The Influence of Gender on Loss of Consciousness with Sevoflurane or Propofol

Comparison of the respiratory effects of commonly utilized general anaesthesia regimes in male Sprague-Dawley rats

Background: Respiratory parameters in experimental animals are often characterised under general anaesthesia. However, anaesthesia regimes may alter the functional and mechanical properties of the respiratory system. While most anaesthesia regimes have been shown to affect the respiratory system, the effects of general anaesthesia protocols commonly used in animal models on lung function have not been systematically compared. Methods: The present study comprised 40 male Sprague-Dawley rats divided into five groups (N = 8 in each) according to anaesthesia regime applied: intravenous (iv) Na-pentobarbital, intraperitoneal (ip) ketamine-xylazine, iv propofol-fentanyl, inhaled sevoflurane, and ip urethane. All drugs were administered at commonly used doses. End-expiratory lung volume (EELV), airway resistance (Raw) and tissue mechanics were measured in addition to arterial blood gas parameters during mechanical ventilation while maintaining positive end-expiratory pressure (PEEP) values of 0, 3, and 6 cm H2O. Respiratory mechanics were also measured during iv methacholine (MCh) challenges to assess bronchial responsiveness. Results: While PEEP influenced baseline respiratory mechanics, EELV and blood gas parameters (p < 0.001), no between-group differences were observed (p > 0.10). Conversely, significantly lower doses of MCh were required to achieve the same elevation in Raw under ketamine-xylazine anaesthesia compared to the other groups. Conclusion: In the most frequent rodent model of respiratory disorders, no differences in baseline respiratory mechanics or function were observed between commonly used anaesthesia regimes. Bronchial hyperresponsiveness in response to ketamine-xylazine anaesthesia should be considered when designing experiments using this regime. The findings of the present study indicate commonly used anaesthetic regimes allow fair comparison of respiratory mechanics in experimental animals undergoing any of the examined anaesthesia protocols.

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.

Estrogen Receptor-A in Medial Preoptic Area Contributes to Sex Difference of Mice in Response to Sevoflurane Anesthesia

A growing number of studies have identified sex differences in response to general anesthesia; however, the underlying neural mechanisms are unclear. The medial preoptic area (MPA), an important sexually dimorphic structure and a critical hub for regulating consciousness transition, is enriched with estrogen receptor alpha (ERα), particularly in neuronal clusters that participate in regulating sleep. We found that male mice were more sensitive to sevoflurane. Pharmacological inhibition of ERα in the MPA abolished the sex differences in sevoflurane anesthesia, in particular by extending the induction time and facilitating emergence in males but not in females. Suppression of ERα in vitro inhibited GABAergic and glutamatergic neurons of the MPA in males but not in females. Furthermore, ERα knockdown in GABAergic neurons of the male MPA was sufficient to eliminate sex differences during sevoflurane anesthesia. Collectively, MPA ERα positively regulates the activity of MPA GABAergic neurons in males but not in females, which contributes to the sex difference of mice in sevoflurane anesthesia.

CYB2B6 CYP2C9 UGT1A9

BACKGROUND

The aim of this study was to investigate the effect of CYB2B6 (c.516G>T, rs3745274), CYP2C9 (c.1075A>C, rs1057910) and UGT1A9 (c.98T>C, rs72551330) polymorphisms on the pharmacokinetics of single-drug propofol in adult patients undergoing intravenous sedation.

METHODS

In this prospective clinical study, a total of 124 patients undergoing anaesthesia with propofol, as a single drug, were evaluated when undergoing colonoscopy procedure. Clinical variables were obtained from the patient's anamnesis prior to performing the anaesthetic procedure, in the moment of the patient's loss of consciousness, during the colonoscopy exam (recorded every 5 min) and in the awakening time.

RESULTS

Polymorphic genotypes for the rs3745274 and rs1057910 polymorphisms were associated with bispectral index, target-controlled infusion (TCI)/effector concentration of propofol and TCI/plasma concentration of propofol values. Based on multivariate analysis, it was observed that weight, age, surgery time, systolic blood pressure and the rs1057910 polymorphism corresponded to predictive values for the dose of propofol used. Weight (B=4.807±0.897), age (B=1.834±0.834) and duration of surgery (B=8.164±1.624) corresponded to factors associated with increased propofol dose, while systolic blood pressure (B=-1.892±0.679) and the genotypes (AA vs CA) of the single nucleotide polymorphism (SNP) rs1057910 CYPP2C9 gene (B=-74.161±26.820) decreased the total dose of propofol used.

