Auditory evoked potential index predicts the depth of sedation and movement in response to skin incision during sevoflurane anesthesia

BACKGROUND: The auditory evoked potential (AEP) index, which is a single numerical parameter derived from the AEP in real time and which describes the underlying morphology of the AEP, has been studied as a monitor of anesthetic depth. The current study was designed to evaluate the accuracy of AEPindex for predicting depth of sedation and anesthesia during sevoflurane anesthesia. METHODS: In the first phase of the study, a single end-tidal sevoflurane concentration ranging from 0.5 to 0.9% was assigned randomly and administered to each of 50 patients. The AEPindex and the Bispectral Index (BIS) were obtained simultaneously. Sedation was assessed using the responsiveness portion of the observer's assessment of alertness-sedation scale. In the second phase of the study, 10 additional patients were included, and the 60 patients who were scheduled to have skin incisions were observed for movement in response to skin incision at the end-tidal sevoflurane concentrations between 1.6 and 2.6%. The relation among AEPindex, BIS, sevoflurane concentration, sedation score, and movement or absence of movement after skin incision was determined. Prediction probability values for AEPindex, BIS, and sevoflurane concentration to predict depth of sedation and anesthesia were also calculated. RESULTS: The AEPindex, BIS, and sevoflurane concentration correlated closely with the sedation score. The prediction probability values for AEPindex, BIS, and sevoflurane concentration for sedation score were 0.820, 0.805, and 0.870, respectively, indicating a high predictive performance for depth of sedation. AEPindex and sevoflurane concentration successfully predicted movement after skin (prediction probability = 0.910 and 0.857, respectively), whereas BIS could not (prediction probability = 0.537). CONCLUSIONS: Auditory evoked potential index can be a guide to the depth of sedation and movement in response to skin incision during sevoflurane anesthesia.     

Auditory Evoked Potential Index Predicts the Depth of Sedation and Movement in Response to Skin Incision during Sevoflurane Anesthesia

Background: The auditory evoked potential (AEP) index, which is a single numerical parameter derived from the AEP in real time and which describes the underlying morphology of the AEP, has been studied as a monitor of anesthetic depth. The current study was designed to evaluate the accuracy of AEPindex for predicting depth of sedation and anesthesia during sevoflurane anesthesia.

Methods: In the first phase of the study, a single end-tidal sevoflurane concentration ranging from 0.5 to 0.9% was assigned randomly and administered to each of 50 patients. The AEPindex and the Bispectral Index (BIS) were obtained simultaneously. Sedation was assessed using the responsiveness portion of the observer's assessment of alertness-sedation scale. In the second phase of the study, 10 additional patients were included, and the 60 patients who were scheduled to have skin incisions were observed for movement in response to skin incision at the end-tidal sevoflurane concentrations between 1.6 and 2.6%. The relation among AEPindex, BIS, sevoflurane concentration, sedation score, and movement or absence of movement after skin incision was determined. Prediction probability values for AEPindex, BIS, and sevoflurane concentration to predict depth of sedation and anesthesia were also calculated.

Results: The AEPindex, BIS, and sevoflurane concentration correlated closely with the sedation score. The prediction probability values for AEPindex, BIS, and sevoflurane concentration for sedation score were 0.820, 0.805, and 0.870, respectively, indicating a high predictive performance for depth of sedation. AEPindex and sevoflurane concentration successfully predicted movement after skin (prediction probability = 0.910 and 0.857, respectively), whereas BIS could not (prediction probability = 0.537).     

The cuffed oropharyngeal airway for spontaneous ventilation anaesthesia. Clinical appraisal in 100 patients

