive force [2–4]. Studies have been conducted on the learning curve for robot-assisted surgical training [5], and various instruments have been developed in attempts to resolve the issues in minimally invasive surgery [6–9]. Nevertheless, the case experience, technical skills and training of individual surgeons remain important factors for surgical success [5, 6, 10–12]. As an alternative approach, studies have also focused on systems that provide haptic feedback from forceps during robot-assisted surgery [13]. However, these generally rely on complicated systems involving computer processing, sensor installation in the forceps and extensive calibration. As a consequence, these systems are difficult to implement in a clinical setting. With a focus on the fundamental surgical technique of tissue grasping, we developed novel types of endoscopic forceps equipped with a simple mechanism to regulate the upper limit of tissue-grasping pressure. The upper limit of the pressure applied to the object grasped when the forceps handle is gripped is designed not to change and remains constant while the mechanism is operating. In addition, the lung was selected as the target organ for this study. Similar to other fragile tissue organs, improper handling during lung surgery can cause major postoperative complications [14–16]. To determine the appropriate grasping pressure needed for manipulating lung tissues, tissue damage levels caused by these novel forceps at different grasping pressures were evaluated in a normal canine lung. MATERIALS AND METHODS Animal statements and animal care In this study, including preliminary experiments, 8 adult beagle dogs were used to evaluate the level of grasping-induced damage to living normal lung tissues. The animal experiments were performed under a protocol approved by Kyoto University’s Committee for Animal Research (R15–91-2). All surgical procedures were performed by a board-certified surgeon. The anaesthetic method used for the experiments was as follows: each dog was first pretreated with 0.03 mg/kg of atropine sulphate and subsequently sedated by an intramuscular injection of 15 mg/kg of ketamine hydrochloride and 7 mg/kg of xylazine. Intubation was performed, and general anaesthesia was maintained through the inhalation of sevoflurane and oxygen. The dogs were sacrificed using deep anaesthesia. All dogs were treated humanely in compliance with the 8th edition of the Guide for the Care and Use of Laboratory Animals published by the National Institutes of Health. Force-limiting forceps The force-limiting mechanism of the novel endoscopic forceps is registered under Japanese patent number 5629357 and was manufactured according to our specifications by HOGY Medical Co., Ltd. (Tokyo, Japan). This mechanism is illustrated in Fig. 1. The leaf spring on the gripping lever of the pivoting handle of the forceps deflects in response to the resistance force generated by grasping the target tissue. A protruding structure with comb-like teeth on the fixed handle engages a receiving groove on the gripping lever. The movement of the pivoting handle is stopped when the comb-like teeth on the fixed handle engage with corresponding notches in the receiving groove, which enables grasping pressure restriction (Fig. 1A–C). In this force-limiting mechanism, the grasping pressure is determined by the thickness of the leaf spring, and the grasping of a target object can be performed under consistent pressure regardless of the target object’s thickness. The handle body (including the leaf spring) of our novel forceps was fabricated using martensitic stainless steel. To prevent misalignment during engagement, the pivoting handle and spring mechanism were separated (Fig. 1D). As this study focused on tissue grasping, our novel forceps were equipped with a double-action upward curved (DAUC) grasping jaw assembly (HJ1112; HOGY Medical Co., Ltd.) for analysis. Figure 1: View largeDownload slide The novel forceps and its force-limiting mechanism. (A) The leaf spring (arrow) on the gripping lever of the pivoting handle deflects in response to the resistance force generated by grasping the target tissue. (B, C) A protruding structure with comb-like teeth on the fixed handle engages a receiving groove on the gripping lever of the pivoting handle. The movement of the pivoting handle is stopped when the comb-like teeth on the fixed handle engage with corresponding notches in the receiving groove, thereby enabling the restriction of the grasping pressure. (D) The pivoting handle (arrowhead) and spring mechanism (arrow) were structurally separated in the force-limiting forceps used in this study. Figure 1: View largeDownload slide The novel forceps and its force-limiting mechanism. (A) The leaf spring (arrow) on the gripping lever of the pivoting handle deflects in response to the resistance force generated by grasping the target tissue. (B, C) A protruding structure with comb-like teeth on the fixed handle engages a receiving groove on the gripping lever of the pivoting handle. The movement of the pivoting handle is stopped when the comb-like teeth on the fixed handle engage with corresponding notches in the receiving groove, thereby enabling the restriction of the grasping pressure. (D) The pivoting handle (arrowhead) and spring mechanism (arrow) were structurally separated in the force-limiting forceps used in this study. Measurement of grasping pressure The measuring device used to estimate the grasping pressure of the novel forceps is shown in Fig. 2. This device contained a very thin uniaxial load cell as a force sensor (TL2-TN-100N; Tec Gihan Co., Ltd., Kyoto, Japan). The measurement site, which incorporated the load cell, had a thickness of 4.5 mm, and grasping pressure was measured by directly applying the forceps to this section (Fig. 2A–D). We measured the grasping pressure of force-limiting DAUC forceps (Fig. 3A) with spring thicknesses of 0.9 mm (hereinafter referred to as ‘DAUC 0.9’), 1.3 mm (‘DAUC 1.3’), 1.6 mm (‘DAUC 1.6’), 2.2 mm (‘DAUC 2.2’) and 2.8 mm (‘DAUC 2.8’). As a control, we also measured the grasping pressure of conventional lung grasping (CLG) forceps (AE15C; YDM Co., Ltd., Tokyo, Japan) with a ratchet mechanism (Fig. 3B). Here, we analysed CLG forceps with 1–4 ratchet teeth. CLG forceps are generally used for retracting lung tissues not only in open surgeries but also in video-assisted thoracoscopic surgeries. Figure 2: View largeDownload slide Device for measuring grasping pressure. (A, B) The measuring device contained a 4.5-mm-thick uniaxial load cell. (C, D) The forceps were directly applied to the centre of the sensor to measure their grasping pressure. Figure 2: View largeDownload slide Device for measuring grasping pressure. (A, B) The measuring device contained a 4.5-mm-thick uniaxial load cell. (C, D) The forceps were directly applied to the centre of the sensor to measure their grasping pressure. Figure 3: View largeDownload slide Forceps tips used in the evaluation of grasping pressure. (A) Double-action upward curved grasping forceps tips for endoscopic surgery were used in the novel force-limiting forceps. (B) Conventional lung grasping forceps were used as the control. Figure 3: View largeDownload slide Forceps tips used in the evaluation of grasping pressure. (A) Double-action upward curved grasping forceps tips for endoscopic surgery were used in the novel force-limiting forceps. (B) Conventional lung grasping forceps were used as the control. Grading of grasping-induced lung tissue damage As a preliminary experiment, 3 dogs were used, and the levels of damage to the living lung tissues induced by a Maryland endoscopic dissector (HJ1019; HOGY Medical Co., Ltd.) with grasping pressure of 750.5 kPa were examined. All lung tissue samples were grasped for 30 min and subsequently examined at 2 time points: immediately after grasping (acute phase) and 1 week after grasping (late phase). The grasping sites were set at the periphery of the lung (Fig. 4A and B). Prior to microscopic examination, the lungs were resected, stretched and fixed with formalin. The grasped tissue was stained with both haematoxylin–eosin and Elastica van Gieson stains, and the stained specimens were used for parenchyma and pleural evaluations, respectively. The findings were confirmed by a pathologist without information on which forceps were used. In the acute phase, the tissue was examined with a focus on pleural changes, alveolar structural changes, bleeding and haematoma (Fig. 5A–C). In the late phase, the tissue was examined for fibroblast formation and interstitial thickening (Fig. 5D–F). Based on this preliminary evaluation and the findings of a previous report [17], we established a grading system for the evaluation of grasping-induced lung tissue damage. The descriptions of the different grades in each parameter are provided in Table 1. Table 1: Pathological lung tissue damage grading system Evaluation item Description Grade Points Alveolar structural changes No alveolar structural changes observed Grade 0 0 Alveolar structural changes observed only beneath the pleura Grade 1 1 Alveolar structural changes observed in deeper tissue Grade 2 2 Atelectasis or destruction of alveolar structure Grade 3 3 Intrapulmonary haemorrhage or haematoma of lung parenchyma No intrapulmonary haemorrhage/haematoma observed Grade 0 0 Intrapulmonary haemorrhage/haematoma observed only beneath the pleura Grade 1 1 Intrapulmonary haemorrhage/haematoma observed in deeper tissue Grade 2 2 Congestion of alveolar capillaries (acute phase) No congestion of alveolar capillaries observed Grade 0 0 Congestion of alveolar capillaries observed only beneath the pleura Grade 1 1 Congestion of alveolar capillaries observed in deeper tissue Grade 2 2 Fibroblast formation (Late phase) No fibroblast formation observed Grade 0 0 Fibroblast formation observed only beneath the pleura Grade 1 1 Fibroblast formation observed in deeper tissue Grade 2 2 Interstitial thickening No interstitial thickening observed 0 Interstitial thickening observed 1 Pleural rupture No pleural rupture observed 0 Pleural rupture observed 1 Pleural deformity or thickening No pleural deformity/thickening observed 0 Pleural deformity/thickening observed 1 Pleural surface bleeding (haematoma) or fibrin deposition No pleural surface bleeding (haematoma)/fibrin deposition observed 0 Pleural surface bleeding (haematoma)/fibrin deposition observed 1 Maximum score 11 points Evaluation item Description Grade Points Alveolar structural changes No alveolar structural changes observed Grade 0 0 Alveolar structural changes observed only beneath the pleura Grade 1 1 Alveolar structural changes observed in deeper tissue Grade 2 2 Atelectasis or destruction of alveolar structure Grade 3 3 Intrapulmonary haemorrhage or haematoma of lung parenchyma No intrapulmonary haemorrhage/haematoma observed Grade 0 0 Intrapulmonary haemorrhage/haematoma observed only beneath the pleura Grade 1 1 Intrapulmonary haemorrhage/haematoma observed in deeper tissue Grade 2 2 Congestion of alveolar capillaries (acute phase) No congestion of alveolar capillaries observed Grade 0 0 Congestion of alveolar capillaries observed only beneath the pleura Grade 1 1 Congestion of alveolar capillaries observed in deeper tissue Grade 2 2 Fibroblast formation (Late phase) No fibroblast formation observed Grade 0 0 Fibroblast formation observed only beneath the pleura Grade 1 1 Fibroblast formation observed in deeper tissue Grade 2 2 Interstitial thickening No interstitial thickening observed 0 Interstitial thickening observed 1 Pleural rupture No pleural rupture observed 0 Pleural rupture observed 1 Pleural deformity or thickening No pleural deformity/thickening observed 0 Pleural deformity/thickening observed 1 Pleural surface bleeding (haematoma) or fibrin deposition No pleural surface bleeding (haematoma)/fibrin deposition observed 0 Pleural surface bleeding (haematoma)/fibrin deposition observed 1 Maximum score 11 points Seven items were used to assess the tissue damage in the acute phase (immediately after grasping) and late phase (1 week after grasping). The maximum score in both phases was 11 points. Table 1: Pathological lung tissue damage grading system Evaluation item Description Grade Points Alveolar structural changes No alveolar structural changes observed Grade 0 0 Alveolar structural changes observed only beneath the pleura Grade 1 1 Alveolar structural changes observed in deeper tissue Grade 2 2 Atelectasis or destruction of alveolar structure Grade 3 3 Intrapulmonary haemorrhage or haematoma of lung parenchyma No intrapulmonary haemorrhage/haematoma observed Grade 0 0 Intrapulmonary haemorrhage/haematoma observed only beneath the pleura Grade 1 1 Intrapulmonary haemorrhage/haematoma observed in deeper tissue Grade 2 2 Congestion of alveolar capillaries (acute phase) No congestion of alveolar capillaries observed Grade 0 0 Congestion of alveolar capillaries observed only beneath the pleura Grade 1 1 Congestion of alveolar capillaries observed in deeper tissue Grade 2 2 Fibroblast formation (Late phase) No fibroblast formation observed Grade 0 0 Fibroblast formation observed only beneath the pleura Grade 1 1 Fibroblast formation observed in deeper tissue Grade 2 2 Interstitial thickening No interstitial thickening observed 0 Interstitial thickening observed 1 Pleural rupture No pleural rupture observed 0 Pleural rupture observed 1 Pleural deformity or thickening No pleural deformity/thickening observed 0 Pleural deformity/thickening observed 1 Pleural surface bleeding (haematoma) or fibrin deposition No pleural surface bleeding (haematoma)/fibrin deposition observed 0 Pleural surface bleeding (haematoma)/fibrin deposition observed 1 Maximum score 11 points Evaluation item Description Grade Points Alveolar structural changes No alveolar structural changes observed Grade 0 0 Alveolar structural changes observed only beneath the pleura Grade 1 1 Alveolar structural changes observed in deeper tissue Grade 2 2 Atelectasis or destruction of alveolar structure Grade 3 3 Intrapulmonary haemorrhage or haematoma of lung parenchyma No intrapulmonary haemorrhage/haematoma observed Grade 0 0 Intrapulmonary haemorrhage/haematoma observed only beneath the pleura Grade 1 1 Intrapulmonary haemorrhage/haematoma observed in deeper tissue Grade 2 2 Congestion of alveolar capillaries (acute phase) No congestion of alveolar capillaries observed Grade 0 0 Congestion of alveolar capillaries observed only beneath the pleura Grade 1 1 Congestion of alveolar capillaries observed in deeper tissue Grade 2 2 Fibroblast formation (Late phase) No fibroblast formation observed Grade 0 0 Fibroblast formation observed only beneath the pleura Grade 1 1 Fibroblast formation observed in deeper tissue Grade 2 2 Interstitial thickening No interstitial thickening observed 0 Interstitial thickening observed 1 Pleural rupture No pleural rupture observed 0 Pleural rupture observed 1 Pleural deformity or thickening No pleural deformity/thickening observed 0 Pleural deformity/thickening observed 1 Pleural surface bleeding (haematoma) or fibrin deposition No pleural surface bleeding (haematoma)/fibrin deposition observed 0 Pleural surface bleeding (haematoma)/fibrin deposition observed 1 Maximum score 11 points Seven items were used to assess the tissue damage in the acute phase (immediately after grasping) and late phase (1 week after grasping). The maximum score in both phases was 11 points. Figure 4: View largeDownload slide Application of the forceps to canine lungs. (A) Grasping of canine lung tissue by the force-limiting double-action upward curved forceps. (B) Grasping of canine lung tissue by conventional lung grasping forceps with 2 ratchet teeth. Peripheral lung tissue was grasped continuously for 30 min in all cases. The grasped tissue was marked with nylon suture. Figure 4: View largeDownload slide Application of the forceps to canine lungs. (A) Grasping of canine lung tissue by the force-limiting double-action upward curved forceps. (B) Grasping of canine lung tissue by conventional lung grasping forceps with 2 ratchet teeth. Peripheral lung tissue was grasped continuously for 30 min in all cases. The grasped tissue was marked with nylon suture. Figure 5: View largeDownload slide Evaluation of lung tissue damage grade on representative examples. Acute-phase microscopic changes: (A) tissue section from the acute phase (immediately after grasping the tissue for 30 min) stained with haematoxylin and eosin; (B, C) in this specimen, the tissue showed alveolar structural changes (Grade 2), bleeding (Grade 2), alveolar capillary congestion (Grade 2), interstitial thickening, pleural rupture, pleural deformity and pleural surface bleeding. Late-phase microscopic changes: (D) tissue section from the late phase (1 week after grasping the tissue for 30 min) stained with haematoxylin and eosin; (E, F) in this specimen, the tissue showed alveolar structural changes (Grade 3), fibroblast formation (Grade 2), interstitial thickening and pleural thickening. The grades of tissue damage are described in the table. Figure 5: View largeDownload slide Evaluation of lung tissue damage grade on representative examples. Acute-phase microscopic changes: (A) tissue section from the acute phase (immediately after grasping the tissue for 30 min) stained with haematoxylin and eosin; (B, C) in this specimen, the tissue showed alveolar structural changes (Grade 2), bleeding (Grade 2), alveolar capillary congestion (Grade 2), interstitial thickening, pleural rupture, pleural deformity and pleural surface bleeding. Late-phase microscopic changes: (D) tissue section from the late phase (1 week after grasping the tissue for 30 min) stained with haematoxylin and eosin; (E, F) in this specimen, the tissue showed alveolar structural changes (Grade 3), fibroblast formation (Grade 2), interstitial thickening and pleural thickening. The grades of tissue damage are described in the table. In the acute phase, we evaluated the following 7 tissue damage parameters with a maximum score of 11 points: (i) changes in alveolar structure were assigned a value of 0–3 points; (ii) intrapulmonary haemorrhage or haematoma formation in the lung parenchyma and (iii) congestion of the alveolar capillaries were assigned values of 0–2 points; and (iv) interstitial thickening, (v) pleural rupture, (vi) pleural deformity or thickening and (vii) pleural surface bleeding (haematoma) or fibrin deposition were assigned values of 0 or 1 point. In the late phase, tissue damage was also assessed using 7 parameters. However, congestion of the alveolar capillaries was replaced by fibroblast formation, which was also assigned a value of 0–2 points. These parameters are selected based on postoperative complications. Animal experiment protocol Five dogs were used for the evaluation of grasping-induced lung tissue damage. Two and 3 dogs were used for acute- and late-phase experiments, respectively. All test sites were in the right lungs. The total number of test sites per right lung varied from 8 to 12 according to