Manual versus target-controlled infusions of propofol

Hypotension after Anesthesia Induction: Target-Controlled Infusion Versus Manual Anesthesia Induction of Propofol

BACKGROUND

Post-induction hypotension frequently occurs and can lead to adverse outcomes. As target-controlled infusion (TCI) obviates the need to calculate the infusion rate manually and helps safer dosing with prompt titration of the drug using complex pharmacokinetic models, the use of TCI may provide a better hemodynamic profile during anesthesia induction. This study aimed to compare TCI versus manual induction and to determine the hemodynamic risk factors for post-induction hypotension.

METHODS

A total of 200 ASA grade 1-3 patients, aged 24 to 82 years, were recruited and randomly assigned to the TCI (n = 100) or manual induction groups (n = 100). Hemodynamic parameters were monitored with the pressure-recording analytic method. The propofol dosage was adjusted to keep the Bispectral Index between 40 and 60.

RESULTS

Post-induction hypotension was significantly higher in the manual induction group than in the TCI group (34% vs. 13%; p < 0.001, respectively). The propofol induction dose did not differ between the groups (TCI: 155 (135-180) mg; manual: 150 (120-200) mg; p = 0.719), but the induction time was significantly longer in the TCI group (47 (35-60) s vs. 150 (105-220) s; p < 0.001, respectively). In the multivariable Cox regression model, the presence of hypertension, stroke volume index (SVI), cardiac power output (CPO), and anesthesia induction method were found to predict post-induction hypotension (p = 0.032, p = 0.013, p = 0.024, and p = 0.015, respectively).

CONCLUSION

TCI induction with propofol provided better hemodynamic stability than manual induction, and the presence of hypertension, a decrease in the pre-induction SVI, and the CPO could predict post-induction hypotension.

Comparison of recovery profiles in target-controlled infusions (TCI) versus manually controlled infusions for total intravenous anesthesia (TIVA) in laparoscopic surgeries. A randomized controlled trial

Background and Aims

Considerable importance has been attached to early recovery and discharge readiness after surgeries. Many centers use total intravenous anesthesia (TIVA) as their anesthesia technique of choice. Target-controlled infusions (TCI) have been proposed as a method to precisely deliver continuous infusions of propofol and opioids as compared to the traditionally used manual-controlled infusion (MCI) methods. However, TCI has also been shown to result in the administration of larger doses of propofol which could cause delayed emergence and recovery from anesthesia. Studies involving TCI have focused mainly on its effects on anesthesia induction but not much literature is available on recovery profiles of patients on TCI. This study was designed to compare the effect of conventionally used MCI methods versus the target-controlled infusion (TCI) method of administering TIVA on recovery characteristics in patients undergoing laparoscopic surgery.

Material and Methods

This was a prospective randomized interventional study on 54 patients. Our primary objective was to compare the rates of recovery from anesthesia as judged by four parameters. Time to return of spontaneous ventilation, time to respond to verbal commands, time to extubation, and time to shift patient out of the operating room after stoppage of propofol infusion. As secondary objectives, intraoperative average bispectral index (BIS) values and total anesthetic drugs (propofol and fentanyl) consumption were also compared.

Results

We noted that for laparoscopic surgeries lasting less than 4 hours, both MCI and TCI techniques of TIVA have comparable rates of recovery after the stoppage of propofol infusion. Total consumption of propofol and fentanyl was also similar; however, with the use of the TCI method of TIVA, better depth of anesthesia as evidenced by lower average BIS levels was noted.

Conclusion

Recovery rates after TIVA using a target-controlled infusion (TCI) system are similar to BIS-guided MCIs in patients undergoing laparoscopic surgery lasting less than 4 hours. TCI resulted in better depths of anesthesia though per kg/min consumption of propofol was found to be more.

Comparison between continuous rate infusion and target-controlled infusion of propofol in dogs: a randomized clinical trial

OBJECTIVE

To compare a propofol continuous rate infusion (CRI) with a target-controlled infusion (TCI) in dogs.

STUDY DESIGN

Randomized prospective double-blinded clinical study.

ANIMALS

A total of 38 healthy client-owned dogs.

