Propofol effective concentration 50 and its relationship to bispectral index

Comparing propofol anaesthesia guided by Bispectral Index monitoring and frontal EEG wave analysis with standard monitoring in laparoscopic surgery: protocol for the 'EEG in General Anaesthesia - More Than Only a Bispectral Index' Trial, a multicentre, double-blind, randomised controlled trial

INTRODUCTION

The use of Bispectral Index (BIS) monitors for assessing depth of sedation has led to a reduction in both the incidence of awareness and anaesthetic consumption in total intravenous anaesthesia. However, these monitors are vulnerable to artefacts. In addition to the processed number, the raw frontal electroencephalogram (EEG) can be displayed as a curve on the same monitor. Anaesthesia practitioners can learn to interpret the EEG in a short tutorial and may be quicker and more accurate thanBIS in assessing anaesthesia depth by recognising EEG patterns. We hypothesise that quality of recovery (QoR) in patients undergoing laparoscopic surgery is better, if propofol is titrated by anaesthesia practitioners able to interpret the EEG.

METHODS AND ANALYSIS

This is a multicentre, double-blind (patients and outcome assessors) randomised controlled trial taking place in four Swiss hospitals. Patients aged 18 years or older undergoing laparoscopic procedures with general anaesthesia using propofol and anaesthesia practitioners with more than 2 years experience will be eligible. The primary study outcome is the difference in QoR 24 hours after surgery. Secondary outcomes are propofol consumption, incidence of postoperative nausea and vomiting (PONV) and postoperative delirium.QoR and propofol consumption are compared between both groups using a two-sample t-test. Fisher's exact test is used to compare the incidences of PONV and delirium. A total of 200 anaesthesia practitioners (and 200 patients) are required to have an 80% chance of detecting the minimum relevant difference for the QoR-15 as significant at the 5% level assuming a SD of 20.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from all responsible ethics committees (lead committee: Ethikkommission Nordwest- und Zentralschweiz, 16 January 2021). The findings of the trial will be published in a peer-reviewed journal, presented at international conferences, and may lead to a change in titrating propofol in clinical practice.

TRIAL REGISTRATION NUMBER

www.

CLINICALTRIALS

gov:NCT04105660.

The median effective concentration of propofol with different doses of esketamine during gastrointestinal endoscopy in elderly patients: A randomized controlled trial

AIMS

Propofol may result in hypotension, bradycardia and loss of protective reflexes, especially in elderly patients, while esketamine, a N-methyl-D-aspartate receptor antagonist, has analgesic, anaesthetic and sympathomimetic properties and is known to cause less cardiorespiratory depression. We hypothesized that esketamine may reduce the median effective concentration (EC₅₀ ) of propofol and coadministration is less likely to produce hypotension during gastrointestinal endoscopy in elderly patients.

METHODS

Ninety elderly patients, aged 65-89 years, undergoing gastrointestinal endoscopy were randomly assigned into 3 groups: SK0 (control) group (0 mg/kg esketamine); SK0.25 group (0.25 mg/kg esketamine); and SK0.5 group (0.5 mg/kg esketamine). Anaesthesia was achieved by plasma target-controlled infusion of propofol with different bolus doses of esketamine. The EC₅₀ of propofol for gastrointestinal endoscopy was determined by using the up-and-down method of Dixon. The initial plasma target concentration is 2.5 μg/mL and the adjacent concentration gradient is 0.5 μg/mL. Cardiovascular variables were also measured.

RESULTS

Propofol EC₅₀ s and its 95% confidence interval for gastrointestinal endoscopy in elderly patients were 3.69 (2.59-4.78), 2.45 (1.85-3.05) and 1.71 (1.15-2.27) μg/mL in the SK0, SK0.25 and SK0.5 groups, respectively (P < .05). The average percent change from baseline mean arterial pressure was -19.7 (7.55), -15.2 (7.14) and -10.1 (6.73), in the SK0, SK0.25 and SK0.5 groups, respectively (P < .001).

CONCLUSION

Combination medication of propofol with esketamine reduced the propofol EC₅₀ during gastrointestinal endoscopy in elderly patients compared with administration of propofol without esketamine. Increasing doses of SK with propofol are less likely to produce hypotension with shorter recovery time.

Volatiles or TIVA: Which is the standard of care for pediatric airway procedures? A pro-con discussion

Anesthesia for pediatric airway procedures constitutes a true art form that requires training and experience. Communication between anesthetist and surgeon to establish procedure goals is essential in determining the most appropriate anesthetic management. But does the mode of anesthesia have an impact? Traditionally, inhalational anesthesia was the most common anesthesia technique used during airway surgery. Introduction of agents used for total intravenous anesthesia (TIVA) such as propofol, short-acting opioids, midazolam, and dexmedetomidine has driven change in practice. Ongoing debates abound as to the advantages and disadvantages of volatile-based anesthesia versus TIVA. This pro-con discussion examines both volatiles and TIVA, from the perspective of effectiveness, safety, cost, and environmental impact, in an endeavor to justify which technique is the best specifically for pediatric airway procedures.