the size of each lung. Sample size was determined from preliminary experiments: 5 and 7 sites were needed in each group of the acute and late phases, respectively. In the late phase, since there was a possibility that the grasping part might be undetectable within 1 week after grasping, 9 grasping sites including spare sites were created in each group. After grasping the lung tissues, the collapse of the target lung was released at chest closure by pressurization with a ventilator. Dogs used for the acute-phase experiments were sacrificed after closure, whereas those used for late-phase experiments were sacrificed after bleeding for 1 week. After the sacrifice, the right lung was removed and fixed in formalin, and only the part, which could be sufficiently confirmed as a test site, was cut out as a sample. The same test site was stained by haematoxylin–eosin and Elastica van Gieson stains and confirmed by the same method as grading system creation. Comparative evaluation of grasping-induced lung tissue damage among the force-limiting double-action upward curved forceps and the conventional lung grasping forceps Based on the grading system described above, we evaluated the damage induced by 3 different versions of the force-limiting DAUC forceps (DAUC 1.3, DAUC 2.2 and DAUC2.8). As a control, we also analysed the damage induced by the CLG forceps with 2 ratchet teeth. The DAUC 0.9 forceps were unable to firmly grip the lung tissue due to inadequate grasping pressure, and thus they were excluded from this analysis. The DAUC 1.6 forceps were also excluded because of their similar grasping pressure with the DAUC 1.3 forceps. For the assessment of acute-phase damage, we assessed 5 test sites in the tissue samples for each of the 4 forceps immediately after 30 min of grasping. For the assessment of late-phase damage, we assessed 9 test sites in the tissue samples for each of the 4 forceps after 1 week had passed. Test sites that demonstrated lung tissue damage were identified and evaluated. Statistical analyses Data groups for each of the acute- and late-phase groups were evaluated for normal distribution using the Shapiro–Wilk test. One-way analysis of variance was performed among the data groups according to the normal distribution, and honestly significant difference test of Tukey–Kramer was performed in comparison of each of the 2 groups. The Kruskal–Wallis test was performed among the data groups not following the normal distribution, and honestly significant difference test of Tukey–Kramer was performed in comparison of each of the 2 groups. In all the tests, a P-value <0.05 was considered as statistically significant. All statistical analyses were performed using JMP Pro® 13 (SAS Institute Inc., Cary, NC, USA). RESULTS Grasping pressure Figure 6 shows the measured grasping pressures of the force-limiting DAUC forceps and the CLG forceps. In the DAUC forceps, grasping pressure increased with increasing spring thickness. Among the 5 measured spring thicknesses (0.9, 1.3, 1.6, 2.2 and 2.8 mm), the grasping pressures ranged from 22.7 to 369.2 kPa. In the CLG forceps, we observed a linear increase in the grasping pressure as the number of ratchet teeth increased; the grasping pressures ranged from 147.2 to 263.9 kPa. Figure 6: View largeDownload slide Measured grasping pressures of the double-action upward curved forceps and the conventional lung grasping forceps. In the double-action upward curved forceps, grasping pressure increased with increasing spring thickness. In the conventional lung grasping forceps, grasping pressure increased linearly as the number of ratchet teeth increased. Figure 6: View largeDownload slide Measured grasping pressures of the double-action upward curved forceps and the conventional lung grasping forceps. In the double-action upward curved forceps, grasping pressure increased with increasing spring thickness. In the conventional lung grasping forceps, grasping pressure increased linearly as the number of ratchet teeth increased. Acute-phase damage induced by the force-limiting double-action upward curved forceps and the conventional lung grasping forceps Acute-phase damage to the lung tissue samples was confirmed in all 20 test sites immediately after being grasped by the 3 DAUC forceps (DAUC 1.3, DAUC 2.2 and DAUC 2.8) and the CLG forceps. The acute-phase damage scores are summarized in Supplementary Material, Table S1. The DAUC forceps caused alveolar capillary congestion and intrapulmonary haemorrhage in the lung tissue samples, but the damage was relatively superficial (within 500 μm). In addition, the DAUC forceps had a limited effect on the pleura. In contrast, the CLG forceps caused various types of tissue damage, including alveolar structural changes, pleural damage, intrapulmonary haemorrhage and alveolar capillary congestion. Late-phase damage induced by the force-limiting double-action upward curved forceps and the conventional lung grasping forceps Late-phase damage to the lung tissue samples was confirmed in 30 of the 36 test sites. DAUC 1.3 and DAUC 2.2 forceps each resulted in damage to 8 test sites; the DAUC 2.8 forceps and the CLG forceps each resulted in damage to 7 test sites. The late-phase damage scores are summarized in Supplementary Material, Table S2. Both the force-limiting DAUC forceps and CLG forceps caused alveolar structural changes, fibroblast formation and interstitial thickening. These changes tended to progress to the deeper tissues as grasping pressure increased. Comparative evaluation of grasping-induced lung tissue damage among the force-limiting double-action upward curved forceps and the conventional lung grasping forceps Figure 7 shows the comparison of lung tissue damage scores among the different forceps. There were no significant differences in acute-phase damage (Fig. 7A) among the DAUC forceps with different spring thicknesses (P = 0.689). However, the CLG forceps caused more severe tissue damage than all of the DAUC forceps (P = 0.003). The CLG forceps had a median acute-phase damage score of 6.0, which was thrice that of the DAUC forceps (2.0). Figure 7: View largeDownload slide Box-plot comparison of lung tissue damage scores between the DAUC forceps and the conventional lung grasping forceps. (A) Comparison of acute-phase tissue damage scores among the force-limiting DAUC forceps with 3 different spring thicknesses and the CLG forceps with 2 ratchet teeth. There were no significant differences in tissue damage among the DAUC forceps, but these forceps caused significantly less tissue damage than the CLG forceps with 2 ratchet teeth. (B) Comparison of late-phase tissue damage scores among the force-limiting DAUC forceps with 3 different spring thicknesses and the CLG forceps with 2 ratchet teeth. There was no significant difference in tissue damage between the DAUC 1.3 and DAUC 2.2 forceps. However, the DAUC 2.8 forceps caused significantly more tissue damage than the other 2 DAUC forceps and had a similar tissue damage score as the CLG forceps with 2 ratchet teeth. DAUC 1.3, DAUC 2.2 and DAUC 2.8 refer to DAUC forceps with spring thicknesses of 1.3, 2.2 and 2.8 mm, respectively. CLG: conventional lung grasping; DAUC: double-action upward curved. Figure 7: View largeDownload slide Box-plot comparison of lung tissue damage scores between the DAUC forceps and the conventional lung grasping forceps. (A) Comparison of acute-phase tissue damage scores among the force-limiting DAUC forceps with 3 different spring thicknesses and the CLG forceps with 2 ratchet teeth. There were no significant differences in tissue damage among the DAUC forceps, but these forceps caused significantly less tissue damage than the CLG forceps with 2 ratchet teeth. (B) Comparison of late-phase tissue damage scores among the force-limiting DAUC forceps with 3 different spring thicknesses and the CLG forceps with 2 ratchet teeth. There was no significant difference in tissue damage between the DAUC 1.3 and DAUC 2.2 forceps. However, the DAUC 2.8 forceps caused significantly more tissue damage than the other 2 DAUC forceps and had a similar tissue damage score as the CLG forceps with 2 ratchet teeth. DAUC 1.3, DAUC 2.2 and DAUC 2.8 refer to DAUC forceps with spring thicknesses of 1.3, 2.2 and 2.8 mm, respectively. CLG: conventional lung grasping; DAUC: double-action upward curved. In the analysis of late-phase damage (Fig. 7B), the DAUC 2.8 forceps caused more tissue damage than the DAUC 1.3 and DAUC 2.2 forceps (P = 0.002). Higher grasping pressure, therefore, caused more severe late-phase damage, and the pressure threshold was between 187.7 (2.2-mm spring thickness) and 369.2 kPa (2.8-mm spring thickness). There was no significant difference in lung tissue damage between the CLG and DAUC2.8 forceps (Fig. 7B). These 2 forceps each had a median late-phase damage score of 5.0, which was approximately twice that of the other 2 DAUC forceps (2.5–3.0). DISCUSSION The primary aim of this study was to develop a simple endoscopic surgical instrument that facilitates the safe and stable manipulation of tissue without the need for extensive training or surgical skill. Through the production of several prototypes, we were able to successfully develop force-limiting endoscopic forceps that fulfilled these criteria. This study also determined the appropriate grasping pressure for the DAUC forceps. In the acute phase, there were no significant differences in tissue damage among the DAUC forceps with different spring thicknesses. However, the higher grasping pressure in the DAUC forceps