Summary

Background: The suggested induction dose of methohexital for electroconvulsive therapy (ECT) varies widely influencing efficacy of ECT and safety of anaesthesia. Bispectral index (BIS), a monitor of consciousness, may be useful to assure adequate hypnosis with optimized methohexital dose. Methods: Patients with medically resistant major depression (ICD10), scheduled for multiple ECT's, were studied. Depth of anaesthesia was BIS controlled. ECT was not performed until BIS dropped below 50. Initially anaesthesia was induced with methohexital 1.0 mg kg−1, and stepwise reduced by 0.1 mg kg−1 during consecutive treatments. If BIS did not drop below 50, the methohexital was supplemented by further boluses of 0.5 mg kg−1, until the desired level of hypnosis was reached. The adequacy of the anaesthetic recommendation for methohexital (1.0–1.5 mg kg−1) as well as the psychiatric recommendation (0.75–1 mg kg−1) was investigated. Results: One-hundred and nine ECT's in 14 patients were studied. The recommended anaesthetic dose (1.0–1.5 mg kg−1) was inadequate in 40% of the treatments, with 12% exceeding 1.5 mg kg−1, and 28% below 1.0 mg kg−1. Psychiatric recommendation (0.75–1.0 mg kg−1) was inadequate in 49%, with 39% exceeding 1.0 mg kg−1 and 10% undershooting at 0.75 mg kg−1. Conclusions: Methohexital for ECT showed a great variability, exceeding as well as undershooting the dosage recommendations widely. BIS monitoring may be useful to secure adequate hypnosis during muscle relaxation and treatment and may optimize ECT efficacy.

Summary

Background and objective: The quality of spinal anaesthesia, often used for Caesarean section, can be improved by adding an opioid to the local anaesthetic. This study compared the quality of anaesthesia, postoperative analgesia, and adverse effects on mother and neonate when either sufentanil 5 μg or morphine 0.2 mg was added to intrathecal hyperbaric bupivacaine for Caesarean section. Methods: This prospective, randomized and double-blind study encompassed 54 females undergoing Caesarean section. Spinal anaesthesia was obtained with 2 mL of 0.5% bupivacaine supplemented with either 0.2 mg morphine or 5 μg sufentanil. Characteristics of spinal block, intraoperative analgesia, maternal and neonatal side-effects and the time to first request for analgesics were assessed. Results: There were no differences in the onset time of sensory block, time to sensory block to T10, time to highest sensory block, highest sensory block level, time to regression of sensory block to T10 level and time to resolution of motor blockade. Perioperative haemodynamic parameters, neonatal Apgar scores, neurological and adaptive capacity scores, umbilical blood gas values, sedation scores, nausea–vomiting and pruritus incidences were similar in both groups. The time to the first request for an analgesic was significantly longer (19.5 ± 4.7 h vs. 6.3 ± 5.2 h) in patients given morphine (P < 0.05). Conclusions: The addition of 5 μg sufentanil or 0.2 mg morphine to hyperbaric bupivacaine for Caesarean section both provided safe and effective anaesthesia. Morphine increased the duration of postoperative analgesia compared with sufentanil without increasing maternal or neonatal side-effects.