CONCLUSION

We concluded that the rs1057910 and rs3745274 polymorphisms affect the metabolism of propofol in patients exclusively submitted to this drug. Thus, the knowledge of the polymorphic genotypes of the CYPP2C9 and CYB2B6 genes may be predictive of different metabolising phenotypes, suggesting expected behaviours of BIS parameter in the anaesthetic procedure, which contributes to safer monitoring by anaesthesiologists during the clinical intervention.

Point-of-care detection of sevoflurane anesthetics in exhaled breath using a miniature TOFMS for diagnosis of postoperative agitation symptoms in children

A miniature TOFMS with MEPEI has been developed for POC diagnosis of postoperative agitation symptoms, and can analyze sevoflurane by direct sampling. The risk is high when the sevoflurane in the exhaled breath is higher than 500 ppmv.

Effect of chemotherapy on effect-site concentration of propofol for loss of consciousness in colorectal cancer patients

Background

The depth of anesthesia is an essential factor in surgical prognosis. The neurotoxic effect of chemotherapeutic drugs affects the sensitivity to anesthetics. This study was conducted to determine whether the effect-site concentration (Ce) of propofol for loss of consciousness (LOC) differs in patients undergoing preoperative chemotherapy.

Methods

A total of 60 patients scheduled for surgery for colorectal cancer under general anesthesia were included in this study. Patients who had received chemotherapy comprised the experimental (C) group, and those without a previous history of chemotherapy comprised the control (N) group. Propofol was administered as an effect-site target-controlled infusion, and the Modified Observer’s Assessment of Alertness/Sedation (MOAA/S) scores were evaluated. When the plasma concentration and Ce were similar, and if the MOAA/S score did not change, the target Ce was increased by 0.2 μg/ml; otherwise, the Ce was maintained for 2 min and then increased.

Results

The Ce values of propofol for loss of verbal contact (LVC) in groups C and N were 2.40 ± 0.39 and 2.29 ± 0.39 μg/ml (P = 0.286), respectively, and those for LOC in groups C and N were 2.69 ± 0.43 and 2.50 ± 0.36 μg/ml (P = 0.069), respectively. No significant difference was observed in Ce values between the two groups.

Conclusions

Chemotherapy had no effect on the Ce of propofol for LVC and LOC in patients with colorectal cancer. We do not recommend reducing the dose of propofol for the induction of LOC in patients with colorectal cancer undergoing chemotherapy.

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.

Comparative evaluation of the bispectral index (BIS) and BISpro during propofol anaesthesia

OBJECTIVE

To compare the accuracy, correlation and agreement between the bispectral index (BIS) and BISpro during propofol anaesthesia.

METHODS

The BIS, BISpro, heart rate, target-concentration of propofol and Observer's Assessment of Alertness and Sedation (OAA/S) score were recorded every 30 s in female patients scheduled for hysteroscopic surgery. Propofol anaesthesia was induced by an initial target-controlled concentration (1.0 μg/ml) followed by a stepwise increase (0.5 μg/ml) until the patient was unresponsive. Spearman's correlation coefficient and prediction probability were calculated for the association between sedation levels and the above parameters. The ability of investigated parameters to distinguish between OAA/S scores was analysed. Bland-Altman analysis was used to compare the agreement between BIS and BISpro. The BIS and BISpro cut-off values for lost response were also determined.

RESULTS

Out of 30 patients in total, a high correlation was found between BIS and BISpro, and both correlated well with OAA/S score. Only BIS was able to distinguish all investigated OAA/S states accurately, but the ability to predict OAA/S score 5 to loss of response was comparable between BIS and BISpro. The calculated cut-off values were 68 for BIS and 70 for BISpro.

CONCLUSION

BISpro and BIS are reliable monitors of general anaesthesia during sedation.Trial registration number: Chinese Clinical Trial Registry (URL: www.chictr.org.cn): ChiCTR1900024037 (retrospectively registered).