METHODS

Dogs premedicated intramuscularly with acepromazine (0.03 mg kg^-1) and an opioid (pethidine 3 mg kg^-1, morphine 0.2 mg kg^-1 or methadone 0.2 mg kg^-1) were allocated to P-CRI group (propofol 4 mg kg^-1 intravenously followed by CRI at 0.2 mg kg^-1 minute^-1), or P-TCI group [propofol predicted plasma concentration (Cp) of 3.5 μg mL^-1 for induction and maintenance of anaesthesia via TCI]. Plane of anaesthesia, heart rate, respiratory rate, invasive blood pressure, oxygen haemoglobin saturation, end-tidal carbon dioxide and body temperature were monitored by an anaesthetist blinded to the group. Numerical data were analysed by unpaired t test or Mann-Whitney U test, one-way analysis of variance and Dunnett's post hoc test. Categorical data were analysed with Fisher's exact test. Significance was set for p < 0.005.

RESULTS

Overall, propofol induced a significant incidence of relative hypotension (mean arterial pressure 20% below baseline, 45%), apnoea (71%) and haemoglobin desaturation (65%) at induction of anaesthesia, with a higher incidence of hypotension and apnoea in the P-CRI than P-TCI group (68% versus 21%, p = 0.008; 84% versus 58%, p = 0.0151, respectively). Propofol Cp was significantly higher at intubation in the P-CRI than P-TCI group (4.83 versus 3.5 μg mL^-1, p < 0.0001), but decreased during infusion, while Cp remained steady in the P-TCI group. Total propofol administered was similar between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Both techniques provided a smooth induction of anaesthesia but caused a high incidence of side effects. Titration of anaesthesia with TCI caused fewer fluctuations in Cp and lower risk of hypotension compared with CRI.

Comparison of the target-controlled infusion and the manual infusion of propofol anesthesia during electroconvulsive therapy: an open-label randomized controlled trial

BACKGROUND

Target-controlled infusion (TCI) of propofol is a well-established method of procedural sedation and has been used in Japan for anesthesia during electroconvulsive therapy (ECT). However, the usefulness of the TCI of propofol for ECT has yet to be determined. This study aimed to compare the TCI and manual infusion (MI) of propofol anesthesia during ECT.

METHODS

A total of forty psychiatric inpatients receiving bitemporal ECT were enrolled in the present study and randomized into the TCI group (N = 20) and the MI group (N = 20). Clinical Global Impression (CGI) and Montreal Cognitive Assessment (MoCA) scores were measured before and after ECT. The clinical outcomes, anesthesia-related variables, and ECT-related variables were compared between the two groups. Generalized estimating equations (GEEs) were used to model the comparison throughout the course of ECT.

RESULTS

A total of 36 subjects completed the present study, with 18 subjects in each group. Both the groups didn't significantly differ in the post-ECT changes in CGI and MoCA scores. However, concerning MoCA scores after 6 treatments of ECT, the MI group had improvement while the TCI group had deterioration. Compared with the MI group, the TCI group had higher doses of propofol, and longer procedural and recovery time. The TCI group seemed to have more robust seizures in the early course of ECT but less robust seizures in the later course of ECT compared with the MI group.

CONCLUSIONS

The present study does not support the use of TCI of propofol for anesthesia of ECT.

TRIAL REGISTRATION

(ClinicalTrials.gov): NCT03863925 . Registered March 5, 2019 - Retrospectively registered.

WITHDRAWN: Target-controlled infusion versus manually-controlled infusion of propofol for general anaesthesia or sedation in adults

July 2016

Owing to the age, retraction of studies (Lehmann 2001; Lehmann 2002; Triem 2006), and possible errors in the conversion of dose for the purpose of analysis the decision has been reached to withdraw the review from the CDSR pending update and amendment of the review.

The editorial group responsible for this previously published document have withdrawn it from publication.

Robust control of burst suppression for medical coma

OBJECTIVE

Medical coma is an anesthetic-induced state of brain inactivation, manifest in the electroencephalogram by burst suppression. Feedback control can be used to regulate burst suppression, however, previous designs have not been robust. Robust control design is critical under real-world operating conditions, subject to substantial pharmacokinetic and pharmacodynamic parameter uncertainty and unpredictable external disturbances. We sought to develop a robust closed-loop anesthesia delivery (CLAD) system to control medical coma.