with thicker springs resulted in more late-phase damage, with the DAUC 2.8 forceps causing significantly more damage compared to those with thinner springs. Based on these findings, we determined that the appropriate grasping pressure for safe manipulation ranged between 53.0 and 187.7 kPa. Taking into account that a higher grasping pressure during surgery would allow a firmer grip of the target tissue with less slippage, we concluded that the DAUC 2.2 forceps (187.7 kPa) would be optimal for surgical use. We further compared the DAUC 2.2 forceps with the CLG forceps. From the results, the damage score of DAUC 2.2 was less than that of the CLG forceps in both phases. As a prerequisite for comparison, while the size and shape of the forceps tips differed between the DAUC and CLG forceps, the basic structure of the interacting grasping surfaces was almost identical and the pressure per unit area was matched with kPa. This result could be due to the fact that the grasped lung tissue was over 4.5 mm, which was the load cell thickness, and that the grasping pressure of the DAUC forceps was independent of tissue thickness, but the actual grasping pressure of the CLG forceps depends on thicker tissues and exceeds the predetermined pressure of 186.8 kPa. From the above results, it was shown that the DAUC forceps set at an optimal grasping pressure are superior to the CLG forceps in the safe handling of tissues with varying thicknesses. Here, emphysema and fibrotic lungs, wherein pleural damage is a critical point, cannot be prepared for these diseased dog lung models, and thus we cannot perform the same evaluation as this study. The determination of optimal spring thickness for these diseased lungs will be derived based on evaluation in clinical trials after approval. In these clinical trials for fragile lungs, such as fibrotic lung and emphysema, it is initially recommended to use 1.3-mm (53.0 kPa) spring thickness to set the weakest pressure that can grasp a normal lung. To our knowledge, only our previous report has examined the relationship between grasping and biological tissue damage [17]. In this report, we investigated the grasping lung tissue damage of conventional forceps using the semi-quantitative evaluation, but we did not consider the relationship between grasping pressure and lung tissue damage [17]. Here, we examined these, and the results will be benchmarks in future similar studies. A study of colon tissues, examining instruments and grasping pressure, has shown that colon thickness decreases as the grasping pressure increases and, from this result, it is possible to reduce the tissue damage by controlling the grasping pressure with real time assessment [18]. The liver is relatively advanced with respect to grasping damage, and a safety margin is derived by examining the grasping pressure and time [19–21]. In our novel forceps, because the forceps tips can be selected by exchanging the shaft, we can also study other organs apart from the lungs in the future. We believe that it is useful to incorporate this force-limiting mechanism in robot-assisted surgery in future studies. In robot-assisted surgery, minimally invasive surgery is performed because the motion range of forceps is expanding in a narrow space. However, this type of surgery lacks haptic feedback, and various studies have been conducted to address this problem [13], but there is still no definite answer. Instead of providing haptic feedback, a force-limiting mechanism of our novel forceps can also be used to safeguard the tissues against excessive grasping. When a reasonable haptic feedback system is developed, together with this mechanism, the surgeon’s excellent technique can be reflected in robot-assisted surgery and further safety can be provided to the patient. Limitations This study had several limitations that should be considered in the interpretation of its findings. First, the study involved normal canine lungs and not emphysematous lungs that require cautious and gentle manipulation. Second, thoracic drainage after thoracotomy was not performed, despite it being standard postoperative management for human patients. The thoracic cavity could not be managed using continuous negative pressure suction, and the lungs could not be fully expanded during the experimental procedures. Third, only the peripheral lung tissue was used for the evaluation, and we did not test the forceps in other areas, such as the hilar region and the central portion of the lobe. CONCLUSION We developed novel endoscopic forceps with a force-limiting mechanism that ensures a predetermined maximum grasping pressure independent of the target tissue’s thickness. These forceps, when set to an optimal grasping pressure, allowed the manipulation of lung tissue with less damage than conventional forceps. SUPPLEMENTARY MATERIAL Supplementary material is available at EJCTS online. ACKNOWLEDGEMENTS The authors thank Ryuichi Yamada, Motonori Aoshima, Koichi Matsushita of HOGY Medical Co., Ltd. (Tokyo, Japan) and Toshiharu Nashimoto of Nashimoto Industries Co., Ltd. (Niigata, Japan) for designing and creating the forceps, and also helping in the animal experiments. Funding This work was supported by the HOGY Medical Co., Ltd., Tokyo, Japan [to T.S. and H.D.]. Conflict of interest: none declared. REFERENCES 1 Tholey G , Desai JP , Castellanos AE. Force feedback plays a significant role in minimally invasive surgery: results and analysis . Ann Surg 2005 ; 241 : 102 – 9 . Google Scholar PubMed 2 Marucci DD , Shakeshaft AJ , Cartmill JA , Cox MR , Adams SG , Martin CJ. Grasper trauma during laparoscopic cholecystectomy . Aust Nz J Surg 2000 ; 70 : 578 – 81 . Google Scholar CrossRef Search ADS 3 Sotelo RJ , Haese A , Machuca V , Medina L , Nuñez L , Santinelli F et al. Safer surgery by learning from complications: a focus on robotic prostate surgery . Eur Urol 2016 ; 69 : 334 – 44 . Google Scholar CrossRef Search ADS PubMed 4 Solaini L , Prusciano F , Bagioni P , di Francesco F , Solaini L , Poddie DB. Video-assisted thoracic surgery (VATS) of the lung: analysis of intraoperative and postoperative complications over 15 years and review of the literature . Surg Endosc 2008 ; 22 : 298 – 310 . Google Scholar CrossRef Search ADS PubMed 5 Jiménez-Rodríguez RM , Rubio-Dorado-Manzanares M , Díaz-Pavón JM , Reyes-Díaz ML , Vazquez-Monchul JM , Garcia-Cabrera AM et al. Learning curve in robotic rectal cancer surgery: current state of affairs . Int J Colorectal Dis 2016 ; 31 : 1807 – 15 . Google Scholar CrossRef Search ADS PubMed 6 Horeman T , Rodrigues SP , Van Den Dobbelsteen JJ , Jansen FW , Dankelman J. Visual force feedback in laparoscopic training . Surg Endosc 2012 ; 26 : 242 – 8 . Google Scholar CrossRef Search ADS PubMed 7 Yang K , Perez M , Hubert N , Hossu G , Perrenot C , Hubert J. Effectiveness of an integrated video recording and replaying system in robotic surgical training . Ann Surg 2017 ; 265 : 521 – 6 . 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J Robot Surg 2017 ; doi:10.1007/s11701-017-0680-6. 12 Rafiq A , Tamariz F , Boanca C , Lavrentyev V , Merrell RC. Objective assessment of training surgical skills using simulated tissue interface with real-time feedback . J Surg Educ 2008 ; 65 : 270 – 4 . Google Scholar CrossRef Search ADS PubMed 13 Johnson PJ , Schmidt DE , Duvvuri U. Output control of da Vinci surgical system’s surgical graspers . J Surg Res 2014 ; 186 : 56 – 62 . Google Scholar CrossRef Search ADS PubMed 14 Ueda K , Tanaka T , Li TS , Tanaka N , Hamano K. Sutureless pneumostasis using bioabsorbable mesh and glue during major lung resection for cancer: who are the best candidates? J Thorac Cardiovasc Surg 2010 ; 139 : 600 – 5 . Google Scholar CrossRef Search ADS PubMed 15 Satoh Y. Management of chest drainage tubes after lung surgery . Gen Thorac Cardiovasc Surg 2016 ; 64 : 305 – 8 . Google Scholar CrossRef Search ADS PubMed 16 Fournel L , Zaimi R , Grigoroiu M , Stern JB , Gossot D. Totally thoracoscopic major pulmonary resections: an analysis of perioperative complications . Ann Thorac Surg 2014 ; 97 : 419 – 24 . Google Scholar CrossRef Search ADS PubMed 17 Muranishi Y , Sato T , Yutaka Y , Sakaguchi Y , Komatsu T , Yoshizawa A et al. Development of a novel lung-stabilizing device for VATS procedures . Surg Endosc 2017 ; 31 : 4260 – 7 . Google Scholar CrossRef Search ADS PubMed 18 Chandler JH , Mushtaq F , Moxley-Wyles B , West NP , Taylor GW , Culmer PR. Real-time assessment of mechanical tissue trauma in surgery . IEEE Trans Biomed Eng 2017 ; 64 : 2384 – 93 . Google Scholar CrossRef Search ADS PubMed 19 Wang J , Yu Q-Y , Li W , Wang B-R , Zhou Z-R. Influence of clamping stress and duration on the trauma of liver tissue during surgery operation . Clin Biomech 2017 ; 43 : 58 – 66 . Google Scholar CrossRef Search ADS 20 Heijnsdijk E , Dankelman J , Gouma D. Effectiveness of grasping and duration of clamping using laparoscopic graspers . Surg Endosc 2002 ; 16 : 1329 – 31 . Google Scholar CrossRef Search ADS PubMed 21 Li W , Jia ZG , Wang J , Shi L , Zhou ZR. Zhou Friction behavior at minimally invasive grasper/liver tissue interface . Tribol Int 2015 ; 81 : 190 – 8 . Google Scholar CrossRef Search ADS © The Author(s) 2018. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png European Journal of Cardio-Thoracic Surgery Oxford University Press

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Oxford University Press
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© The Author(s) 2018. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.
