Canadian Journal of Anesthesia/Journal canadien d anesthésie

Tardif, Jean-Claude; Juneau, Martin

doi: 10.1007/bf03011898pmid: 8896848

Ansley, David M.; O’Connor, J. Patrick; Merrick, Pamela M.; Ricci, Donald R.; Dolman, John; Kapnoudhis, Paul

doi: 10.1007/bf03011899pmid: 8896849

PurposeA paucity of information exists to validate the accuracy and reliability of ECG monitoring in the operating room or ICU. The purpose of this study was to determine the accuracy, sensitivity, specificity, and predictive values of the Marquette ECG monitor for detection of perioperative myocardial ischaemia (PMI) as measured by ST segment changes in a high risk population.MethodsMonitoring for PMI in 28 patients scheduled for aortocoronary bypass surgery was done with the Cardiodata PR® ambulatory continuous electrocardiography (ACECG) monitor lead V5, and compared with lead V5 of the Marquette® Series 7000 ECG/ Surgical operating room monitor, and ECG/Resp ICU monitor. The Marquette lead V5 was evaluated using current criteria for the assessment of diagnostic tests including concordance, sensitivity, specificity, positive and negative predictive values, false positive and false negative rates and compared with the ACECG monitor which served as the reference or “gold standard.” Agreement beyond chance between the two methods was assessed using the Kappa statistic.ResultsOf the 53 observation data points, 27 were defined as ischaemic episodes by ACECG. Concordance between lead V5 in each system was 83% (44/53 episodes). Discordance was 17% (9/53 episodes), predominantly in the postbypass interval (77%, 7/9; P = 0.0184). The incidences of false negatives and false positives for Marquette lead V5 was 26% (7/27) and 7.7% ( 2/26), respectively. The sensitivity and specificity of the Marquette was 0.74 and 0.92. Positive predictive value was 0.91, negative predictive value was 0.77, and Kappa statistic was 66%.ConclusionAutomated ST segment analysis with the Marquette® Series 7000 monitoring system demonstrates good diagnostic accuracy, moderate sensitivity, and high specificity. However, clinically significant false negative and false positive rates of ischaemia detection are associated with its use, especially in the postoperative period.

Saitoh, Yuhji; Nakazawa, Koichi; Tanaka, Hiroyoshi; Toyooka, Hidenori; Amaha, Keisuke

doi: 10.1007/bf03011900pmid: 8896850

PurposeWe present a new stimulating pattern: double burst stimulation2,3 (DBS2,3) for evaluating residual neuromuscular block.MethodsForty adult patients were studied. For DBS2,3, two burst stimuli were applied every 750 msec. The first consisted of two tetanic stimuli of 0.2 msec duration and the second of three tetanic stimuli of 0.2 msec duration. At varying degrees of neuromuscular block induced by vecuronium, the presence or absence of fade, or the presence or absence of waxing (i.e., the feeling that the muscular contraction in response to the second burst was stronger than that to the first) was determined by an observer blinded to the depth of neuromuscular block. In addition, the relationship between the train-of-four (TOF) ratio and DBS2,3 ratio was established at varying depths of neuromuscular block (TOF ratio 0.04–1.00).ResultsThe probabilities of tactile detection of fade in response to DBS2,3 were 100, 76, 15, 9, 3, 0, and 0% at a TOF ratio of 0–0.40, 0.41–0.50, 0.51–0.60, 0.61–0.70, 0.71–0.80, 0.81–0.90, and 0.91–1.00, respectively. Waxing in response to the DBS2,3 was identified in 0, 6, 32, 84, and 98% of cases when the TOF ratios were 0.00–0.60, 0.61–0.70, 0.71–0.80, 0.81–0.90, and 0.91–1.00, respectively. A close linear relationship existed between the TOF ratio and DBS2,3 ratio (r = 0.96, P < 0.000001).ConclusionDBS2,3 is of clinical use because when residual neuromuscular block is clinically important, fade can be identified, but once neuromuscular function returns to a sufficient level, waxing can be detected.

