TY - JOUR
AU - PhD, Ephraim Bar-Yishay,
AB - ABSTRACT Objective: Mobile RTX (MRTX), a portable light-weighted ventilator, provides noninvasive respiratory support using biphasic extrathoracic cuirass-assisted ventilation. Despite the effectiveness of chemical–biological–radiological–nuclear (CBRN) gas masks, they cause respiratory loading as a result of added dead space and resistance. This prospective comparative pilot study was conducted to investigate the safety and efficacy of assisted ventilation provided by MRTX in healthy adult volunteers wearing CBRN gas masks at rest. Methods: Cardiorespiratory parameters were monitored in 11 healthy adult volunteers breathing spontaneously or with assisted ventilation provided by MRTX, freely or with the mask on. Comparisons were made by single-factor analysis of variance. Results: AV significantly increased minute ventilation (p < 0.001). MRTX increased minute ventilation by 6.4 L/min (mean, 95% confidence interval: 3.1, 9.8; p < 0.005) and by 4.7 L/min (1.8, 7.5; p < 0.01) during spontaneous breathing and with the mask on, respectively. Simultaneously, end-tidal carbon dioxide partial pressure decreased by 3.6 mmHg (2.2, 5.1; p < 0.001) and by 6.5 mmHg (3.8, 9.1; p < 0.001). Discussion: Biphasic extrathoracic cuirass assisted ventilation provided by MRTX is safe and effective in supporting adequate needs at rest even when wearing protective masks. MRTX should be further assessed as a possible adjunct to currently used field ventilation in CBRN scenarios. INTRODUCTION Chemical–biological–radiological–nuclear (CBRN) gas masks are widely used against toxic fumes in the industrial setting as well as for protection against toxic chemical warfare agents such as nerve agents (NAs).1,–3 In the last decades, operational experience has been gained in the use of these masks in regional conflicts such as in the Iran–Iraq War during the 1980s,4,–6 and more recently during the Syrian civil war. Initial resuscitative efforts for victims focus upon immediate antidotal treatment and respiratory support to prevent death from hypoxia.7 Current therapeutic protocols stress the need for urgent laryngoscopy and intubation defined as definite airway, with concomitant provision of positive pressure ventilation until signs of muscle paralysis disappear.7 We have recently offered an alternative to this highly specialized procedure8,9 suitable for resuscitating multiple victims who are highly diverse in age and size and in an atmosphere of chaos where there will inevitably be a shortage of personnel who are well trained in airway management. The MRTX respirator (MRTX) is a lightweight, easy-to-operate portable ventilator that can provide external high-frequency oscillation (EHFO) via a cuirass tightly fitted around the patient's chest. The MRTX respirator is a modern version of the already known Hayek Oscillator long used for administering ventilatory supports for adult as well as pediatric patients (Fig. 1).10,–17 The respirator, more accurately described as biphasic cuirass-assisted ventilation (BiCAV), is capable of ventilating a wide variety of subjects, from infants to obese adults, by choosing the proper size of cuirass. Both inspiratory and expiratory phases are active and the chest is oscillated around a variable negative baseline pressure. This method of ventilation was found to be effective in a variety of clinical settings: pressure range, −25 to +15 cmH2O; inspiratory–expiratory (I/E) ratios, 1:1 to 1:3; and frequencies, 60 to 150 cycles per minute (CPM).8,10,–12 However, BiCAV has never been tested for safety and effectiveness in the presence of added dead space and inspiratory resistance imposed on a subject wearing a CBRN gas mask. In the setting of exposure to chemical warfare agents, as long as casualties are not evacuated from the contaminated area, the aim is to provide medical support without removing the masks from the