Bispectral index, predicted and measured drug levels of target-controlled infusions of remifentanil and propofol during laparoscopic cholecystectomy and emergence

Impact of female sex on anaesthetic awareness, depth, and emergence: a systematic review and meta-analysis

BACKGROUND

Suggested anaesthetic dose ranges do not differ by sex, likely because of limited studies comparing sexes. Our objective was to systematically synthesise studies with outcomes of unintended anaesthesia awareness under anaesthesia, intraoperative connected consciousness, time to emergence from anaesthesia, and dosing to achieve adequate depth of anaesthesia, and to compare between females and males.

METHODS

Studies were identified from MEDLINE, Embase, and the Cochrane library databases until August 2, 2022. Controlled clinical trials (randomised/non-randomised) and prospective cohort studies that reported outcomes by sex were included. Results were synthesised by random effects meta-analysis where possible, or narrative form.

RESULTS

Of the 19 749 studies identified, 64 (98 243 participants; 53 143 females and 45 100 males) were eligible for inclusion, and 44 citations contributed to meta-analysis. Females had a higher incidence of awareness with postoperative recall (33 studies, odds ratio 1.38, 95% confidence interval [CI] 1.09-1.75) and connected consciousness during anaesthesia (three studies, OR 2.09, 95% CI 1.04-4.23) than males. Time to emergence was faster in females, including time to eye-opening (10 studies, mean difference -2.28 min, 95% CI -3.58 to -0.98), and time to response to command (six studies, mean difference -2.84 min, 95% CI -4.07 to -1.62). Data on depth of anaesthesia were heterogenous, limiting synthesis to a qualitative review which did not identify sex differences.

CONCLUSIONS

Female sex was associated with a greater incidence of awareness under general anaesthesia, and faster emergence from anaesthesia. These data suggest reappraisal of anaesthetic care, including whether similar drug dosing for females and males represents best care.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42022336087.

Reliability of the Minto model for target-controlled infusion of remifentanil during cardiac surgery with cardiopulmonary bypass

BACKGROUND

The Minto pharmacokinetic model is used for target-controlled infusion of remifentanil. The reliability of this model has never been evaluated during normothermic cardiac surgery with cardiopulmonary bypass (CPB). The aim of this study was to assess the predictive performance of the model during CPB to determine its reliability during cardiac surgery.

METHODS

This was a single-centre observational study. Arterial blood samples were drawn at five time points: T1, after tracheal intubation; T2, immediately before CPB; T3, 10 min after starting CPB; T4, 45 min after starting CPB; T5, 10 min after weaning off CPB. Prediction error (PE) and absolute prediction error (APE) were calculated for each sample and used to determine median prediction error (MDPE) and median absolute prediction error (MDAPE) per patient. Risk factors for APE >30% were assessed using multivariable analysis. Results are presented as medians with inter-quartile ranges.

RESULTS

Fifty-eight patients with 283 blood samples (110 during CPB) were included. In the pre-CPB period, MDPE and MDAPE were -17.3 [-32.9 to 2.3] and 24.6 [12-37.7]%, whereas during CPB, they were -1.8 [-15.6 to 11.1] and 14.0 [6.74-27.1]%, respectively. There was no statistically significant difference between measured and predicted remifentanil plasma concentrations during CPB. Age, preoperative albumin concentrations, temperature, and haemodilution were not independently associated with MDAPE >30%.

CONCLUSIONS

The Minto model accurately predicts plasma remifentanil concentrations during cardiac surgery with CPB.

CLINICAL TRIAL REGISTRATION

2017-A03153-50.

Location matters: Overlooked ethnic-geographic effect in China and Austria on propofol/cisatracurium sex differences among a population pharmacokinetic/pharmacodynamic (PopPK/PD) covariate analysis in men, women, and one transgender subject

A quick literature search using "sex/gender" vs. the commonly used hypnotic propofol or neuromuscular-blocking agent cisatracurium will reveal numerous contradictory sex difference publications depending on the ethnic-geographic location of where these studies were conducted. We induced anesthesia with cisatracurium besylate (GlaxoSmithKline) 100 μg kg^-1 administered exactly 1 minute following propofol (AstraZeneca) 2 mg kg^-1 . In 20 male and 20 female ethnic Han-Chinese test set patients (Xi'an China), and in similar ethnic white Austrian validation set patients (Graz Austria), we quantified propofol/cisatracurium pharmacodynamic parameters namely propofol onset time, lag time, plasma concentrations (C_p ) at loss-of-behavioral response (LOBR) using bispectral index (BIS); cisatracurium onset time, lag time, and C_p at T₁ % (first twitch of train-of-four) complete twitch suppression using mechanomyography (MMG). Serial arterial blood samples were collected for population pharmacokinetic (PopPK) analysis of all demographic and biological covariates (region, sex, age, weight, and height) versus volumes of distribution and clearances pharmacokinetic parameters. In Chinese women (but not in white women), propofol C_p at LOBR was 33.60% lower than men and cisatracurium C_p at T₁ % complete twitch suppression was 21.49% lower than men, a clear pharmacodynamic assertion. Region and weight were significant PopPK covariates. We demonstrated that sex differences are influenced by ethnic-geographic location as only in Chinese women (but not in white women) propofol C_p at LOBR and cisatracurium C_p at T₁ % complete twitch suppression were lower than in men. When defining sex differences, ethnic-geographic location should be taken into consideration as a predictive factor for optimizing propofol/cisatracurium initial loading recommended dosages.

Comparison of clinical performance of i-gelⓇ and Baska MaskⓇ during laparoscopic cholecystectomy

BACKGROUND

The supraglottic airway device is an appropriate alternative to tracheal intubation in laparoscopic surgery. We compared the Baska MaskⓇ with i-gelⓇ by measuring the oropharyngeal leak pressure (OLP) and hemodynamic and respiratory parameters during laparoscopic cholecystectomy.

METHODS

A total of 97 patients were randomly allocated to either i-gel group (n = 49) or Baska Mask group (n = 48). Insertion time, number of insertion attempts, fiber-optic view of the glottis, and OLP were recorded. Heart rate, mean arterial pressure, peak airway pressure (PAP), lung compliance, and perioperative complications were assessed before, during, and after pneumoperitoneum.

RESULTS

There were no significant differences between the two groups regarding demographic data, insertion time, fiber-optic view of the glottis, and the use of airway manipulation. The OLP was higher in the Baska Mask group than in the i-gel group (29.6 ± 6.8 cmH2O and 26.7 ± 4.5 cmH2O, respectively; P = 0.014). Heart rate, mean arterial pressure, PAP, and lung compliance were not significantly different between the groups. The incidence of perioperative complications was small and not statistically significant.

CONCLUSIONS

Both the i-gel and Baska Mask provided a satisfactory airway during laparoscopic cholecystectomy. Compared with the i-gel, the Baska Mask demonstrated a higher OLP.

