Skin conductance monitoring compared with bispectral index monitoring to assess emergence from general anaesthesia using sevoflurane and remifentanil

Background. Changes in skin conductance have previously beenreported to correlate well with plasma levels of stress hormonesand awakening stimuli. In this study, monitoring of skin conductanceduring emergence from general anaesthesia was compared withthe monitoring of bispectral index (BIS). Methods. Twenty-five patients undergoing minor elective surgerywere investigated. The number of fluctuations in mean skin conductance(NFSC), BIS and haemodynamic parameters were recorded simultaneously.The performance of the monitoring devices to predict and distinguishbetween the clinical states ‘steady-state anaesthesia’,‘first reaction’ and ‘extubation’ werecompared using the method of prediction probability (P_K) calculation. Results. Both monitors showed similar performance in distinguishingbetween ‘steady-state anaesthesia’ vs ‘firstreaction’ (P_K NFSC 0.89; BIS^® 0.94) and ‘steady-stateanaesthesia’ vs ‘extubation’ (P_K NFSC 0.96;BIS^® 0.96). The response times of the monitors, to indicatethe likelihood of ‘first reaction’, were not significantlydifferent. Conclusions. NFSC, as a parameter of skin conductance, performedsimilarly to BIS in patients waking after a general anaesthetic.     

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Gordon Drummond of Edinburgh contacted us regarding the articleon ‘Pharmacokinetics and Anaesthesia’ by Fred Robertsand Dan Freshwater-Turner (CEACCP 2007; 7(1): 25–29).He was unhappy with the assertion that ‘an inhaled drug...crossesthe alveolar membrane into the blood along its partial pressuregradient. This produces an exponential wash-in...’. DrDrummond writes that ‘This suggests that the exponentialwash-in is caused by a partial pressure gradient. This is notso. Volatile anaesthetics are believed by almost all to equilibraterapidly and virtually fully, between alveolar gas and alveolarcapillary blood, and     

Extreme value theory applied to postoperative breathing patterns

Background. There has been little published work on the statisticalfeatures of breath times in postoperative patients. We appliedextreme value theory (a statistical method) to the variationin the timing of postoperative breathing. Methods. We observed 49 patients 3–6 h after a varietyof surgical procedures, once they had achieved a stable breathingpattern. The breathing patterns could be one of the three typespredicted by the extreme value model. ‘Finite’ breathingpatterns (n=30) have a finite upper limit of duration for anyapnoea. Patients that displayed one of the other two patterns(‘standard’ and ‘extended’) have, potentially,no limit in duration of apnoea. Results. The type of breathing pattern observed in each patientwas not reliably identified by most of the commonly used riskfactors (age, type of surgery, opioid type, dose, and routeof administration). A finite pattern was observed in 13 of 26patients receiving epidural (vs 17 of 23 parenteral analgesia:P=0.15), and 15 of 19 receiving morphine (vs 15 of 30 otheropioids: P=0.05). The patients with ‘finite’ patternswere also significantly less drowsy (score 1.04 (0.92) vs 1.62(0.62), P<0.05). Conclusions. The breathing pattern was not related to mean breathtimes, suggesting that the prevalence of apnoeas cannot be reliablypredicted by measurement of the respiratory rate alone. Br J Anaesth 2002; 88: 61–4     

Skin conductance monitoring compared with Bispectral Index to assess emergence from total i.v. anaesthesia using propofol and remifentanil