Comparative Analysis of Phase Lag Entropy and Bispectral Index as Anesthetic Depth Indicators in Patients Undergoing Thyroid Surgery with Nerve Integrity Monitoring

BACKGROUND

Most depth of anesthesia (DOA) monitors rely on the temporal characteristics of a single-channel electroencephalogram (EEG) and cannot provide spatial or connectivity information. Phase lag entropy (PLE) reflects DOA by calculating diverse connectivity from temporal patterns of phase relationships. The aim of this study was to compare the performance of PLE and bispectral index (BIS) monitors for assessing DOA during anesthesia induction, nerve integrity monitoring (NIM), and anesthesia emergence.

METHODS

Thirty-five patients undergoing elective thyroid surgery with recurrent laryngeal nerve NIM received propofol and remifentanil via target-controlled infusion. After applying PLE and BIS monitors, propofol infusion was initiated at a calculated effect site concentration (Ce) of 2 μg/mL and then increased in 1-μg/mL Ce increments. After propofol Ce reached 5 μ/mL, a remifentanil infusion was begun, and anesthesia induction was considered complete. During NIM, PLE and BIS values were compared at a specific time points from platysma muscle exposure to subcutaneous tissue closure. PLE and BIS values were recorded continuously from preanesthetic state to full recovery of orientation; bias and limits of agreement between monitors were calculated.

RESULTS

PLE and BIS values decreased progressively with increasing propofol Ce during anesthetic induction and increased by stages during emergence. The prediction probabilities of PLE and BIS for detecting propofol Ce changes were 0.750 and 0.756, respectively, during induction and 0.749 and 0.746, respectively, during emergence. No aberrant PLE or BIS values occurred during NIM. Correlation coefficients for BIS and PLE were 0.98 and 0.92 during induction and emergence, respectively. PLE values were significantly higher than BIS values at full recovery of orientation. Estimated bias between monitors was -4.16 ± 8.7, and 95% limits of agreement were -21.21 to 12.89.

CONCLUSION

PLE is a reasonable alternative to BIS for evaluating consciousness and DOA during general anesthesia and during NIM.

TRIAL REGISTRATION

Clinical Research Information Service Identifier: KCT0003490.

Effects of sedation on subjective perception of pain intensity and autonomic nervous responses to pain: A preliminary study

Rather than relying solely on subjective pain evaluation using means such as the visual analogue scale (VAS), in clinical situations it is possible to observe evoked responses of the autonomic nervous system (ANS) as objective indicators. Few studies, however, have reported these relationships under finely controlled sedation. 16 healthy male participants were administrated in intravenous sedation with either propofol or midazolam randomly. We initially determined, using pharmacokinetic simulation, the effect-site concentration (Ce) of anaesthetic at loss of response to verbal command and eyelash reflex (Ce-LOR). Then subsequently adjusted Ce to 75%, 50%, and 25% of Ce-LOR to achieve deep, moderate, and light sedation. At awake control state and each sedation level, a noxious electrical stimulation was applied three times at the right forearm, an average pain intensity of the three stimuli was rated on a VAS (0–10). Changes in the peripheral perfusion index measured by oximetry were used as an indicator of ANS response. We analyzed the influence of sedation level on VAS and ANS responses compared to the awake control state. While ANS responses were similar in all conditions, VAS was statistically significantly lower in moderate (5.6±0.6, p <0.005) or deep (5.3±0.6, p <0.001) sedation than in the awake state (7.2±0.4). This study revealed that even when the ANS responds similarly to the same stimulation, subjective pain perception is attenuated by sedation. A cerebral mechanism other than that of the brainstem might determine subjective pain intensity.

Race-Specific Pharmacodynamic Model of Propofol-Induced Loss of Consciousness

We present a race-specific model of propofol-induced loss of consciousness that is based on pharmacodynamic data collected and adapted from the peer-reviewed literature. In the proposed race-specific model that includes EC05 and EC95 concentrations, the median (EC50) (and where available 95%CI) propofol concentrations at the effect site compartment for propofol-induced loss of consciousness for whites, Chinese, blacks, and Indians are 2.8 (2.7-2.9), 2.2 (2.2-2.3), 2.0, and 1.9 μg/mL, respectively.

The influence of propofol and sevoflurane on intestinal motility during laparoscopic surgery

BACKGROUND

Volatile anaesthetics have an influence on small bowel peristalsis during laparoscopic surgery. A recent study concluded that desflurane increased intestinal motility compared to sevoflurane. Hence, a desflurane-based anaesthesia protocol may reduce surgical exposure during intestinal suturing or stapling due to small bowel hyperperistalsis. The effect of propofol on intestinal motility is not well studied. We tested the hypothesis that a propofol-remifentanil anaesthesia increases intestinal contractions in comparison with a sevoflurane-remifentanil anaesthesia.

METHODS

Patients scheduled for laparoscopic gastric bypass surgery were randomized in this single blind randomized controlled trial to receive remifentanil combined with sevoflurane or propofol (ISRCTN 12921661). Bispectral index monitoring was used to guide depth of anaesthesia. Visual observation of peristaltic waves was performed during 1 min at the planned site of the jejunostomy. Statistical analysis was performed using Wilcoxon two-sample test.