Naguib, Mohamed; Dawlatly, Abdel Azim El; Ashour, Mahmoud; Bamgboye, Elijah A.

doi: 10.1007/bf03011901pmid: 8896851

PurposeFollowing transsternal thymectomy, up to 50% of patients may require postoperative ventilation. The aim of this study was to identify the variables most useful in predicting the myasthenic patient who needs postoperative mechanical ventilation.MethodsWe applied multivariate discriminant analysis to preoperative physical, historical, laboratory and intraoperative data of 51 myasthenic patients who underwent transcervical-transsternal thymectomy to select those variables most useful in predicting the postoperative need for mechanical ventilation. The receiver operating characteristic (ROC) curve was also used to describe the discrimination abilities and to explore the trade-offs between sensitivity and specificity of the model.ResultsDiscriminant analysis identified seven risk factors that correlated with the need for postoperative ventilation: FVC, FEF25–75%, MEF50% and their percentages of the predicted values, as well as, sex. The model correctly predicted the actual ventilatory outcome in 88.2% of patients. The area under the ROC curve verified that our model correctly predicted the actual ventilatory outcome with a probability of 88.2%.ConclusionsThis model can be used for predicting the need for postoperative mechanical ventilation in myasthenia gravis patients.

Herrick, Ian A.; Gelb, Adrian W.; Nichols, Bruce; Kirkby, Joyce

doi: 10.1007/bf03011902pmid: 8896852

PurposeLittle information is available regarding the use of patient-controlled sedation (PCS) among elderly patients undergoing operative procedures under local or regional anaesthesia. This prospective, randomized study evaluated the safety of propofol PCS, and the attitude among elderly patients toward self-administration of sedation during cataract surgery.MethodsProspective, randomized study conducted in a University affiliated, tertiary-care hospital. Fifty-five elderly patients (aged 65–79 yr) were randomized to receive propofol patient-controlled sedation (PCS) (n = 28) or no intraoperative sedation (n = 27) during cataract surgery performed under peribulbar block. The PCS parameters consisted of a lockout interval of three minutes and a PCS dose of 0.3 mg · kg−1. Study groups were compared with respect to sedation, anxiety and discomfort visual analogue scores (VAS), cognitive functioning, patient satisfaction and the incidence of intraoperative complications.ResultsPatients in the PCS group administered a mean propofol dose of 65 ±49 mg during procedures with a mean duration of 46 min. The incidence of intraoperative complications and sedation, anxiety and discomfort VAS were similar between groups. Patient satisfaction with PCS was high. In the PCS group, 10 (35%) of the 28 patients did not use the device because they were comfortable and did not feel they needed sedation. Satisfaction was higher in the PCS group (P = 0.02), whether or not they used the PCS device, compared with patients who did not receive a PCS device.ConclusionsPropofol PCS represents a safe sedation technique among elderly patients in a monitored care setting. Elderly patients appear to prefer the option of receiving some form of intraoperative sedation and respond favourably to the opportunity to control administration.

Inada, Takefumi; Shingu, Koh; Uchida, Morio; Kawachi, Shoji; Tsushima, Kohichi; Niitsu, Tateki