Background. Arousal after sevoflurane anaesthesia has been detectableby monitoring changes in skin conductance (SC) with similaraccuracy as monitoring Bispectral Index (BIS^®). As SC monitoringdetects changes in sympathetic tone, the measurements mightbe confounded by the sympatholytic properties of propofol, acomponent of total i.v. anaesthesia (TIVA). Therefore in thisstudy, monitoring of SC during emergence from TIVA was comparedwith the monitoring of BIS^®. Methods. Twenty-five patients undergoing plastic surgery wereinvestigated. The number of fluctuations of SC per second (NFSC),BIS^® and haemodynamic variables [systolic blood pressure(SBP) and heart rate (HR)] were recorded simultaneously. Theperformance of the monitoring devices in distinguishing betweenthe clinical states ‘steady-state anaesthesia’,‘first clinical reaction’ and ‘extubation’were compared using the method of prediction probability (Pk)calculation. Results. BIS^® showed the best performance in distinguishingbetween ‘steady-state anaesthesia’ and ‘firstreaction’ (Pk BIS^® 0.99 vs NFSC 0.80; P<0.01),and ‘steady-state anaesthesia’ and ‘extubation’(Pk BIS^® 1.00 vs NFSC 0.91; P<0.05); the time from firstchange of BIS^® or NFSC to a first clinical reaction wassignificantly longer for NFSC (median BIS^® 135 s vs NFSC191 s; P<0.05). BIS^® and NFSC performed better in distinguishingbetween the investigated clinical states than SBP and HR. Conclusions. In this study, BIS^® was found to predict arousalwith a higher probability but slower response times than NFSCin patients waking after TIVA.     

Cardioprotective effects of desflurane: effect of timing and duration of administration in rat myocardium

Background. We compared the cardioprotective effects of 1 minimumalveolar concentration (MAC) desflurane administered before,during or after ischaemia, or throughout the experiment (before,during and after ischaemia) on myocardial infarct size following30 min occlusion of the left anterior descending coronary arteryand 3 h reperfusion in adult rats. Methods. Fifty male Sprague–Dawley rats were anaesthetizedwith pentobarbital, intubated and mechanically ventilated. Bloodgases, pH and body temperature (37.5–38°C) were controlled.Heart rate and arterial pressure were measured continuously.Animals were randomly assigned to the following groups (n=10in each group): pentobarbital only (‘Pento’); 15min desflurane administration followed by 10 min of washoutbefore 30 min ischaemia and 3 h reperfusion (‘Precond’);30 min desflurane administration during ischaemia period (‘Isch’);desflurane administration during the 15 first min of reperfusion(‘Reperf’) and desflurane administration throughoutthe experiment (before, during and after ischaemia; ‘Long’).Volumes at risk and infarct sizes were assessed by Indian inkand with 2,3,5-triphenyltetrazolium chloride staining, respectively. Results. Physiological parameters and volumes at risk were notsignificantly different between groups. In the Pento group,mean myocardial infarct size was 65 (SD 15)% of the volume atrisk; myocardial infarct size was reduced to a significant andcomparable extent in the desflurane-treated groups (Precond42 (14)%; Isch 34 (11)%; Reperf 41 (15)%; Long 33 (10)%; P<0.0002vs Pento group). Conclusions. In rats, desflurane 1 MAC significantly decreasedmyocardial infarct size whatever the period and duration ofadministration. Br J Anaesth 2004; 92: 552–7     

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We received correspondence from Nick Lavies of Worthing in connectionwith the article by Radha Ravi and Tanya Howell on ‘Anaesthesiafor paediatric ear nose and throat surgery’ (CEACCP 2007;7(2): 33–37). Dr Lavies commented on the issues of airwaymanagement, management of the bleeding tonsil, and anaesthesiafor oesophagoscopy. He questioned the statement that ‘only16% of anaesthetists used the reinforced laryngeal mask airwayroutinely. However, no mention is made of the CJD problem whichforced me and I suspect a good     