RESULTS

After obtaining written informed consent 50 patients were included. Groups were similar for demographic variables, and depth of anaesthesia during the observations. The median number of peristaltic waves was lower in the sevoflurane-remifentanil group compared to the propofol-remifentanil group (0 vs. 6, P < 0.001).

CONCLUSION

Propofol-remifentanil increases intestinal motility compared with sevoflurane-remifentanil during laparoscopic gastric bypass surgery. A sevoflurane-based protocol can help to avoid disturbing peristalsis.

Effect of acute hypervolemic hemodilution of 6% hydroxyethyl starch 130/0.4 on the EC50 of propofol at two clinical endpoints in patients

Preoperative acute hypervolemic hemodilution (AHHD) is a technique used in anesthesia to reduce the number of blood cells lost during intraoperative bleeding. The aim of the present study was to evaluate the effect of the hypervolemic hemodilution of 6% hydroxyethyl starch 130/0.4 on the EC₅₀ of propofol at two clinical endpoints. A total of 20 patients undergoing AHHD following epidural anesthesia were studied, and 20 patients who did not receive hemodilution were used as a control group. All patients were American Society of Anesthesiologists grade I, aged 20-40 years and undergoing hip arthroplasty surgery. In the AHHD group, 10 ml/kg lactated Ringer's solution was infused over 20 min at the same time as the epidural test dose. The infusion was followed by the infusion of 6% hydroxyethyl starch 130/0.4 over 30 min. Patients in the control group received 10 ml/kg Ringer's solution over 50 min. Propofol was then delivered by a Diprifusor target-controlled infusion. The predicted blood and effect-site propofol concentrations were recorded at loss of consciousness (LOC) and return of consciousness (ROC). Probit analysis was used to estimate the values for predicted blood and effect-site concentrations at the two clinical endpoints. The results showed that the potency of propofol was decreased during AHHD. Compared with the controls, the predicted blood and effect-site concentrations of propofol at LOC were higher in patients of the hemodilution group, resulting in higher EC₅₀ values (P=0.001 and 0.025, respectively). At ROC, the effect-site EC₅₀ was 2.9 µg/ml [95% confidence interval (CI), 2.8-3.0] in hemodilution patients and 2.5 µg/ml (95% CI, 2.2-2.6) in control patients (P=0.001). With AHHD, the LOC time was significantly longer and the propofol dose was higher, while ROC times were comparable. In conclusion, AHHD increases the requirement for propofol at LOC and prolongs LOC time. Patients with AHHD recovered consciousness at higher effect-site concentrations of propofol. Thus, the induction dose of propofol should be increased during AHHD.

Total intravenous anesthesia will supercede inhalational anesthesia in pediatric anesthetic practice

Inhalational anesthesia has dominated the practice of pediatric anesthesia. However, as the introduction of agents such as propofol, short-acting opioids, midazolam, and dexmedetomidine a monumental change has occurred. With increasing use, the overwhelming advantages of total intravenous anesthesia (TIVA) have emerged and driven change in practice. These advantages, outlined in this review, will justify why TIVA will supercede inhalational anesthesia in future pediatric anesthetic practice.

Propofol EC50 for inducing loss of consciousness is lower in the luteal phase of the menstrual cycle

BACKGROUND

Varying levels of female sex hormones during the menstrual cycle were found to influence the central nervous system. The goal of the present study was to investigate whether the median (50%) effective effect-concentration (EC50) of propofol inducing loss of consciousness (LOC) varies between the luteal and the follicular phases of the menstrual cycle.

METHODS

Twenty-two patients (follicular phase) and 20 patients (luteal phase) undergoing gynaecological procedures under general anaesthesia were enrolled on the study. Anaesthesia was conducted with a target-controlled infusion (TCI) of propofol. The initial target effect-site propofol concentration (Ceprop) was 3.5 µg ml(-1) and was adjusted stepwise by 0.5 µg ml(-1) at 4 min intervals by an up-down sequential method to reach LOC. Anaesthesia was maintained with a propofol TCI guided by the bispectral index. The correlation between female sex hormones and predicted Ceprop at the time of LOC was analysed and emergence time from anaesthesia was recorded.

RESULTS

Propofol EC50 to induce LOC was higher in patients in the follicular phase than those in the luteal phase (4.17 vs 3.58 µg ml(-1), P<0.05). Progesterone correlated significantly with Ceprop at LOC. Emergence time was also longer in the follicular group than in the luteal group (6.5 vs 5.0 min, P<0.05).

CONCLUSIONS

During general anaesthesia, patients in the luteal phase of the menstrual cycle had a lower propofol EC50 for LOC and a shorter emergence time compared with those in the follicular phase. Differences in progesterone levels between menstrual phases may contribute to these anaesthetic effects. Registry number of clinical trial ChiCTR-RCH-12002755.