APPROACH

We developed a robust CLAD system to control the burst suppression probability (BSP). We developed a novel BSP tracking algorithm based on realistic models of propofol pharmacokinetics and pharmacodynamics. We also developed a practical method for estimating patient-specific pharmacodynamics parameters. Finally, we synthesized a robust proportional integral controller. Using a factorial design spanning patient age, mass, height, and gender, we tested whether the system performed within clinically acceptable limits. Throughout all experiments we subjected the system to disturbances, simulating treatment of refractory status epilepticus in a real-world intensive care unit environment.

MAIN RESULTS

In 5400 simulations, CLAD behavior remained within specifications. Transient behavior after a step in target BSP from 0.2 to 0.8 exhibited a rise time (the median (min, max)) of 1.4 [1.1, 1.9] min; settling time, 7.8 [4.2, 9.0] min; and percent overshoot of 9.6 [2.3, 10.8]%. Under steady state conditions the CLAD system exhibited a median error of 0.1 [-0.5, 0.9]%; inaccuracy of 1.8 [0.9, 3.4]%; oscillation index of 1.8 [0.9, 3.4]%; and maximum instantaneous propofol dose of 4.3 [2.1, 10.5] mg kg(-1). The maximum hourly propofol dose was 4.3 [2.1, 10.3] mg kg(-1) h(-1). Performance fell within clinically acceptable limits for all measures.

SIGNIFICANCE

A CLAD system designed using robust control theory achieves clinically acceptable performance in the presence of realistic unmodeled disturbances and in spite of realistic model uncertainty, while maintaining infusion rates within acceptable safety limits.

Dental sedation for patients with intellectual disability: a prospective study of manual control versus Bispectral Index-guided target-controlled infusion of propofol

STUDY OBJECTIVE

To investigate the use of propofol sedation using Bispectral Index (BIS)-guided target-controlled infusion (TCI) in dental patients with intellectual disability.

DESIGN

Single-center, prospective, randomized clinical trial.

SETTING

Academic outpatient clinic.

SUBJECTS

40 ASA physical status 1 and 2 patients with intellectual disability.

INTERVENTIONS

Patients were randomized to two groups. The manual control (MC) group (n = 20) had sedation by manually controlled infusion of propofol without a BIS index monitor. The BIS-TCI group (n = 20) had sedation by BIS-guided TCI of propofol.

MEASUREMENTS

The required dose of propofol, recovery time for the eyelash reflex, and spontaneous eye opening times were recorded.

MAIN RESULTS

BIS-TCI significantly reduced the dose of propofol and shortened the recovery times for eyelash reflex and spontaneous eye opening.

CONCLUSION

Propofol sedation using BIS-guided TCI is a useful and safe method in the management of patients with intellectual disability.

Two distinct application habits for propofol: an observational study

BACKGROUND AND OBJECTIVES

In total intravenous anaesthesia, two different application modes for propofol are widely used: infusion by means of manually controlled infusion pumps, and infusion by means of microprocessor-controlled infusion pumps operating according to pharmacokinetic algorithms (target controlled infusion, TCI). The parallel use of these two methods in our department by various anaesthetists offered the opportunity to retrospectively compare both application patterns regarding clinical effects and drug consumption.

METHODS

Ninety-six anaesthesia records from general anaesthesias with propofol and opioids from gynaecological laparoscopic operations were retrospectively evaluated. Forty-eight records were derived from six anaesthetists using manual propofol infusion (retrospective allocation to group C) and 48 other records from six anaesthetists using TCI infusion (retrospective allocation to group M). We assessed the intraoperative haemodynamic course, drug consumption, awakening time and postoperative side effects.

RESULTS

The awakening time after TCI was significantly shorter than after manual propofol infusion (M: 4.9 +/- 3.1 min vs. C: 9.9 +/- 5.7 min). We observed a nonsignificantly rarer occurrence of postoperative side effects such as postoperative nausea and vomiting and pain. Only insignificant differences in drug consumption could be found.