Tight control of prehospital ventilation by capnography in major trauma victims

Background. Tracheal intubation combined with controlled ventilationof the lungs is an important part of the prehospital managementof major trauma victims, but gauging the adequacy of ventilationremains a major problem. Methods. Ninety-seven major trauma victims who underwent trachealintubation in the field and controlled ventilation of the lungsduring prehospital treatment by a Helicopter Emergency MedicalService were assigned randomly to one of two groups: (1) monitorgroup (n=57) and (2) monitor-blind group (n=40), according towhether the anaesthetist could or could not see an attachedcapnograph screen. In the monitor-blind group ventilation wasset by using a tidal-volume of 10 ml kg^–1 estimated bodyweight and an age-appropriate ventilatory frequency. In themonitor group, ventilation was adjusted to achieve target end-tidalcarbon dioxide values determined by the ‘physiologicalstate’ of the trauma victim. Arterial blood gases weremeasured upon hospital admission while maintaining the ventilationinitiated in the field and the Pa_CO2 value obtained was usedas the determinant of the adequacy of prehospital ventilation. Results. The incidence of ‘normoventilation’ wassignificantly higher (63.2 vs 20%; P<0.0001) and the incidenceof ‘hypoventilation’ upon hospital admission wassignificantly lower (5.3 vs 37.5%; P<0.0001) in the monitorgroup; patients with severe head and chest trauma and haemodynamicallyunstable patients and those with a high injury severity scorewere significantly more likely to be ‘normoventilated’upon hospital admission in the monitor group than in the monitor-blindgroup. Conclusions. The data support the routine use of prehospitalcapnographic monitoring using target end-tidal carbon dioxidevalues adapted to the physiological state of the patient inmajor trauma victims requiring tracheal intubation in the field. Br J Anaesth 2003; 90: 327–32     

Predictive performance of a physiological model for enflurane closed-circuit anaesthesia: effects of continuous cardiac output measurements and age-related solubility data

Background. The disposition of inhalation anaesthetics is governedby the factors described in the Fick principle. Methods. We have recalibrated a previously validated physiologicalmodel for enflurane closed-circuit inhalation anaesthesia, usingindividual continuous cardiac output measurements as well asage-related enflurane solubility coefficients as inputs to themodel. Two model versions using ‘calculated’ (Brody’sformula) or ‘measured’ (thoracic electrical bioimpedance)cardiac output values, and two versions with ‘standard’(fixed) or ‘age-related’ solubility coefficientswere formulated. Results. Data from 62 ophthalmic surgical patients were usedto validate the predictive performance of the four model versions.The root mean squared errors (total error) and scatters (errorvariation) were similar with the extended model versions, butthe group biases (systematic error component) were significantlyless with the model versions that included age-related solubilitycompared with the versions using standard solubility coefficients(bias –0.76/–0.78% vs –3.44/–3.60%). Conclusion. The inclusion of age-related solubility coefficientsbut not of continuous cardiac output measurements improves thepredictive performance of the physiological model for closed-circuitinhalation anaesthetic conditions in routine clinical practice. Br J Anaesth 2002; 88: 38–45     

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The purpose of this section of CEACCP is to provide a forumfor debate and clarification of any controversies arising fromprevious articles David Levy of Nottingham queried the statement regarding i.v.anaesthetic agents in the elderly that ‘Reduced hepaticclearance leads to an increased recovery time even when givenat the correct dose’ (CEACCP 2004; 4: 193–6). DrLevy wrote     

Stress in UK intensive care unit doctors

Background. Doctors have long been considered at risk of occupationalstress. Methods. A postal survey of all members of the Intensive CareSociety using validated instruments. Results. Eight-five per cent of members returned questionnairesand 70% were eligible for the study. Twenty-nine per cent weresuffering General Health Questionnaire-12 (GHQ-12) identifieddistress and 12% Symptom Checklist-Depression (SCL-D) defineddepression. There were no significant age or sex differencesbetween staff suffering distress or depression and those whodid not. Dissatisfaction with career correlated highly withboth distress and depression (P<0.01). Twenty doctors (3%)were bothered by suicidal thoughts. The most stressful aspectsof work were bed allocation, being over-stretched, effect ofhours of work and stress on personal/family life, and compromisingstandards when resources are short. Logistic regression revealedmental health problems were predicted by five stressors: ‘lackof recognition of one’s own contribution by others’;‘too much responsibility at times’; ‘effectof stress on personal/family life’; ‘keeping upto date with knowledge’; and ‘making the right decisionalone’. Conclusions. Nearly one in three ICU doctors appeared distressed(GHQ), and one in 10 depressed (SCL-D); this is no greater thanthat reported in other specialities. Perceived stressors revealsome key areas of concern for the employer and the specialty. Br J Anaesth 2002; 89: 873–81     