casualties unless it compromises their health. In a previous study, we showed the success of using BiCAV in a pig model of organophosphate poisoning.9 FIGURE 1. View largeDownload slide The MRTX portable ventilator has a flexible, transparent polycarbonate cuirass, which is available in 10 different sizes according to weight and is built to fit patients ranging from neonates to obese adults. The cuirass is connected using a wide bore tube to a small rugged power unit. The ventilator is supplied with battery power and is able to function for up to 4 hours. FIGURE 1. View largeDownload slide The MRTX portable ventilator has a flexible, transparent polycarbonate cuirass, which is available in 10 different sizes according to weight and is built to fit patients ranging from neonates to obese adults. The cuirass is connected using a wide bore tube to a small rugged power unit. The ventilator is supplied with battery power and is able to function for up to 4 hours. The aim of this pilot study was to investigate the safety and efficacy of ventilatory assistance provided by the MRTX respirator in healthy adult volunteers while wearing CBRN gas masks. METHODS Subjects Eleven healthy adult volunteers (6 males), 30.9 ± 12.0 (mean ± SD) years old, gave informed consent to participate in this prospective, comparative study, performed as outlined in the declaration of Helsinki. Their personal data are presented in Table I. TABLE I. Anthropometric Data of 11 Volunteers No.  Age (Year)  Sex  Weight (kg)  Height (cm)     1    19  M    62    174     2    35  F    54    171     3    18  M    72    176     4    18  M    75    180     5    18  M    68    175     6    38  F    61    168     7    47  F    71    185     8    34  F    70    173     9    24  M    75    174     10    49  M    81    178     11    40  F    65    160  Mean ± SD  30.9 ± 12.0     68.5 ± 7.6  174.0 ± 6.5  No.  Age (Year)  Sex  Weight (kg)  Height (cm)     1    19  M    62    174     2    35  F    54    171     3    18  M    72    176     4    18  M    75    180     5    18  M    68    175     6    38  F    61    168     7    47  F    71    185     8    34  F    70    173     9    24  M    75    174     10    49  M    81    178     11    40  F    65    160  Mean ± SD  30.9 ± 12.0     68.5 ± 7.6  174.0 ± 6.5  View Large TABLE I. Anthropometric Data of 11 Volunteers No.  Age (Year)  Sex  Weight (kg)  Height (cm)     1    19  M    62    174     2    35  F    54    171     3    18  M    72    176     4    18  M    75    180     5    18  M    68    175     6    38  F    61    168     7    47  F    71    185     8    34  F    70    173     9    24  M    75    174     10    49  M    81    178     11    40  F    65    160  Mean ± SD  30.9 ± 12.0     68.5 ± 7.6  174.0 ± 6.5  No.  Age (Year)  Sex  Weight (kg)  Height (cm)     1    19  M    62    174     2    35  F    54    171     3    18  M    72    176     4    18  M    75    180     5    18  M    68    175     6    38  F    61    168     7    47  F    71    185     8    34  F    70    173     9    24  M    75    174     10    49  M    81    178     11    40  F    65    160  Mean ± SD  30.9 ± 12.0     68.5 ± 7.6  174.0 ± 6.5  View Large Study Design Respiratory parameters were monitored during room air tidal breathing while the subjects were seated. Monitoring lasted for 5 minutes and variables were recorded and averaged over the last minute (spontaneous breathing [control], SB[C]). The volunteers were then connected to a biphasic extrathoracic ventilator (MRTX portable ventilator, Medivent, London, United Kingdom) and were instructed to relax maximally, not interfering with the machine and trying not to augment ventilation. Once the subjects acclimatized with the MRTX and ventilation reached stable conditions (up to 3 minutes in all subjects), monitoring was repeated and values were averaged over the last minute of recording (AV[C]). The subjects then proceeded to wear