CONCLUSION

Both observed application patterns for propofol showed similar clinical profiles. Using TCI, awakening time was 5 min earlier than with manual infusion mode, thus showing a potential pharmaco-economical advantage in anaesthesias for gynaecological laparoscopy. The detected differences did not have a statistically significant influence on the early postoperative outcome.

Somatosensory Evoked Potentials suppression due to remifentanil during spinal operations; a prospective clinical study

BACKGROUND

Somatosensory evoked potentials (SSEP) are being used for the investigation and monitoring of the integrity of neural pathways during surgical procedures. Intraoperative neurophysiologic monitoring is affected by the type of anesthetic agents. Remifentanil is supposed to produce minimal or no changes in SSEP amplitude and latency. This study aims to investigate whether high doses of remifentanil influence the SSEP during spinal surgery under total intravenous anesthesia.

METHODS

Ten patients underwent spinal surgery. Anesthesia was induced with propofol (2 mg/Kg), fentanyl (2 mcg/Kg) and a single dose of cis-atracurium (0.15 mg/Kg), followed by infusion of 0.8 mcg/kg/min of remifentanil and propofol (30-50 mcg/kg/min). The depth of anesthesia was monitored by Bispectral Index (BIS) and an adequate level (40-50) of anesthesia was maintained. Somatosensory evoked potentials (SSEPs) were recorded intraoperatively from the tibial nerve (P37) 15 min before initiation of remifentanil infusion. Data were analysed over that period.

RESULTS

Remifentanil induced prolongation of the tibial SSEP latency which however was not significant (p > 0.05). The suppression of the amplitude was significant (p < 0.001), varying from 20-80% with this decrease being time related.

CONCLUSION

Remifentanil in high doses induces significant changes in SSEP components that should be taken under consideration during intraoperative neuromonitoring.

[Propofol administration systems. Handling, hemodynamics and propofol consumption]

BACKGROUND

During anaesthesia propofol is administered either by manual controlled infusion (MCI) or by target controlled infusion (TCI) techniques. In this study two different TCI systems for propofol administration were evaluated with regard to handling, patient safety, and costs and compared to administration of propofol by the MCI technique.

METHODS

In a prospective study, 90 patients scheduled for elective surgery of the nose or nasal sinuses were randomly enrolled in three groups. The two TCI systems were examined in two groups of 30 patients: one group received propofol following the pharmacokinetic TCI model of Schnider (TCI-Schnider) and the other group received propofol following the TCI model of Marsh (TCI-Marsh). A manual perfusion technique (MCI, n=30) was used in the control group. Depth of anesthesia was controlled using the bispectral index (BSI) which was adjusted to fall within the range of 40-55. Hemodynamics, extubation times and time of awaking, rate and quality of propofol dose adjustment, total drug requirements, costs, and quality of recovery were documented. The incidence of postoperative nausea and vomiting (PONV) as well as shivering and patient satisfaction were also documented.

RESULTS

Demographics, hemodynamics and perioperative data did not differ between the groups. Propofol consumption within the first 60 min also showed no significant differences. In the course of extended anaesthesia, propofol consumption was significantly less in both TCI groups compared to the control group (MCI) and the TCI-Schnider group also showed less episodes of bradycardia. The necessity of propofol dose adjustment did not differ significantly between the TCI groups. Administration and consumption of anaesthesia co-medication (fentanyl, remifentanil, cisatracurium) did not differ between the groups.

CONCLUSION

The investigated propofol administration procedures using the MCI or TCI techniques were safe and easy to handle under BIS monitoring. No differences were found concerning extubation times and time of awaking. During extended anaesthesia procedures (>60 min), propofol consumption was lower with both TCI techniques and thus costs could be saved.