Summary

Background and objectives: To compare pain relief and motor impairment of 0.25% levobupivacaine with either an equivalent (0.25%) or equipotent (0.4%) concentration of ropivacaine for continuous interscalene block after open shoulder surgery. Methods: Seventy-two adult patients scheduled for elective major shoulder surgery received an interscalene injection of mepivacaine 1.5% 30 mL followed by 24 h patient-controlled interscalene analgesia (basal infusion rate: 5 mL h−1; incremental bolus: 2 mL; lockout period: 10 min; maximum boluses per hour: 4) with either 0.25% levobupivacaine (n = 24), 0.25% ropivacaine (n = 24) or 0.4% ropivacaine (n = 24). A blinded observer recorded the evolution of pain relief and recovery of motor block during the first 24 h. Motor function was assessed as the maximum pressure developed while squeezing a sphygmomanometer cuff with the blocked hand. The reduction from preoperative values was considered as an index of motor impairment. Results: No differences were reported among the three groups in the quality of postoperative analgesia. The number of incremental patient-controlled interscalene analgesia doses, total volume of local anaesthetic infused during the 24-h patient-controlled interscalene analgesia, and number of rescue ketoprofen analgesia were higher in the ropivacaine 0.25% group than in the other two groups ( P = 0.0005). The hand strength recovered to ≥90% of baseline values within the first 24 h of infusion in all groups, without differences among the three groups. Conclusion: When providing patient-controlled interscalene analgesia after open shoulder surgery 0.25% levobupivacaine and 0.4% ropivacaine performed equally in terms of pain relief, motor block and number of patient-controlled boluses required, while patients receiving 0.25% ropivacaine needed significantly more boluses and rescue analgesia to control their pain.

Summary

Background and objectives: Ischaemic preconditioning is commonly regarded as one of the most powerful protective mechanisms against a subsequent lethal ischaemic injury during coronary artery bypass graft surgery but is not practiced routinely. Experimentally, isoflurane, a commonly used volatile anaesthetic agent, provides myocardial protection through a signal transduction cascade that is remarkably similar to the pathways identified in ischaemic preconditioning. The aim of our study was to investigate whether pre-ischaemic administration of isoflurane exerted protection against prolonged ischaemia with functional recovery and reduced necrosis among patients undergoing coronary artery bypass graft surgery. Methods: Forty patients scheduled for elective coronary artery bypass graft operations were prospectively randomized into the control or isoflurane groups. In the isoflurane group, isoflurane 2.5 minimum alveolar concentration was administered for 15 min followed by a 5-min washout period before aortic cross-clamping. The control group received a time-matched period of isoflurane-free cardiopulmonary bypass. The conduction of anaesthesia and surgery were standardized in all patients. Haemodynamic data, troponin I release and inotropic support were measured and recorded perioperatively. Results: There were no adverse effects related to isoflurane administration. In the isoflurane group, the mean cardiac index after cardiopulmonary bypass was significantly higher than the pre-bypass value (P < 0.05), whereas no difference was found in the control group. At 15 min after cardiopulmonary bypass and 6 h after surgery, the changes in cardiac index and stroke volume index were significantly higher in the isoflurane group than in the control group (P < 0.05). There was a consistently lower release of troponin I in the isoflurane group compared to the control group. Compared to the controls, the mean troponin I level was significantly reduced in the isoflurane group at 24 h after surgery (P = 0.042). Conclusions: The present results support the preconditioning effect of isoflurane in patients undergoing coronary artery bypass graft surgery as clinically feasible and providing optimal cardiac protection.

Summary

Background: This study was designed to evaluate the feasibility of propofol infusion by a closed-loop system for the titration of anaesthetic induction guided by Bispectral Index. Methods: Forty patients were prospectively and randomly allocated into two groups: the target control infusion (TCI) group, where propofol titration was performed manually guided by the Bispectral Index using a commercial pharmacokinetic model (Diprifusor device) and the closed-loop group where titration was performed using a proportional differential algorithm. For both groups, the objective was to achieve a Bispectral Index of 50. Remifentanil TCI was infused at a target of 2 ng mL−1 and was maintained constant throughout the study. Feasibility of automatic induction was evaluated with performance error and haemodynamic data. Results: Bispectral Index overshoot (−9 ± 13% vs. −16 ± 20%, P = 0.035) and mean duration of induction (381 ± 106 s vs. 490 ± 131 s, P = 0.004) were lower in the closed-loop group than in the TCI group. Haemodynamic data were similar between groups with a similar use of ephedrine bolus. Conclusion: The system was able to allow induction clinically for all patients. Automated titration guided by Bispectral Index for propofol infusion was feasible without increase in haemodynamic adverse effects.