Sex and gender aspects in anesthetics and pain medication

The influence of sex and gender on anesthesia and analgesic therapy remains poorly understood, nevertheless the numerous physiological and pharmacological differences present between men and women. Although in anesthesiology sex-gender aspects have attracted little attention, it has been reported that women have a greater sensitivity to the non-depolarizing neuroblocking agents, whereas males are more sensitive than females to propofol. It has been suggested that men wake slower than women after general anesthesia and have less postoperative nausea and vomiting. Sexual hormones seem to be of importance in the onset of differences. Nevertheless, in the last years, sex-gender influences on pain and analgesia have become a hot topic and data regarding sex-gender differences in response to pharmacologic and non-pharmacologic pain treatments are still scanty, inconsistent, and non-univocal. In particular, females seem to be more sensitive than males to opioid receptor agonists. Women may experience respiratory depression and other adverse effects more easily if they are given the same doses as males. Evidently, there is an obvious need for more research, which should include psychological and social factors in experimental preclinical and clinical paradigms in view of their importance on pain mechanism, in order to individualize analgesia to optimize pain relief.

Retrospective review of propofol dosing for procedural sedation in pediatric patients

OBJECTIVES

The purpose of this study was to determine the total propofol dose (mg/kg) for non-emergent pediatric procedural sedation and evaluate dosing differences with regard to a patient's sex, age, and body mass index. Adverse events were recorded and evaluated to determine whether certain patient groups were at a higher risk than others.

METHODS

This study was a retrospective observational pilot study including patients 0 to 18 years of age admitted between January 2008 and November 2009 for non-emergent gastrointestinal endoscopic procedures or radiologic imaging, who received propofol for procedural sedation. Data gathered included sex, age, height, weight, chronic medical conditions and medication use, concomitant anesthetic gas, preprocedure midazolam, procedure length, propofol dose in mg/kg, other medications administered during procedure, and adverse events that occurred. Comparisons between adverse event groups and categories of baseline characteristics were made using the Wilcoxon signed-rank, Kruskal-Wallis nonparametric and Pearson's chisquare tests, as appropriate.

RESULTS

A total of 101 patients met inclusion criteria and were included in the analysis. The mean dose of propofol required for female patients was 3.7 mg/kg versus 3.4 mg/kg for males (p=0.3). The mean dose of propofol for patients ≤9 years, 10 to 12 years, and >12 years was 3.2, 3.9, and 3.9 mg/kg, respectively (p=0.25). The mean dose of propofol for underweight, healthy weight, overweight, and obese patients was 4.2, 3.9, 3.6, and 2.6 mg/kg, respectively (p=0.38). Hypotension occurred in 42.6% of patients, and bradycardia occurred in 13.9% of patients.

CONCLUSIONS

There were no differences in dose requirements based on sex or age. The difference in dosing between different body weight categories was not statistically significant. The dose of propofol was higher in patients that experienced bradycardia and hypotension, but there was no statistical significance. Given the above, future studies with larger sample sizes should be conducted to establish if statistical significance exists.

Propofol pharmacokinetics in young healthy Indian subjects

OBJECTIVES

To analyze population pharmacokinetics of Propofol in Indian patients after single bolus dose of Propofol using WINNONLIN program.

MATERIALS AND METHODS

Population pharmacokinetics of Propofol was investigated in Indian subjects in 26 elective surgical patients (14 males and 12 females) following single bolus dose of 2 mg/kg propofol. A total of 364 samples were estimated by High Performance Liquid Chromatography and pharmacokinetic parameters were derived using WINNONLIN (5.2). The effect of demographic characters of the study population on pharmacokinetic parameters was investigated.

RESULTS

Three-compartment model was used to describe the pharmacokinetic data of Propofol in Indian subjects. Initial volume of distribution (V1) clearance (Cl) and steady state volume of distribution (Vd(ss)) was 13.5 ± 3.3 l, 1.08 ± 0.42 l/min, and 77.69 ± 48.0 l, respectively. Body weight best described the volume of central compartment (V1) as well as elimination clearance (P<0.01).

CONCLUSION

Pharmacokinetics of Propofol in young healthy Indian subjects show lower volume of distribution and clearance as compared with most of the western data. Body weight best describes the V1, Vd(ss), and Clearance in this group.

Predicted effect-site concentration of propofol and sufentanil for gynecological laparoscopic surgery

BACKGROUND

this study was to estimate the predicted effect-site concentration of propofol administered by a target-controlled infusion (TCI) for maintenance of anesthesia based on the bispectral (BIS) index as a measure of hypnosis in laparoscopic surgery.

METHOD

one-hundred and sixty unpremedicated patients undergoing gynecologic laparoscopy were assigned randomly to receive one of the target effect-site concentrations of propofol 2.0, 2.5, 3.0, 3.5 and 4.0 microg/ml during TCI with propofol and sufentanil. The dose-response relationship of propofol for the maintenance of adequate anesthesia based on BIS, movement and hemodynamic response was investigated using a fixed effect-site concentration of sufentanil (0.2 ng/ml). The BIS values, hemodynamic variables, time course during emergence and intraoperative awareness were also assessed.

RESULTS

the predicted effect-site propofol concentrations for adequate anesthesia at the skin incision in 50% (EC(50) ) and 95% (EC(95) ) of patients undergoing gynecologic laparoscopy were 2.2 and 3.7 microg/ml, respectively. The predicted propofol EC(50) and EC(95) to maintain adequate anesthesia in these patients were 2.6 microg/ml (95% CI 2.3-2.7 microg/ml) and 3.6 microg/ml (95% CI 3.3-4.0 microg/ml), respectively. The BIS values, effect-site concentration of propofol, hemodynamic data and time course during emergence and post-operative adverse events were comparable in each group. There were no reports of intraoperative awareness in the post-anesthetic care unit.

CONCLUSION

based on the anesthetic depth assessed by the clinical signs and BIS monitoring, the predicted effect-site propofol concentrations for the maintenance of anesthesia in patients undergoing gynecologic laparoscopy were similar in those administered adequate anesthesia at the skin incision during TCI.

Monitoring the depth of anaesthesia

One of the current challenges in medicine is monitoring the patients’ depth of general anaesthesia (DGA). Accurate assessment of the depth of anaesthesia contributes to tailoring drug administration to the individual patient, thus preventing awareness or excessive anaesthetic depth and improving patients’ outcomes. In the past decade, there has been a significant increase in the number of studies on the development, comparison and validation of commercial devices that estimate the DGA by analyzing electrical activity of the brain (i.e., evoked potentials or brain waves). In this paper we review the most frequently used sensors and mathematical methods for monitoring the DGA, their validation in clinical practice and discuss the central question of whether these approaches can, compared to other conventional methods, reduce the risk of patient awareness during surgical procedures.