Sex effects on behavioral markers of emergence from propofol and isoflurane anesthesia in rats

Clinical studies have demonstrated sex-related differences in recovery from surgical anesthesia. This study aimed to characterize the emergence pattern following two anesthesia regimens in both sexes of rats. We considered six different markers of emergence from anesthesia: sigh, eye blinking, forelimb movement, mastication, neck extension, and recovery of the righting reflex (RORR). Spontaneous motor activity 24 h after the anesthesia induction was also examined. Our results showed that the rank order of the emergence latency after intraperitoneal propofol, PRO, exposure was forelimb movement < sigh < blink < mastication < neck extension < RORR, while after inhaled isoflurane, ISO, anesthesia the sequence was changed as sigh < blink < mastication < forelimb movement < neck extension < RORR in both male and female rats. Moreover, the latency to emergence after PRO in female rats was significantly higher than male rats, although following ISO there was no difference between the sexes (P < 0.001; P > 0.05, respectively). Open-field testing revealed no difference in PRO and ISO spontaneous locomotor activity due to drug administration (P > 0.05). These two anesthetics presented different emergence sequences. Although clinical data suggests that females arouse faster than males from anesthesia with propofol, our intraperitoneal technique in a rodent model had the opposite effect. Pharmacokinetic analysis demonstrated increased absorption of injected propofol for the female rats in our study, emphasizing the role of sexual dimorphism in drug distribution in rodents. Despite these pharmacokinetic differences, the pharmacodynamic effects of the drugs were remarkably consistent among both sexes through emergence.

Propofol-sparing effect of different concentrations of dexmedetomidine : Comparison of gender differences

Background

The pharmacodynamics of propofol are closely linked to gender. Dexmedetomidine can decrease propofol needs during propofol anesthesia. The aim of this study was to compare the gender differences on the calculated effect site median effective concentration (EC₅₀) of propofol for loss of consciousness (LOC) after pretreatment with different concentrations of dexmedetomidine.

Methods

In this study 60 male and 60 female patients were randomly allocated to receive dexmedetomidine at target plasma concentrations of 0.0 ng/ml (0.0 group), 0.4 ng/ml (0.4 group), 0.6 ng/ml (0.6 group) and 0.8 ng/ml (0.8 group). Propofol was administered after dexmedetomidine had been intravenously infused for 15 min. The propofol infusion was targeted to provide an initial effect-site concentration of 1.0 μg/ml, followed by increments by 0.2 μg/ml when the effect-site concentration and target concentration of propofol were in equilibrium until LOC was established, where LOC was defined by the observer’s assessment of alertness/sedation scale (OAA/S) score < 2.

Results

The calculated effect-site EC₅₀ of propofol LOC was higher in males than in females in the 0.0, 0.4, 0.6, and 0.8 groups (2.43 vs. 2.17, 1.99 vs. 1.82, 1.72 vs. 1.56 and 1.50 vs. 1.32 μg/ml, respectively, all p < 0.05). The hypnotic interaction between dexmedetomidine and propofol could be described with an additive model of pharmacodynamic interaction.

Conclusion

Gender significantly influenced the calculated effect-site EC₅₀ of propofol for LOC after pretreatment with different concentrations of intravenous dexmedetomidine. It was concluded that an additive interaction could describe the results seen. Thus, gender has to be considered when these drugs are co-administered.

Protective effect of sevoflurane on myocardial ischemia-reperfusion injury in rat hearts and its impact on HIF-1α and caspase-3 expression

This study was designed to investigate possible protective effects of sevoflurane on myocardial ischemia-reperfusion injury (MIRI) and its impact on expression of HIF-1α and caspase-3 in rats, so as to provide new insights for the treatment of MIRI. Forty SD rats were randomly divided into four groups (n=10) including Sham operation (Sham), ischemia-reperfusion (IR), sevoflurane preconditioning group (Sevo-Pre) and sevoflurane post-conditioning (Sevo-Post) groups. Perfusion was performed using ex vivo heart perfusion. The baseline values of cardiac function were recorded in each group at the end of balanced perfusion and after 60 min of reperfusion. Myocardial infarct size (MIS) was calculated at the end of perfusion using TTC staining. Levels of HIF-1α and caspase-3 protein and HIF-1α (western blotting) and Bcl-2 mRNA (RT-qPCR) were detected at the end of reperfusion. Our results showed no significant differences in cardiac function between the groups at the end of the balanced perfusion. After reperfusion for 60 min, however, the cardiac functions of the Sevo-Pre and Sevo-Post groups were significantly better than those in the IR group, and the MIS at the end of reperfusion was significantly decreased. Western blotting and RT-qPCR showed that expression of HIF-1α protein was significantly increased, expression of caspase-3 protein was significantly decreased and expression of HIF-1α and Bcl-2 mRNA were significantly increased in Sevo-Pre and Sevo-Post groups compared with the levels in the IR group at the end of reperfusion. There were no significant differences in experimental results between Sevo-Pre and Sevo-Post groups. Our data support the idea that sevoflurane can improve MIRI in rats by improving cardiac function and reducing MIS. This protective effect seems to be achieved by activation of HIF-1α and inhibition of caspase-3.