Summary

Background and objective: Despite the introduction of various less-invasive concepts of cardiac output measurement, pulmonary arterial thermodilution is still the most common measurement technique. Methods: This prospective controlled study was designed to compare different methods of cardiac output measurement simultaneously. Pulmonary arterial thermodilution, transpulmonary thermodilution (PiCCO™), trans-oesophageal echo-Doppler probe (HemoSonic™) and partial carbon dioxide rebreathing technique (NICO™ monitor) were evaluated against a peri-aortic transit-time flow-probe as reference method in a clinically relevant animal model. After approval from the Local Ethics Committee on Animal Research, the investigations were conducted in nine anesthetized domestic pigs. Systemic haemodynamics were modulated systematically by the application of catecholamines, caval occlusion and exsanguination. Statistical analysis was performed with Bland–Altman and linear regression. Results: A total of 366 paired cardiac output measurements were carried out at a reference cardiac output between 0.5 and 7 L min−1. The correlation coefficients for pulmonary arterial and transpulmonary thermodilution against reference were 0.93 and 0.95, for trans-oesophageal Doppler and partial rebreathing technique 0.84 and 0.77. Pulmonary arterial thermodilution and transpulmonary thermodilution showed comparable bias and limits of agreement. Where HemoSonic™ showed an overestimation of cardiac output at a higher precision, NICO™ overestimated low and underestimated higher cardiac output values. Conclusions: Our data suggest that pulmonary arterial thermodilution and PiCCO™ may be interchangeably used for cardiac output measurement even under acute haemodynamic changes. The method described by Bland and Altman demonstrated an overestimation of cardiac output for both thermodilution methods. HemoSonic™ and NICO™ offer non-invasive alternatives and complementary monitoring tools in numerous clinical situations. Trend monitoring and haemodynamic optimizing can be applied sufficiently, when absolute measures are judged critically in a clinical context. The use of the NICO™ system seems to be limited during acute circulatory changes.

Summary

Background and objective: Bispectral Index® correlates with depth of hypnosis in adult patients. Bispectral index monitoring has been separately examined and validated during both mild and moderate hypothermic cardiopulmonary bypass. However, the effect on bispectral index of these two differing cardiopulmonary bypass temperature regimes has not previously been compared, particularly with the use of volatile anaesthetic agents. Methods: Following Institutional Ethics Committee approval and informed consent, 30 patients undergoing coronary artery bypass grafting had additional bispectral index monitoring. Sixteen patients had mild hypothermic bypass (32–34°C), and 14 had moderate hypothermic bypass (28–30°C). Anaesthesia was standardized, and was maintained with enflurane throughout surgery. Scores were recorded at 14 specific event-related time points during surgery. Results: This study has demonstrated that in this adult population, a relationship exists between bispectral index score and temperature throughout the duration of cardiac surgery, which included mild or moderate hypothermic cardiopulmonary bypass. It also demonstrated that patients which were categorized as having received moderately hypothermic cardiopulmonary bypass had lower bispectral index scores than those patients who received mild hypothermic cardiopulmonary bypass, at time points corresponding approximately with median steady-state bypass temperature, pre-re-warming and early re-warming periods. Conclusions: Moderate hypothermic cardiopulmonary bypass has lower bispectral index scores when compared to mild hypothermic cardiopulmonary bypass, at a steady state of inspired enflurane. This may reflect an actual increase in the depth of hypnosis. However, as this study did not address the physico-chemical changes of the volatile agent or the accuracy of the bispectral index algorithm at lower temperatures, we would not advocate a change in practice based solely on this report.