Effect of open-chest surgery in the lateral position on blood propofol concentration during target-controlled infusion of propofol

Our research hypothesis was that single lung ventilation during thoracic surgery in the lateral position increases the blood concentration of propofol during target-controlled infusion. Thirty adult patients in two tertiary referral hospitals undergoing open-chest surgery were studied. Anaesthesia was induced and maintained with propofol using a Diprifusor (Graseby 3500) computer-controlled pump set to deliver a blood concentration of 4 tg.ml(-1). Blood samples were taken with the patient positioned in (1) the supine position 20 minutes after induction (supine); (2) the lateral position just prior to one-lung ventilation (lateral); (3) the lateral position five minutes after commencing one-lung ventilation (OLV5) and (4) the lateral position 20 minutes after commencing one-lung ventilation (OLV20). Propofol concentrations were determined by high performance liquid chromatography. The target-controlled infusion target level was maintained at 4 microg.ml(-1) during the study period for all cases. The mean (SD) propofol blood concentration (microg.ml(-1)) at each stage was 5.5 (1.5) supine, 5.3 (1.1) lateral, 5.3 (1.2) OLV5 and 5.1 (1.2) OLV20. Repeated measures ANOVA showed an F value 1.9, lambda 5.5 and P value 0.15. Post hoc analysis did not identify a significant difference between the sample times. During target-controlled infusion of propofol, mean blood propofol concentrations did not change significantly from those obtained with the patient supine after up to 50 minutes in the lateral position during thoracic surgery, or 20 minutes after commencing one-lung ventilation.

Sex, age, and genetics in anesthesia

PURPOSE OF REVIEW

Pharmacology is one of the corner stones of anesthesia. Outcome of anesthesia is related, in part, to both pharmacodynamics and pharmacokinetics of anesthetic drugs. Recent developments have indicated that among individuals, major differences exist in pharmacological effects. In this regard, sex, age, and genetic profile are increasingly considered to be of importance.

RECENT FINDINGS

For a number of anesthetic drugs, it has been demonstrated that sex differences influence their effects and thus can alter the outcome of anesthesia. Also other genetically determined differences than sex are important.

SUMMARY

In the future, it is expected that an individual's pharmacological needs will be based on age, sex, and genomics.

Population pharmacokinetics of sevoflurane in conjunction with the AnaConDa: toward target-controlled infusion of volatiles into the breathing system

BACKGROUND

The Anesthetic Conserving Device (AnaConDa) uncouples delivery of a volatile anesthetic (VA) from fresh gas flow (FGF) using a continuous infusion of liquid volatile into a modified heat-moisture exchanger capable of adsorbing VA during expiration and releasing adsorbed VA during inspiration. It combines the simplicity and responsiveness of high FGF with low agent expenditures. We performed in vitro characterization of the device before developing a population pharmacokinetic model for sevoflurane administration with the AnaConDa, and retrospectively testing its performance (internal validation).

MATERIALS AND METHODS

Eighteen females and 20 males, aged 31-87, BMI 20-38, were included. The end-tidal concentrations were varied and recorded together with the VA infusion rates into the device, ventilation and demographic data. The concentration-time course of sevoflurane was described using linear differential equations, and the most suitable structural model and typical parameter values were identified. The individual pharmacokinetic parameters were obtained and tested for covariate relationships. Prediction errors were calculated.

RESULTS

In vitro studies assessed the contribution of the device to the pharmacokinetic model. In vivo, the sevoflurane concentration-time courses on the patient side of the AnaConDa were adequately described with a two-compartment model. The population median absolute prediction error was 27% (interquartile range 13-45%).

CONCLUSION

The predictive performance of the two-compartment model was similar to that of models accepted for TCI administration of intravenous anesthetics, supporting open-loop administration of sevoflurane with the AnaConDa. Further studies will focus on prospective testing and external validation of the model implemented in a target-controlled infusion device.

An investigation of potential genetic determinants of propofol requirements and recovery from anaesthesia

BACKGROUND AND OBJECTIVE

The objectives of this study were, firstly, to characterize the inter-patient variability in the dose of propofol required to achieve a bispectral index <70 and 'time to eye opening' following propofol infusion and, secondly, to determine if the pharmacodynamic parameter 'time to achieve bispectral index <70' was influenced by genotype of the sex-linked drug receptor gene GABRE or if pharmacokinetic parameters such as clearance and 'time to eye opening' were influenced by the genotype of the metabolizing enzyme CYP2B6.

METHODS

One hundred and fifty patients received a standardized anaesthetic. Apparent systemic clearance values were estimated. Correlation was sought between carriers of different CYP2B6 and GABRE genotypes and apparent systemic clearance, 'time to achieve bispectral index <70' and 'time to eye opening'.

RESULTS

Propofol induction/emergence characteristics varied, with slow recovery times in a subset of males. Time to loss of verbal contact and time to bispectral index <70 varied 6.6- and 4.3-fold, respectively. At emergence, there was a 15.5- to 111-fold variability in the measured time intervals. Clearance varied from 9.1 to 55.8 mL min-1 kg-1. The CYP2B6 C1459T (R487C) genotype frequencies were TT 1%, TC 22% and CC 67%. The three major haplotypes of CYP2B6 (R487C, K262R and Q172H variants) were not significantly associated with time to eye opening or clearance. Clearance was similar in 487C carriers and 487RR genotypes. There was no statistically significant correlation between the four major haplotypes of GABRE variants investigated ([mRNA358]G/T, 20118C/T, 20326C/T and 20502 A/T) and the observed anaesthesia induction time.

CONCLUSIONS

Great inter-patient variability exists in the dose of propofol required to achieve bispectral index <70, apparent systemic propofol clearance and time to eye opening. Common haplotypic differences at the CYP2B6 and GABRE genes do not appear to account for the majority of the observed inter-patient variability.

Changes of bispectral index during recovery from general anesthesia with 2% propofol and remifentanil in children

BACKGROUND

The bispectral (BIS) index is a pharmacodynamic measure of the effect of anesthesia on the central nervous system. The aim of this study was to investigate the relationship between BIS index and predicted plasma concentration of propofol delivered by target controlled infusion (TCI) during emergence in children.

METHODS

With approval of IRB, 30 patients (2-7 years) were included in this study. Anesthesia was with TCI propofol 3-5 microg.ml(-1) and remifentanil 7.5 ng.ml(-1) to maintain BIS 40-60 and the propofol concentration was fixed at 3 microg.ml(-1) Remifentanil infusion was stopped 10 min before the end of surgery. BIS values were recorded after reducing propofol in decrement of 0.2 microg.ml(-1). BIS values were checked when spontaneous respiration occurred and children were able to obey a command (eye opening or hand grasping).

RESULTS

Spearman's correlation analysis showed negative correlation between BIS and propofol plasma concentration (r = -0.559, P < 0.001). When respiration returned, mean BIS was 77.2 +/- 5.3 and propofol plasma concentration 1.6 +/- 0.3 microg.ml(-1) and when a verbal command was obeyed, BIS was 82.4 +/- 5.6 and propofol plasma concentration 1.5 +/- 0.3 microg.ml(-1).

CONCLUSIONS

In preschool children, BIS moderately correlated with the predicted plasma concentration of propofol.

Gender differences between predicted and measured propofol C(P50) for loss of consciousness

OBJECTIVE

To investigate gender differences in the effective dose of 50% for loss of consciousness (C(P50LOC)) for propofol using Diprifusor, the most commonly used target-controlled infusion system.

DESIGN

Prospective, randomized, comparative study.

SETTING

University-affiliated hospital.