The cuffed oropharyngeal airway is a modified Guedel airway with a distal inflatable cuff and a proximal connector for attachment to an anaesthesia circuit. The purpose of this study was to evaluate this device for spontaneous ventilation anaesthesia in 100 adult patients. Anaesthesia was induced with fentanyl and propofol and maintained with nitrous oxide and isoflurane in oxygen. The device was inserted when anaesthetic depth was judged to be adequate. Adverse airway events and interventions (i.e., manoeuvres performed in order to provide a clear airway) were analysed from video recordings and detailed notes. The position of the device was assessed fibreoptically during spontaneous ventilation. The device provided a clear airway in 98% of patients during manually assisted ventilation, in 100% during spontaneous ventilation and in 100% during emergence. However, 91% of patients required at least one airway intervention at some time. Jaw life was required for 33% of the time during manually assisted ventilation and 21% of the time during spontaneous ventilation. Most interventions occurred during the first 3 min of either manually assisted or spontaneous ventilation. The incidence of adverse airway events during manually assisted ventilation was 8%, during spontaneous ventilation was 5% and during emergence was 5%. Oxygen saturation briefly fell to between 87 and 89% on six occasions. On fibreoptic assessment, the vocal cords were visible in 29% of patients on fibreoptic assessment and the epiglottis was visible in 90%. Mild sore throat occurred in 4% of patient. We conclude that the cuffed oropharyngeal airway is suitable for spontaneous ventilation anaesthesia and has a low complication rate but that most patients require one or more interventions to provide a clear airway.     

Effect of remifentanil on the auditory evoked response and haemodynamic changes after intubation and surgical incision

We have observed the effect of intubation and incision, as measured by the auditory evoked response (AER) and haemodynamic variables, in 12 patients undergoing hernia repair or varicose vein surgery who received remifentanil as part of either an inhaled anaesthetic technique using isoflurane or as part of a total i.v. technique using propofol. Anaesthesia was induced with remifentanil 1 microgram kg-1 and propofol, neuromuscular block was achieved with atracurium 0.6 mg kg-1 before intubation, and anaesthesia was maintained with a continuous infusion of remifentanil in combination with either a continuous infusion of propofol or inhaled isoflurane. The AER and haemodynamic variables were measured before and after intubation and incision. The effects of intubation and incision on the AER and haemodynamic variables were not significantly different between the remifentanil- propofol and remifentanil-isoflurane groups. However, the study had a low power for this comparison. When the data for the two anaesthetic combinations were pooled, the only significant effects were increases in diastolic arterial pressure and heart rate immediately after intubation; these were not seen 5 min after intubation. There were no cardiovascular responses to incision. There were no significant changes in the AER after intubation or incision.      

Closed-loop anaesthesia delivery system (CLADS) using bispectral index: a performance assessment study

The development of electroencephalographic indices of anaesthetic depth has in turn generated interest in automated anaesthesia delivery systems using these as the input variable. In this paper, one patented closed loop anaesthesia delivery system (CLADS) (502/DEL/2003) is compared to manual control of propofol delivery titrated to the bispectral index (BIS). Forty ASA I-II patients undergoing elective surgery under general anaesthesia were enrolled in the study. The study participants were randomised using computer generated random numbers to two equal groups. One group received propofol titrated by the CLADS while in the other group (control), anaesthetic delivery was manually titrated to BIS. Closed loop anaesthetic delivery using our patented system led to lower induction doses of propofol (P < 0.05) and less overshoot of the target BIS (P < 0.05). The closed loop system maintained BIS to within +/-10 of target for a significantly longer time during the maintenance phase of anaesthesia (P < 0.01). Smaller amounts of anaesthetic agent were required (P < 0.01) and there was faster postoperative recovery (P < 0.05). Manual delivery of propofol required the infusion rate to be changed a median of 30 times (IQR 12-45), which required considerable time and attention by the anaesthetist. In conclusion, automated delivery of propofol adjusted to the bispectral index using our CLADS was both effective and efficient as compared to manual control.     

Relationship between calculated blood concentration of propofol and electrophysiological variables during emergence from anaesthesia: comparison of bispectral index, spectral edge frequency, median frequency and auditory evoked potential index

We studied four electrophysiological variables (bispectral index (BIS), 95% spectral edge frequency (SEF), median frequency (MF) and auditory evoked potential index (AEP index) in 10 patients during emergence from anaesthesia. We compared correlation of the signals with gradually decreasing calculated blood propofol concentrations, and evaluated the signal differences between preinduction and emergence from anaesthesia. Values of BIS, MF and SEF correlated with calculated blood concentrations of propofol during emergence from anaesthesia. The correlation was best with BIS, but was poor with MF and SEF at low calculated blood propofol concentrations. Although AEP index values did not correlate with calculated blood concentrations of propofol during emergence from anaesthesia, values after eye opening and before anaesthesia were well distinguished from those during emergence from anaesthesia. BIS correlated best with calculated blood concentrations of propofol. AEP index appeared to distinguish the awake from asleep state.      