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Abstract

Abstract OBJECTIVES In endoscopic surgery, fragile tissues may be damaged by the application of excessive force. Thus, we developed novel endoscopic forceps with a simple force-limiting mechanism. METHODS The novel forceps were constructed with a leaf spring, and the spring thickness determines grasping pressure. We established an evaluation system (maximum score is 11 points) for lung tissue damage leading to complications. We tested the conventional forceps (186.8 kPa) and 3 novel spring forceps with the following thicknesses: 1.3 mm (53.0 kPa), 2.2 mm (187.7 kPa) and 2.8 mm (369.2 kPa). After grasping, peripheral canine lung tissues were microscopically examined for acute- and late-phase damages. RESULTS In the acute phase (20 sites), the novel forceps caused capillary congestion and haemorrhage in the subpleural tissue, whereas the conventional forceps caused deep tissue and pleural damages. In the late phase (30 sites), both forceps caused fibroblast formation and interstitial thickening, which progressed to the deeper tissues as grasping pressure increased. In the acute phase, the median scores were 2.0 and 6.0 for the novel and conventional forceps, respectively (P = 0.003). In the late phase, the median scores were 2.0, 2.5 and 5.0 for 1.3-, 2.2- and 2.8-mm thick forceps, respectively, and 5.0 for the conventional forceps (P < 0.001). In both phases, the novel forceps with grasping pressure set below 187.7 kPa (2.2 mm) caused significantly less lung tissue damage than the conventional forceps. CONCLUSIONS The novel endoscopic forceps are able to regulate the tissue-grasping pressure and induce less damage in lung tissues than conventional forceps. Grasping forceps , Force-limiting mechanism , Lung tissue damage , Novel instrument INTRODUCTION The use of endoscopic and robot-assisted surgery has become increasingly common in recent years. While conventional open surgeries are conducted through direct visualization and manipulation of the surgical site, endoscopic surgeries are performed based on visual information via a monitor and weak haptic feedback through surgical tools [1]. Robot-assisted surgery is an advanced form of endoscopic surgery that is performed using only visual information displayed on a monitor, which deprives surgeons from any haptic feedback during the procedure. Due to the technical difficulties inherent in endoscopic and robot-assisted surgery, inexperienced surgeons may damage fragile tissues through the application of excessive force [2–4]. Studies have been conducted on the learning curve for robot-assisted surgical training [5], and various instruments have been developed in attempts to resolve the issues in minimally invasive surgery [6–9]. Nevertheless, the case experience, technical skills and training of individual surgeons remain important factors for surgical success [5, 6, 10–12]. As an alternative approach, studies have also focused on systems that provide haptic feedback from forceps during robot-assisted surgery [13]. However, these generally rely on complicated systems involving computer processing, sensor installation in the forceps and extensive calibration. As a consequence, these systems are difficult to implement in a clinical setting. With a focus on the fundamental surgical technique of tissue grasping, we developed novel types of endoscopic forceps equipped with a simple mechanism to regulate the upper limit of tissue-grasping pressure. The upper limit of the pressure applied to the object grasped when the forceps handle is gripped is designed not to change and remains constant while the mechanism is operating. In addition, the lung was selected as the target organ for this study. Similar to other fragile tissue organs, improper handling during lung surgery can cause major postoperative complications [14–16]. To determine the appropriate grasping pressure needed for manipulating lung tissues, tissue damage levels caused by these novel forceps at different grasping pressures were evaluated in a normal canine lung. MATERIALS AND METHODS Animal statements and animal care In this study, including preliminary experiments, 8 adult beagle dogs were used to evaluate the level of grasping-induced damage to living normal lung tissues. The animal experiments were performed under a protocol approved by Kyoto University’s Committee for Animal Research (R15–91-2). All surgical procedures were performed by a board-certified surgeon. The anaesthetic method used for the experiments was as follows: each dog was first pretreated with 0.03 mg/kg of atropine sulphate and subsequently sedated by an intramuscular injection of 15 mg/kg of ketamine hydrochloride and 7 mg/kg of xylazine. Intubation was performed, and general anaesthesia was maintained through the inhalation of sevoflurane and oxygen. The dogs were sacrificed using deep anaesthesia. All dogs were treated humanely in compliance with the 8th edition of the Guide for the Care and Use of Laboratory Animals published by the National Institutes of Health. Force-limiting forceps The force-limiting mechanism of the novel endoscopic forceps is registered under Japanese patent number 5629357 and was manufactured according to our specifications by HOGY Medical Co., Ltd. (Tokyo, Japan). This mechanism is illustrated in Fig. 1. The leaf spring on the gripping lever of the pivoting handle of the forceps deflects in response to the resistance force generated by grasping the target tissue. A protruding structure with comb-like teeth on the fixed handle engages a receiving groove on the gripping lever. The movement of the pivoting handle is stopped when the comb-like teeth on the fixed handle engage with corresponding notches in the receiving groove, which enables grasping pressure restriction (Fig. 1A–C). In this force-limiting mechanism, the grasping pressure is determined by the thickness of the leaf spring, and the grasping of a target object can be performed under consistent pressure regardless of the target object’s thickness. The handle body (including the leaf spring) of our novel forceps was fabricated using martensitic stainless steel. To prevent misalignment during engagement, the pivoting handle and spring mechanism were separated (Fig. 1D). As this study focused on tissue grasping, our novel forceps were equipped with a double-action upward curved (DAUC) grasping jaw assembly (HJ1112; HOGY Medical Co., Ltd.) for analysis. Figure 1: View largeDownload slide The novel forceps and its force-limiting mechanism. (A) The leaf spring (arrow) on the gripping lever of the pivoting handle deflects in response to the resistance force generated by grasping the target tissue. (B, C) A protruding structure with comb-like teeth on the fixed handle engages a receiving groove on the gripping lever of the pivoting handle. The movement of the pivoting handle is stopped when the comb-like teeth on the fixed handle engage with corresponding notches in the receiving groove, thereby enabling the restriction of the grasping pressure. (D) The pivoting handle (arrowhead) and spring mechanism (arrow) were structurally separated in the force-limiting forceps used in this study. Figure 1: View largeDownload slide The novel forceps and its force-limiting mechanism. (A) The leaf spring (arrow) on the gripping lever of the pivoting handle deflects in response to the resistance force generated by grasping the target tissue. (B, C) A protruding structure with comb-like teeth on the fixed handle engages a receiving groove on the gripping lever of the pivoting handle. The movement of the pivoting handle is stopped when the comb-like teeth on the fixed handle engage with corresponding notches in the receiving groove, thereby enabling the restriction of the grasping pressure. (D) The pivoting handle (arrowhead) and spring mechanism (arrow) were structurally separated in the force-limiting forceps used in this study. Measurement of grasping pressure The measuring device used to estimate the grasping pressure of the novel forceps is shown in Fig. 2. This device contained a very thin uniaxial load cell as a force sensor (TL2-TN-100N; Tec Gihan Co., Ltd., Kyoto, Japan). The measurement site, which incorporated the load cell, had a thickness of 4.5 mm, and grasping pressure was measured by directly applying the forceps to this section (Fig. 2A–D). We measured the grasping pressure of force-limiting DAUC forceps (Fig. 3A) with spring thicknesses of 0.9 mm (hereinafter referred to as ‘DAUC 0.9’), 1.3 mm (‘DAUC 1.3’), 1.6 mm (‘DAUC 1.6’), 2.2 mm (‘DAUC 2.2’) and 2.8 mm (‘DAUC 2.8’). As a control, we also measured the grasping pressure of conventional lung grasping (CLG) forceps (AE15C; YDM Co., Ltd., Tokyo, Japan) with a ratchet mechanism (Fig. 3B). Here, we analysed CLG forceps with 1–4 ratchet teeth. CLG forceps are generally used for retracting lung tissues not only in open surgeries but also in video-assisted thoracoscopic surgeries. Figure 2: View largeDownload slide Device for measuring grasping pressure. (A, B) The measuring device contained a 4.5-mm-thick uniaxial load cell. (C, D) The forceps were directly applied to the centre of the sensor to measure their grasping pressure. Figure 2: View largeDownload slide Device for measuring grasping pressure. (A, B) The measuring device contained a 4.5-mm-thick uniaxial load cell. (C, D) The forceps were directly applied to the centre of the sensor to