PATIENTS

50 ASA physical status I and II patients, aged 20 to 50 years, scheduled for minor surgery.

INTERVENTIONS

Patients were randomized into two groups of 25 patients each. A target-controlled infusion of propofol (Diprifusor) was maintained at a predetermined target concentration. After a 10-minute steady state, blinded investigators evaluated patients' consciousness using verbal commands. The propofol test concentration was predetermined using a modified version of Dixon's up-and-down method (starting at 2.5 mug/mL; step size of 0.1 microg/mL).

MEASUREMENT

Predicted and measured C(P50LOC) values and bispectral index (BIS) were obtained by averaging the crossover midpoint (ie, consciousness to unconsciousness). Those values were analyzed by unpaired t test: P < 0.05 was considered significant.

RESULTS

The predicted C(P50LOC) for men was 2.14 +/- 0.10 microg/mL, which was lower than that for women, 2.55 +/- 0.11 microg/mL (P < 0.0001). No significant difference was found for measured C(P50LOC) in men (2.37 +/- 0.41 microg/mL) and in women (2.30 +/- 0.28 microg/mL) or for BIS measurements.

CONCLUSION

Predicted C(P50LOC) by Diprifusor for men tended to be underestimated; that for women tended to be overestimated. Our data support a review of Diprifusor (Astra Zeneca, Osaka, Japan) pharmacokinetic parameters to avoid awareness during operation, particularly for women.

Nitrous Oxide and Anesthetic Requirement for Loss of Response to Command During Propofol Anesthesia

The blood concentration associated with loss of response (LOR) to command in 50% of subjects (CP50(LOR)) is an important measure of anesthetic potency. We therefore determined the CP50(LOR) in 40 healthy surgical patients, aged 18-60 yr old, receiving propofol alone or propofol with 67% nitrous oxide (N2O). Patients were randomized to receive 100% oxygen or 67% N2O in oxygen via facemask. Three minutes later, a target-controlled propofol infusion was commenced at a concentration determined by the response of the previous patient in the same group. Fifteen minutes later, response to command was assessed by a blinded observer. Arterial blood samples were taken for propofol assay, and the bispectral index (BIS) was monitored continuously. At testing for response to command, both the measured and target propofol concentrations were significantly larger and BIS values significantly smaller in the propofol-alone group compared with the propofol-N2O group. The CP50(LOR) of propofol in the propofol-alone group was 4.58 mug/mL (95% confidence interval [CI], 1.14-15.36) and 2.67 microg/mL (95% CI, 2.28-3.17) in the propofol-N2O group. The BIS value when 50% of patients responded to command was 60 (95% CI, 55-65) in the propofol-alone group and 75 (95% CI, 73-83) in the propofol-N2O group.

Why do women wake up faster than men from propofol anaesthesia?

BACKGROUND

It has repeatedly been shown that female patients wake up faster from propofol anaesthesia than male patients. The reason for this is not clear. It is possible that female patients have a more rapid decline in plasma propofol concentration after termination of an infusion, or there could be gender differences in the sensitivity to propofol, making women wake up at higher concentrations. We tested the hypothesis that women wake up faster because of a more rapid decline in plasma propofol.

METHODS

Sixty adult patients (30 female and 30 male; ASA I or II) undergoing lower limb surgery under regional anaesthesia, were enrolled in an open study. Propofol was given as the only hypnotic drug, administered by the plasma target control system (TCI) Diprifusor, titrated to bispectral index (BIS) values of 40-60. Blood samples for propofol measurements were taken just before the propofol infusion was stopped and when the patients woke up.

RESULTS

The female patients woke up faster than the male patients (5.6 vs 8.2 min, P=0.003). The plasma propofol concentration declined more rapidly in the women (P=0.02). An additional significant finding was that the TCI algorithm had a better fit for the women than for the men, with a median prediction error (MDPE) of 2% in the female patients compared with 40% in the male patients (P<0.001). At emergence the men had a significantly higher measured propofol concentration than the women (P=0.05).

CONCLUSION

The female patients had a more rapid decline in plasma propofol at the end of infusion. Gender differences in pharmacokinetics could explain the faster emergence for female patients after propofol anaesthesia, and gender differences in propofol sensitivity may also be present.

Acupressure and preoperative parental anxiety: a pilot study

In this randomized sham-controlled study we examined the anxiolytic and sedative effects of acupressure on parents in the preoperative holding area before their children's surgery. Sixty-one parents received acupressure either at the Yintang point (midpoint between the two eyebrows) or at a sham point. Anxiety (as measured by the Stait-Trait Anxiety Inventory), arterial blood pressure, and heart rate were assessed before and after the intervention and a Bispectral Index monitor was used to continuously monitor hypnotic sedation levels. Repeated-measures analysis of variance showed that parents in the acupressure group reported significantly less anxiety at 20 min post-intervention as compared with parents in the sham group (37 +/- 10 versus 45 +/- 13, P = 0.03). Bispectral Index values, heart rate, and arterial blood pressure, however, did not differ between the two study groups (P = not significant). We conclude that acupressure at the Yintang point may be used as a treatment for parental preoperative anxiety. Future studies are needed to quantify the magnitude and duration of the anxiolytic effect.

Einfluss des Geschlechts auf Propofolverbrauch und Aufwachzeiten bei standardisierter Anästhesietiefe

INTRODUCTION

We investigated gender differences of drug consumption and recovery times for propofol-remifentanil anaesthesia.

METHODS

Adult patients scheduled for minor orthopaedic surgery were randomised to receive a propofol-remifentanil anaesthesia controlled either by EEG monitoring (Narcotrend or BIS) or solely by clinical parameters. Anaesthesia was induced with remifentanil 0.4 microg/kg/min and a propofol target-controlled infusion (TCI) at 3.5 microg/ml. After intubation remifentanil was reduced to 0.2 microg/kg/min whereas propofol TCI was adjusted according to clinical parameters or to the following EEG target values: during maintenance to "D(0)" (Narcotrend) or "50" (BIS), 15 min before the end of surgery to "C(1)" (Narcotrend) or "60" (BIS). Recovery times were recorded and average normalised propofol consumption was calculated from induction and maintenance doses.

RESULTS

A total of 60 male and 60 female patients completed the study. Gender differences were observed for recovery times (with standard practice) and for propofol consumption (with BIS monitoring). In the standard protocol group, propofol consumption was nearly identical for male and female patients whereas recovery times were significantly longer in the male group. In both EEG-guided groups propofol consumption was less for male patients while recovery times were slightly longer. In the group of female patients higher propofol TCI concentrations had to be used to reach the same BIS or Narcotrend values.

CONCLUSION

With propofol-remifentanil anaesthesia, gender has impact on recovery times and propofol consumption. If the same amounts of propofol are applied, males awake later, with BIS or Narcotrend monitoring males receive less propofol for comparable EEG effects.

Requirements of propofol at different end-points without adjuvant and during two different steady infusions of remifentanil

BACKGROUND

Some reports show no interaction between propofol and opioids, whereas others state such interactions. We evaluated the influence of remifentanil on propofol requirements at certain anesthesia end-points.