Summary

Background and objective: Awareness with postoperative recall of intraoperative events is a rare but serious complication of general anaesthesia. This survey investigated the attitude of anaesthetists in the UK to awareness and depth of anaesthesia monitoring. Methods: Questionnaires were sent to 4927 consultant anaesthetists in 285 hospitals in the UK in September 2004. The responses were recorded in an electronic database, summarized and compared with the results of studies performed in Australia and the USA. Results: The response rate was 44%. When judged against published awareness rates, anaesthetists underestimated the incidence of awareness in their own practice (median 1: 5000). One-third of respondents have dealt with patients who have experienced intraoperative recall. The majority of anaesthetists perceived awareness as a minor problem on an 11-point scale (modal score 2, median score 3, IQR 2–5). Eighty-six percent of anaesthetists considered clinical signs unreliable but 91% felt that measurement of end-tidal anaesthetic agent concentration reduces the likelihood of awareness. The majority of anaesthetists would use a monitor at least some of the time if one was available to them. Overall, the attitudes of anaesthetists in the UK, USA and Australia are remarkably similar. Conclusions: Anaesthetists tend not to view awareness as a serious problem. Although most accept that clinical signs are unreliable indicators of awareness, few believe that monitors of anaesthetic depth should be used for routine cases.

Summary

Background and objective: Oral morphine may be useful for postoperative pain relief, but few studies have tested its use after in-hospital surgery. Methods: We evaluated clinical efficacy and the pharmacokinetic parameters of oral morphine after total hip arthroplasty. We recruited 60 patients who had total hip arthroplasty under general anaesthesia. The patients were randomized to receive placebo, 10 mg morphine sulphate or 20 mg morphine sulphate orally every 4 h for 24 h. The oral administration was started 3 h after the morphine-loading dose in the Post Anaesthesia Care Unit and then patients used intravenous morphine patient-controlled analgesia for 24 h. Pain score at rest (scored by patients on a visual analogue scale), sedation, nausea, vomiting and urinary retention were monitored. In 11 additional total hip arthroplasty patients, we determined the pharmacokinetics of morphine and its metabolites after oral administration of 20 mg morphine sulphate every 4 h for 16 h. Results: The amount of morphine administered via patient-controlled analgesia over 24 h was reduced in the 20-mg group compared with that in the placebo group (19.0 ± 2.7 mg vs. 33.0 ± 5.5 mg; P = 0.03). No significant morphine-sparing effect was observed in the 10-mg group. Pain scores and side-effects were similar in all groups. The pharmacokinetic study revealed a limited and slow absorption of morphine. Conclusion: Despite a limited absorption of oral morphine postoperatively, high doses of oral morphine have a significant analgesic effect after total hip arthroplasty.

Summary

Backgrounds: The purpose of this study was to evaluate the effect of ephedrine and phenylephrine on propofol concentrations and bispectral index during propofol anesthesia. Methods: General anaesthesia was induced with propofol and was maintained with propofol (4 mg kg−1 h−1) and fentanyl. Vecuronium was used to facilitate the artificial ventilation of the lungs. Patients with systolic blood pressure > 90 mmHg were defined as the control group (n = 16). Patients who had to be treated for larger decreases in arterial blood pressure (systolic blood pressure <90 mmHg) were randomly assigned to receive ephedrine 0.1 mg kg−1 (n = 20) or phenylephrine 2 μg kg−1 (n = 20). Propofol concentrations were determined before (baseline) and at 3 and 10 min after the administration of ephedrine or phenylephrine. Bispectral index was monitored continuously. Cardiac output was determined using a pulmonary arterial catheter. Results: Ten minutes after drug injection, bispectral index in the ephedrine group increased significantly compared with the baseline and was significantly larger than that in the control or phenylephrine group. Eight patients in the ephedrine group had bispectral index >60, whereas no patient in the control or phenylephrine groups had bispectral index >60. There were no significant differences in propofol concentrations or cardiac output relative to baseline at 3 or 10 min after the administration of ephedrine or phenylephrine. Conclusions: Ephedrine increases bispectral index values without decreasing propofol concentrations during general anesthesia.