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The purpose of this section of CEACCP is to provide a forumfor debate and clarification of any controversies arising fromprevious articles This month we received correspondence from Drs Andy Petros,Richard Sarginson, Mark Fox and Rick van Saene of London andLiverpool commenting on the article by Ken Inweregbu, JayshreeDave and Alison Pittard on ‘Nosocomial infections’(CEACCP 2005; 5: 14–17). Dr Petros and colleagues stated     

Enhanced visual memory effect for negative versus positive emotional content is potentiated at sub-anaesthetic concentrations of thiopental

Background. Emotional information has the ability to alter theformation and strength of a memory (‘memory modulation’).Memory modulation by negative emotion is mediated by the amygdala.It is not known how gamma aminobutyric acid (GABA)ergic drugsaffect the processes involved in memory modulation. This studyinvestigates whether memory for negative emotional stimuli ismore refractory to the effects of GABAergic drugs. Methods. Eighty-three healthy volunteers were shown a randomizedsequence of 60 visual stimuli consisting of negative, positiveand neutral emotive pictures, while receiving a controlled infusionof thiopental (n=31), propofol (n=31), dexmedetomidine (n=10)or placebo (n=11). After a 5 h retention interval, when drugconcentration was negligible, subjects performed a recognitiontask with ‘old’ pictures randomly mixed with ‘new’pictures. Drug effect was calculated as the proportionate reductionin recognition for images of each emotional valence. Results. Forty-eight subjects were included in a within-subjectlogistic dose–response model analysis. In the thiopentalgroup there was a smaller drug effect seen for negative vs positiveimages (proportional memory reduction from baseline 0.27 (SD0.20) vs 0.56 (0.25), P<0.001, n=20 included in analysis).A similar trend was seen in the propofol group (0.25 (0.28)vs 0.54 (0.30), n=10), but this did not attain statistical significance.No trend was seen in the dexmedetomidine group (0.33 (0.26)vs 0.24 (0.22), n=7). Conclusions. Over a specific dose range of thiopental (targetserum concentration 2–7 µg ml^–1), impairmentof explicit memory for images with negative emotional valenceis less than that for images with positive emotional valence.There is a strong possibility that propofol (target serum concentration0.3–2.4 µg ml^–1) causes a similar effect.Modulation of visual memory by negative emotional content continuesat sub-anaesthetic concentrations of GABAergic drugs associatedwith explicit memory impairment.     

The 'swoosh' test--an evaluation of a modified 'whoosh' test in children

Background. Caudal analgesia is widely used in paediatric anaestheticpractice. In adults, the ‘whoosh’ test has beenrecommended as a guide to successful needle insertion, but ithas not been extensively studied in paediatric patients. Wehave investigated a modification of the ‘whoosh’test, which we have christened the ‘swoosh’ test.It avoids the injection of air by performing auscultation duringinjection of the local anaesthetic solution. We have comparedit with clinical judgement of correct placement. Methods. We studied 113 children undergoing elective surgery.During insertion of the caudal block, a stethoscope was placedover the lower lumbar spine and the presence or absence of anaudible ‘swoosh’ noted. The operator’s clinicalimpression of successful insertion was also recorded. Results. The overall success rate of caudal anaesthesia was95.6%. Of the 108 patients with a successful block, 98 had apositive ‘swoosh’ test. There were no false positiveresults. Calculations show the ‘swoosh’ test tohave a sensitivity of 91%, a specificity of 100% and a positivepredictive value of 100%. Conclusions. The ‘swoosh’ test is a simple and accuratetest to confirm successful caudal insertion in children, andis especially useful as a teaching aid for anaesthetists newto the technique. Br J Anaesth 2003; 90: 62–5     