METHODS

Elective surgical patients were randomly assigned to three groups of 15 patients each. Premedication was with oral diazepam 0.1 mg kg(-1). Patients were blindly given equal volumes of saline or remifentanil (7.5 or 30 microg kg(-1). h(-1)) 1 min before induction of anesthesia with infusion of propofol, 30 mg kg(-1). h(-1). We recorded times to, propofol requirements, and bispectral index at loss of counting (LC), loss of verbal command (LVC), loss of reaction to tetanic stimulation (LRT), and onset of burst suppression pattern (BSP) of electroencephalography.

RESULTS

In the remifentanil groups end-points were attained significantly faster and with lower doses of propofol than in the saline group. BIS-values were significantly different at LRT and BSP end-points.

CONCLUSIONS

We conclude that remifentanil infusion started before induction of propofol anesthesia significantly reduces propofol requirements at all end-points. The results suggest that remifentanil accelerates the hypnotic onset of propofol.

Comparison of recovery properties of desflurane and sevoflurane according to gender differences

BACKGROUND

The aim of this study was to investigate the recovery properties of desflurane and sevoflurane in patients undergoing elective surgery, according to the gender differences.

METHODS

In the study, 160 ASA class I-II patients aged between 20 and 60 years were included. The patients were assigned into two groups according to their gender, and these groups were randomly divided into two groups according to a selected volatile anaesthetic agent. Intraoperative bispectral index, time of postoperative achievement for end-tidal concentrations of volatile agents to decline 50% (ET-AA%50), time for extubation, time for eye opening and orientation, and time for bispectral index values to reach control values were recorded. Aldrete scores and error points of a delayed memory recall test were determined.

RESULTS

Desflurane groups had a shorter ET-AA%50 time, extubation and eye-opening time in male and female patients compared to the sevoflurane groups, and these results were statistically significant (P < 0.05). In both the desflurane and sevoflurane groups, ET-AA%50 time, extubation and eye-opening time were shorter in male patients than in female patients, and these results were also statistically significant (P < 0.05). There were no significant differences among the groups in terms of Aldrete scores and error points of delayed memory recall test (P > 0.05).

CONCLUSION

In conclusion, early recovery time was shorter in male patients compared to female patients in both the desflurane and sevoflurane groups. Additionally, in the desflurane groups it was shorter in the sevoflurane groups for both genders.

Unconscious auditory priming during surgery with propofol and nitrous oxide anaesthesia: a replication

BACKGROUND

Priming during anaesthesia has been hard to replicate and the conditions under which it occurs remain poorly understood. We replicated and extended a recent study to determine whether intraoperative priming during propofol and nitrous oxide anaesthesia is a reliable phenomenon, whether it occurs due to awareness during word presentation and whether it is suppressed by a dose of fentanyl at induction.

METHODS

Words were played through headphones during surgery to 62 patients receiving propofol and nitrous oxide anaesthesia. Thirty-two patients received fentanyl 1.5 microg kg(-1) at induction and 30 received no fentanyl. Neuromuscular blocking drugs were not used. Depth of anaesthesia was measured using the bispectral index (BIS). Anaesthetic variables were recorded at 1 min intervals during word presentation. On recovery, implicit and explicit memory were assessed using an auditory word-stem completion test and a yes-no word-recognition test, respectively.

RESULTS

BIS, blood pressure, end-tidal carbon dioxide and heart rate during word presentation did not differ between the study groups. The infusion rate of propofol and the patients' ventilatory frequency were significantly higher in the group not receiving fentanyl. No patient had unprompted explicit recall of surgery, although there was above-zero performance in six patients on the yes-no recognition task (P<0.05). There was no physiological evidence of awareness during anaesthesia (median mean-BIS=38 in the no-fentanyl group and 42 in the fentanyl group). There was evidence for priming (mean priming score=0.09, P<0.05 in the no-fentanyl study group; mean priming score=0.07, P<0.05 in the fentanyl group) even when patients with momentary light anaesthesia (maximum recorded BIS> or =60) and/or positive recognition scores were excluded from the analysis.

CONCLUSIONS

Existing knowledge can be primed by information presented during propofol and nitrous oxide anaesthesia. This priming is evidence of unconscious information processing and not the result of moments of awareness.

The effect of different stages of neuromuscular block on the bispectral index and the bispectral index-XP under remifentanil/propofol anesthesia

Facial electromyographic activity and neuromuscular block could influence bispectral index (BIS) depth of anesthesia monitoring. In this study we examined, in 30 patients undergoing general surgical procedures, the effect of different stages of neuromuscular block on BIS monitoring and compared the conventional A-2000 BIS trade mark (BIS(3.4)) with the new BIS-XP trade mark (BIS(XP)). At deep surgical anesthesia BIS(3.4) of approximately 40, under a propofol 3.61 microg/mL target-controlled infusion and a 0.15-0.3 microg. kg(-1). min(-1) remifentanil infusion, mivacurium 0.15 mg/kg was administered. The onset of neuromuscular block triggered a brief transient odd divergence in response that manifested as a BIS(3.4) increase from 43 +/- 4 to 49 +/- 7 (P = 0.007) and a BIS(XP) decline from 41 +/- 3 to 35 +/- 3 (P = 0.003) at 1 +/- 0.2 min. Then, 2.5 +/- 1 min after mivacurium administration, both monitors returned to baseline values of 43 +/- 5 and 40 +/- 4, respectively. After that, BIS(3.4) and BIS(XP) did not significantly change during complete neuromuscular block or during various levels of neuromuscular recovery. At all phases, BIS(XP) was significantly lower than BIS(3.4). Our study indicated that the BIS(3.4)/BIS(XP) bias and the wide limits of agreement do not allow values given by the two monitors to be used interchangeably.

Anaesthesia for carotid endarterectomy: comparison of hypnotic- and opioid-based techniques †

BACKGROUND

Although the synergistic interaction between hypnotics and opioids for total i.v. anaesthesia has been repeatedly demonstrated, questions about different dose combinations of hypnotics and opioids remain. The optimal combination would be based on maximal synergy, using the lowest dose of both drugs and having the lowest incidence of side-effects.

METHODS

The major goal of this prospective randomized study was to compare two different dose combinations of propofol and remifentanil (both administered by target controlled infusion (TCI)) in respect of haemodynamics during surgery and recovery, and the need for cardiovascular treatment in the recovery room. A secondary goal was to compare pain scores (VAS) and morphine consumption in the recovery room. Anaesthesia was induced in both groups using TCI propofol, adjusted to obtain a bispectral index score (BIS) value between 40 and 60. TCI for remifentanil commenced at an initial effect-site concentration of 0.5 ng ml(-1), and was adjusted according to haemodynamics. Patients were divided into one of two groups during anaesthesia: (i). Group H, hypnotic anaesthesia (n=23), propofol effect-site concentration maintained at 2.4 microg x ml(-1); and (ii). Group O, opioid anaesthesia (n=23), propofol effect-site concentration maintained at 1.2 microg x ml(-1). In both groups, remifentanil effect-site concentration was adjusted according to haemodynamics and changes in BIS value.