The influence of the severity of chronic virus-related liver disease on propofol requirements during propofol-remifentanil anesthesia

PURPOSE

The purpose of this study was to investigate the influence of chronic virus- related liver disease severity on propofol requirements.

MATERIALS AND METHODS

In this study, 48 male patients with chronic hepatitis B infection were divided into three groups according to Child-Turcotte-Pugh classification of liver function (groups A, B, and C with mild, moderate and severe liver disease, respectively). After intubation, propofol concentration was adjusted by ± 0.3 μg/mL increments to maintain bispectral index in the range of 40-60. Target propofol concentrations at anesthesia initiation, pre-intubation and pre-incision were recorded.

RESULTS

The initial concentration used in group C was significantly lower than that used in group A or B (p<0.05), whereas no difference was observed between groups A and B. At pre-intubation, the actual required concentration of propofol increased significantly (3.2 μg/mL) in group A (p<0.05), which lead to significant differences between the groups (p<0.05). At pre-incision, the requirements for propofol decreased significantly in both groups A and B (3.0 μg/mL and 2.7 μg/mL, respectively) compared with those at pre-intubation (p<0.05), and were significantly different for all three groups (p<0.05), with group C demonstrating the lowest requirement (2.2 μg/mL). The required concentrations of propofol at pre-incision were similar to those at induction.

CONCLUSION

In this study, propofol requirements administered by target-controlled infusion to maintain similar depths of hypnosis were shown to depend on the severity of chronic virus-related liver dysfunction. In other words, patients with the most severe liver dysfunction required the least amount of propofol.

The effect of pre-procedure anxiety on sedative requirements for sedation during colonoscopy

This study investigated the effects of pre-procedural anxiety (assessed using the Beck Anxiety Inventory) on sedative requirements in 135 patients undergoing sedation for colonoscopy. Deep sedation was defined as loss of consciousness and no response to colonoscopy, and was achieved by target-controlled infusion of propofol. Patients' characteristics, baseline haemodynamic profiles, Beck Anxiety Inventory scores, effect-site propofol concentration at loss of consciousness and characteristics of recovery were recorded. No correlations were found between Beck Anxiety Inventory scores and effect-site propofol concentration at loss of consciousness or baseline haemodynamic profiles. There was no statistical difference in the characteristics of recovery among patients with different levels of anxiety. In conclusion, in patients receiving deep sedation for colonoscopies, the level of pre-procedural anxiety did not relate to the sedative requirement or post-procedural recovery characteristics.

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

STUDY OBJECTIVE

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

DESIGN

Single-center, prospective, randomized clinical trial.

SETTING

Academic outpatient clinic.

SUBJECTS

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

INTERVENTIONS

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

MEASUREMENTS

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

MAIN RESULTS

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

CONCLUSION

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

Bi-spectral index, entropy and predicted plasma propofol concentrations with target controlled infusions in Indian patients

OBJECTIVE

Many processed electroencephalographic signals are used now to help the anaesthesiologist titrate the depth of sedation. We investigated the relationship between target plasma propofol concentration and objective end-points of sedation- Bispectral Index (BIS), State Entropy (SE) and Response Entropy (RE)-at clinical end-points as assessed by Modified Observer Assessment of Alertness/sedation Scale (MOAAS) in Indian patients.

METHODS

Eighteen ASA 1 and 2 Indian adult patients scheduled to undergo elective surgery were included. The target control infusion (TCI) of propofol was administered using 'Diprifusor'. The level of sedation was assessed using MOAAS by the anaesthesiologist. BIS, SE, RE were recorded throughout. TCI was started at 0.5 μg/ml and increased by 0.5 μg/ml every 6 min till MOAAS scores reached 0 or there was sustained BIS value less than 30.

RESULTS

The EC(50) and EC(95) of predicted plasma propofol concentration for loss of consciousness (assessed by loss of response to verbal command), were 2.3 and 2.8 μg/ml respectively and for loss of response to painful stimuli (trapezius squeeze) were 4.0 and 5.0 μg/ml respectively. The BIS and entropy values (EC(50) and EC(95)) for loss of consciousness and response to painful stimuli in Indian patients were estimated. The preliminary relation of target plasma propofol concentration with BIS was found to be BIS = 100.5-16.4 × (Target concentration).

CONCLUSIONS

The target plasma propofol concentrations required to produce unconsciousness and loss of response to painful stimuli in Indian patients have been estimated. Also, the relations between target plasma concentration and objective measures of different levels of anaesthesia have been established.

A clinical prospective comparison of anesthetics sensitivity and hemodynamic effect among patients with or without obstructive jaundice

BACKGROUND

To compare isoflurane anesthesia in patients with or without hyperbilirubinemia undergoing hepatobiliary surgery.

METHODS

Forty-two patients with obstructive jaundice and 40 control patients with normal liver function scheduled for hepatobiliary surgery under isoflurane anesthesia were studied. Anesthesia was induced with propofol (1.5-2 mg/kg) and remifentanil (2 microg/kg). After tracheal intubation, anesthesia was titrated using isoflurane in oxygen-enriched air, adjusted to maintain a bispectral index (BIS) value of 46-54. Ephedrine, atropine and remifentanil were used to maintain hemodynamic parameters within 30% of the baseline. The mean arterial blood pressure (MAP), heart rate (HR), drug doses and the time taken to recover from anesthesia were recorded.