doi: 10.1007/bf03011903pmid: 8896853

PurposeTo investigate changes of cerebral arteriovenous oxygen content difference (AVDO2) induced by surgical incision and to determine carbon dioxide (CO2) reactivity of the cerebral circulation during sevoflurane and isoflurane anaesthesia.MethodsTwenty-one ASA 1–2 patients undergoing elective surgery for supratentorial tumours were randomly allocated to receive either 1.3 MAC sevoflurane/N2O anaesthesia (n =10) or equi-MAC isoflurane/N2O anaesthesia (n = 11). Before and after incision, haemodynamic measurements and AVDO2 determinations were performed. After opening the dura, AVDO2 was determined before and after the respiration rate was increased by 50%.ResultsIncision produced an increase in mean arterial pressure from 69 ±11 to 97 ±22 mmHg (mean ±SD) (P < 0.0005) and from 71 ±6 to 89 ±12 mmHg (P < 0.0001) in the sevoflurane and isoflurane groups, respectively, whereas the heart rate increased from 60 ±9 to 72 ±8 bpm (P < 0.001) and from 65 ±6 to 70 ±7 bpm (P < 0.001), respectively. Arterial carbon dioxide tension (PaCO2) was increased from 33.6 ±2.3 to 34.6 ±1.8 mmHg (P < 0.05) with incision in the sevoflurane group. The AVDO2 was decreased from 6.5 ±1.6 to 5.3 ±1.6 vol% (P < 0.0005) in the sevoflurane group and from 6.7 ±1.1 to 6.0 ±1.1 vol% (P < 0.01) in the isoflurane group. The % change of AVDO2 was larger in the sevoflurane group than in the isoflurane group (−18.3 ±8.4% vs −9.1 ±9.0%; P < 0.05) but no difference remained after the postincisional AVDO2 value of the sevoflurane group was corrected for pre-incisional PaCO2. Carbon dioxide reactivity, calculated as the percent change in AVDO2 per mmHg change in PaCO2, was 6.1 ±3.0% mmHg−1 in the sevoflurane group and 5.9 ±2.4% · mmHg−1 in the isoflurane group (P = NS).ConclusionsSevoflurane and isoflurane are associated with similar impairment of cerebral flow-metabolism coupling at incision, while CO2 reactivity is maintained during both anaesthetics.ObjectifÉtudier les changements de la différence artérioveineuse du contenu en oxygène cérébral (AVDO2) produits par l’incision et déterminer la réactivité au gaz carbonique (CO2) de la circulation cérébrale sous anesthésie au sévoflurane et à l’isoflurane.MéthodesVingt et un patients ASA 1 et 2 subissant une chirurgie non urgente pour tumeur supratentorielle ont été aléatoirement assignés à recevoir soit une anesthésie au sévoflurane/N2O 1,3 MAC (n = 10) soit une anesthésie à l’isoflurane/N2O équi-MAC (n = 11). Avant et après l’incision, les mesures hémodynamiques ont été effectuées et AVDO2 déterminée. Après l’ouverture de la dure-mère, AVDO2 a été calculée avant et après une augmentation de la fréquence respiratoire de 50%.RésultatsL’incision a provoqué une augmentation de la pression artérielle moyenne respective de 69 ±11 à 97 ±22 mmHg (moyenne ±ET) (P < 0,0005) et 71 ±6 à 89 ±12 (P < 0,0001) dans les groupes sévoflurane et isoflurane; la fréquence cardiaque augmentait respectivement de 60 ±9 à 72 ±8 bpm (P < 0,001) et de 65 ±6 à 70 ±7 bpm (P < 0,001). Dans le groupe sévoflurane, la PaCO2 augmentait de 33,6 ±2,3 à 34,6 ±1,8 (P < 0,05) avec l’incision. Dans le groupe sévoflurane, AVDO2 diminuait de 6,5 ±1,6 à 5,3 ±1,6 vol% (P < 0,0005) et dans le groupe isoflurane, de 6,7 ±1,1 à 6,0 ±1,1 vol% (P < 0,01). Le pourcentage de changement de AVDO2 était plus important dans le groupe sévoflurane que dans le groupe isoflurane (−18,3 ±8,4% vs −9,1 ±9,0%; P < 0,05); cette différence est disparue une fois la valeur post-incision du groupe sévoflurane corrigée pour la valeur de PaCO2 pré-incision. La réactivité du gaz carbonique, calculée en pourcentage de changement en AVDO2 par mmHg de changement de PaCO2 était 6,1 ±3,0% · mmHg−1 dans le groupe sévoflurane et 5,9 ±2,4% · mmHg−1 dans le groupe isoflurane (P = NS).ConclusionLe sévoflurane et l’isoflurane sont associés à une perturbation identique du couplage débit-métabolisme à l’incision, alors que la réactivité au CO2 est maintenue avec les deux anesthésiques.

Ledsome, John R.; Cole, Colm; Sharp-Kehl, Jeannie M.

doi: 10.1007/bf03011904pmid: 8896854

PurposeThe objective of the study was to evaluate the effects of moderate hypoxia and hypocapnia on the latency and amplitude of cortical somatosensory evoked potentials (SSEPs) in conscious human subjects.MethodsIn ten volunteers the amplitude and latency of the cortical somatosensory evoked potentials were recorded during stimulation of the left posterior tibial nerve. Measurements of SSEPs and respiratory variables were made breathing ambient air, air containing a reduced oxygen percentage (17% O2, 14% O2(n = 6) or 11% O2 (n = 10)), and again during voluntary hyperventilation breathing ambient air (PEtCO2 = 20 mmHg, n = 10).ResultsHypoxia (11% O2) caused mild stimulation of ventilation (P < 0.05) but had no effects on the latency or amplitude of the SSEP. Lesser degrees of hypoxia had no effects. Hyperventilation caused a small (2–4%) decrease) in the latency of the SSEP and an increase in the amplitude of the SSEP (P< 0.05).ConclusionsThese findings in conscious subjects were consistent with previous observations in anaesthetized humans and anaesthetized dogs and show that the decrease in latency of the SSEP associated with hypocapnia is not due to changes in the depth of anaesthesia. These effects of hypocapnia may contribute to small variations in the latency of the SSEP when monitoring is performed during surgery, but are unlikely to be large enough to be of clinical concern.