RESULTS

In Group O, more episodes of intraoperative hypotension (P<0.02) and hypertension (P<0.01), and fewer episodes of tachycardia were observed. More patients in Group O required nicardipine administration for postoperative hypertension (8 patients in Group H vs 15 patients in Group O, P<0.04). During recovery, morphine titration was necessary in approximately 50% of patients. No significant difference between groups was observed concerning pain scores or requirement for morphine titration.

CONCLUSIONS

Maintenance of anaesthesia predominantly with propofol and a low dose of remifentanil, both administered using TCI, is associated with greater stability in perioperative haemodynamics than anaesthesia predominantly with remifentanil alone. Postoperative pain was identical in both groups of patients who underwent relatively short duration, and relatively painless surgery.

Bispectral index, serum drug concentrations and emergence associated with individually adjusted target-controlled infusions of remifentanil and propofol for laparoscopic surgery

BACKGROUND

Target-controlled infusions (TCI) are used to simplify administration and increase precision of i.v. drugs during general anaesthesia. However, there is a limited relationship between preset targets and measured concentrations of drugs and between measured concentrations and measures of brain function, such as the bispectral index (BIS).

METHODS

We set out to evaluate the performance of TCI devices for propofol (Diprifusor) and remifentanil (Remifusor, prototype), during laparoscopic cholecystectomy in 21 patients. We also checked if there was any correlation between serum concentrations of propofol and BIS during individually adjusted anaesthesia.

RESULTS

The Diprifusor and Remifusor had a median absolute performance error of 60% and 25% respectively. Propofol concentrations were underpredicted by a median of 60%, and remifentanil concentrations were slightly overpredicted by a median of 7%. When anaesthesia was adjusted to keep BIS values between 45 and 60, no correlation existed between measured concentrations of propofol and the corresponding BIS values, although both BIS and serum propofol concentration discriminated well between the awake and asleep states. Emergence was rapid and uneventful in all patients. Female patients had a more rapid emergence than male patients (6.6 and 11.6 min respectively).

CONCLUSIONS

TCI devices for remifentanil and propofol result in large variation in measured serum concentrations. The lack of correlation between BIS and serum concentrations of propofol adds to the debate about whether BIS measures hypnosis as a graded state during surgery. This study confirms that women wake up faster than men, but provides no explanation for this repeatedly shown difference.

Assessing Propofol Induction of Anesthesia Dose Using Bispectral Index Analysis

In this study we sought to determine the propofol requirement and hemodynamic effects as guided by bispectral index (BIS) analysis during induction of anesthesia. Sixty patients were enrolled in this study. Propofol, 2 mg/kg, was given to Group I for induction. Propofol was administered for induction until loss of response to verbal commands and until BIS values were around 50 to Groups II and III. After induction, the smallest BIS value was different in Group I. Decreases in total propofol dose were 36% and 43% in Groups II and III respectively as compared with Group I. The dose of propofol assessed by BIS analysis results in an important reduction of propofol requirement without side effects.

IMPLICATIONS

Hypotension during induction of anesthesia with propofol is common. This study has shown that propofol requirement assessed by bispectral index analysis during anesthesia induction may decrease the dose and side effects and provide for satisfactory depth of anesthesia.

Optimization of desflurane administration in morbidly obese patients: a comparison with sevoflurane using an ‘inhalation bolus’ technique

BACKGROUND

The concept of an 'inhalation bolus' can be used to optimize inhaled drug administration. We investigated the depth of anaesthesia, haemodynamic stability, and recovery time in morbidly obese patients resulting from bispectral index (BIS)-guided sevoflurane or desflurane administration and BIS-triggered inhalation boluses of sevoflurane or desflurane combined with titration of remifentanil.

METHODS

Fifty morbidly obese patients undergoing laparoscopic gastroplasty received either BIS-guided sevoflurane or desflurane anaesthesia in combination with a remifentanil target-controlled infusion. Intraoperative haemodynamic stability and BIS control were measured. Immediate recovery was recorded.

RESULTS

Intraoperatively, the BIS was between 40 and 60 for a greater percentage of time in the sevoflurane (78 (13)% of case time) than in the desflurane patients (64 (14)% of case time), owing to too profound anaesthesia in the desflurane patients at the start of the procedure. However, fewer episodes of hypotension were found in the desflurane group, without the occurrence of more hypertensive episodes. During immediate recovery, eye opening, extubation, airway maintenance, and orientation occurred sooner in the desflurane group.

CONCLUSIONS

Immediate recovery was significantly faster in the desflurane group. Overall hypnotic controllability measured by BIS was less accurate with desflurane. Overall haemodynamic controllability was better when using desflurane. Fewer episodes of hypotension were found in the desflurane group. The use of the inhalation bolus was found to be appropriate in both groups without causing severe haemodynamic side effects. Minimal BIS values were significantly lower after a desflurane bolus.

ARX-derived auditory evoked potential index and bispectral index during the induction of anesthesia with propofol and remifentanil

A new commercial auditory evoked potential (AEP) monitor (A-line AEP monitor) was developed to calculate an index (ARX AEP index; AAI) by automatically using the amplitudes and latencies of the AEP. We investigated 30 patients before spine surgery. AAI; bispectral index (BIS); relative (%) delta, theta, alpha, and beta; spectral edge frequency; median frequency; mean arterial blood pressure; heart rate; and oxygen saturation were obtained simultaneously during stepwise (1.0 micro g/mL) induction of target-controlled propofol concentration until 5.0 micro g/mL, followed by an infusion of 0.3 micro g. kg(-1). min(-1) of remifentanil. Every minute, the patients were asked to squeeze the observer's hand. Prediction probability (Pk), receiver operating characteristic, and logistic regression were used to calculate the probability to predict the conditions AWAKE, UNCONSCIOUSNESS (first loss of hand squeeze), and steady-state ANESTHESIA (5.0 micro g/mL of propofol and 0.3 micro g. kg(-1). min(-1) of remifentanil). Although a statistically significant difference among the conditions was observed for AAI, BIS, mean arterial blood pressure, median frequency, and %alpha, only AAI and BIS were able to distinguish UNCONSCIOUSNESS versus AWAKE and ANESTHESIA versus AWAKE with better than Pk = 0.90. The modern electroencephalographic variables AAI and BIS were superior to the classic electroencephalographic and hemodynamic variables to distinguish the observed anesthetic conditions.

IMPLICATIONS

The modern electroencephalographic ARX-derived auditory evoked potential index and the bispectral index were superior to the classic electroencephalographic and hemodynamic variables for predicting anesthetic conditions. Variables derived from the auditory evoked potential did not provide an advantage over variables derived from spontaneous electroencephalogram.

A randomized controlled study of three targets of propofol plasma concentration in patients undergoing uterine dilation and curettage

AIM

To compare the efficacy and the complications of three target levels of propofol plasma concentration in patients undergoing uterine dilation and curettage.