a standard CBRN gas mask (Model M15-4A1, Shalon Chemical Industries, Kiryat Gat, Israel) and separate recordings were made during either spontaneous (mask on, SB[M]) or assisted ventilation as described earlier (AV[M]). The order of the tests was unchanged in all subjects. Respiratory variables measured were tidal volume (VT), respiratory rate (RR), minute ventilation (VE), end-tidal carbon dioxide partial pressure (PetCO2), oxygen saturation (SaO2), and heart rate (HR). VT, RR, and VE were measured using an SLE monitor (2100VPM, SLE Life Support, Croydon, United Kingdom). PetCO2 was measured using a Microstream capnograph (JS-02260, Spegas Industries, Israel), and SaO2 and HR were measured using a pulse oximeter (Biox 3800, Datex-Ohmeda, Helsinki, Finland). The Biphasic Extrathoracic Cuirass Ventilator The MRTX ventilator is a relatively small (14 × 14 × 18 cm), lightweight (2 kg, battery 1 kg), battery-operated, and rugged ventilator (Fig. 1). It consists of a flexible, lightweight polycarbonate cuirass that covers the anterior part of the chest and upper abdomen, having a wide, soft foam rubber rim, which creates an airtight seal. It has a backplate and is secured by Velcro straps around the patient's chest.15 The cuirass is connected by wide-bore flexible tubing to a mobile microprocessor-controlled power unit. The power unit works by creating cyclic pressure changes inside the cuirass, thus controlling both phases of the respiratory cycle. The frequency, inspiratory and expiratory cuirass chamber pressures, and I/E ratio are automatically set and controlled by a negative feedback loop.14 I/E ratio can be set from 1/6 to 6/1, and frequencies from 6 to 1,200 CPM, allowing the respirator to operate both as a low-frequency respirator and as a high-frequency oscillator. In this study, MRTX was set to deliver –10 and +8 cmH2O inspiratory and expiratory driving pressures at an RR of 20 and I/E ratio of 1:1. VT and VE were not controlled and were determined by the volunteers themselves as long as PetCO2 did not fall below 33 mmHg. CBRN gas masks are designed to protect the eyes, face, and respiratory tract against CBRN agents. Shalon civilian masks are the standard approved CBRN respirators of the Israeli Civil Defense Authorities (Model M15-4A1, Shalon Chemical Industries). Dead space of this face mask is 150 mL. Filter canisters used with the 4A1 (type 80, Shalon Chemical Industries) are classified in accordance with Israeli specification EN 141 and provide a particulate filtering efficiency of at least 99.99% at a flow rate of 30 L/min. Resistance of the filter (inspiratory resistance, Rinsp) is documented as 1.4 cmH2O at 30 L/min and expiratory resistance is negligible (<1 cmH2O). Obviously, during deep inspirations, Rinsp may reach values as high as 10 cmH2O. Statistical Analysis All values are presented as mean ± SD or 95% confidence interval. The four sessions were treated as four independent samples using a single-factor analysis of variance (ANOVA) with Bartlett's test for homogeneity of variances and Bonferroni post-multiple comparisons test. Differences among treatments were likewise analyzed using ANOVA. The p-values were considered to be significant when <0.05. RESULTS Results for SB and MRTX AV while breathing either freely or with CBRN gas masks on are summarized in Table II. As expected, VE increased significantly from SB (C) (p < 0.001 by ANOVA). Applying the MRTX while breathing freely (AV[C]) significantly increased VE by 6.4 L/min (mean, 95% confidence interval: 3.1, 9.8; p < 0.001). Wearing the mask significantly increased VE from baseline by 3.5 L/min (1.3, 5.6; p = 0.01), with a further increase by 4.7 L/min, AV(M) (1.8, 7.5; p < 0.005) with both mask and MRTX on. TABLE II. Mean ± SD Values of Cardiopulmonary Variables During Spontaneous Versus Subjects Relaxation with Assisted Ventilation During Normal Breathing (Control) and While