Peroperative depth of anaesthesia may influence postoperative opioid requirements

BACKGROUND: Studies on monitoring the depth of anaesthesia have shown that with the use of these monitors the peroperative consumption of anaesthetics can be reduced. Studies have also indicated that the peroperative depth of anaesthesia may affect the postoperative course. The purpose of this study was to evaluate a possible relation between the depths of anaesthesia and the postoperative pain score and consumption of morphine. METHODS: We used middle latency auditory evoked potentials (MLAEPs) for monitoring the depth of anaesthesia. The study was prospective, observer blinded and included 50 women scheduled for elective abdominal hysterectomy. Anaesthesia was induced using propofol and remifentanil. Before leaving the recovery room the patients were provided with a programmed patient-controlled pump (PCA), which was only activated on demand. Auditory evoked potentials were registered from just before induction of anaesthesia and during the whole procedure, but the anaesthetist did not have access to the monitor. RESULTS: Fifty patients were included and seven were excluded. The remaining 43 patients were divided into two groups: Group High (n=12) with an AAI>28 for >5% of the registration time and Group Low (n=31) with an AAI>28 for <5% of the registration time. Group High had significantly higher morphine requirements in the recovery and activated the PCA-pump more frequently during the first 24 postoperative hours. CONCLUSION: The results indicate that the peroperative depth of anaesthesia may have effects on the postoperative analgesic requirements.     

Learning placement of a new oropharyngeal intubation (Copa)

OBJECTIVE: To assess learning of Copa (cuffed oropharyngeal airway) technique required for insertion and manual ventilation. STUDY DESIGN: Open prospective clinical study. PERSONS: Four staff members, two anaesthetists and two nurse anaesthetists and 74 ASA I or II patients without difficult intubation criteria presenting for minor surgery in the supine position under general anaesthesia. METHODS: After induction of anaesthesia, the Copa was inserted by each doctor and nurse in at least 16 patients and the ventilation manually assisted until spontaneous breathing resumed. RESULTS: The success rate of insertion at the first attempt was 97%. Therefore no learning period was required. Two laryngospasms and two episodes of cough occurred during Copa placement. Additional manipulations to optimise the ventilation were needed in 48 patients. CONCLUSION: Copa is easy to use without previous training. Further studies are required to assess its side effects and the appropriate depth of anaesthesia required for its insertion.     

Management of hypertrophic pylorus stenosis with ultrasound guided single shot epidural anaesthesia--a retrospective analysis of 20 cases

Aim: To retrospectively describe the performance of ultrasound guided thoracic epidural anaesthesia under sedation for anaesthesia management of open pyloromyotomy. Background: Anaesthesia management for hypertrophic pylorus stenosis (HPS) is usually performed under general anaesthesia with tracheal intubation. Only a few publications describe avoidance of tracheal intubation in infants by using spinal or caudal anaesthesia. The present retrospective analysis describes the performance of ultrasound guided thoracic epidural anaesthesia under sedation for anaesthetic management of open pyloromyotomy. Methods: Twenty consecutive infants scheduled for pyloromyotomy according to the Weber–Ramstedt technique were retrospectively analysed. After sedation with nalbuphine and propofol, an ultrasound guided single shot thoracic epidural anaesthesia was performed with 0.75 ml·kg^?1 ropivacaine 0.475%. Insufficient blockade was defined as increase of HR > 15% from initial value and/or any movements at skin incision. In those cases we were prepared for rapid sequence intubation according to the departmental standard. Results: All pyloromyotomies could be performed under single shot thoracic epidural anaesthesia and sedation. One case of moderate oxygen desaturation was treated with intermittent ventilation via face mask. Conclusions: Thoracic epidural anaesthesia under sedation for pyloromyotomy has been a useful technique in this retrospective series of infants suffering from HPS. In 1/20 infants short term assisted ventilation via face mask was required. Undisturbed surgery was possible in all cases.     

