Closed-loop control of propofol anaesthesia using bispectral index: performance assessment in patients receiving computer-controlled propofol and manually controlled remifentanil infusions for minor surgery

Background. In a previous study we used the bispectral index(BIS)^TM for automatic control of propofol anaesthesia, usinga proportional-integral-differential control algorithm. As controlwas less than optimal in some patients, we revised the constantsof the control algorithm. The aim of the current study was tomeasure the performance of the revised system in patients undergoingminor surgery under propofol and remifentanil anaesthesia. Methods. Twenty adult patients scheduled for body surface surgerywere enrolled. Anaesthesia was manually induced with target-controlledinfusions (TCI) of propofol and remifentanil. After the startof surgery, when anaesthesia was clinically adequate, automaticcontrol of the propofol TCI was commenced using the revisedclosed-loop system. For patients 11–20, effect-site steeringwas also incorporated into the closed-loop control algorithm.Adequacy of anaesthesia during closed-loop control was assessedclinically, and by calculating the median performance error(MDPE), the median absolute performance error (MDAPE) and themean offset of the control variable. Results. The system provided adequate operating conditions andstable cardiovascular values in all patients during closed-loopcontrol. The mean MDPE and MDAPE were –0.42% and 5.63%,respectively. Mean offset of the BIS^TM from setpoint was –0.2.No patients reported awareness or recall of intraoperative events. Conclusions. The system was able to provide clinically adequateanaesthesia in all patients, with better accuracy of controlthan in the previous study. There was a tendency for more accuratecontrol in those patients in whom the control algorithm incorporatedeffect-site steering. Br J Anaesth 2003; 90: 737–41     

Doxapram and aminophylline on bispectral index under sevoflurane anaesthesia: a comparative study

BACKGROUND AND OBJECTIVE: To evaluate and compare the effect of two clinically available central nervous system stimulants, namely doxapram and aminophylline on arousal from sevoflurane anaesthesia and bispectral index. METHODS: This randomized, double-blind, placebo-controlled, prospective study was conducted in 90 adult females, ASA I-II, scheduled for elective lower abdominal surgeries at Taipei Medical University Hospital. At 5 min before the completion of surgery, under sevoflurane anaesthesia, patients were divided into three groups to receive doxapram 1 mg kg(-1), aminophylline 2 mg kg(-1) or saline placebo intravenous. Standard vital signs, end-tidal CO(2), end-expiratory sevoflurane concentration, bispectral index and neuromuscular blockade were measured plus clinical parameters of recovery from general anaesthesia. RESULTS: Compared with the control group, patients receiving doxapram or aminophylline showed a similarly faster recovery from sevoflurane anaesthesia correlated with increase in bispectral index. CONCLUSION: Intravenous administration of doxapram 1 mg kg(-1) or aminophylline 2 mg kg(-1) hastened the early recovery from sevoflurane anaesthesia. The arousal effect of aminophylline and doxapram appears to be similar.     

Spike-monitoring of anaesthesia for corpus callosotomy using bilateral bispectral index

During corpus callosotomy for intractable epilepsy, the electrocorticogram is commonly recorded from electrodes placed on the brain surface to monitor of epileptic activity and assess the synchronisation of epileptic signals between the left and the right hemispheres. We evaluated the usefulness of bilateral bispectral index monitoring using two monitors and two sensors placed above the frontal region. Spikes were readily detected on the electroencephalogram on the bispectral index monitor, and the frequency of their occurrence increased or decreased in response to adjustment of the sevoflurane concentration. The disappearance of synchronisation between the left and the right hemispheres was observed with use of the bispectral index – in concordance with the electrocorticogram. Thus, 'spike-monitoring anaesthesia' using bilateral bispectral index was useful in assessing both the effect of anaesthetics on the electroencephalogram signals and the surgical therapeutic effect.     