Wearing the CBRN Gas Mask Parameter  SB  AV  ANOVA  Control, SB(C)  CBRN Mask, SB(M)  Control, AV(C)  CBRN Mask, AV(M)  p Value  VE (L/min)  10.5 ± 3.5  13.9 ± 4.2  16.9 ± 5.2  18.6 ± 6.5  0  VE (mL/min/kg)   155 ± 63   205 ± 65   251 ± 91   277 ± 118     VT (mL)   655 ± 256   981 ± 363   883 ± 282   994 ± 379  0.07  VT (mL/kg)    9.6 ± 3.7  14.3 ± 4.7  13.3 ± 5.3  14.9 ± 7.4  0.11  RR (per minute)   17 ± 4   15 ± 3   19 ± 2   19 ± 2  0.003  PetCO2 (mmHg)   37 ± 5   41 ± 5   31 ± 6   35 ± 5  0.02  SaO2 (%)   97 ± 2   97 ± 2   97 ± 2   97 ± 1  0.81  HR (per minute)   76 ± 15   76 ± 14   75 ± 17   75 ± 18  0.99  Parameter  SB  AV  ANOVA  Control, SB(C)  CBRN Mask, SB(M)  Control, AV(C)  CBRN Mask, AV(M)  p Value  VE (L/min)  10.5 ± 3.5  13.9 ± 4.2  16.9 ± 5.2  18.6 ± 6.5  0  VE (mL/min/kg)   155 ± 63   205 ± 65   251 ± 91   277 ± 118     VT (mL)   655 ± 256   981 ± 363   883 ± 282   994 ± 379  0.07  VT (mL/kg)    9.6 ± 3.7  14.3 ± 4.7  13.3 ± 5.3  14.9 ± 7.4  0.11  RR (per minute)   17 ± 4   15 ± 3   19 ± 2   19 ± 2  0.003  PetCO2 (mmHg)   37 ± 5   41 ± 5   31 ± 6   35 ± 5  0.02  SaO2 (%)   97 ± 2   97 ± 2   97 ± 2   97 ± 1  0.81  HR (per minute)   76 ± 15   76 ± 14   75 ± 17   75 ± 18  0.99  View Large TABLE II. Mean ± SD Values of Cardiopulmonary Variables During Spontaneous Versus Subjects Relaxation with Assisted Ventilation During Normal Breathing (Control) and While Wearing the CBRN Gas Mask Parameter  SB  AV  ANOVA  Control, SB(C)  CBRN Mask, SB(M)  Control, AV(C)  CBRN Mask, AV(M)  p Value  VE (L/min)  10.5 ± 3.5  13.9 ± 4.2  16.9 ± 5.2  18.6 ± 6.5  0  VE (mL/min/kg)   155 ± 63   205 ± 65   251 ± 91   277 ± 118     VT (mL)   655 ± 256   981 ± 363   883 ± 282   994 ± 379  0.07  VT (mL/kg)    9.6 ± 3.7  14.3 ± 4.7  13.3 ± 5.3  14.9 ± 7.4  0.11  RR (per minute)   17 ± 4   15 ± 3   19 ± 2   19 ± 2  0.003  PetCO2 (mmHg)   37 ± 5   41 ± 5   31 ± 6   35 ± 5  0.02  SaO2 (%)   97 ± 2   97 ± 2   97 ± 2   97 ± 1  0.81  HR (per minute)   76 ± 15   76 ± 14   75 ± 17   75 ± 18  0.99  Parameter  SB  AV  ANOVA  Control, SB(C)  CBRN Mask, SB(M)  Control, AV(C)  CBRN Mask, AV(M)  p Value  VE (L/min)  10.5 ± 3.5  13.9 ± 4.2  16.9 ± 5.2  18.6 ± 6.5  0  VE (mL/min/kg)   155 ± 63   205 ± 65   251 ± 91   277 ± 118     VT (mL)   655 ± 256   981 ± 363   883 ± 282   994 ± 379  0.07  VT (mL/kg)    9.6 ± 3.7  14.3 ± 4.7  13.3 ± 5.3  14.9 ± 7.4  0.11  RR (per minute)   17 ± 4   15 ± 3   19 ± 2   19 ± 2  0.003  PetCO2 (mmHg)   37 ± 5   41 ± 5   31 ± 6   35 ± 5  0.02  SaO2 (%)   97 ± 2   97 ± 2   97 ± 2   97 ± 1  0.81  HR (per minute)   76 ± 15   76 ± 14   75 ± 17   75 ± 18  0.99  View Large PetCO2 also changed significantly between treatments (p < 0.005 by ANOVA). As expected, a small but significant elevation of PetCO2 was observed following the application of the CBRN gas mask as a result of increased dead space ventilation within the mask (3.6 mmHg; 2.0, 5.3; p < 0.01), and this occurred despite the increase in VE (3.5 L/min; 1.3, 5.6; p = 0.01). This increase was corrected by the application of MRTX, which significantly decreased PetCO2 to below control values (p < 0.05). No further changes in PetCO2 were observed when subjects were wearing the CBRN gas masks, changes in PetCO2 being 0.8 mmHg (−1.2, 2.8; p = NS) with PetCO2 values still significantly below control values (p < 0.001). Changes in VT with CBRN gas mask on and with AV just failed to reach a significant level by ANOVA (p = 0.07). During SB, VT increased by 326 mL (178, 473; p < 0.005) after wearing the CBRN gas mask, accompanied by a slight but insignificant fall in RR. RR, however, increased significantly with AV (p < 0.005), and this was the main contributory factor to the significant increase in VE. SB(C) measurements were repeated in 7 subjects just before applying the MRTX and with the exception of a small difference in VT. All values were similar to those in the initial recordings. DISCUSSION The results of this