Target-controlled infusion versus manually-controlled infusion of propofol for general anaesthesia or sedation in adults

BACKGROUND

Continuous infusions of the intravenous anaesthetic propofol are commonly used to induce and maintain sedation and general anaesthesia. Infusion devices can be manually controlled (MCI) where the anaesthetist makes each change to the infusion rate or target-controlled (TCI) where the anaesthetist sets a target blood or effect-site concentration and the computerised infusion device makes the necessary changes to the infusion rate. Randomized trials have explored the differences in quality of anaesthesia, adverse event rate and cost between TCI and MCI but the effectiveness of TCI compared with MCI remains controversial. As TCI is in widespread international use, and potentially may be more expensive without added benefit, a systematic review of randomized controlled trials comparing TCI and MCI is warranted.

OBJECTIVES

To assess whether TCI of propofol is as effective as MCI of propofol with respect to quality of anaesthesia or sedation, adverse events and propofol drug cost.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2007, Issue 3); PubMED (1950 to July week 2 2007); and EMBASE via OVID (1980 to week 28 2007). We also searched LILACS, CINAHL, ISI Web Knowledge, Panteleimon, KoreaMed and IndMed. We searched for ongoing trials via the National Research Register and metaRegister of Controlled Trials.

SELECTION CRITERIA

We planned to include all published and unpublished randomized controlled trials that compared TCI of propofol with MCI of propofol for general anaesthesia or sedation in adult surgical patients. Only published studies were included as no unpublished studies were identified.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted outcome data. We contacted study authors and the pharmaceutical industry for additional information.

MAIN RESULTS

Twenty trials of poor quality that involved 1759 patients were included. Heterogeneity was high (that is the trials were not comparing the same things). TCI was associated with higher total doses of propofol than was MCI resulting in marginally higher propofol drug costs. However, fewer interventions were required by the anaesthetist during the use of TCI compared with MCI. No clinically significant differences were demonstrated in terms of quality of anaesthesia or adverse events.

AUTHORS' CONCLUSIONS

This systematic review does not provide sufficient evidence for us to make firm recommendations about the use of TCI versus MCI in clinical anaesthetic practice.

A computerized infusion pump for control of tissue tracer concentration during positron emission tomography in vivo pharmacokinetic/pharmacodynamic measurements

BACKGROUND

A computer controlled infusion pump (UIPump) for regulation of target tissue concentration of radioactive compounds was developed for use in biological research and tracer development for PET.

METHODS

Based on observed tissue or plasma kinetics after a bolus injection of the tracer an algorithm calculates the infusion needed to obtain a specified target kinetic curve. A computer feeds this infusion scheme into an infusion pump connected to an animal via a venous catheter. The concept was validated using [11C]Flumazenil administrated to Sprague-Dawley rats where the whole brain distribution and kinetic of the tracer was measured over time using a microPET-scanner. The accuracy and precision of the system was assessed by producing steady-state levels of the tracer and by mimicking kinetics after oral administration.

RESULTS

Various kinetic profiles could be generated, including rapid achievement of constant levels, or step-wise increased levels. The resulting tissue curves had low deviation from the target curves according to the specified criteria: AUC (%): 4.2 +/- 2.8, Maximal deviation (%): 13.6 +/- 5.0 and R2: 0.95 +/- 0.02.

CONCLUSION

The UIPump-system is suitable for use in PET-research for assessment of PK/PD properties by simulation of different tracer tissue kinetics in vivo.

Positron emission tomography and target-controlled infusion for precise modulation of brain drug concentration

INTRODUCTION

There are several instances when it is desirable to control brain concentration of pharmaceuticals, e.g., to modulate the concentration of anesthetic agents to different desired levels fitting to different needs during the course of surgery. This has so far only been possible using indirect estimates of drug concentration such as assuming constant relation between tissue and blood including extrapolations from animals.

METHODS

A system for controlling target tissue concentration (UIPump) was used to regulate whole-brain concentrations of a central benzodiazepine receptor antagonist at therapeutic levels with input from brain kinetics as determined with PET. The system was tested by using pharmacological doses of flumazenil mixed with tracer amounts of [11C]flumazenil. Flumazenil was used as a model compound for anesthesia. An infusion scheme to produce three different steady-state levels in sequence was designed based on kinetic curves obtained after bolus injection. The subjects (Sprague-Dawley rats, n=6) were monitored in a microPET scanner during the whole experiment to verify resulting brain kinetic curves.