RESULTS

Demographic data, duration and BIS values were similar in both groups. Anesthesia induction and maintenance were associated with more hemodynamic instability in the patients with jaundice and they received more ephedrine and atropine and less remifentanil and isoflurane (51.1+/-24.2 vs. 84.6+/-20.3 mg/min; P for all <0.05) than control patients. Despite less anesthetic use, the time to recovery and extubation was significantly longer than that in control.

CONCLUSION

Patients with obstructive jaundice have an increased sensitivity to isoflurane, more hypotension and bradycardia during anesthesia induction and maintenance and a prolonged recovery time compared with controls.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Comparison between Sevoflurane/Remifentanil and Propofol/Remifentanil Anaesthesia in Providing Conditions for Somatosensory Evoked Potential Monitoring during Scoliosis Corrective Surgery

Somatosensory evoked potential (SSEP) monitoring is an important tool in spinal corrective surgery. Anaesthesia has a significant influence on SSEP monitoring and a technique which has the least and shortest suppressant effect on SSEP while facilitating a fast recovery from anaesthesia is ideal. We compared the effect of sevoflurane/remifentanil and propofol/remifentanil anaesthesia on SSEPs during scoliosis corrective surgery and assessed patients’ clinical recovery profiles.

Twenty patients with idiopathic scoliosis receiving surgical correction with intraoperative SSEP monitoring were prospectively randomised to receive sevoflurane/remifentanil anaesthesia or propofol/remifentanil anaesthesia. During surgery, changes in anaesthesia dose and physiological variables were recorded, while SSEP was continuously monitored. A simulated ‘wake-up’ test was performed postoperatively to assess speed and quality of recovery from anaesthesia.

The effects of propofol and sevoflurane resulted in SSEP amplitude variability between 18.0% ± 3.5% to 28.7% ± 5.9% and SSEP latency variability within 1.3% ± 0.4% to 2.6% ± 1.2%. Patients receiving sevoflurane had faster suppression and faster recovery of SSEP amplitude compared to propofol (P <0.05), although propofol anaesthesia showed less within-patient variability in Cz amplitude and latency (P <0.05). On cessation of anaesthesia, time to eye-opening (5.2 vs. 16.5 minutes) and toe movement (5.4 vs. 17.4 minutes) was shorter following sevoflurane (all P <0.05).

These findings indicate that propofol produces a better SSEP signal than sevoflurane. However, adjustments in sevoflurane concentration result in faster changes in the SSEP signal than propofol. Assessment of neurological function was facilitated more rapidly after sevoflurane anaesthesia.

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

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

Can anaesthetists be taught to interpret the effects of general anaesthesia on the electroencephalogram? Comparison of performance with the BIS and spectral entropy

BACKGROUND

Unlike the other physiological waveforms monitored in anaesthesia, the EEG lacks a regularly repeating pattern, implying that it would be very difficult for an anaesthetist to obtain any useful information from the raw EEG. There are, however, clear changes in the EEG caused by GABA-ergic anaesthetic agents. The anaesthetized EEG still looks like a random waveform, but clearly a different random waveform from that seen when conscious.

METHODS

The aim of this study was to assess how 40 anaesthetists would perform at interpreting intra-operative EEGs compared with two processed EEG (pEEG) monitors, BIS and entropy, after a short educational presentation. Short segments of EEGs were used from the pre-induction phase, the intra-operative phase with adequate surgical anaesthesia, and the transition phase between these two states.

RESULTS

While anaesthetists' performance varied widely, most could reliably differentiate an anaesthetized from a conscious EEG. Further, both humans (41% wrong) and machines (30% wrong) made mistakes. Unlike the anaesthetists, the pEEG monitors did not make a major error (i.e. producing a number in the conscious range (>85) when analysing an anaesthetized EEG or the converse error).

CONCLUSION

A brief PowerPoint presentation enables anaesthetists to recognize the effects on the EEG of GABA-ergic anaesthetic agents. In the clinical context, it remains likely that the combination of a pEEG monitor that clearly presents the EEG and a clinician who has a good, basic understanding of, and a willingness to look at, the raw EEG will result in more accurate interpretation of the intra-operative EEG.

Comparison of 1.5% lidocaine and 0.5% ropivacaine epidural anesthesia combined with propofol general anesthesia guided by bispectral index

OBJECTIVE

To compare the effects of epidural anesthesia with 1.5% lidocaine and 0.5% ropivacaine on propofol requirements, the time to loss of consciousness (LOC), effect-site propofol concentrations, and the hemodynamic variables during induction of general anesthesia guided by bispectral index (BIS) were studied.