pilot study suggest that biphasic extrathoracic AV by the portable MRTX ventilator can provide a safe and effective ventilatory support (AV) to resting adults when wearing CBRN gas masks. No changes were observed in HR or SaO2 and none had to stop the test because of subjective uncomfort or shortness of breath. In addition, no PetCO2 buildup was observed with the application of AV either with or without the CBRN gas mask on, indicating that AV was capable of supplying ample fresh gas. Since the subjects were not paralyzed, the question at hand is that of controlling the variables tested. In other words, did the MRTX ventilator truly supply sufficient fresh gas to a perfectly relaxed subject, or whether the subjects actively supplemented the ventilator action to control for PetCO2 homeostasis. Since PetCO2 buildup was observed when subjects put on the CBRN gas masks, albeit the increase in VE, and that this buildup was corrected by the application of the MRTX, we believe that our trained volunteers were truly relaxed. Furthermore, assuming a normal respiratory system compliance of 0.07 L/cmH2O, the ventilatory support by the MRTX in a truly relaxed subject can be estimated. A ventilator setting of pressure swings of 18 cmH2O and assuming a 35% pressure leakage of the cuirass' imperfect seal around the torso would yield true driving pressure swings of roughly 12 cmH2O, which would generate a VT of 0.8 L. Since mean actual VT was found to be slightly less than 0.9 L for AV(C), not significantly different than that predicted for the MRTX ventilator with no active subject augmentation, we believe that our findings can be safely extrapolated to a situation where the MRTX ventilator carries the full ventilatory load. It is of course possible that these settings may be insufficient for larger subjects having greater VT's. The increase in VT is fully accounted for by the mask's dead space of 150 mL, whereas the slight decrease in RR may be attributable to the introduction of respiratory load by the mask's filter imposing a noticeable inspiratory resistance. It is noted that all volunteers indicated that the added resistance was appreciable and that the MRTX alleviated this sensation. This finding can be explained by −10 cmH2O negative extrathoracic pressure imposed by the MRTX ventilator, which assumed to have lowered the work of breathing. It is also interesting to note that the observed increase in VT during SB when putting the mask on was not seen during assisted ventilation by MRTX (AV[C] to AV[M]). This can be explained by the excess ventilation, and lower PetCO2 in AV(C). From the manufacturer's specification sheet, we expect this increase to be in the order of 3 L/min assuming no change in RR. Thus, the increases in VE upon wearing the gas mask (3.5 L/min; 1.3, 5.6 during SB, and 1.75 L/min; −1.4, 4.8 during AV) are believed to be solely attributed to increased dead space ventilation. We do not believe that the MRTX performed differently during the application of the gas mask, since AV increased VE similarly while breathing freely or when wearing the mask. The MRTX respirator is relatively small and portable, and can be easily deployed by rescue personnel even when conditions are less than ideal, and available for operation in any indoor or outdoor location. EHFO and more recently the BiCAV are relatively new modalities of noninvasive ventilation that control both phases of respiration.18 In BiCAV, both inspiratory and expiratory phases of ventilation are active and both peak inspiratory and expiratory chamber pressures are controllable. The inspiratory pressure will always be negative to expand the chest and inflate the lungs, but the expiratory pressure may be negative, atmospheric, or positive to produce an end-expiratory lung volume above, at, or below functional residual capacity, respectively.19,VT is determined by the pressure difference between the expiratory