Summary

Background and objective: Anaesthesiologists need parameters that measure the depth of anaesthesia. In the context of this need, the present study investigated in rats how two variables from the electroencephalogram, the burst suppression ratio and effective correlation dimension correlated with a measure of anaesthetic depth as measured in the strength of a noxious withdrawal reflex. Methods: Eight rats were exposed to different inspiratory concentrations of sevoflurane, each rat in two separate experiments. In the first experiment, spontaneously breathing animals could move freely and no painful stimuli were applied. In the second experiment, in mechanically ventilated restrained anaesthetized rats, the withdrawal reflex was measured every 80 s. In both experiments the electroencephalogram was continuously recorded. The concentration in the effector compartment was estimated using a first order two compartment model. Correlation dimension was computed following the Grassberger/Procaccia/Takens approach with optimized parameter settings to achieve maximum sensitivity to anaesthetic drug effects and enable real-time computation. The Hill, equation was fitted to the data, describing the effect as a function of sevoflurane concentration. Results: Good correlations of Depth of Anaesthesia with correlation dimension as well as burst suppression ratio were established in both types of experiments. Arousal by noxious stimuli decreased burst suppression ratio and increased correlation dimension. The effective sevoflurane concentration associated with 50% of the maximum effect (C50) was higher in experiment II (stimulation) than in experiment I (no stimulation): i.e. for correlation dimension 2.18% vs. 0.60% and for burst suppression ratio 3.07% vs. 1.73%. The slope factors were: γCD = 4.15 vs. γCD = 1.73 and γBSR = 5.2 vs. γBSR = 5.4. Correlation dimension and burst suppression ratio both correlated with the strength of the withdrawal reflex with correlation coefficients of 0.46 and 0.66 respectively (P < 0.001). Conclusions: Both correlation dimension and burst suppression ratio are related to anaesthetic depth and are affected by noxious stimuli. The relationship between anaesthetic depth and burst suppression ratio is confirmed and the potential of correlation dimension is demonstrated.

Summary

Background and objective: The aim of this prospective study was to compare the effect of the administration of desflurane or sevoflurane to a fixed neuromuscular block. Methods: After written consent, 12 patients were anaesthetized with propofol and sufentanil. Atracurium was administered via a continuous infusion in order to obtain 85% twitch depression of the control value assessed by repeated accelerometric stimulation at the adductor pollicis. Once stabilized over the course of 30 min, propofol was discontinued and either desflurane (n = 6) or sevoflurane (n = 6) was delivered at 1 MAC in a mixture of 50% O2 in air. Study parameters were the magnitude and the time of twitch height variations. Results are presented in mean ± SD. Result: Exposure to halogenated agents led to a significant reduction in twitch height with similar magnitude between the two agents. However, interaction with desflurane showed an initial and transient rise (35 ± 22%) in twitch height before subsequent depression occurred. The time to reach 50% of the signal depression in the desflurane group was significantly delayed (25 ± 7 vs. 11 ± 4 min in the sevoflurane group; P < 0.01). Conclusions: On a stable neuromuscular block elicited by continuous infusion of atracurium, the abrupt administration of desflurane or sevoflurane reduces the accelerometric responses of the adductor pollicis in a similar way. This potentiating effect is produced faster after sevoflurane than after desflurane. With desflurane, a biphasic effect (of a transient and moderate increase followed by depression of the signal) was recorded.