Male patients require higher optimal effect-site concentrations of propofol during i-gel insertion with dexmedetomidine 0.5 μg/kg

BACKGROUND

The pharmacokinetics and pharmacodynamics of an anesthetic drug may be influenced by gender. The purpose of this study was to compare effect-site half maximal effective concentrations (EC50) of propofol in male and female patients during i-gel insertion with dexmedetomidine 0.5 μg/kg without muscle relaxants.

METHODS

Forty patients, aged 20-46 years of ASA physical status I or II, were allocated to one of two groups by gender (20 patients per group). After the infusion of dexmedetomidine 0.5 μg/kg over 2 min, anesthesia was induced with a pre-determined effect-site concentration of propofol by target controlled infusion. Effect-site EC50 values of propofol for successful i-gel insertion were determined using the modified Dixon's up-and-down method.

RESULTS

Mean effect-site EC50 ± SD of propofol for successful i-gel insertion was significantly higher for men than women (5.46 ± 0.26 μg/ml vs. 3.82 ± 0.34 μg/ml, p < 0.01). The EC50 of propofol in men was approximately 40% higher than in women. Using isotonic regression with a bootstrapping approach, the estimated EC50 (95% confidence interval) of propofol was also higher in men [5.32 (4.45-6.20) μg/ml vs. 3.75 (3.05-4.43) μg/ml]. The estimated EC95 (95% confidence interval) of propofol in men and women were 5.93 (4.72-6.88) μg/ml and 4.52 (3.02-5.70) μg/ml, respectively.

CONCLUSIONS

During i-gel insertion with dexmedetomidine 0.5 μg/kg without muscle relaxant, male patients had higher effect-site EC50 for propofol using Schnider's model. Based on the results of this study, patient gender should be considered when determining the optimal dose of propofol during supraglottic airway insertion.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02268656. Registered August 26, 2014.

The Influence of Differences in Solvents and Concentration on the Efficacy of Propofol at Induction of Anesthesia

Background. Propofol is a popular intravenous anesthetic and varieties of formulations were produced from different laboratories. The present study compared efficacy of propofol of different laboratories and different concentrations (1 and 2%) during induction of anesthesia. Methods. Seventy-five scheduled surgical patients were randomly allocated into three groups. The patients of group D1 received AstraZeneca Diprivan 1% (Osaka, Japan) at a rate of 40 mg kg⁻¹ h⁻¹. Group M1 was given 1% Maruishi (Maruishi Pharmaceutical, Osaka, Japan) and group M2 was given 2% formulation at the same rate of propofol. Achieving hypnosis was defined as failure to open their eyes in response to a verbal command and the venous blood sample was withdrawn. Results. The hypnotic doses of M2 were significantly larger (D1: 91.4 ± 30.9, M1: 90.7 ± 26.7, and M2: 118.4 ± 40.2 mg, resp. (mean ± SD). p < 0.005). Age and gender were selected as statistically significant covariates using general linear model-ANOVA. The blood concentration showed no significant difference among the groups (3.73 ± 2.34, 4.10 ± 3.04, and 4.70 ± 2.12 μg mL⁻¹, resp.). Conclusion. The required dose of propofol was different among the formulations; however, the serum concentration showed no significant difference. This trial is registered with UMIN Clinical Trial Registry: UMIN000019925.

Technological advances in perioperative monitoring: Current concepts and clinical perspectives

Minimal mandatory monitoring in the perioperative period recommended by Association of Anesthetists of Great Britain and Ireland and American Society of Anesthesiologists are universally acknowledged and has become an integral part of the anesthesia practice. The technologies in perioperative monitoring have advanced, and the availability and clinical applications have multiplied exponentially. Newer monitoring techniques include depth of anesthesia monitoring, goal-directed fluid therapy, transesophageal echocardiography, advanced neurological monitoring, improved alarm system and technological advancement in objective pain assessment. Various factors that need to be considered with the use of improved monitoring techniques are their validation data, patient outcome, safety profile, cost-effectiveness, awareness of the possible adverse events, knowledge of technical principle and ability of the convenient routine handling. In this review, we will discuss the new monitoring techniques in anesthesia, their advantages, deficiencies, limitations, their comparison to the conventional methods and their effect on patient outcome, if any.

The fentanyl concentration required for immobility under propofol anesthesia is reduced by pre-treatment with flurbiprofen axetil

PURPOSE

We hypothesized that nonsteroidal anti-inflammatory drugs decrease the plasma fentanyl concentration required to produce immobility in 50% of patients in response to skin incision (Cp50incision) compared with placebo under target-controlled infusion (TCI) propofol anesthesia.