and peak inspiratory chamber pressure and frequency. Increasing the earlier-mentioned pressure difference increases VT while increasing frequency reduces it. Since VE is the product of frequency and VT, VE increases as long as the increment in frequency is higher than the decrease in VT.20 As both inspiratory and expiratory phases are controlled, high RRs (up to 1,200 CPM) may be achieved in contrast to normal negative pressure ventilation without the active component of expiration. Nevertheless, optimal CO2 removal is achieved with a rate of 90 CPM. The I/E ratio of 1:1 is optimal although in patients with inspiratory or expiratory obstruction, prolonging that phase of respiration with the increased resistance may be needed for optimal ventilation.20 In this preliminary study, the I/E ratio was not changed albeit the addition of an external resistor (the mask's filter). In case of exposure to chemical warfare agents, mass casualties are to be anticipated.7 The safest mode of airway protection in the case of NA poisoning is probably endotracheal intubation. However, some concerns may arise from a possible low success rate of intubation when performed by physicians called upon in a mass casualty scenario who are not familiar with the procedure on a daily basis and required to perform it in the prehospital setting with less than ideal conditions. In this regard, the application of BiCAV using the MRTX ventilator saves the need for laryngoscopy and intubation—acts that may also be cumbersome in the described scenario because of protective gear wear by the medical personnel, which impair visual acuity and manual dexterity.21 In addition, secondary contamination of first responders can cause ocular signs and symptoms, such as severe miosis, dim vision, and persistent rhinorrhea, which, although not lethal, can compromise physician's ability to function.22,–24 Another possible benefit for providing emergency respiratory support without the need to perform laryngoscopy is saving the use of muscle relaxants that might act unpredictably in cases of underlying systemic inhibition of acetylcholinesterase.25 Trials in animals and humans proved the efficacy of EHFO in ventilating normal and sick lungs.11,12,17 The potential to preserve cardiac output using EHFO as compared to its reduction when conventional positive pressure ventilation11 is instituted might be favorable facing the NA-induced negative inotropic effects.26 Nevertheless, when using this method of ventilation, no adequate separation of the digestive and respiratory tracts is maintained. In addition, lung ventilation might be compromised by the anticipated increase in airway resistance and tracheobronchial hypersecretion. It is important to note, however, that the early use of antidotes, especially atropine, is expected to reduce the amount of secretions. Hence, it would be prudent to replace the negative pressure ventilation of the cuirass by an endotracheal tube as soon as possible (i.e., after the rescue and evacuation phase of the victim or when admitted to the hospital emergency department). This is especially true, when respiratory failure may be prolonged and support will be needed for an extended period of time, as in the case of severe organophosphate poisoning. Our study includes 11 healthy adult volunteers, and this may raise an issue of sample size limitation, which is indeed crucial when an intervening protocol is tested. 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TI - The Application of Biphasic Extrathoracic Cuirass-Assisted Ventilation in Normal Subjects Wearing Chemical–Biological–Radiological–Nuclear (CBRN) Gas Masks
JF - Military Medicine
DO - 10.7205/MILMED-D-16-00275
DA - 2017-03-01
UR - https://www.deepdyve.com/lp/oxford-university-press/the-application-of-biphasic-extrathoracic-cuirass-assisted-ventilation-JPN2eLZywd
SP - e1801
EP - e1805
VL - 182
IS - 3
DP - DeepDyve
ER -