Summary

Background and objective: Motor function recovers rapidly but the extended duration of sensory block after spinal anaesthesia with hyperbaric ropivacaine may delay patients' ambulation after surgery. We tested whether compensating a reduction of the ropivacaine dose with a small dose of lidocaine would be adequate for surgery and shorten recovery from spinal anaesthesia. Methods: Fifty-six consecutive outpatients, who were scheduled for lower extremity surgery under spinal anaesthesia, were randomized into two groups to receive either a hyperbaric solution of lidocaine 20 mg and ropivacaine 5 mg (Group LR) or hyperbaric ropivacaine 10 mg (Group R). Sensory block was tested with pinprick and motor block on the Bromage scale at 5-min intervals until 30 min, then at 15-min intervals until 90 min, and thereafter at 30-min intervals until full bilateral recovery. Blinded interviews were performed on the first and seventh postoperative day. Results: The groups did not differ significantly regarding success of sensory block reaching T10 dermatome on the operative side, 24 (86%) in Group LR and 23 (82%) in Group R, median (range) onset time 5 (5–20) vs. 10 (5–25) min or median duration of T10 sensory block 68 (5–115) vs. 50 (20–115) min, respectively. Two patients in each group required general anaesthesia. Recovery did not differ between the groups, median time of full motor recovery was 75 min in both groups, sensory recovery of S2 2.5 h vs. 2.8 h, first voluntary micturition 4.2 (2.2–6.1) vs. 4.5 (2.4–6.6) h in the LR vs. R Group, respectively. Transient neurological symptoms did not appear. Conclusion: It is concluded that spinal anaesthesia with hyperbaric lidocaine 20 mg + ropivacaine 5 mg and hyperbaric ropivacaine 10 mg was quite similar regarding frequency, onset, duration of T10 dermatome sensory block and recovery. The patients would have been ready for discharge after voluntary micturition, 4.2–4.5 h from the subarachnoid injection of local anaesthetics.

Summary

Background and objective: Gabapentin has been suggested to decrease acute postoperative pain. We evaluated the effect of gabapentin on pain after abdominal hysterectomy. Methods: Sixty patients scheduled for abdominal hysterectomy were randomized to receive orally gabapentin 400 mg 6 hourly or placebo. Treatment started 18 h preoperatively and continued for 5 postoperative days. Pain (visual analogue score) and consumption of morphine for 48 h and of oral paracetamol/codeine were recorded after 2, 4, 8, 24 and 48 h and on days 3–5 postoperatively. After 1 month, patients were interviewed by phone for pain, and analgesic intake after hospital discharge. Results: Morphine consumption (mean ± SD) was 35 ± 15.7 mg in the control and 28 ± 12.1 mg in the gabapentin group (P = 0.21). Median number (range) of paracetamol 500 mg/codeine 30 mg tablets taken during days 3–5 was 1.0 (0–6) in the control and 2.0 (0–9) in the gabapentin group (P = 0.35). The visual analogue scores at rest and after cough did not differ between the two groups (F = 0.92, df = 1, P = 0.34 and F = 0.56, df = 1, P = 0.46, respectively). One month after surgery, 22/27 (81%) of the control group and 9/25 (36%) of the gabapentin group reported pain in the surgical area (χ2 = 11.15, P = 0.002), while 11/27 (41%) of controls and 7/25 (28%) of gabapentin patients consumed analgesics for pain (χ2 = 0.93, P = 0.39). The intensity of pain was decreased in the gabapentin group (χ2 = 12.6, P = 0.003). Conclusions: Gabapentin has no effect on immediate pain after abdominal hysterectomy but decreases pain 1 month postoperatively.

Summary

Background: The aim of this prospective study was to compare continuous cardiac output measurements of the non-invasive cardiac output system (NICO) with the pulmonary artery catheter during off-pump coronary bypass surgery. Methods: Twenty-two patients enrolled for off-pump coronary surgery received both a pulmonary artery catheter and a non-invasive cardiac output system for measurement of cardiac output. Data were compared by the Bland–Altman method to calculate the degree of agreement and to analyse if a significant difference existed between the two methods of cardiac output measurements. Results: Perioperatively, the non-invasive cardiac output underestimated cardiac output, but postoperatively overestimated it. The limits of agreement were larger during surgery compared to the postoperative period (−3.1; +2.5 vs. −1.4; +2.2 L min−1). Perioperatively, cardiac output measured with the pulmonary artery catheter varied from 0.5 to 7.5 L min−1 (mean 3.6 L min−1) and with the non-invasive cardiac output from 0.5 to 8.4 L min−1 (mean 3.9 L min−1). Postoperatively, these were 2.5–7.7 L min−1 (mean 4.5 L min−1) and 2.3–8.4 L min−1 (mean 4.9 L min−1), respectively. Conclusion: During off-pump cardiac surgery, the non-invasive cardiac output reliably measures cardiac output and does it more rapidly than a pulmonary artery catheter and may be more useful in order to detect rapid haemodynamic changes.