METHODS

Sixty-nine patients were randomly allocated to receive propofol target controlled infusion at different target concentrations of 4 (group I), 5 (group II) and 6 (group III) mcg/mL combined with 1 microg/kg of fentanyl and 66% of nitrous oxide. Patients' movement during the procedure, hemodynamic variables, oxygen saturation, end tidal carbon dioxide, time to sleep and awake, and bispectral index score were recorded.

RESULTS

Seven patients in group I, one in group II, and none in group III (P < 0.05) moved grossly during the procedure. More patients in group III developed hypotension (5 vs 0 and 2 in group I and II, P < 0.05), but no difference was found regarding respiratory complication. No difference was found in time to sleep, but time to wake was longer in group III.

CONCLUSION

Propofol infusion at the target concentration of 5 microg/mL was recommended for uterine dilation and curettage when it was administered with fentanyl 1 microg/kg and nitrous oxide 66% under close monitoring and appropriate respiratory management.

Gender differences in drug effects: implications for anesthesiologists

BACKGROUND

The gender aspect in pharmacokinetics and pharmacodynamics of anesthetics has attracted little attention. Knowledge of previous work is required to decide if gender-based differences in clinical practice is justified, and to determine the need for research.

METHODS

Basis for this paper was obtained by Medline searches using the key words 'human' and 'gender' or 'sex,' combined with individual drug names. The reference lists of these papers were further checked for other relevant studies.

RESULTS

Females have 20-30% greater sensitivity to the muscle relaxant effects of vecuronium, pancuronium and rocuronium. When rapid onset of or short duration of action is very important, gender-modified dosing may be considered. Males are more sensitive than females to propofol. It may therefore be necessary to decrease the propofol dose by 30-40% in males compared with females in order to achieve similar recovery times. Females are more sensitive than males to opioid receptor agonists, as shown for morphine as well as for a number of kappa (OP2) receptor agonists. On this basis, males will be expected to require 30-40% higher doses of opioid analgesics than females to achieve similar pain relief. On the other hand, females may experience respiratory depression and other adverse effects more easily if they are given the same doses as males.

CONCLUSION

These examples illustrate that gender should be taken into account as a factor that may be predictive for the dosage of several anesthetic drugs. Moreover, there is an obvious need for more research in this area in order to further optimize drug treatment in anesthesia.

Different benefit of bispectal index (BIS) in desflurane and propofol anesthesia

BACKGROUND

Bispectal index (BIS) monitoring may reduce drug usage and hasten recovery in propofol and inhalation anesthesia. The faster emergence profile of desflurane may reduce the effect of BIS monitoring on recovery from desflurane compared with propofol. This study compared hypnotic drug usage, recovery, patient satisfaction and incidence of inadequate sedation in BIS monitored and nonmonitored women anesthetized with desflurane or propofol.

METHODS

One hundred and sixty patients scheduled for elective gynecological surgery were randomly assigned to desflurane or propofol anesthesia with and without BIS monitoring. Fentanyl, vecuronium and remifentanil were administered according to clinical criteria. The BIS monitor was used in all patients, but the monitor screen was covered in the controls. A BIS level between 45 and 55 was targeted in the BIS monitored patients whereas depth of anesthesia was assessed by clinical criteria in the controls.

RESULTS

The mean (SD) desflurane MAC-hours administered with and without BIS were 0.70 (0.15) and 0.76 (0.12), respectively, resulting in extubation times of 6.5 (4.1) and 8.3 (6.1) min. (NS). Bispectal index monitoring was associated with improved patient satisfaction, reduced postoperative nausea and antiemetic drug requirement, and fewer episodes with sustained BIS levels > 60. The mean (SD) propofol infusion rates were 6.0 (1.4) and 6.6 (0.9) mg kg(-1)h(-1) with and without the BIS monitor (P = 0.023), resulting in mean (SD) extubation times of 6.8 (4.6) and 10.5 min (5.9), respectively (P < 0.05).

CONCLUSION

Bispectal index monitoring reduced propofol usage and hastened recovery after propofol anesthesia, whereas in desflurane anesthesia it was associated with improved patient satisfaction, probably because of decreased postoperative nausea and fewer episodes of inadequate hypnosis.

Target-controlled infusion for remifentanil in vascular patients improves hemodynamics and decreases remifentanil requirement

Remifentanil is a potent ultra-short-acting opioid, which permits rapid emergence. However, remifentanil is expensive and may have detrimental effects on hemodynamics in case of overdose. Target-controlled infusion (TCI) permits adapting infusion to pharmacokinetic models. In this prospective randomized study, we compared intra- and postoperative hemodynamics, remifentanil requirement during anesthesia, and postoperative morphine requirement in patients scheduled for carotid surgery, and receiving either continuous IV weight-adjusted infusion of remifentanil (RIVA) or TCI for remifentanil (TCIR). Forty-six patients were enrolled in this study: all were anesthetized by using TCI for propofol. Twenty-three received RIVA (0.5 micro g. kg(-1) x min(-1)) for the induction of anesthesia and endotracheal intubation, with the infusion rate decreased to 0.25 micro g x kg(-1) x min(-1) after intubation, then adapted by step of 0.05 micro g x kg(-1) x min(-1) according to hemodynamics. Twenty-three patients received TCIR (Minto model, Rugloop), with an effect-site concentration at 4 ng/mL during induction, then adapted by step of 1 ng/mL according to hemodynamics. All patients received atracurium and a 50% mixture of N(2)O/O(2). Hemodynamic variables were recorded each minute. The number and duration of hemodynamic events were collected, and total doses of anesthetics (remifentanil and propofol) and vasoactive drugs were noted in both groups of patients. Data were analyzed by using unpaired t-tests. RIVA was significantly associated with more frequent episodes of intraoperative hypotension (16 versus 6, P < 0.001) and more frequent episodes of postoperative hypertension and/or tachycardia requiring more frequent administration of beta-adrenergic blockers (16 vs 10, P < 0.04) in comparison with TCIR. The need for morphine titration was not significantly different between groups. TCIR led to a significantly smaller requirement of remifentanil (700 +/- 290 versus 1390 +/- 555 micro g, P < 0.001) without difference in propofol requirement. This prospective randomized study demonstrated that, during carotid endarterectomy, in comparison with patients receiving remifentanil using continuous RIVA, TCI results in less hypotensive episodes during the induction of anesthesia, in fewer episodes of tachycardia and/or hypertension and a smaller beta-adrenergic blocker requirement during recovery, and a decrease in remifentanil requirement. Recommendations to prefer TCI for remifentanil administration during carotid endarterectomy may be justified.

IMPLICATIONS

Remifentanil for intraoperative analgesia in carotid artery surgery is associated with a better stability in perioperative hemodynamics when administered in target-controlled infusion compared with continuous weight-adjusted infusion. This may be related to a smaller requirement of this drug when using target-controlled infusion, as well as a smooth mode of administration.

Remifentanil-propofol vs. sufentanil-propofol: optimal combinations in clinical anesthesia

BACKGROUND

Two opioid regimens, computer-simulated to provide optimal general anesthesia in combination with propofol, were compared using clinical criteria.