METHODS

Sixty-two unpremedicated patients scheduled to undergo gynecologic laparoscopy were randomly assigned to receive placebo (control group) or flurbiprofen axetil 1 mg·kg(-1) (flurbiprofen group) preoperatively. General anesthesia was induced with fentanyl and propofol, and intubation was performed after succinylcholine 1 mg·kg(-1). Propofol was administered via a target-controlled infusion (TCI) system (Diprifusor™) set at an effect-site concentration of 5 μg·mL(-1). Fentanyl was given by a TCI system using the STANPUMP software (Schafer model). The concentration for the first patient was set at 3 ng·mL(-1) and modified in each group according to the up-down method. Skin incision was performed after more than ten minutes equilibration time. Serum fentanyl concentration, bispectral index (BIS), and hemodynamic parameters were measured two minutes before and after skin incision. The Cp50incision of fentanyl was derived from the mean of the crossovers (i.e., the serum fentanyl concentrations of successive participants who responded and those who did not or vice versa).

RESULTS

Ten and 11 independent crossover pairs were collected in the control and flurbiprofen groups, respectively, representing 42 of 62 enrolled patients. The mean (SD) fentanyl Cp50incision was less in the flurbiprofen group [0.84 (0.63) ng·mL(-1)] than in the control group [1.65 (1.15) ng·mL(-1)]; P = 0.007; however, there were no differences in BIS, blood pressure, or heart rate, between groups.

CONCLUSION

Preoperative flurbiprofen axetil decreased the Cp50incision of fentanyl by 49% during propofol anesthesia without changing the BIS or hemodynamic variables.

Clinical vs. bispectral index-guided propofol induction of anesthesia: A comparative study

BACKGROUND

Clinically optimized focusing of drug administration to specific need of patient with bispectral index (BIS) monitoring results in reduced dose and faster recovery of consciousness. This study was planned with an aim to study and compare the conventional clinical end point or BIS on the requirement of dosage of propofol, hemodynamic effects, and BIS alterations following propofol induction.

METHODS

70 patients, ASA I and II, 20-60 years undergoing elective surgical procedure under general anesthesia with endotracheal intubation were selected and divided into two groups. Group A received (inj.) fentanyl (2 μg/kg), followed 3 min later by inj. propofol at the rate of 30 mg/kg/hr infusion till the loss of response to verbal command while group B received inj. fentanyl (2 μg/kg), followed 3 min later by inj. propofol at the rate of 30 mg/kg/hr infusion. The end point of hypnosis was when the BIS value was sustained for 1 min at 48±2. The patients were intubated. Total induction dose of propofol was noted in each group. The value of BIS and hemodynamic parameters (heart rate, systolic/diastolic blood pressure) were noted at the time of loss of consciousness, at the time of intubation, and 1 min after intubation, thereafter every minute for first 10 min and thereafter every 10 min till end of surgery. Any involuntary muscle activity such as jerky movements, dystonic posturing, and opisthotonos were also recorded.

RESULTS

The mean dose of propofol used in groups A and B were 1.85±0.48 mg/kg and 1.79±0.41 mg/kg, respectively. The dosage used in group B were less but not clinically significant (P=0.575). On comparing the dosage of propofol in males among the groups there was a significantly lower dosage of propofol required in group B (2.06±0.45 mg/kg and 1.83±0.32 mg/kg, respectively, P=0.016). This decrease however was not seen in female patients dosage being 1.65±0.44 mg/kg and 1.75±0.49 mg/kg, respectively (P=0.372). The hemodynamic variables including heart rate, systolic/diastolic blood pressure and BIS were comparable within the group at induction, post-induction, and intubation. However, there was a significant increase in all the parameters at postintubation readings (P<0.001).

CONCLUSION

No significant difference in the induction dose of propofol was observed when assessed clinically (loss of verbal response) or by BIS monitoring. Traditional teaching to titrate the dose of propofol and depth of anesthesia during intubation by loss of verbal response is as good as BIS value monitoring.

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.

The influence of duration of fluid abstinence on hypotension during propofol induction

BACKGROUND

Prolonged preoperative fasting might be expected to exacerbate hypotension during the induction of general anesthesia. We aimed to establish whether the duration of preoperative abstinence from fluids independently contributed to arterial blood pressure changes and dosage requirements during propofol induction.