Intraoperative awareness--a three year prospective study using bispectral index monitor (BIS)

Patients who experience awareness under surgery may suffer from the post-traumatic stress disorder (PTSD) with its long-lasting psychological damage. In addition, there are also media attention and legal consequences. In spite of understanding its causes, it is still occurring worldwide. This prospective study was conducted to determine the incidence of awareness using the bispectral index monitor (BIS) when its causes are eliminated. There were 2328 patients admitted to the study. Their ages ranged from 14-104 yr (mean 38.6 yr). All patients were interviewed in the postoperative period. There was no report of awareness during the course of surgery. Pre-and intraoperative anesthetic attention to patients presented for surgery, together with the use of modern anesthetic delivery units possessing facilities for monitoring BIS, and anesthetic gases, and the provision of good analgesia, are the most important combination in eliminating awareness during surgery.     

Differences between bispectral index and spectral entropy during xenon anaesthesia: a comparison with propofol anaesthesia

We enrolled 114 patients, aged 65–83 years, undergoing elective surgery (duration > 2h) into a randomised, controlled study to evaluate the performance of bispectral index and spectral entropy for monitoring depth of xenon versus propofol anaesthesia. In the propofol group, bispectral index and state entropy values were comparable. In the xenon group, bispectral index values resembled those in the propofol group, but spectral entropy levels were significantly lower. Mean arterial blood pressure was higher and heart rate was lower in the xenon group than in the propofol group. Bispectral index and spectral entropy considerably diverged during xenon but not during propofol anaesthesia. We therefore conclude that these measures are not interchangeable for the assessment of depth of hypnosis and that bispectral index is likely to reflect actual depth of anaesthesia more precisely compared with spectral entropy.     

Adjustment of anaesthesia depth using bispectral index prolongs seizure duration in electroconvulsive therapy

Electroconvulsive therapy (ECT) under propofol anaesthesia induces relatively shorter seizures compared to barbiturate anaesthesia. Since significant correlation between seizure duration and bispectral index (BIS) value immediately before electrical stimulus has been reported among patients, adjustment of anaesthesia depth as determined by BIS may be effective in obtaining a longer seizure length. In the present study, we examined this hypothesis in those patients whose muscular seizure duration was less than 40s. ECT was prescribed to 20 patients suffering from endogenous depression. General anaesthesia was induced with propofol 1 mg/kg. Succinylcholine chloride 1 mg/kg was then given. The efficacy of electrical stimulation was determined using a tourniquet technique, electromyogram, and electroencephalography. When a patient had a seizure less than 40s in their second ECT treatment, the subsequent treatment was modified such that the electrical stimulus was given after waiting for a higher BIS value (+10-20). Intensity of electrical stimulus and anaesthesia conditions were identical in the two treatments. All 20 patients had longer seizures as determined by the electromyogram and/or electroencephalography when the stimulus was delivered at the higher BIS value. Seizure duration measured by muscle movement was 31+/-5 s when the stimulus was delivered without waiting and 46+/-10 s when delivered after waiting. There was a significant difference in seizure duration between the two treatments (P<0.01). Waiting for a recovery in BIS value before electrical stimulation can prolong seizure duration.     

Closed loop control of anaesthesia: an assessment of the bispectral index as the target of control

We investigated the performance of a closed-loop system for administration of general anaesthesia, using the bispectral index as a target for control. One hundred patients undergoing gynaecological or general surgery were studied. In 60 patients, anaesthesia was maintained by intravenous infusion of a propofol/alfentanil mixture. In 40, an isoflurane/nitrous oxide based technique was used. For each technique, patients were randomly allocated to receive either closed-loop or manually controlled administration of the relevant agents (propofol/alfentanil or isoflurane), with an intra-operative target bispectral index of 50 in all cases. Closed-loop and manually controlled administration of anaesthesia resulted in similar intra-operative conditions and initial recovery characteristics. During maintenance of anaesthesia, cardiovascular and electro-encephalographic variables did not differ between closed-loop and manual control groups and deviation of bispectral index from the target value was similar. Intra-operative concentrations of propofol, alfentanil and isoflurane were within normal clinical ranges. Episodes of light anaesthesia were more common in the closed-loop group for patients receiving propofol/alfentanil anaesthesia and in the manual group for patients receiving isoflurane/nitrous oxide anaesthesia. Convenience aside, the closed-loop system showed no clinical advantage over conventional, manually adjusted techniques of anaesthetic administration.     