Patient satisfaction with anaesthesia care: development of a psychometric questionnaire and benchmarking among six hospitals in Switzerland and Austria

Background. We describe the development and comparison of apsychometric questionnaire on patient satisfaction with anaesthesiacare among six hospitals. Methods. We used a rigorous protocol: generation of items, constructionof the pilot questionnaire, pilot study, statistical analysis(construct validity, factor analysis, reliability analysis),compilation of the final questionnaire, main study, repeatedanalysis of construct validity and reliability. We comparedthe mean total problem score and the scores for the dimensions:‘Information/Involvement in decision-making’, and‘Continuity of personal care by anaesthetist’. Theinfluence of potential confounding variables was tested (multiplelinear regression). Results. The average problem score from all hospitals was 18.6%.Most problems are mentioned in the dimensions ‘Information/Involvementin decision-making’ (mean problem score: 30.9%) and ‘Continuityof personal care by anaesthetist’ (mean problem score:32.2%). The overall assessment of the quality of anaesthesiacare was good to excellent in 98.7% of cases. The most importantdimension was ‘Information/Involvement in decision-making’.The mean total problem score was significantly lower for twohospitals than the total mean for all hospitals (significantlyhigher at two hospitals) (P<0.05). Amongst the confoundingvariables considered, age, sex, subjective state of health,type of anaesthesia and level of education had an influenceon the total problem score and the two dimensions mentioned.There were only marginal differences with and without the influenceof the confounding variables for the different hospitals. Conclusions. A psychometric questionnaire on patient satisfactionwith anaesthesia care must cover areas such as patient information,involvement in decision-making, and contact with the anaesthetist.The assessment using summed scores for dimensions is more informativethan a global summed rating. There were significant differencesbetween hospitals. Moreover, the high problem scores indicatea great potential for improvement at all hospitals. Br J Anaesth 2002; 89: 863–72     

Anaesthetist's responses to patients' self-reported drug allergies

Background. Patients with drug allergies are commonplace inanaesthetic practice. We investigated the incidence and natureof drug ‘allergies’ reported by surgical patientsattending a hospital pre-admission clinic, and went on to ascertainto what degree drug allergies recorded in the records influenceddrug prescribing during the patients’ hospital stay anddetermine whether any adverse events occurred in relation todrug prescribing in this population. Methods. Patients attending for anaesthetic assessment at aPre-Admission Clinic over a 30 week period were questioned concerningdrug allergies. Medical records of these patients were thenexamined after their hospitalization to assess medications prescribedduring that period. Results. Of 1260 patients attending the Pre-admission clinicduring the study period 420 (33.4%) claimed to have a totalof 644 individual drug ‘allergies’. The most commonagents implicated were antibiotics (n=272), opioid analgesics(n=118) and NSAIDs (n=62); the most common form of these reactionswere dermatological (n=254) and nausea and vomiting (n=124).There were 41 self-reports specifically of anaphylaxis and afurther 61 where there was significant respiratory system involvement. Conclusions. The majority of the self-reported allergies werein fact simply accepted adverse effects of the drugs concerned.The patients’ reported drug ‘allergy’ historywas generally well respected by anaesthetists and other medicalstaff. There were 13 incidents, mainly involving morphine, wherepatients were given a drug to which they had claimed a specificallergy. There were 101 incidents in 89 patients where drugsof the same pharmacological group as that of their allergicdrug were used. There were no untoward reactions in 84 patientswho had claimed a prior adverse reaction to penicillin who weregiven cephalosporins. There were no sequelae from any otherevents. While anaesthetists generally respected patients self-reported‘allergies', more attention needs to be paid to the accuraterecording of patients’ events and a clear distinctionshould be made both in medical records and to the patient betweentrue drug allergy and simple adverse drug reactions.     