METHODS

Forty-five patients were divided into three groups to receive epidurally administered saline (Group S), 1.5% (w/w) lidocaine (Group L), or 0.5% (w/w) ropivacaine (Group R). Propofol infusion was started to produce blood concentration of 4 mug/ml. Once the BIS value reached 40~50, endotracheal intubation was facilitated by 0.1 mg/kg vecuronium. Measurements included the time to LOC, effect-site propofol concentrations, total propofol dose, mean arterial blood pressure (MABP), and heart rate (HR) at different study time points.

RESULTS

During induction of anesthesia, both Groups L and R were similar for the time to LOC, effect-site propofol concentrations, total propofol dose, MABP, HR, and BIS. The total doses of propofol administered until 1 min post-intubation were significantly less in patients of Groups R and L compared with Group S. MABP and HR were significantly lower following propofol induction compared with baseline values in the three groups, or MABP was significantly increased following intubation as compared with that prior to intubation in Group S but not in Groups R and L while HR was significantly increased following intubation in the three groups.

CONCLUSION

Epidural anesthesia with 1.5% lidocaine and 0.5% ropivacaine has similar effects on the time to LOC, effect-site propofol concentrations, total propofol dose, and the hemodynamic variables during induction of general anesthesia.

Anesthetic management for surgical placement of greater occipital nerve stimulators in the treatment of primary headache disorders

We will present a case series looking at the anesthetic management of 4 patients undergoing surgical placement of greater occipital nerve stimulators for chronic headache. The anesthetic technique described uses total intravenous anesthesia with the guidance of Bispectral Index Scale to smoothen the transition between different anesthetic depths required for this novel operation.

Performance of the Cerebral State Index During Increasing Levels of Propofol Anesthesia: A Comparison with the Bispectral Index

BACKGROUND

The cerebral state monitor is a new device to measure depth of anesthesia. In this study we compared the cerebral state monitor with the bispectral index (BIS) monitor during propofol anesthesia.

METHODS

Fifteen healthy patients received a continuous infusion of propofol (300 mL/h). The cerebral state index (CSI) and the BIS values were recorded until burst suppression ratio > or =60%. Baseline variability, prediction probability, and agreement analysis between indices were evaluated. Clinical markers of loss of consciousness were also assessed.

RESULTS

Mean awake BIS and CSI values were 95.6 and 91.6, respectively (P = 0.01). BIS and CSI prediction probability values (mean +/- sd) were estimated to be 0.87 +/- 0.08 and 0.86 +/- 0.08, respectively (NS). The CSI tended to stabilize at values of 60-40 when estimated propofol concentrations at the effect site increased from 5 to 8 mug/mL. The BIS stabilized at values of 40-20 when the propofol concentrations at the effect site increased from 7 to 10 mug/mL. The mean BIS-CSI difference was -7.4 with 95% limits of agreement of 22.2 and -36.9. The BIS and CSI correlation with the burst suppression ratio was -0.60 and -0.97, respectively (P < 0.01). Predicted BIS and CSI values for loss of eyelash reflex in 50% and 95% of the patients were different (P < 0.05).

CONCLUSION

The overall performance of both monitors during propofol induction was similar. However, the different dynamic profiles of these monitors indicate that BIS may be a more useful index for evaluating intermediate anesthetic levels, whereas CSI may be better for evaluating deeper anesthetic levels.

Effects of epidural anesthesia with 0.2% and 1% ropivacaine on predicted propofol concentrations and bispectral index values at three clinical end points

STUDY OBJECTIVE

To compare the effects of 0.2% epidural ropivacaine and those of 1% epidural ropivacaine on predicted propofol concentrations and bispectral index scores (BISs) at three clinical end points.

DESIGN

Randomized double-blind study.

SETTING

University hospital.

PATIENTS

Thirty-five (35) ASA physical status I and II patients scheduled for elective surgery of the lower abdomen.

INTERVENTIONS

Patients were randomly divided into 2 groups to receive epidurally 8 mL of 0.2% or 1% ropivacaine followed by the same solution at a rate of 6 mL/h.

MEASUREMENTS

Twenty minutes after starting ropivacaine, a target-controlled infusion of propofol was started to provide a predicted blood concentration of 3 microg/mL; it increased by 0.5 microg/mL every 60 seconds until all 3 clinical end points were reached, as follows: P1, when patients lost consciousness; P2, when patients failed to show pupillary dilation and skin vasomotor reflex to transcutaneous electric stimulation applied to the upper level of loss of cold sensation; and P3, when patients failed to show pupillary dilation and skin vasomotor reflex to transcutaneous electric stimulation applied to C5.

MAIN RESULTS

The effective concentration 50 values for both predicted blood and effect-site propofol concentrations were significantly larger in the 0.2% group than in the 1% group at all end points. The BIS at every end point was significantly smaller in the 0.2% group than in the 1% group.

CONCLUSIONS

During combined epidural-propofol anesthesia, unconsciousness and lack of response to noxious stimulation occurred at lower predicted concentrations with 1% epidural ropivacaine than with 0.2% epidural ropivacaine. The results also suggest that the BIS may not be a good indicator when propofol anesthesia is combined with epidural anesthesia.