Propofol anaesthesia via target controlled infusion or manually controlled infusion: effects on the bispectral index as a measure of anaesthetic depth.

Target controlled infusions (TCI) of propofol allow anaesthetists to target constant blood concentrations and respond promptly to signs of inappropriate anaesthetic depth. Studies comparing propofol TCI with manually controlled infusion (MCI) reported similar control of anaesthesia, but did not use an objective measure of anaesthetic depth. We therefore tested whether the Bispectral Index (BIS), an electroencephalographic (EEG) variable, is more stable during propofol TCI or MCI. Forty patients received midazolam and fentanyl before induction and were randomized to TCI or MCI. Target propofol concentrations in the TCI group were 3 to 8 microg/ml. The MCI group received propofol bolus (approximately 2 mg/kg) and infusion (3 to 10 mg/kg/h). Neuromuscular blockade was achieved with rocuronium. Following endotracheal intubation, nitrous oxide (66%) in oxygen was delivered and propofol infusion and fentanyl boluses were titrated against clinical signs. Blood pressure, heart rate and EEG were recorded, although the anaesthetist was blind to BIS values. The ideal BIS for general anaesthesia was defined as 50. Performance error, absolute performance error, wobble and divergence of BIS, and maximum changes in blood pressure and heart rate were compared using two-sample t-tests or rank-sum tests where appropriate. There was no difference in absolute performance errors during maintenance of anaesthesia with propofol TCI or MCI (23 +/- 11% vs 23 +/- 9%; P=0.97). The two groups did not differ significantly in performance error, wobble, divergence on haemodynamic changes. We conclude that TCI and MCI result in similar depth of anaesthesia and haemodynamic stability when titrated against traditional clinical signs.     

Comparison of a new composite index based on midlatency auditory evoked potentials and electroencephalographic parameters with bispectral index (BIS) during moderate propofol sedation

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 C(50) 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 P(K) 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.     

Clinical evaluation of a simultaneous closed-loop anaesthesia control system for depth of anaesthesia and neuromuscular blockade*

We developed a closed-loop system to control the depth of anaesthesia and neuromuscular blockade using the bispectral index and the electromyogram simultaneously and evaluated the clinical performance of this combined system for general anaesthesia. Twenty-two adult patients were included in this study. Anaesthesia was induced by a continuous infusion of remifentanil at 0.4 μg.kg(-1) .min(-1) (induction dose) and then 0.25 μg.kg(-1) .min(-1) (maintenance dose) and propofol at 2 mg.kg(-1) 3 min later. The combined automatic control was started 2 min after tracheal intubation. The depth of anaesthesia was recorded using bispectral index monitoring using a target value of 40. The target value of neuromuscular blockade, using mivacurium, was a T1/T1(0) twitch height of 10%. The precision of the system was calculated using internationally defined performance parameters. Twenty patients were included in the data analysis. The mean (SD) duration of simultaneous control was 129 (69) min. No human intervention was necessary during the computer-controlled administration of propofol and mivacurium. All patients assessed the quality of anaesthesia as 'good' to 'very good'; there were no episodes of awareness. The mean (SD) median performance error, median absolute performance error and wobble for the control of depth of anaesthesia and for neuromuscular blockade were -0.31 (1.78), 6.76 (3.45), 6.32 (2.93) and -0.38 (1.68), 3.75 (4.83), 3.63 (4.69), respectively. The simultaneous closed-loop system using propofol and mivacurium was able to maintain the target values with a high level of precision in a clinical setting.     