Clonidine decreases propofol requirements during anaesthesia: effect on bispectral index

Assessment of the effect of clonidine on depth of anaesthesiais difficult because clonidine combines analgesic, sedativeand direct haemodynamic effects. We thus evaluated the influenceof clonidine on the bispectral index (BIS) and its potentialdose-sparing effect on propofol. After induction of anaesthesiawith target-controlled infusion of propofol and obtaining anunchanged bispectral index (pre-BIS), clonidine 4 µg kg^–1or placebo was administered randomly to 50 patients in a double-blindmanner. Subsequently, if there was a decrease in BIS we reducedthe target concentration of propofol until pre-BIS was reached.The pre-BIS was maintained and a remifentanil infusion was addedduring surgery. The courses of the BIS, heart rate and bloodpressure were recorded and the total amounts of intra-operativepropofol and remifentanil were determined. Assessment of implicitmemory during anaesthesia was performed with an auditory implicitmemory test consisting of item sequences. Administration ofclonidine resulted in a decrease in the BIS from 45 (SD 4) to40 (6) (P<0.001), which allowed a reduction of propofol targetconcentration from 3.3 (0.6) to 2.7 (0.7) µg ml^–1(P<0.001) and measured propofol concentration from 2.9 (0.6)to 2.5 (0.7) µg ml^–1 (P=0.009) in order tomaintain the pre-BIS value. During subsequent surgery, propofolrequirements were reduced by 20% (P=0.002) in the clonidinegroup and a similar amount of remifentanil was used in eachgroup. The increase in anaesthetic depth given by clonidinecan therefore be measured with bispectral EEG analysis and allowsreduction of the propofol dose to achieve a specific depth ofanaesthesia. Br J Anaesth 2001; 86: 627–32     

Sevoflurane requirements during ambulatory surgery: a clinical study of bispectral index and auditory evoked potential guided anaesthesia

The bispectral index (BIS) is processed passively from the EEG, while the auditory evoked potential (AEP) response actively tests brain activity. In the present study 60 patients undergoing elective day surgery (knee arthroscopy) were randomised to titrate sevoflurane (with O₂:N₂O, 1:2) either clinically or in combination with either a target BIS-index of 60±5 (20 patients) or AEP-index of 30±5 (20 patients). Induction was with propofol and fentanyl (0.1 mg). The BIS- or AEP-index did not improve either sevoflurane consumption or emergence times. In minor ambulatory anaesthesia, without muscle relaxants, neither BIS nor AEP-index guidance reduces anaesthetic consumption or emergence times.     

Sevoflurane requirements during ambulatory surgery: a clinical study of bispectral index and auditory evoked potential guided anaesthesia

The bispectral index (BIS) is processed passively from the EEG, while the auditory evoked potential (AEP) response actively tests brain activity. In the present study 60 patients undergoing elective day surgery (knee arthroscopy) were randomised to titrate sevoflurane (with O₂:N₂O, 1:2) either clinically or in combination with either a target BIS-index of 60±5 (20 patients) or AEP-index of 30±5 (20 patients). Induction was with propofol and fentanyl (0.1 mg). The BIS- or AEP-index did not improve either sevoflurane consumption or emergence times. In minor ambulatory anaesthesia, without muscle relaxants, neither BIS nor AEP-index guidance reduces anaesthetic consumption or emergence times.     

Comparison of sevoflurane-nitrous oxide anaesthesia with the conventional intravenous-inhalational technique using bispectral index monitoring

Ninety-one patients were randomly allocated to one of two groups. Group A was induced with a single vital capacity breath of 6% (end-tidal) sevoflurane in nitrous oxide-oxygen (2 : 1 l.min-1), whereas group B was induced with intravenous fentanyl 1 microg.kg-1 + propofol 2 mg.kg-1 followed by nitrous oxide-oxygen (2 : 1 l.min-1) and sevoflurane. Induction was considered to have been achieved when the bispectral index value decreased to below 70. Mean induction time in group A (95.2 s, 95% CI 88.5-101.9 s) was longer than group B (70.3 s, 95% CI 66.3-74.3 s; p < 0.0001). Mild coughing was more common in group A, but relative hypotension was more common in group B. There was no difference in the emergence times. Thirty minutes after emergence, there was no difference in the incidence of adverse effects, with the exception of essentially mild abdominal pain which was more frequent in group A.     