Update on bispectral index monitoring

Since 1997, bispectral index (BIS; Aspect Medical Systems Inc., Natick, MA) has been in clinical practice and a wealth of experimental research has accumulated on its use. Originally, the device was approved only for monitoring hypnosis and has now received an indication for reducing the incidence of intraoperative awareness during anesthesia. Numerous studies have documented the ability of BIS to reduce intermediate outcomes such as hypnotic drug administration, extubation time, postoperative nausea and shortened recovery room discharge. Two recent large-scale outcome studies using BIS (one randomized controlled trial and one prospective, nonrandomized historical cohort study) identified an approximately 80% reduction in the incidence of recall after anesthesia. BIS provides clinicians with unique information that can be used to tailor hypnotic drug doses to individual patient requirements. BIS does not predict movement or hemodynamic response to stimulation, nor will it predict the exact moment consciousness returns. This review will also discuss other BIS applications including use in pediatrics, intensive care and for procedural sedation. Some limitations exist to the use of BIS and it is not useful for some individual hypnotic agents (ketamine, dexmedetomidine, nitrous oxide, xenon, opioids). BIS technology is moving out of the operating room and into diverse environments where conscious and deep sedation are provided. Anesthesiologists need to be actively involved in promoting patient safety and helping transition this technology into broader use.

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.

Comparative evaluation of the cerebral state index and the bispectral index during target-controlled infusion of propofol

BACKGROUND

Cerebral state index (CSI) has recently been introduced as an intra-operative monitor of anaesthetic depth. We compared the performance of the CSI to the bispectral index (BIS) in measuring depth of anaesthesia during target-controlled infusion (TCI) of propofol.

METHODS

Twenty Chinese patients undergoing general anaesthesia were recruited. CSI and BIS, and predicted effect-site concentration of propofol were recorded. The level of sedation was tested by Modified Observer's Assessment of Alertness/Sedation Scale (MOAAS) every 20 s during stepwise increase (TCI, 0.5 microg ml(-1)) of propofol. The loss of verbal contact (LVC) and loss of response (LOR) were defined by MOAAS values of 2-3 and less than 2, respectively. Baseline variability and the prediction probability (P(K)) were calculated for the BIS and CSI. The values of BIS(05) and CSI(05), BIS(50) and CSI(50), BIS(95) and CSI(95) were calculated at each end-point (LVC and LOR).

RESULTS

Baseline variability of CSI was more than that of BIS. Both CSI and BIS showed a high prediction probability for the steps awake vs LVC, awake vs LOR, and LVC vs LOR, and good correlations with MOAAS values.

CONCLUSION

Despite larger baseline variation, CSI performed as well as BIS in terms of P(K) values and correlations with step changes in sedation.

Comparative Cost-Analysis of a Propofol-Cisatracurium-Based Anesthesia With Remifentanil or Fentanyl for Laparoscopic Surgery

To compare the intraoperative costs of intravenous propofol-based anesthesia for laparoscopic cholecystectomy, a total of 42 patients were randomly assigned to receive remifentanil or fentanyl as adjuvant using the bispectral index anesthesia monitoring. The average anesthesia calculated costs per hour (and per minute) were 79.45 (1.32) in the fentanyl group and 65.36 (1.09) in the remifentanil group. The calculated mean cost per patient was 76.56 in the fentanyl group and 58.86 in the remifentanil group. In conclusion, for propofol-cisatracurium-based anesthesia for laparoscopic surgery, when applying the bispectral index to guide the administration of hypnotic anesthetic drugs and ensure an adequate and stable depth of anesthesia, the cost of anesthesia is lower using remifentanil as an adjuvant rather than fentanyl. The clinical relevance is that it could be the intravenous anesthesia technique of choice in laparoscopic surgery for cholecystectomy from a cost-minimization standpoint.

Relationship between Bispectral Index, electroencephalographic state entropy and effect-site EC 50 for propofol at different clinical endpoints

BACKGROUND

State entropy (SE) is a newly available monitor for depth of anaesthesia. We investigated whether the relationship between predicted effect-site propofol concentration and both bispectral index (BIS) and SE values is useful for predicting loss of verbal contact and loss of consciousness during steady-state conditions.

METHODS

Twenty unpremedicated patients undergoing elective major abdominal surgery were recruited. A target-controlled infusion of propofol was administered using Schneider's pharmacokinetic model. The propofol infusion was set at an initial site-effect concentration of 1.0 microg ml(-1), and increased by 1.0 microg ml(-1) steps every 4 min, up to 6.0 microg ml(-1). A 4-min interval was chosen to ensure that steady-state site-effect concentrations were obtained. Propofol site-effect concentrations and BIS and SE values were recorded at loss of verbal contact (LVC) and loss of consciousness (LOC). Population values for predicted effect-site concentrations at the clinical endpoints were estimated and correlated with BIS and SE values.

RESULTS

For LVC, the effect-site concentration for 90% of patients was 1.1 (1.1-3.2) microg ml(-1) and for LOC 2.8 (2.8-5.65) microg ml(-1). LVC occurred in 90% of patients at a BIS value of 70.2 (70.2-90.2) and an SE value of 60.3 (60.3-75.5) and LOC occurred at a BIS value of 38.2 (38.2-70.4) and an SE value of 42.2 (42.2-60.4).