SOME VENTILATORY EFFECTS OF PROPOFOL AS SOLE ANAESTHETIC AGENT

Ventilatory effects of propofol, used as a sole agent for theinduction and maintenance of general anaesthesia, were studiedin 14 healthy unpremedicated patients. Subarachnoid anaesthesiawas established before induction of general anaesthesia. Inductionwas with propofol 2.5 mg kg^–1 given while the patientsbreathed 100% oxygen. We intended to start an infusion of propofol100 µg kg^–1 min^–1; maintain it for at least25 min; make a first set of quasi-steady-state observations;double the infusion; and repeat observations after 25 min. Thesingle induction bolus plus single rate infusion was not totallysatisfactory: further boluses were usually needed. At inductionthere was apnoea in all but three patients, sometimes lastingmore than 3 min; hyperventilation before induction, combinedwith hyperoxia, probably exaggerated this. Established ventilatoryrates were generally 30% higher than awake. One patient becamebrady-pnoeic. Tidal volume and minute ventilation, and the T/.T¹⁰¹ratio, were reduced. Doubling the infusion rate had no cleareffect on frequency or tidal volume, but it further reducedthe T/.T¹⁰¹ ratio and caused an increase in PE'_co2 of 1 kPa.The ventilatory response to carbon dioxide was 58% of baselineawake control (95% confidence limits ± 26%) at the lowerinfusion rate, with further slight depression when the infusionrate was doubled. Doubling the rate of infusion of propofoldid not give twice the effect on ventilation, and probably isnot giving twice the "depth " of anaesthesia. We cannot sayif this is for pharmacokinetic or pharmacodynamic reasons.     

Anaesthesia for cardioversion. A comparison between propofol, thiopentone and midazolam

This study compares the induction and recovery characteristics, haemodynamic changes and side effects of propofol, thiopentone and midazolam when used as the anaesthetic agents for cardioversion. Recovery after midazolam was significantly longer (p less than 0.05) than with either thiopentone or propofol. There was no difference in the recovery times between thiopentone and propofol. There was a significant decrease in mean arterial pressure 2 minutes after induction with propofol and midazolam. Three patients each in the thiopentone and propofol groups needed assisted ventilation because of apneoea, and four patients each in the propofol and midazolam groups had low Spo2 values (less than 95%). Flumazenil was used to reverse the effects of midazolam in eight patients and five of these were still drowsy 4 hours after the procedure. This study indicates that thiopentone is the most satisfactory agent for anaesthesia for cardioversion.     

Evaluation of 2 modalities of use of propofol in cerebral angiography

Fifty eight adult patients suffering from different intracranial lesions and scheduled for cerebral angiography were given propofol. In the first group (38 patients) brief periods of anaesthesia were induced and reinduced by means of 1.5 mg/kg of propofol iv and sometimes extended with boluses of 25-50 mg of this anesthetic. The patients were premedicated with 0.5 mg atropine im 30-40 min before the induction. Fentanyl, droperidol and diazepam in various combinations and doses were injected, im together with the atropine and iv 1-2 min before the induction, to obtain long-lasting sedations. In the second group (20 patients) the induction of the anaesthesia started 20-35 min after 0.5 mg of atropine im and 1 min after 0.1 mg of fentanyl iv. The induction was based on a bolus of 2.5 mg/kg of propofol and it was followed by suxamethonium, tracheal intubation and mechanical ventilation with N2O 70% in O2. An adequate depth of anaesthesia was maintained with supplemental doses of 50 mg of propofol, frequently associated with 25 mg of suxamethonium. Both methods proved to be reliable and safe. Nevertheless, the second method provided a better stability as far as a number of physiologic variables is concerned.     

Effects of methylene blue on propofol requirement during anaesthesia induction and surgery

Delayed emergence from anaesthesia and neurological disturbances have been reported in patients undergoing parathyroidectomy who received methylene blue (MB) pre-operatively. We hypothesised that MB would decrease propofol requirements. The Bispectral index (BIS) and a target-controlled infusion of propofol were used in two groups of 11 matched patients. Patients in one group were pretreated with MB. During induction, clinical sedation scores and BIS values were significantly lower at the predicted effect-site propofol concentration of 2 microg x ml(-1) in the MB compared with the control group. Intra-operatively, although similar BIS values were achieved in the two groups, patients pretreated with MB required a mean 50% lower dose of propofol compared with controls. In view of these findings, care should be taken to ensure an adequate depth of anaesthesia by titrating the administration of anaesthetic agents whenever MB is infused peri-operatively.     