Ganapathy, Sugantha; Razvi, Hassan; Moote, Carrol; Parkin, John; Yee, Irvan; Gverzdys, Sharunas; Dain, Steven; Denstedt, John D.

doi: 10.1007/bf03011905pmid: 8896855

PurposeEutectic mixture of local anaesthetics (EMLA®) produces cutaneous analgesia. This randomized, double blind, placebo controlled study evaluated the efficacy of EMLA cream during extracorporeal shock wave lithotripsy (ESWL) using the Dornier® MFL 5000 lithotripter.MethodsPatients scheduled to undergo lithotripsy of renal or pelviureteric junction stones were randomized to receive either 30 g EMLA cream (E) or placebo (P) over the kidney area 60–90 min before the procedure. During lithotripsy all patients received alfentanil via a PCA machine (dose —10 μ · kg−1, lockout time —three minutes, no basal infusion). Additional bolus doses of 5 μg · kg−1 alfentanil were administered by the anaesthetist if analgesia was inadequate. Visual analogue scores (VAS) for pain were documented prior to application of the cream. On arrival in the post anaesthesia care unit VAS pain scores were documented for maximum pain and average pain felt during the procedure as well as for satisfaction of the analgesic technique used. Total time spent in the PACU and the Aldrete scores on arrival were compared.ResultsEighty-three patients completed the study. Demographic data were similar between the two groups. Also, VAS for maximal pain, average pain and satisfaction and the total number of shock waves were similar although the EMLA group received more shock waves at the lower energy level (kV) (P < 0.0001). Total dose of alfentanil, dose as boluses, rate of alfentanil use, total number of PCA attempts and missed attempts were similar. The incidence of adverse events such as bradypnoea, airway obstruction, transient hypoxaemia, pruritus and nausea were small and similar. There was a slightly higher incidence of inadequate analgesia documented by the anaesthetist in the EMLA group. There was no difference between the groups with regards to duration of stay in the PACU, incidence of nausea or Aldrete scores on admission to PACU.ConclusionsDuring lithotripsy EMLA cream does not modify the pain perceived nor does it have any opioid sparing effect. It does not facilitate early discharge from the PACU.

Aoyama, Kazuyoshi; Takenaka, Ichiro; Sata, Takeyoshi; Shigematsu, Akio

doi: 10.1007/bf03011906pmid: 8896856

PurposeTo assess the effect of cricoid pressure on the positioning of and ventilation through the laryngeal mask airway (LMA).MethodsIn a double-blind, randomized design, the LMA was inserted with (CP[+] group, n = 20) or without double-handed cricoid pressure (CP[−] group, n = 20). Ventilation through the LMA was assessed by measuring expiratory tidal volume and judged as adequate when a mean expiratory tidal volume of ≥10 ml · kg−1 could be obtained. The LMA position was examined by fibreoscopy. The position of the mask relative to the cricoid cartilage and the cervical spine was radiologically examined (n = 10 in each group).ResultsVentilation was adequate in all patients in the CP[−] group but in only five patients (25%) of the CP[+] group (P < 0.001). The glottis was visible fibreoptically below the mask aperture in all patients in the CP[−] group, but in only three patients in the CP[+] group (P < 0.001). Fibreoscopy showed that the mask was not inserted far enough in the remaining 17 patients of the CP[+] group. The reason for unsuccessful ventilation in the CP[+] group was excessive gas leakage (n = 2) and/or partial or complete airway obstruction (n = 13), which was noted fibreoptically. The radiographs showed that the tip of the mask in the CP[−] group was located below the level of the cricoid cartilage (C6 or C7 vertebra). The mask tip in the CP[+] group was above this level (C4 or C5 vertebra) (P < 0.01).ConclusionCricoid pressure impedes positioning of and ventilation through the LMA.

Yang, Homer

doi: 10.1007/bf03011907pmid: 8896857

PurposeTo review the application of intraoperative computerized ST analysis and its potential impact on postoperative outcomes.SourceExisting anaesthesia and cardiology literature.Principal findingsComputerized ST analysis was introduced into the operating room using exercise electrocardiographic (ECG) systems. In spite of sophisticated algorithms, errors do occur. Downsloping or horizontal ST depression are the classical criteria for ischaemia. Although algorithms have been developed and evaluated in exercise stress testing, only limited evaluation has been carried out in the operating room. This may be a concern since circumstances in the operating room may frequently lead to false positives. Similarly, studies suggest that all myocardial ischaemia may not exhibit ST changes. The diagnostic accuracy of ST depression in exercise stress testing also cannot be assumed in the operating room. Finally, if ST analysis is applied widely, without considering the population or disease prevalence, misdiagnosis may occur.ConclusionGiven the number of anaesthetic tasks at-hand, on-line computerized ST analysis in the operating room can be a useful asset. The technology has its problems and should be applied with an understanding of its limitations and potential for errors. It should be applied in the operating room within the context of the population and disease prevalence.