METHODS

We prospectively recruited 130 ASA I or II nonhypertensive patients, ages 18 to 65 years scheduled for surgery under general anesthesia. Standard physiological and electroencephalographic bispectral index (BIS) monitoring was applied to each patient. Intravenous propofol infusion was commenced at 40 mg · kg(-1) · h(-1) and reduced to 8 mg · kg(-1) · h(-1) when the BIS decreased to 50. Frequent cardiovascular data were collected for 15 minutes. The primary endpoint was maximal percentage decrease from baseline mean arterial blood pressure (max%ΔMAP). The secondary endpoint was the propofol dose at which BIS decreased to 50 (PDBIS50). Univariate linear regression and then multivariate linear regression was used to analyze the associations between potential predictors, including fasting time, and these 2 endpoints.

RESULTS

Mean fluid abstinence time was 694 minutes (range: 115 to 1263 minutes). Unstandardized regression coefficients (95% confidence intervals [CIs]) for fluid abstinence (minutes) versus max%ΔMAP (%) and PDBIS50 (mg) were, respectively, 0.003% (-0.002% to + 0.009%) and 0.021 mg (-0.017 mg to + 0.059 mg). On adjusting for other, significant predictors in a multivariate model and applying type II sum of squares tests, the corresponding values were -0.0001% (-0.004% to + 0.004%, P = 0.94) and -0.006 mg (-0.039 mg to + 0.026 mg, P = 0.70). The effect of a 1-hour increase in fluid abstinence on max%ΔMAP was therefore -0.01% (-0.26% to + 0.24%) and on PDBIS50, -0.38 mg (-2.34 mg to + 1.58 mg).

CONCLUSION

When propofol is infused rapidly for induction of anesthesia in healthy adults younger than 65 years, the duration of preoperative fluid abstinence does not appear to affect MAP or propofol dose requirements.

The effects of sevoflurane with propofol and remifentanil on tracheal intubation conditions without neuromuscular blocking agents

Background

Propofol and remifentanil are used for tracheal intubation in the absence of neuromuscular blocking agents. We hypothesized that the addition of sevoflurane to propofol and remifentanil would improve intubation conditions and provide hemodynamic stability.

Methods

Seventy-six patients scheduled for elective surgery were randomly allocated to be ventilated with either 4% (group I) or 7% sevoflurane (group II) after propofol injection (2 mg/kg). All patients received remifentanil (1 µg/kg) 30 seconds after administration of propofol. Ninety seconds after remifentanil was given, laryngoscopy and tracheal intubation were performed. Intubation conditions and hemodynamic changes were evaluated.

Results

The overall incidence of clinically acceptable intubation conditions was significantly higher in group II (92%) than group I (58%) (P = 0.001). Scores for vocal cord position, coughing, and limb movement were significantly better in group II (P < 0.05). Mean blood pressure remained significantly lower than the pre-induction level throughout the investigation in both groups (P < 0.001), but there was no incidence of bradycardia or hypotension requiring treatment.

Conclusions

Tracheal intubation without neuromuscular blocking agents can be achieved safely and reliably by adding 7% sevoflurane to propofol (2 mg/kg) and remifentanil (1 µg/kg).

Analysis of pharmacodynamic interaction of sevoflurane and propofol on Bispectral Index during general anaesthesia using a response surface model

BACKGROUND

Propofol and sevoflurane act on the GABA(A) receptor, modulating the function of this receptor in an additive manner. The pharmacodynamic interaction of both drugs considering their effect on EEG activity analysed by the bispectral index (BIS) was identified as additive, but this has not been studied in a clinical setting. The objective of this study was to analyse the pharmacodynamic interaction of propofol and sevoflurane on BIS using a surface response model in patients undergoing general anaesthesia with i.v. induction and inhalation maintenance.

METHODS

We performed a prospective study in 24 patients undergoing general anaesthesia with propofol induction and sevoflurane maintenance. Anaesthetic depth was measured with a BIS VISTA Bilateral monitor. Propofol biophase concentration was determined using a three-compartment pharmacokinetic model, and sevoflurane end-tidal concentration was measured continuously. The response surface model described by Minto and colleagues was used to analyse the interaction. Statistical analysis was performed with Excel 2002 and SPSS v11.0.

RESULTS

The mean value of U(50)(theta) was 0.956 (sd 0.029) in the overall estimated data, and remained within the predefined range for all ratios of the drugs, fulfilling the criterion of additivity. The median of the weighted residuals between the actual BIS value and the BIS value predicted by the model was -5.926%.