measure their grasping pressure. Figure 3: View largeDownload slide Forceps tips used in the evaluation of grasping pressure. (A) Double-action upward curved grasping forceps tips for endoscopic surgery were used in the novel force-limiting forceps. (B) Conventional lung grasping forceps were used as the control. Figure 3: View largeDownload slide Forceps tips used in the evaluation of grasping pressure. (A) Double-action upward curved grasping forceps tips for endoscopic surgery were used in the novel force-limiting forceps. (B) Conventional lung grasping forceps were used as the control. Grading of grasping-induced lung tissue damage As a preliminary experiment, 3 dogs were used, and the levels of damage to the living lung tissues induced by a Maryland endoscopic dissector (HJ1019; HOGY Medical Co., Ltd.) with grasping pressure of 750.5 kPa were examined. All lung tissue samples were grasped for 30 min and subsequently examined at 2 time points: immediately after grasping (acute phase) and 1 week after grasping (late phase). The grasping sites were set at the periphery of the lung (Fig. 4A and B). Prior to microscopic examination, the lungs were resected, stretched and fixed with formalin. The grasped tissue was stained with both haematoxylin–eosin and Elastica van Gieson stains, and the stained specimens were used for parenchyma and pleural evaluations, respectively. The findings were confirmed by a pathologist without information on which forceps were used. In the acute phase, the tissue was examined with a focus on pleural changes, alveolar structural changes, bleeding and haematoma (Fig. 5A–C). In the late phase, the tissue was examined for fibroblast formation and interstitial thickening (Fig. 5D–F). Based on this preliminary evaluation and the findings of a previous report [17], we established a grading system for the evaluation of grasping-induced lung tissue damage. The descriptions of the different grades in each parameter are provided in Table 1. Table 1: Pathological lung tissue damage grading system Evaluation item Description Grade Points Alveolar structural changes No alveolar structural changes observed Grade 0 0 Alveolar structural changes observed only beneath the pleura Grade 1 1 Alveolar structural changes observed in deeper tissue Grade 2 2 Atelectasis or destruction of alveolar structure Grade 3 3 Intrapulmonary haemorrhage or haematoma of lung parenchyma No intrapulmonary haemorrhage/haematoma observed Grade 0 0 Intrapulmonary haemorrhage/haematoma observed only beneath the pleura Grade 1 1 Intrapulmonary haemorrhage/haematoma observed in deeper tissue Grade 2 2 Congestion of alveolar capillaries (acute phase) No congestion of alveolar capillaries observed Grade 0 0 Congestion of alveolar capillaries observed only beneath the pleura Grade 1 1 Congestion of alveolar capillaries observed in deeper tissue Grade 2 2 Fibroblast formation (Late phase) No fibroblast formation observed Grade 0 0 Fibroblast formation observed only beneath the pleura Grade 1 1 Fibroblast formation observed in deeper tissue Grade 2 2 Interstitial thickening No interstitial thickening observed 0 Interstitial thickening observed 1 Pleural rupture No pleural rupture observed 0 Pleural rupture observed 1 Pleural deformity or thickening No pleural deformity/thickening observed 0 Pleural deformity/thickening observed 1 Pleural surface bleeding (haematoma) or fibrin deposition No pleural surface bleeding (haematoma)/fibrin deposition observed 0 Pleural surface bleeding (haematoma)/fibrin deposition observed 1 Maximum score 11 points Evaluation item Description Grade Points Alveolar structural changes No alveolar structural changes observed Grade 0 0 Alveolar structural changes observed only beneath the pleura Grade 1 1 Alveolar structural changes observed in deeper tissue Grade 2 2 Atelectasis or destruction of alveolar structure Grade 3 3 Intrapulmonary haemorrhage or haematoma of lung parenchyma No intrapulmonary haemorrhage/haematoma observed Grade 0 0 Intrapulmonary haemorrhage/haematoma observed only beneath the pleura Grade 1 1 Intrapulmonary haemorrhage/haematoma observed in deeper tissue Grade 2 2 Congestion of alveolar capillaries (acute phase) No congestion of alveolar capillaries observed Grade 0 0 Congestion of alveolar capillaries observed only beneath the pleura Grade 1 1 Congestion of alveolar capillaries observed in deeper tissue Grade 2 2 Fibroblast formation (Late phase) No fibroblast formation observed Grade 0 0 Fibroblast formation observed only beneath the pleura Grade 1 1 Fibroblast formation observed in deeper tissue Grade 2 2 Interstitial thickening No interstitial thickening observed 0 Interstitial thickening observed 1 Pleural rupture No pleural rupture observed 0 Pleural rupture observed 1 Pleural deformity or thickening No pleural deformity/thickening observed 0 Pleural deformity/thickening observed 1 Pleural surface bleeding (haematoma) or fibrin deposition No pleural surface bleeding (haematoma)/fibrin deposition observed 0 Pleural surface bleeding (haematoma)/fibrin deposition observed 1 Maximum score 11 points Seven items were used to assess the tissue damage in the acute phase (immediately after grasping) and late phase (1 week after grasping). The maximum score in both phases was 11 points. Table 1: Pathological lung tissue damage grading system Evaluation item Description Grade Points Alveolar structural changes No alveolar structural changes observed Grade 0 0 Alveolar structural changes observed only beneath the pleura Grade 1 1 Alveolar structural changes observed in deeper tissue Grade 2 2 Atelectasis or destruction of alveolar structure Grade 3 3 Intrapulmonary haemorrhage or haematoma of lung parenchyma No intrapulmonary haemorrhage/haematoma observed Grade 0 0 Intrapulmonary haemorrhage/haematoma observed only beneath the pleura Grade 1 1 Intrapulmonary haemorrhage/haematoma observed in deeper tissue Grade 2 2 Congestion of alveolar capillaries (acute phase) No congestion of alveolar capillaries observed Grade 0 0 Congestion of alveolar capillaries observed only beneath the pleura Grade 1 1 Congestion of alveolar capillaries observed in deeper tissue Grade 2 2 Fibroblast formation (Late phase) No fibroblast formation observed Grade 0 0 Fibroblast formation observed only beneath the pleura Grade 1 1 Fibroblast formation observed in deeper tissue Grade 2 2 Interstitial thickening No interstitial thickening observed 0 Interstitial thickening observed 1 Pleural rupture No pleural rupture observed 0 Pleural rupture observed 1 Pleural deformity or thickening No pleural deformity/thickening observed 0 Pleural deformity/thickening observed 1 Pleural surface bleeding (haematoma) or fibrin deposition No pleural surface bleeding (haematoma)/fibrin deposition observed 0 Pleural surface bleeding (haematoma)/fibrin deposition observed 1 Maximum score 11 points Evaluation item Description Grade Points Alveolar structural changes No alveolar structural changes observed Grade 0 0 Alveolar structural changes observed only beneath the pleura Grade 1 1 Alveolar structural changes observed in deeper tissue Grade 2 2 Atelectasis or destruction of alveolar structure Grade 3 3 Intrapulmonary haemorrhage or haematoma of lung parenchyma No intrapulmonary haemorrhage/haematoma observed Grade 0 0 Intrapulmonary haemorrhage/haematoma observed only beneath the pleura Grade 1 1 Intrapulmonary haemorrhage/haematoma observed in deeper tissue Grade 2 2 Congestion of alveolar capillaries (acute phase) No congestion of alveolar capillaries observed Grade 0 0 Congestion of alveolar capillaries observed only beneath the pleura Grade 1 1 Congestion of alveolar capillaries observed in deeper tissue Grade 2 2 Fibroblast formation (Late phase) No fibroblast formation observed Grade 0 0 Fibroblast formation observed only beneath the pleura Grade 1 1 Fibroblast formation observed in deeper tissue Grade 2 2 Interstitial thickening No interstitial thickening observed 0 Interstitial thickening observed 1 Pleural rupture No pleural rupture observed 0 Pleural rupture observed 1 Pleural deformity or thickening No pleural deformity/thickening observed 0 Pleural deformity/thickening observed 1 Pleural surface bleeding (haematoma) or fibrin deposition No pleural surface bleeding (haematoma)/fibrin deposition observed 0 Pleural surface bleeding (haematoma)/fibrin deposition observed 1 Maximum score 11 points Seven items were used to assess the tissue damage in the acute phase (immediately after grasping) and late phase (1 week after grasping). The maximum score in both phases was 11 points. Figure 4: View largeDownload slide Application of the forceps to canine lungs. (A) Grasping of canine lung tissue by the force-limiting double-action upward curved forceps. (B) Grasping of canine lung tissue by conventional lung grasping forceps with 2 ratchet teeth. Peripheral lung tissue was grasped continuously for 30 min in all cases. The grasped tissue was marked with nylon suture. Figure 4: View largeDownload slide Application of the forceps to canine lungs. (A) Grasping of canine lung tissue by the force-limiting double-action upward curved forceps. (B) Grasping of canine lung tissue by conventional lung grasping forceps with 2 ratchet teeth. Peripheral lung tissue was grasped continuously for 30 min in all cases. The grasped tissue was marked with nylon suture. Figure 5: View largeDownload slide Evaluation of lung tissue damage grade