Summary

Background and objective: The cerebral state index (CSI™) derived from a new small handheld electroencephalogram monitor was studied during routine day surgical anaesthesia titrated according to the bispectral index (BIS™). The objective was to determine the degree of agreement between the two monitors. Methods: Anaesthesia was induced with propofol and fentanyl (0.1 mg) in 38 patients undergoing general anaesthesia for routine day-surgery. Maintenance anaesthesia (sevoflurane (20/38), desflurane (10/38) or propofol (8/38)) titrated by BIS XP (Aspect Medical, Natwick, MA, USA) and BIS and CSI (cerebral State Monitor, Danmeter; Odense, Denmark) index values were recorded every minute. No patient received muscle relaxation. Observer's Assessment of Alertness/Sedation rating scale was used to assess level of sedation. Results: Pair-wise recordings (914) of CSI and BIS were collected. The indices showed similar pattern and decreased with increasing level of sedation, however with large ranges for each level of sedation. Median indices were similar during surgery (BIS: 50 (14–89); CSI: 51 (7–88)) and both indices increased (P < 0.01) when minor movements occurred (BIS 65 (40–83); CSI 67 (40–89)). During maintenance of anaesthesia CSI > 20% from BIS-index in 24% of readings, and on rare occasions CSI indices deviated >100% from the BIS reading. When BIS < 40, CSI decreased slower than BIS and with wider spreading. Conclusions: When used for day-surgery anaesthesia without muscle relaxation, CSI and BIS show similar patterns and numerical values but with the incidence of occasionally large discrepancies between pair-wise readings. Which monitor is the more dependable remains to be established and cannot be implied from this initial explorative study.

Summary

Background and objective: Derived parameters of the electroencephalogram and auditory evoked potentials can be used to determine depth of anaesthesia and sedation. However, it is not known whether any parameter can identify the occurrence of awareness in individual patients. We have compared the performance of bispectral index and a new composite index derived from auditory evoked potentials and the electroencephalogram (AAI 1.61) in predicting consciousness, explicit and implicit memory during moderate sedation with propofol. Methods: Twenty-one patients with spinal anaesthesia received intraoperatively propofol at the age-corrected C50 for loss of consciousness and were presented test words via headphones. Bispectral index and AAI 1.61 (auditory evoked potentials, AEP-Monitor2) were recorded in parallel as well as the Observer's Assessment of Alertness/Sedation-score. Postoperatively, testing for explicit and implicit memory formation was performed. Results: Bispectral index and AAI 1.61 correlated well with loss of consciousness defined by an Observer's Assessment of Alertness/Sedation-score of 2 (identical PK of 0.87), but did not allow a prediction of postoperative explicit or implicit recall. Conclusions: Both bispectral index and AAI may be indices of depth of sedation rather than indicators of memory formation, which persists during propofol sedation even after loss of consciousness.

Summary

Background and objectives: During partial liquid ventilation perfluorocarbons are instilled into the airways from where they subsequently evaporate via the bronchial system. This process is influenced by multiple factors, such as the vapour pressure of the perfluorocarbons, the instilled volume, intrapulmonary perfluorocarbon distribution, postural positioning and ventilatory settings. In our study we compared the effects of open and closed breathing systems, a heat-and-moisture-exchanger and a sodalime absorber on perfluorocarbon evaporation during partial liquid ventilation. Methods: Isolated rat lungs were suspended from a force transducer. After intratracheal perfluorocarbon instillation (10 mL kg−1) the lungs were either ventilated with an open breathing system (n = 6), a closed breathing system (n = 6), an open breathing system with an integrated heat-and-moisture-exchanger (n = 6), an open breathing system with an integrated sodalime absorber (n = 6), or a closed breathing system with an integrated heat-and-moisture-exchanger and a sodalime absorber (n = 6). Evaporative perfluorocarbon elimination was determined gravimetrically. Results: When compared to the elimination half-life in an open breathing system (1.2 ± 0.07 h), elimination half-life was longer with a closed system (6.4 ± 0.9 h, P < 0.01), a sodalime absorber (5.0 ± 0.6 h, P < 0.01) or a heat-and-moisture-exchanger (4.5 ± 0.8 h, P < 0.01). The combination of all three methods (7.1 ± 0.8 h) showed no significant additional effects (P > 0.05) when compared to a closed system. Conclusions: Evaporative perfluorocarbon loss can be reduced effectively with closed breathing systems, followed by the use of sodalime absorbers and heat-and-moisture-exchangers.