RESULTS

A steady-state brain concentration was rapidly achieved corresponding to a whole-brain concentration of 118+/-6 ng/ml. As the infusion rate decreased to lower the exposure by a factor of 2, the brain concentration decreased to 56+/-4 ng/ml. A third increased steady-state level of anesthesia corresponding to a whole-brain concentration of 107+/-7 ng/ml was rapidly achieved.

CONCLUSION

The experimental setup with computerized pump infusion and PET supervision enables accurate setting of target tissue drug concentration.

Use of a target-controlled infusion system for propofol does not improve subjective assessment of anaesthetic depth by inexperienced anaesthesiologists*

BACKGROUND AND OBJECTIVES

Target-controlled infusion, via the calculated effect compartment concentrations, may help anaesthesiologists to titrate anaesthetic depth and to shorten recovery from anaesthesia.

METHODS

In this prospective, randomized clinical study, we compared the performance of six inexperienced anaesthesiologists with <1 yr of training when using target- or manually controlled infusion of propofol, combined with manual dosing of fentanyl. Ninety-two premedicated ASA I-III patients undergoing minor elective urological or gynaecological surgery were assigned to the manual- or target-controlled infusion group. Bispectral index was recorded in a blinded manner. Subjective assessment of anaesthetic depth on a 10 point numerical scale (1 = very deep anaesthesia, 10 = awake) was asked at regular intervals and the correlation with the blinded bispectral index was analysed using the prediction probability, PK. The propofol concentration profile was calculated post hoc.

RESULTS

Propofol administration was similar in both groups with no significant difference for the administered amount and concentrations of propofol. Recovery times were also not different. In both groups, a large percentage of the bispectral index data points recorded during surgery showed bispectral index values below the recommended value of 40, but in the target-controlled infusion group there were significantly less bispectral index values above the recommended upper limit of 60 (2.5% vs. 5.1%).

CONCLUSIONS

A target-controlled infusion system does not help inexperienced anaesthesiologists to assess anaesthetic depth or to shorten recovery times, but may reduce episodes of overly light anaesthesia and thus help to prevent awareness.

IMPROVED TRANSFORMATION OF MORPHOMETRIC MEASUREMENTS FOR A PRIORI PARAMETER ESTIMATION IN A PHYSIOLOGICALLY-BASED PHARMACOKINETIC MODEL OF ETHANOL

Prescription of the brain's time course of exposure to experimentally administered ethanol can be achieved with intravenous infusion profiles computed from a physiologically-based pharmacokinetic (PBPK) model of alcohol distribution and elimination. Previous parameter estimation employed transformations of an individual's age, height, weight and gender inferred from the literature, with modeling errors overcome with real-time, intermittent feedback. Current research applications, such as ethanol exposures administered during fMRI scanning, require open-loop infusions, thus improved transformation of morphometric measurements.Records of human breath alcohol concentration (BrAC) clamp experiments were analyzed. Optimal, unique PBPK parameters of a model of the distribution and elimination of ethanol were determined for each record and found to be in concordance with parameter values published by other investigators. A linear transformation between the readily measurable physical characteristics or morphometrics, including gender, age, height, weight, and TBW estimates, and the model parameters were then determined in a least squares sense according to the formula theta=F(x)=F(m)x where x=(age height weight TBW)(T)inR(4) and theta =(R(C) V(P) V(B) m(max)k(AT))(T)inR(5).The transformation was then evaluated with several parameter prediction performance measures. A substantial improvement in all error statistics, in relation to an earlier affine transformation that used only body weight as the relevant morphometric was obtained. Deviation from the measured response was reduced from 27 to 20%. Error in parameter estimation was reduced from 109 to 38%. Percent alcohol provided in error was reduced from 46 to 28%. Error in infusion profile estimation was reduced from 55 to 33%.The algorithm described, which optimizes individual pharmacokinetic parameter values and then subsequent extension to a priori prediction, while not unique, can be readily be adapted to other molecules and pharmacokinetic models. This includes those used for distinct purposes, such as automated control of anesthetic agents.

Subjective assessment of depth of anaesthesia by experienced and inexperienced anaesthetists

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.