on representative examples. Acute-phase microscopic changes: (A) tissue section from the acute phase (immediately after grasping the tissue for 30 min) stained with haematoxylin and eosin; (B, C) in this specimen, the tissue showed alveolar structural changes (Grade 2), bleeding (Grade 2), alveolar capillary congestion (Grade 2), interstitial thickening, pleural rupture, pleural deformity and pleural surface bleeding. Late-phase microscopic changes: (D) tissue section from the late phase (1 week after grasping the tissue for 30 min) stained with haematoxylin and eosin; (E, F) in this specimen, the tissue showed alveolar structural changes (Grade 3), fibroblast formation (Grade 2), interstitial thickening and pleural thickening. The grades of tissue damage are described in the table. Figure 5: View largeDownload slide Evaluation of lung tissue damage grade on representative examples. Acute-phase microscopic changes: (A) tissue section from the acute phase (immediately after grasping the tissue for 30 min) stained with haematoxylin and eosin; (B, C) in this specimen, the tissue showed alveolar structural changes (Grade 2), bleeding (Grade 2), alveolar capillary congestion (Grade 2), interstitial thickening, pleural rupture, pleural deformity and pleural surface bleeding. Late-phase microscopic changes: (D) tissue section from the late phase (1 week after grasping the tissue for 30 min) stained with haematoxylin and eosin; (E, F) in this specimen, the tissue showed alveolar structural changes (Grade 3), fibroblast formation (Grade 2), interstitial thickening and pleural thickening. The grades of tissue damage are described in the table. In the acute phase, we evaluated the following 7 tissue damage parameters with a maximum score of 11 points: (i) changes in alveolar structure were assigned a value of 0–3 points; (ii) intrapulmonary haemorrhage or haematoma formation in the lung parenchyma and (iii) congestion of the alveolar capillaries were assigned values of 0–2 points; and (iv) interstitial thickening, (v) pleural rupture, (vi) pleural deformity or thickening and (vii) pleural surface bleeding (haematoma) or fibrin deposition were assigned values of 0 or 1 point. In the late phase, tissue damage was also assessed using 7 parameters. However, congestion of the alveolar capillaries was replaced by fibroblast formation, which was also assigned a value of 0–2 points. These parameters are selected based on postoperative complications. Animal experiment protocol Five dogs were used for the evaluation of grasping-induced lung tissue damage. Two and 3 dogs were used for acute- and late-phase experiments, respectively. All test sites were in the right lungs. The total number of test sites per right lung varied from 8 to 12 according to the size of each lung. Sample size was determined from preliminary experiments: 5 and 7 sites were needed in each group of the acute and late phases, respectively. In the late phase, since there was a possibility that the grasping part might be undetectable within 1 week after grasping, 9 grasping sites including spare sites were created in each group. After grasping the lung tissues, the collapse of the target lung was released at chest closure by pressurization with a ventilator. Dogs used for the acute-phase experiments were sacrificed after closure, whereas those used for late-phase experiments were sacrificed after bleeding for 1 week. After the sacrifice, the right lung was removed and fixed in formalin, and only the part, which could be sufficiently confirmed as a test site, was cut out as a sample. The same test site was stained by haematoxylin–eosin and Elastica van Gieson stains and confirmed by the same method as grading system creation. Comparative evaluation of grasping-induced lung tissue damage among the force-limiting double-action upward curved forceps and the conventional lung grasping forceps Based on the grading system described above, we evaluated the damage induced by 3 different versions of the force-limiting DAUC forceps (DAUC 1.3, DAUC 2.2 and DAUC2.8). As a control, we also analysed the damage induced by the CLG forceps with 2 ratchet teeth. The DAUC 0.9 forceps were unable to firmly grip the lung tissue due to inadequate grasping pressure, and thus they were excluded from this analysis. The DAUC 1.6 forceps were also excluded because of their similar grasping pressure with the DAUC 1.3 forceps. For the assessment of acute-phase damage, we assessed 5 test sites in the tissue samples for each of the 4 forceps immediately after 30 min of grasping. For the assessment of late-phase damage, we assessed 9 test sites in the tissue samples for each of the 4 forceps after 1 week had passed. Test sites that demonstrated lung tissue damage were identified and evaluated. Statistical analyses Data groups for each of the acute- and late-phase groups were evaluated for normal distribution using the Shapiro–Wilk test. One-way analysis of variance was performed among the data groups according to the normal distribution, and honestly significant difference test of Tukey–Kramer was performed in comparison of each of the 2 groups. The Kruskal–Wallis test was performed among the data groups not following the normal distribution, and honestly significant difference test of Tukey–Kramer was performed in comparison of each of the 2 groups. In all the tests, a P-value <0.05 was considered as statistically significant. All statistical analyses were performed using JMP Pro® 13 (SAS Institute Inc., Cary, NC, USA). RESULTS Grasping pressure Figure 6 shows the measured grasping pressures of the force-limiting DAUC forceps and the CLG forceps. In the DAUC forceps, grasping pressure increased with increasing spring thickness. Among the 5 measured spring thicknesses (0.9, 1.3, 1.6, 2.2 and 2.8 mm), the grasping pressures ranged from 22.7 to 369.2 kPa. In the CLG forceps, we observed a linear increase in the grasping pressure as the number of ratchet teeth increased; the grasping pressures ranged from 147.2 to 263.9 kPa. Figure 6: View largeDownload slide Measured grasping pressures of the double-action upward curved forceps and the conventional lung grasping forceps. In the double-action upward curved forceps, grasping pressure increased with increasing spring thickness. In the conventional lung grasping forceps, grasping pressure increased linearly as the number of ratchet teeth increased. Figure 6: View largeDownload slide Measured grasping pressures of the double-action upward curved forceps and the conventional lung grasping forceps. In the double-action upward curved forceps, grasping pressure increased with increasing spring thickness. In the conventional lung grasping forceps, grasping pressure increased linearly as the number of ratchet teeth increased. Acute-phase damage induced by the force-limiting double-action upward curved forceps and the conventional lung grasping forceps Acute-phase damage to the lung tissue samples was confirmed in all 20 test sites immediately after being grasped by the 3 DAUC forceps (DAUC 1.3, DAUC 2.2 and DAUC 2.8) and the CLG forceps. The acute-phase damage scores are summarized in Supplementary Material, Table S1. The DAUC forceps caused alveolar capillary congestion and intrapulmonary haemorrhage in the lung tissue samples, but the damage was relatively superficial (within 500 μm). In addition, the DAUC forceps had a limited effect on the pleura. In contrast, the CLG forceps caused various types of tissue damage, including alveolar structural changes, pleural damage, intrapulmonary haemorrhage and alveolar capillary congestion. Late-phase damage induced by the force-limiting double-action upward curved forceps and the conventional lung grasping forceps Late-phase damage to the lung tissue samples was confirmed in 30 of the 36 test sites. DAUC 1.3 and DAUC 2.2 forceps each resulted in damage to 8 test sites; the DAUC 2.8 forceps and the CLG forceps each resulted in damage to 7 test sites. The late-phase damage scores are summarized in Supplementary Material, Table S2. Both the force-limiting DAUC forceps and CLG forceps caused alveolar structural changes, fibroblast formation and interstitial thickening. These changes tended to progress to the deeper tissues as grasping pressure increased. Comparative evaluation of grasping-induced lung tissue damage among the force-limiting double-action upward curved forceps and the conventional lung grasping forceps Figure 7 shows the comparison of lung tissue damage scores among the different forceps. There were no significant differences in acute-phase damage (Fig. 7A) among the DAUC forceps with different spring thicknesses (P = 0.689). However, the CLG forceps caused more severe tissue damage than all of the DAUC forceps (P = 0.003). The CLG forceps had a median acute-phase damage score of 6.0, which was thrice that of the DAUC forceps (2.0). Figure 7: View largeDownload slide Box-plot comparison of lung tissue damage scores between the DAUC forceps and the conventional lung grasping forceps. (A) Comparison of acute-phase tissue damage scores among the force-limiting DAUC forceps with 3 different spring thicknesses and the CLG forceps with 2 ratchet teeth. There were no significant differences in tissue damage among the DAUC forceps, but these forceps caused significantly less tissue damage than the CLG forceps with 2 ratchet teeth. (B) Comparison of late-phase tissue damage scores among the force-limiting DAUC