Cerebral haemodynamic changes during propofol-remifentanil or sevoflurane anaesthesia: transcranial Doppler study under bispectral index monitoring

Background. Sevoflurane or propofol–remifentanil-basedanaesthetic regimens represent modern techniques for neurosurgicalanaesthesia. Nevertheless, there are potential differences relatedto their activity on the cerebrovascular system. The magnitudeof such difference is not completely known. Methods. In total 40 patients, treated for spinal or maxillo-facialdisorders, were randomly allocated to either i.v. propofol–remifentanilor inhalational sevoflurane anaesthesia. Transcranial Dopplerwas used to assess changes in cerebral blood flow velocity,carbon dioxide reactivity, cerebral autoregulation and the bispectralindex to assess the depth of anaesthesia. Results. Time-averaged mean flow velocity (MFV) was significantlyreduced after induction of anaesthesia in both sevoflurane andpropofol–remifentanil groups (P<0.001). At deeper levelsof anaesthesia, MFV increased in the sevoflurane group, suggestingan uncoupling flow/metabolism, whereas it was further reducedin the propofol–remifentanil group (P<0.001). Indicesof cerebral autoregulation were reduced in patients with high-dosesevoflurane whereas autoregulation was preserved in patientsanaesthetized with propofol–remifentanil (P<0.001).Higher CO₂ concentrations impaired cerebral autoregulation inthe sevoflurane group but not in patients anaesthetized withpropofol–remifentanil. Conclusions. Propofol–remifentanil anaesthesia induceda dose-dependent low-flow state with preserved cerebral autoregulation,whereas sevoflurane at high doses provided a certain degreeof luxury perfusion.     

Measuring depth of anaesthesia using changes in directional connectivity: a comparison with auditory middle latency response and estimated bispectral index during propofol anaesthesia

General anaesthesia is associated with changes in connectivity between different regions of the brain, the assessment of which has the potential to provide a novel marker of anaesthetic effect. We propose an index that quantifies the strength and direction of information flow in electroencephalographic signals collected across the scalp, assess its performance in discriminating ‘wakefulness’ from ‘anaesthesia’, and compare it with estimated bispectral index and the auditory middle latency response. We used a step-wise slow induction of anaesthesia in 10 patients to assess graded changes in electroencephalographic directional connectivity at propofol effect-site concentrations of 2 μg.ml⁻¹, 3 μg.ml⁻¹ and 4 μg.ml⁻¹. For each stable effect-site concentration, connectivity was estimated from multichannel electroencephalograms using directed coherence, together with middle latency response and estimated bispectral index. We used a linear support vector machine classifier to compare the performance of the different electroencephalographic features in discriminating wakefulness from anaesthesia. We found a significant reduction in the strength of long-range connectivity (interelectrode distance > 10 cm) (p < 0.008), and a reversal of information flow from markedly postero-frontal to fronto-posterior (p < 0.006) between wakefulness and a propofol effect-site concentration of 2 μg.ml⁻¹. This then remained relatively constant as effect-site concentration increased, consistent with a step change in directed coherence with anaesthesia. This contrasted with the gradual change with increasing anaesthetic dose observed for estimated bispectral index and middle latency response. Directed coherence performed best in discriminating wakefulness from anaesthesia with an accuracy of 95%, indicating the potential of this new method (on its own or combined with others) for monitoring adequacy of anaesthesia.     

Cost-reduction analysis of propofol versus sevoflurane: maintenance of anaesthesia for gynaecological surgery using the bispectral index