METHODS

Fifty patients undergoing thyroid surgery were blindly, prospectively and randomly allocated to receive either (a) i.v. remifentanil (1.5 micro g kg-1, followed by 0.2 micro g kg-1 min-1) or (b) i.v. sufentanil (0.2 micro g kg-1 followed by 0.2 micro g kg-1 h-1). Remifentanil infusion was stopped at the last skin suture. Sufentanil infusion was stopped 30 min before the end of surgery. Intravenous propofol was titrated to keep BIS at 50+/-5. Remifentanil and sufentanil groups were compared with regards to (a) propofol delivery, (b) hemodynamic and recovery variables, and (c) effect-site propofol levels during a steady-state period for effect-site remifentanil and sufentanil levels. P<0.05 was significant.

RESULTS

Groups were similar in demographic data; types and durations of surgery; total propofol consumption; and response, extubation and emergence times. During the steady-state period for the opioid delivery, the remifentanil and sufentanil effect-site levels were 5.3 ng ml-1 and 0.18 ng ml-1, respectively (potency ratio=30). In both opioid groups, in accordance with previous computer-simulations, the effect-site propofol concentrations remained (a) within a narrow range unaffected by surgical stimuli, (b) significantly smaller in the remifentanil group than in the sufentanil group, but (c) smaller than expected from previous computer-simulations. More patients required ephedrine following induction of anesthesia in the remifentanil compared with the sufentanil group.

CONCLUSIONS

The present clinical trial conducted in thyroid surgery is consistent with previous computer-simulated opioid-propofol combinations with respect to intraoperative and recovery variables. Effect-site propofol ranges were, however, lower than expected.

Narcotrend, bispectral index, and classical electroencephalogram variables during emergence from propofol/remifentanil anesthesia

The aim of this study was to investigate modern and classical electroencephalographic (EEG) variables in response to remifentanil and propofol infusions. We hypothesized that modern EEG variables may indicate the effects of propofol but not of remifentanil. Twenty-five patients were included in the study after the end of elective spine surgery without any surgical stimulation. Baseline values were defined with remifentanil 0.3 microg. kg(-1). min(-1) and target-controlled infusion of propofol 3.0 microg/mL. EEG changes were evaluated 1, 3, 5, 7, and 9 min after the stop of remifentanil infusion, followed by a step-by-step reduction (0.2 microg/mL) every 3 min of target-controlled infusion propofol. Narcotrend (NT; classifying EEG stages from awake to deep anesthesia), bispectral index (BIS), EEG spectral frequency bands (%), 50% (Median) and 95% percentiles (spectral edge frequency), mean arterial blood pressure, heart rate, and oxygen saturation were detected at every time point. The end of remifentanil application resulted in significant increases in %alpha, spectral edge frequency, mean arterial blood pressure, and %theta and decreases in %delta (P < 0.05). NT, BIS, Median, heart rate, and oxygen saturation were unchanged. Decreases in propofol concentration were associated with statistically significant increases in NT and BIS (P < 0.05). Thus, the sedative-hypnotic component of propofol could be estimated by modern EEG variables (NT and BIS), whereas the analgesic component provided by remifentanil was not indicated. However, during conditions without surgical stimulation, neither NT nor BIS provided an adequate assessment of the depth of anesthesia when a remifentanil infusion was used.

IMPLICATIONS

We investigated modern and classical electroencephalographic (EEG) variables during emergence from propofol/remifentanil anesthesia. Modern EEG variables indicate changes of infusion in propofol, but not in remifentanil. Thus, modern EEG variables did not provide an adequate assessment of depth of anesthesia when remifentanil was used.

Target-controlled infusion of propofol induction with or without plasma concentration constraint in high-risk adult patients undergoing cardiac surgery

BACKGROUND

Calculated plasma (Cp) and calculated effect site concentrations (Ce) of propofol associated with loss of consciousness (LOC) have been studied in young healthy patients. The aim of the study was to evaluate the calculated propofol concentrations required to induce LOC in ASA III adult patients undergoing cardiac surgery using a smooth target controlled infusion of propofol.

METHODS

After informed consent, 44 patients were premedicated with 0.5 mg alprazolam orally. Propofol TCI using the pharmacokinetic set of Marsh et al. incorporated in the Diprifusor (ThalfKeo of 2.6 min) was used. Propofol Ce was progressively increased by 0.5 micro g/ml until LOC was obtained. The constraint on the maximum gradient between Cp and Ce was either 1 micro g/ml in group 1 or not limited in group 2. Hemodynamic variations were assessed.

RESULTS

Mean preoperative left ventricular ejection fractions were 44 +/- 15.4% and 56 +/- 11.4% in groups 1 and 2, respectively (P < 0.01). At LOC, mean Cp was 1.9 micro g/ml in both groups but mean Ce was 1.08 +/- 0.31 and 1.43 +/- 0.42 micro g/ml in groups 1 and 2, respectively (P < 0.01). The mean induction time was 12.8 +/- 7.1 min in group 1 and 8.5 +/- 2.7 min in group 2 (P < 0.05). No episode of hypotension has been observed in either group.

CONCLUSION

In ASA III patients undergoing cardiac surgery, smooth propofol TCI induction, using the pharmacokinetic set of Marsh et al. incorporated in the Diprifusor, is associated with LOC at a low mean calculated plasma concentration of 1.9 micro g/ml and good hemodynamic stability.

Propofol metabolites in man following propofol induction and maintenance

BACKGROUND

The pharmacokinetics of propofol in man is characterized by a rapid metabolic clearance linked to glucuronidation of the parent drug to form the propofol-glucuronide (PG) and sulfo- and glucuro-conjugation of hydroxylated metabolite via cytochrome P450 to produce three other conjugates. The purpose of this study was to assess the urine metabolite profile of propofol following i.v. propofol anaesthesia in a Caucasian population.

METHODS

The extent of phase I and phase II metabolism of propofol was studied in 18 female and 17 male patients after an anaesthesia induced and maintained for at least 4 h with propofol. The infusion rates (mg kg(-1) h(-1)) of propofol were (mean (SD)) 4.1 (1.0) and 4.5 (1.3) for males and females, respectively. Urine was collected from each patient for the periods 0-4, 4-8, 8-12, and 12-24 h after the start of propofol administration. In a preliminary study, the three main glucuro-conjugated metabolites were isolated from urine and characterized by magnetic resonance spectroscopy. The quantification of these metabolites for the different collection periods was then performed by a HPLC-UV assay.

RESULTS

Total recovery of propofol in the metabolites studied amounts to 38%, of which 62% was via the PG metabolite and 38% via cytochrome P-450. This percentage is significantly higher than that previously reported from patients after a bolus dose of propofol. Extreme values for PG (0-24 h period) were included from 73 to 49%. There was no significant difference between female and male patients in the metabolite ratio.

CONCLUSIONS

We conclude that the extent of hydroxylation in propofol metabolism was higher than in previous findings after administration of anaesthetic doses of propofol. Moreover, the ratio between hydroxylation and glucuronidation of propofol is subject to an inter-patient variability but this does not correlate with the dose of propofol. However, the variation of the metabolite profile observed in the present report does not seem to indicate an extended role of metabolism in pharmacokinetic variability.

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.