不同麻醉方式对炎性细胞因子的影响

目的比较雷米芬太尼-丙泊酚全凭静脉麻醉与异氟醚静吸复合全身麻醉用于胆囊切除术对促炎性和抗炎性细胞因子的影响。方法慢性胆囊炎或胆囊结石患者28例,ASAⅠ或Ⅱ级,随机均分为全凭静脉麻醉组(T组)和静吸复合麻醉组(I组),测定两组患者麻醉前、术后4、12h血浆细胞因子白细胞介素-6(IL-6)和白细胞介素-10(IL-10)水平。结果两组血浆IL-6、IL-10水平在术后4h均显著升高(P<0.05)。术后12hT组血浆IL-6水平显著低于I组(P<0.05)。结论雷米芬太尼-丙泊酚全凭静脉麻醉可增强抗炎细胞因子反应,有利于减轻手术应激的炎症反应。     

Anaesthesia for ultrasound guided oocyte retrieval: midazolam/remifentanil versus propofol/fentanyl regimens

To evaluate the quality of intra-operative anaesthesia and recovery characteristics of two different anaesthesia regimens, 60 healthy women undergoing ultrasound guided oocyte retrieval for in vitro fertilization procedures were randomly allocated to receive either a propofol/fentanyl or a midazolam/remifentanil based anaesthesia. The surgical procedure was successful in all patients and no severe side effects were reported by any patient. Four patients in the midazolam/remifentanil group (13%) would not accept the same anaesthetic procedure for further in vitro fertilization treatment due to intra-operative awareness, while all propofol/fentanyl patients were prepared to accept the same procedure again (P < 0.05). Patients in the propofol/fentanyl group required manual ventilation more frequently through a facemask than those patients treated with the midazolam/remifentanil combination (50% and 30%, respectively; P < 0.05). The time to achieve an Aldrete's score of 10 was shorter in the midazolam/remifentanil patients (2 +/- 2 min) than in those who received propofol/fentanyl (4 +/- 2 min) (P < 0.001), but no differences were observed in the time required to be 'fit to discharge' from the post-anaesthesia care unit. We conclude that the use of a midazolam/remifentanil regimen is as effective and safe as a fentanyl/propofol regimen in patients undergoing transvaginal oocyte retrieval for in vitro fertilization procedures.     

General anaesthesia with target controlled infusion of propofol for planned caesarean section: maternal and neonatal effects of a remifentanil-based technique

The present case series evaluated maternal and neonatal effects of remifentanil, combined with propofol, during general anaesthesia for caesarean delivery. Following written informed consent, ten patients scheduled for semi-elective caesarean section were recruited to this prospective, unblinded trial. All patients with non-reassuring fetal status were excluded. A 0.50-micrograms/kg bolus of remifentanil was given intravenously, followed by a continuous infusion of 0.20 micrograms.kg(-1)min(-1). Anaesthesia was induced using propofol target controlled infusion set at a blood concentration of 5 micrograms/mL, 45 s after the remifentanil bolus. Following tracheal intubation the propofol target was reduced to 2.5 micrograms/mL and remifentanil maintained at 0.20 micrograms.kg(-1)min(-1). Mean arterial pressure remained stable throughout anaesthesia. Two patients experienced episodes of hypotension (mean arterial pressure decrease >20%). Although neonatal depression occurred in six babies and assisted mask ventilation was required briefly, recovery was rapid without the need for naloxone or tracheal intubation. Umbilical artery pH was >7.20 in all infants. We conclude that the results of the present case series using a remifentanil/propofol-based technique of general anaesthesia for caesarean section provide a basis to study the safety of this technique in a larger population. Under the conditions of the present trial, this anaesthetic technique seems safe for mother and infant, provided adequate precautions are taken to manage brief, self-limiting infant respiratory depression. At the moment we cannot advise the routine use of this technique, especially since it has not been studied in situations of fetal compromise.     

General anaesthesia and undrained pneumothorax

A patient who required pleurectomy had a 30% pneumothorax when she was presented for anaesthesia. She had refused to have this drained, and it had not responded to conservative management. She was anaesthetised using a computer-controlled propofol infusion system, without the use of nitrous oxide, and a chest drain was inserted before the institution of positive pressure ventilation. This technique reduces the hazards associated with general anaesthesia in the presence of an undrained pneumothorax. It may be a safe alternative method of induction of anaesthesia in other conditions in which positive pressure ventilation must be avoided, such as bronchopleural fistula.