forceps with 3 different spring thicknesses and the CLG forceps with 2 ratchet teeth. There was no significant difference in tissue damage between the DAUC 1.3 and DAUC 2.2 forceps. However, the DAUC 2.8 forceps caused significantly more tissue damage than the other 2 DAUC forceps and had a similar tissue damage score as the CLG forceps with 2 ratchet teeth. DAUC 1.3, DAUC 2.2 and DAUC 2.8 refer to DAUC forceps with spring thicknesses of 1.3, 2.2 and 2.8 mm, respectively. CLG: conventional lung grasping; DAUC: double-action upward curved. Figure 7: View largeDownload slide Box-plot comparison of lung tissue damage scores between the DAUC forceps and the conventional lung grasping forceps. (A) Comparison of acute-phase tissue damage scores among the force-limiting DAUC forceps with 3 different spring thicknesses and the CLG forceps with 2 ratchet teeth. There were no significant differences in tissue damage among the DAUC forceps, but these forceps caused significantly less tissue damage than the CLG forceps with 2 ratchet teeth. (B) Comparison of late-phase tissue damage scores among the force-limiting DAUC forceps with 3 different spring thicknesses and the CLG forceps with 2 ratchet teeth. There was no significant difference in tissue damage between the DAUC 1.3 and DAUC 2.2 forceps. However, the DAUC 2.8 forceps caused significantly more tissue damage than the other 2 DAUC forceps and had a similar tissue damage score as the CLG forceps with 2 ratchet teeth. DAUC 1.3, DAUC 2.2 and DAUC 2.8 refer to DAUC forceps with spring thicknesses of 1.3, 2.2 and 2.8 mm, respectively. CLG: conventional lung grasping; DAUC: double-action upward curved. In the analysis of late-phase damage (Fig. 7B), the DAUC 2.8 forceps caused more tissue damage than the DAUC 1.3 and DAUC 2.2 forceps (P = 0.002). Higher grasping pressure, therefore, caused more severe late-phase damage, and the pressure threshold was between 187.7 (2.2-mm spring thickness) and 369.2 kPa (2.8-mm spring thickness). There was no significant difference in lung tissue damage between the CLG and DAUC2.8 forceps (Fig. 7B). These 2 forceps each had a median late-phase damage score of 5.0, which was approximately twice that of the other 2 DAUC forceps (2.5–3.0). DISCUSSION The primary aim of this study was to develop a simple endoscopic surgical instrument that facilitates the safe and stable manipulation of tissue without the need for extensive training or surgical skill. Through the production of several prototypes, we were able to successfully develop force-limiting endoscopic forceps that fulfilled these criteria. This study also determined the appropriate grasping pressure for the DAUC forceps. In the acute phase, there were no significant differences in tissue damage among the DAUC forceps with different spring thicknesses. However, the higher grasping pressure in the DAUC forceps with thicker springs resulted in more late-phase damage, with the DAUC 2.8 forceps causing significantly more damage compared to those with thinner springs. Based on these findings, we determined that the appropriate grasping pressure for safe manipulation ranged between 53.0 and 187.7 kPa. Taking into account that a higher grasping pressure during surgery would allow a firmer grip of the target tissue with less slippage, we concluded that the DAUC 2.2 forceps (187.7 kPa) would be optimal for surgical use. We further compared the DAUC 2.2 forceps with the CLG forceps. From the results, the damage score of DAUC 2.2 was less than that of the CLG forceps in both phases. As a prerequisite for comparison, while the size and shape of the forceps tips differed between the DAUC and CLG forceps, the basic structure of the interacting grasping surfaces was almost identical and the pressure per unit area was matched with kPa. This result could be due to the fact that the grasped lung tissue was over 4.5 mm, which was the load cell thickness, and that the grasping pressure of the DAUC forceps was independent of tissue thickness, but the actual grasping pressure of the CLG forceps depends on thicker tissues and exceeds the predetermined pressure of 186.8 kPa. From the above results, it was shown that the DAUC forceps set at an optimal grasping pressure are superior to the CLG forceps in the safe handling of tissues with varying thicknesses. Here, emphysema and fibrotic lungs, wherein pleural damage is a critical point, cannot be prepared for these diseased dog lung models, and thus we cannot perform the same evaluation as this study. The determination of optimal spring thickness for these diseased lungs will be derived based on evaluation in clinical trials after approval. In these clinical trials for fragile lungs, such as fibrotic lung and emphysema, it is initially recommended to use 1.3-mm (53.0 kPa) spring thickness to set the weakest pressure that can grasp a normal lung. To our knowledge, only our previous report has examined the relationship between grasping and biological tissue damage [17]. In this report, we investigated the grasping lung tissue damage of conventional forceps using the semi-quantitative evaluation, but we did not consider the relationship between grasping pressure and lung tissue damage [17]. Here, we examined these, and the results will be benchmarks in future similar studies. A study of colon tissues, examining instruments and grasping pressure, has shown that colon thickness decreases as the grasping pressure increases and, from this result, it is possible to reduce the tissue damage by controlling the grasping pressure with real time assessment [18]. The liver is relatively advanced with respect to grasping damage, and a safety margin is derived by examining the grasping pressure and time [19–21]. In our novel forceps, because the forceps tips can be selected by exchanging the shaft, we can also study other organs apart from the lungs in the future. We believe that it is useful to incorporate this force-limiting mechanism in robot-assisted surgery in future studies. In robot-assisted surgery, minimally invasive surgery is performed because the motion range of forceps is expanding in a narrow space. However, this type of surgery lacks haptic feedback, and various studies have been conducted to address this problem [13], but there is still no definite answer. Instead of providing haptic feedback, a force-limiting mechanism of our novel forceps can also be used to safeguard the tissues against excessive grasping. When a reasonable haptic feedback system is developed, together with this mechanism, the surgeon’s excellent technique can be reflected in robot-assisted surgery and further safety can be provided to the patient. Limitations This study had several limitations that should be considered in the interpretation of its findings. First, the study involved normal canine lungs and not emphysematous lungs that require cautious and gentle manipulation. Second, thoracic drainage after thoracotomy was not performed, despite it being standard postoperative management for human patients. The thoracic cavity could not be managed using continuous negative pressure suction, and the lungs could not be fully expanded during the experimental procedures. Third, only the peripheral lung tissue was used for the evaluation, and we did not test the forceps in other areas, such as the hilar region and the central portion of the lobe. CONCLUSION We developed novel endoscopic forceps with a force-limiting mechanism that ensures a predetermined maximum grasping pressure independent of the target tissue’s thickness. These forceps, when set to an optimal grasping pressure, allowed the manipulation of lung tissue with less damage than conventional forceps. SUPPLEMENTARY MATERIAL Supplementary material is available at EJCTS online. ACKNOWLEDGEMENTS The authors thank Ryuichi Yamada, Motonori Aoshima, Koichi Matsushita of HOGY Medical Co., Ltd. (Tokyo, Japan) and Toshiharu Nashimoto of Nashimoto Industries Co., Ltd. (Niigata, Japan) for designing and creating the forceps, and also helping in the animal experiments. Funding This work was supported by the HOGY Medical Co., Ltd., Tokyo, Japan [to T.S. and H.D.]. Conflict of interest: none declared. REFERENCES 1 Tholey G , Desai JP , Castellanos AE. Force feedback plays a significant role in minimally invasive surgery: results and analysis . Ann Surg 2005 ; 241 : 102 – 9 . Google Scholar PubMed 2 Marucci DD , Shakeshaft AJ , Cartmill JA , Cox MR , Adams SG , Martin CJ. Grasper trauma during laparoscopic cholecystectomy . Aust Nz J Surg 2000 ; 70 : 578 – 81 . Google Scholar CrossRef Search ADS 3 Sotelo RJ , Haese A , Machuca V , Medina L , Nuñez L , Santinelli F et al. Safer surgery by learning from complications: a focus on robotic prostate surgery . Eur Urol 2016 ; 69 : 334 – 44 . Google Scholar CrossRef Search ADS PubMed 4 Solaini L , Prusciano F , Bagioni P , di Francesco F , Solaini L , Poddie DB. 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Surg Endosc 2002 ; 16 : 1329 – 31 . Google Scholar CrossRef Search ADS PubMed 21 Li W , Jia ZG , Wang J , Shi L , Zhou ZR. Zhou Friction behavior at minimally invasive grasper/liver tissue interface . Tribol Int 2015 ; 81 : 190 – 8 . Google Scholar CrossRef Search ADS © The Author(s) 2018. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

Journal

European Journal of Cardio-Thoracic SurgeryOxford University Press

Published: Jun 6, 2018

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