BACKGROUND AND OBJECTIVE: The study was designed to compare the costs of propofol versus sevoflurane for the maintenance of the hypnotic component of anaesthesia during general anaesthesia, guided by the bispectral index, for gynaecological laparoscopic surgery. METHODS: Forty ASA Grade I-II female patients scheduled for gynaecological laparoscopy were randomly allocated to two groups. All patients received a continuous infusion of remifentanil (0.25 microg kg(-1) min(-1)) for 2 min. Then anaesthesia was induced with propofol 1% at 300 mL h(-1) until loss of consciousness. To guide the bispectral index between 40 and 60, Group 1 patients received propofol 10 mg kg(-1) h(-1) initially, which was increased or decreased by 2 mg kg(-1) h(-1) steps; Group 2 patients received sevoflurane, initially set at 2 vol.% and adjusted with steps of 0.2-0.4%. The time and quality of anaesthesia and recovery were assessed in two postoperative standardized interviews. RESULTS: Patient characteristics, the propofol induction dose, the bispectral index and the haemodynamic profiles during induction of anaesthesia, and its duration, were similar between the groups. In Group 1, 7.55 +/- 1.75 mg kg(-1) h(-1) propofol and in Group 2, 0.20 +/- 0.09 mL kg(-1) h(-1) liquid sevoflurane were used for maintenance. The cost for maintenance, including wasted drugs, was higher when using propofol (Euro 25.14 +/- 10.69) than sevoflurane (Euro 12.80 +/- 2.67). Postoperatively, recovery profiles tended to be better with propofol; however, the day after discharge no differences were found. CONCLUSIONS: When applying the bispectral index to guide the administration of hypnotic anaesthetic drugs, propofol-based maintenance of anaesthesia was associated with the highest cost. A trend towards a better recovery profile was obtained with propofol. However, on the day after discharge, no differences in quality were observed.     

Effect of a single dose of esmolol on the bispectral index scale (BIS) during propofol/fentanyl anaesthesia

Background. Esmolol, a short-acting ß₁-antagonist,can reduce anaesthetic requirements and decrease seizure activityduring electroconvulsive therapy even after a single dose of80 mg. We studied the effect of esmolol on the bispectralindex scale (BIS), which is a processed EEG recently introducedto monitor depth of anaesthesia. Methods. We gave esmolol 80 mg to 30 healthy male patientsafter induction of anaesthesia using propofol, with either fentanyl(group 1) or placebo (group 2). Patients were ventilated mechanicallythrough a laryngeal mask airway and anaesthesia was maintainedusing propofol to keep the BIS value between 55 and 60. Results. Esmolol did not affect the BIS index value in eithergroup. In group 1, the areas (mean (SD)) under the BIS vs timecurve 3 min before and 3 min after esmolol administrationwere 145 (9) and 146 (8) respectively (P=0.116). In group 2values were 147 (8) and 146 (7) respectively (P=0.344). In contrast,in group 1 the area under the systolic arterial pressure (SAP)curve was 299 (31) before and 270 (29) after esmolol (P<0.001),and 156 (17) and 141 (17) respectively for heart rate (P<0.001).In group 2 values were 326 (36) and 302 (41) for SAP (P<0.001)and 182 (25) and 155 (22) for heart rate (P<0.001). Conclusions. The results suggest that a single dose of esmololaffects the SAP and heart rate but does not affect BIS values. B J Anaesth 2002; 89: 509–11     

General anesthesia by propofol infusion for delivery by cesarean section compared with sevoflurane anesthesia using bispectral index (BIS) monitoring

BACKGROUND: We compared the postoperative effects of propofol and sevoflurane used for anesthesia during elective cesarean section, using bispectral index (BIS) monitoring. METHODS: Fourteen parturients were randomized into two groups (Propofol group; P group, Sevoflurane group; S group). All patients received thiopental and suxamethonium for induction and had orotracheal intubation in rapid sequence. All patients received 1% sevoflurane until delivery. In the P group, sevoflurane was stopped after delivery and propofol infusion was started, to achieve target BIS values below 60; the infusion rate was 6. 17 +/- 0.98 mg x kg(-1) x h(-1). Patients in the S group received 1% sevoflurane. All patients were given fentanyl and vecuronium as required. RESULTS:There were no significant differences between the two groups in their times for beginning drinking, walking, eating or removal of urinary catheters after the operations. There were no significant differences in total blood loss or intraoperative dose of oxytocin, but postoperative and total doses of oxytocin were significantly higher in those in the P group. CONCLUSIONS: Comparing the effects of propofol and sevoflurane on the postoperative condition of parturients, no differences could be detected. We can choose to use propofol instead of sevoflurane for cesarean section.