CONCLUSIONS

Under the study conditions, it was confirmed that sevoflurane and propofol have an additive effect on BIS, with no evidence suggesting the existence of a synergistic effect for the concentrations of both drugs typically used in clinical practice.

[Assessing the depth-of-hypnosis]

BACKGROUND

There has been a breakthrough in the understanding of anaesthetic drug effects during the last two decades, and new monitors aimed at quantifying such effects have been developed.

MATERIAL AND METHODS

This review is based on publications from the last 15 years, oral presentations, and rewritten parts of the author's PhD thesis.

RESULTS

General anaesthesia can be regarded as a combination of hypnosis (sleep), analgesia and muscle relaxation. Modern anaesthetic drugs aim at each of these effects separately. Pharmacological variation makes it impossible to find one dose suitable for all, so tools for measuring drug effects in the individual patient are warranted. Monitors for measuring depth-of-hypnosis and partly analgesic effect are commercially available. Among these, BIS (bispectral index), based on EEG, is by far the best documented. BIS is proven useful for preventing undesired awareness and overdosing, but there are major limitations. Use of such technology in clinical practice is under constant debate.

INTERPRETATION

Even though the BIS technology is promising and used widely, no health authorities have so far recommended that such monitors should be compulsory during general anaesthesia, but rather that it should be considered on an individual basis. So far, it seems like this is a sensible approach in Norway as well.

Patient Sex and its Influence on General Anaesthesia

Physiological and pharmacological differences exist between men and women. Women wake faster than men following general anaesthesia. Women also differ from men in their postoperative recovery as reflected by differences in postoperative pain, nausea and vomiting and overall quality of recovery. These gender differences seem to be more pronounced in premenopausal women, suggesting hormonal mechanisms are a major contributing factor.

Recovery profiles from dexmedetomidine as a general anesthetic adjuvant in patients undergoing lower abdominal surgery

BACKGROUND

Dexmedetomidine induces less change in hemodynamic values during the extubation period. This drug may be useful in anesthetic management requiring smooth emergence from anesthesia. We sought to determine the effects of co-administration of dexmedetomidine on the recovery profiles from sevoflurane and propofol, which usually provide safe and rapid recovery when administered alone.

METHODS

Sixty patients undergoing lower abdominal surgery were randomly divided into four groups according to the anesthetic to be administered; namely, sevoflurane (group S), propofol (group P), both sevoflurane and dexmedetomidine (group SD), or propofol and dexmedetomidine (group PD) as maintenance general anesthetics. After induction, anesthesia was maintained with sevoflurane (0.6%-1.5%) in group S, propofol (2-5 mg/kg/h) in group P, sevoflurane and dexmedetomidine (1 microg/kg over 10 min followed by 0.4 microg/kg/h until the end of surgery) in group SD, and propofol and dexmedetomidine in group PD with continuous epidural infusion. Bispectral Index values were maintained within 45 +/- 5 by changing the concentration of sevoflurane or the infusion rate of propofol in all groups. The time between the interruption of maintenance general anesthetics and eye opening was measured. Postoperative cognitive function was evaluated using the Short Orientation Memory Concentration Test.

RESULTS

The time to eye opening of groups S (8.5 +/- 2.5 min, mean +/- SD; n = 15) and SD (12.0 +/- 3.3 min) were comparable, whereas that of group PD (21.7 +/- 7.1 min) was longer than that of group P (11.0 +/- 4.4 min). The time to eye opening of group PD was significantly (P < 0.001) longer than those of the other three groups. The scores of Short Orientation Memory Concentration Test between groups S and P were similar and were not changed by co-administration of dexmedetomidine.

CONCLUSION

When co-administered with dexmedetomidine, sevoflurane produced a shorter time to eye opening than propofol. Postoperative cognitive function was not affected by dexmedetomidine administration. These results suggest dexmedetomidine may delay recovery when given as an adjuvant to propofol during total i.v. anesthesia.

Anesthetic issues and anxiety management in the female oral and maxillofacial surgery patient

Gender differences in preoperative anxiety, perioperative pain experience, and physiologic responses to anesthesia exist. Pharmacokinetic and pharmacodynamic gender differences in anesthetic drugs are especially significant for propofol and nondepolarizing muscle relaxants. Nonobstetric anesthesia for the pregnant patient is briefly reviewed.