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The purpose of this section of CEACCP is to provide a forumfor debate and clarification of any controversies arising fromprevious articles. We have received correspondence relating to two topics in theOctober 2003 edition of BJA CEPD Reviews. Dr Jeremy Weinbren of London commented on the article on ‘Percutaneoustracheostomy’ by      

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We received correspondence from Dr Bruce Powell of FremantleHospital, Western Australia and Drs Marie Healy and Peter Shirleyof the Royal London Hospital in connection with the articleby John Hunter, Katy Gregg and Zaherali Damani on Rhabdomyolysis(     

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The purpose of this section of CEACCP is to provide a forumfor debate and clarification of any controversies arising fromprevious articles We have received correspondence from David Elcock of Shrewsburyregarding the article on Nitrous Oxide by Amelia Banks and JonathanHardman (CEACCP 2005, 5,5: 145–8), in which it was statedthat filling ratios of nitrous oxide cylinders are less in tropicalcountries. Dr     

Release by hypoxia of a soluble vasoconstrictor from rabbit small pulmonary arteries

Background. Soluble pulmonary vasoconstrictors released in responseto hypoxia have been reported in pig and rat preparations, butnot in rabbit preparations. Methods. We used myography to evaluate the contribution of asoluble factor to constriction in rabbit small pulmonary arteries(external diameter 300–475 µm) exposed to 45 minhypoxia (PO₂=9 mm Hg). Results. Hypoxia produced gradually intensifying constriction.Return to euoxia (PO₂=145 mm Hg) for 30 min relaxed onlyapproximately 30% of the constriction, whereas elution of themyograph bath yielded full relaxation. Reapplication of theeluent gradually restored the constriction to its pre-elutionlevel over a 30-min period. Conclusions. In this closed system, a soluble factor contributessubstantially to hypoxic pulmonary vasoconstriction. Br J Anaesth 2003; 91: 592–4     

Randomized evaluation of the performance of single-use laryngoscopes in simulated easy and difficult intubation

Background. Single-use laryngoscopes are becoming used morewidely. Methods. We compared six types of single-use laryngoscope withthe standard Macintosh laryngoscope using the Laerdal SimMan^TMpatient simulator. Twenty anaesthetists attempted to intubatethe simulator with standardized airway settings allowing a fullview of the vocal cords (‘easy intubation’). Theairway settings were then changed so that only the posteriorpart of the glottis was visible (‘difficult intubation’)and the anaesthetists were asked to intubate the simulator again. Results. The time to intubate with the standard laryngoscopewas less in both easy (P<0.05) and difficult (P<0.01)intubations. The performance of five laryngoscopes during easyintubation (P<0.01) and four during difficult intubation(P<0.001) was significantly worse than that of the Macintosh.There was a significant difference in Cormack and Lehane gradingbetween the laryngoscopes tested in both easy (P<0.05) anddifficult (P<0.05) intubation. The percentage of glotticopening visible (POGO score) also differed between laryngoscopesin both the easy (P<0.01) and difficult (P<0.001) groups.The highest POGO scores were obtained with the Macintosh laryngoscope.During the difficult intubation simulation, the reusable Macintoshlaryngoscope needed less use of a bougie and had fewer failedintubations than the single-use laryngoscopes, but these differencesdid not reach statistical significance. Conclusions. Of the laryngoscopes tested, the standard reusableMacintosh laryngoscope performed best. The Europa^TM was thebest single-use laryngoscope. Some single-use laryngoscopestested were significantly inferior to the Macintosh. This raisesconcern over their use in clinical practice, particularly ifintubation is difficult. Br J Anaesth 2003; 90: 8–13