Summary

Background and objective: To measure ‘depth of anaesthesia’, anaesthesiologists use a combination of observable end-points such as immobility and autonomic stability. Unconsciousness and amnesia are not reliably observable end-points, but correlate with parameters derived from the electroencephalogram. We investigated the association of subjective assessment and electroencephalographic measures of anaesthetic depth in a group of experienced (>4 yr of experience) and a group of inexperienced (<2 yr of experience) anaesthesiologists. Methods: One hundred ASA I or II patients were assigned to either group. Anaesthesiologists assessed ‘anaesthetic depth’ using an 11-point numeric and a 5-point verbal scale. Bispectral index and spectral entropy were recorded as electroencephalogram parameters. The association between the subjective assessment and the electroencephalogram parameters was calculated using the prediction probability, PK. Results: Association between subjective assessment and electroencephalographic parameters showed a tendency to a better prediction probability in the experienced group. The difference was significant (P < 0.05) for the bispectral index (PK 0.76 ± 0.01 for experienced and 0.71 ± 0.01 for inexperienced anaesthesiologists). In both groups, a large percentage of the data points recorded during surgery showed bispectral index values above the recommended value of 60 (13.2% in the experienced and 34.3% in the inexperienced group) despite a subjective assessment of ‘deep’ or ‘very deep’ anaesthetic depth. Conclusion: The study demonstrates that the association between subjectively assigned values of anaesthetic depth and electroencephalographic parameters of anaesthetic depth is better for anaesthesiologists with more clinical experience. However, in the ‘inexperienced’ as well as ‘experienced’ group a high percentage of bispectral index and entropy values above 60 occurred despite a subjective assessment of adequate anaesthetic depth. Although there was no evidence for explicit memory, this may indicate a risk for memory formation.

Summary

Background and objective: This study was designed to determine if subhypnotic propofol reduces postoperative behavioural disturbances in children undergoing sevoflurane induction compared with intravenous propofol induction for elective adenoidectomy and tonsillectomy. Methods: Following Ethics Committee approval and parental informed consent, ASA I–II, 120 children (2–10 yr) were recruited. Parents were not allowed to accompany their child. Unpremedicated children were randomly allocated to groups receiving inhalation induction with sevoflurane, 2–2.5 mg kg−1 intravenous propofol induction or inhalation induction with sevoflurane followed by subhypnotic dose of propofol (1 mg kg−1). Anaesthesia was maintained with 2–4% sevoflurane, O2 and N2O. Anxiety on arrival to operating theatre, at anaesthesia induction and 30 min after emergence was assessed. Parents completed a state–trait anxiety inventory test preoperatively and a post hospitalization behaviour questionnaire a week later to assess children's postoperative behavioural disturbances. Kruskal–Wallis test, Wilcoxon signed rank sum test, Bonferroni's test, Paired t-test, t-test, Pearson and Spearman's rank correlation test, χ2-test were used for statistical analysis. Results: The anxiety level at induction was high in all groups (P < 0.05). There was no difference between groups in respect to anxiety at other measurement times. A relation between preoperative anxiety level and postoperative behavioural disturbances was determined (P < 0.05). Some behavioural disturbances as nightmare/night fear and desire of sleeping with parents were rarely seen in intravenous propofol induction group (P < 0.05). Conclusion: Addition of subhypnotic dose of propofol to sevoflurane induction did not reduce the incidence of postoperative behavioural disturbances.