EEG power spectrum analysis for monitoring depth of anaesthesia during experimental surgery

The first attempts to introduce computerized power spectrum analysis of the electroencephalogram (EEG) as an intraoperative anaesthesia monitoring device started approximately 30 years ago. Since that time, the effects of various anaesthetic agents, sedative and analgesic drugs on the EEG pattern have been addressed in numerous studies in human patients and different animal species. These studies revealed dose-dependent changes in the EEG power spectrum for many intravenous and volatile anaesthetics. Moreover, EEG responses evoked by surgical stimuli during relative light levels of surgical anaesthesia have been classified as 'arousal' and 'paradoxical arousal' reaction, previously referred to as 'desynchronization' and 'synchronization', respectively. Contrasting reports on the correlation between quantitative EEG (QEEG) variables derived from power spectrum analysis (i.e. spectral edge frequency, median frequency) and simultaneously recorded clinical signs such as movement and haemodynamic responses, however, limited the routine use of intraoperative EEG monitoring. In addition, the appearance of EEG burst suppression pattern and isoelectricity at clinically relevant concentrations/doses of newer general anaesthetics (i.e. isoflurane, sevoflurane, propofol) may have weakened the dose-related EEG changes previously reported. Despite these findings, the EEG power spectrum analysis may still provide valuable information during intraoperative monitoring in the individual subject. The information obtained from EEG power spectrum analysis may be further supplemented by newer EEG indices such as bispectral index and approximate entropy or other neurophysiological monitors including auditory evoked potentials or somatosensory evoked potentials.

Multi-level approach to anaesthetic effects produced by sevoflurane or propofol in humans: 1. BIS and blink reflex †

BACKGROUND

The relative roles of forebrain and brainstem in producing adequate anaesthesia are unclear.

METHODS

We simultaneously analysed the effects of sevoflurane (Group S; n = 18) or propofol (Group P; n = 29) on the bispectral index (BIS) and the first component of the blink reflex (R1). The dose of anaesthetic agent was increased until loss of blink reflex. After discontinuation and reappearance of blink reflex activity, the amount was increased again. The area under curve R1 (area-R1) of the electromyogram of the orbicularis oculi muscle after electrical stimulation of the supraorbital nerve was measured. Using a sigmoid E(max) model and a first-order rate constant k(e0), we characterized the dose-response relationships for BIS and area-R1.

RESULTS

Concentration-dependent depression of BIS and area-R1 was adequately modelled. The concentration that causes an effect midway between minimum and maximum (EC50) for area-R1 was smaller than EC50 for BIS in both groups [0.34 (0.19) vs 1.29 (0.19) vol% and 1.78 (0.65) vs 2.69 (0.67) mug ml(-1); mean (sd)]. At doses of sevoflurane and propofol with equivalent depression of BIS, sevoflurane depressed area-R1 more than propofol. The k(e0) for area-R1 was about half that for BIS in both groups: 0.24 (0.19-0.29) vs 0.48 (0.38-0.60) min(-1) for Group S; 0.28 (0.23-0.34) vs 0.46 (0.40-0.54) min(-1) for Group P, geometric mean (95% CI).

CONCLUSIONS

The blink reflex (brainstem function) is more sensitive to sevoflurane or propofol than BIS (forebrain function). Sevoflurane suppresses the blink reflex more than propofol. Different k(e0)s for blink reflex vs BIS indicate different effect sites.

Influence of age and sex on pharmacodynamics of propofol in neurosurgical patients: model development

AIM

To determine propofol concentration in the cerebral spinal fluid (CSF) of neurosurgical patients and carry out a preliminary population pharmacodynamic study.

METHODS

Twenty-seven elective neurosurgical patients (12 men and 15 women) aged 17-74 years received propofol in a bolus dose of 2 mg/kg for 5 min and an infusion of 10 mg/kg per h for 5 min. Frequent CSF samples were drawn and assayed for propofol concentration. The bispectral index (BIS) was used to measure the drug effect. All data were analyzed first with the Excel software package, then pharmacodynamics modeling was performed using the NONMEM software package.

RESULTS

The CSF concentration was related to the drug effect with linear and sigmoid Emax models. The parameters for the linear addictive model were a=1.11 and b=95.4. The parameters for the linear exponential model were a=1.05 and b=92.7. The parameters for the sigmoid E(max) model were E(max)=119, EC(50)=53.6 ng/mL, and N=1.51. When the covariates of age, weight and sex were considered, the parameters of models, objective function, the standard error of the mean and the prediction error were not optimized.

CONCLUSION

Linear additive, linear exponential and sigmoid E(max) models can be used to describe the pharmacodynamics of propofol with respect to the concentration in CSF. In this small population, age (17-74 years), weight (47-98 kg) and sex did not influence any of the pharmacodynamic parameters of propofol. To verify these preliminary results, a larger study population is required.