CONCLUSIONS

LVC and LOC occurred within a defined range of predicted effect-site concentrations. SE had a smaller range than BIS and higher correlation with effect-site concentration and may be more useful than BIS in predicting both LVC and LOC.

Relationship between Bispectral Index, electroencephalographic state entropy and effect-site EC 50 for propofol at different clinical endpoints

BACKGROUND

State entropy (SE) is a newly available monitor for depth of anaesthesia. We investigated whether the relationship between predicted effect-site propofol concentration and Bispectral Index (BIS) and SE values is useful for predicting loss of verbal contact and loss of consciousness during steady-state conditions.

METHODS

Twenty unpremedicated patients undergoing elective major abdominal surgery were recruited. A target-controlled infusion of propofol was administered using Schneider's pharmacokinetic model. The propofol infusion was set at an initial site effect concentration of 1.0 microg ml(-1) and increased by 1.0 microg ml(-1) steps every 4 min up to 6.0 microg ml(-1). A 4-min interval was chosen to ensure that steady-state effect-site concentrations were obtained. Propofol site effect concentrations and BIS and SE values were recorded at loss of verbal contact (LVC) and loss of consciousness (LOC). Population values for predicted effect-site concentrations at the clinical endpoints were estimated and correlated with BIS and SE values.

RESULTS

For LVC, the effect-site concentration for 90% of patients was 1.1 (1.1-3.2) microg ml(-1) and for LOC it was 2.8 (2.8-5.65) microg ml(-1). LVC occurred in 90% of patients at a BIS value of 70.2 (70.2-90.2) and an SE value of 60.3 (60.3-75.5), and LOC occurred at a BIS value of 38.2 (38.2-70.4) and an SE value of 42.2 (42.2-60.4).

CONCLUSIONS

LVC and LOC occurred within a defined range of predicted effect-site concentrations. SE had a smaller range than BIS and greater correlation with effect-site concentration and may be more useful than BIS in predicting both LVC and LOC.

Individual effect-site concentrations of propofol are similar at loss of consciousness and at awakening

Reported effect-site concentrations of propofol at loss of consciousness and recovery of consciousness vary widely. Thus, no single concentration based on a population average will prove optimal for individual patients. We therefore tested the hypothesis that individual propofol effect-site concentrations at loss and return of consciousness are similar. Propofol effect-site concentrations at loss and recovery of consciousness were estimated with a target-control infusion system in 20 adults. Propofol effect-site concentrations were gradually increased until the volunteers lost consciousness (no response to verbal stimuli); unconsciousness was maintained for 15 min, and the volunteers were then awakened. This protocol was repeated three times in each volunteer. Our major outcomes were the concentration producing unconsciousness and the relationship between the estimated effect-site concentrations at loss and recovery of consciousness. The target effect-site propofol concentration was 2.0 +/- 0.9 at loss of consciousness and 1.8 +/- 0.7 at return of consciousness (P <0.001). The average difference between individual effect-site concentrations at return and loss of consciousness was only 0.17 +/- 0.32 microg/mL (95% confidence interval for the difference 0.09-0.25 microg/mL). Our results thus suggest that individual titration to loss of consciousness is an alternative to dosing propofol on the basis of average population requirements.

[Clinical applications of intravenous anaesthetics pharmacology: the example of hypnotics and opioids]

OBJECTIVE

To review the general principles of pharmacokinetics and pharmacodynamics models by focusing on intravenous anaesthetics (hypnotics and opioids).

DATA SOURCES

Medline references, lectures from the French congress of anaesthesiology and intensive care medicine, abstracts.

DATA SYNTHESIS

Pharmacokinetic and pharmacodynamic modelling allows simple estimation of becoming of anaesthetic drugs in the body, instead of classical pharmacologic approach. However, pharmacokinetic as well as pharmacodynamic parameters are often considered as resulting from complex mathematic approaches and remain then poorly used in practice by physicians. The aim of this article is to simply expose concepts underlying PK-PD models building and to explain significance of the main PK-PD parameters (first-order rate constants, k(e0), T(1/2)k(e0), T(peak), context-sensitive half-time, context-sensitive decrement times). Clinical consequences for using intravenous anaesthetic drugs (hypnotics and opioids) are exposed either during bolus injection or continuous infusion, when injected alone or co-administered.

Patient-controlled sedation with propofol in minor oral surgery

PURPOSE

We sought to evaluate the benefits of patient-controlled sedation with propofol for minor oral surgery.

PATIENTS AND METHODS

After instructions were given on how to use the technique, 28 male and 24 female patients sedated themselves during minor oral surgery with titrating 18-mg bolus doses of propofol with a lockout period of 1 minute.

RESULTS

Surgery lasted from 5 to 29 minutes; 28 patients were moderately and 17 were deeply sedated. Seven patients were oversedated. All of those who were oversedated responded to commands within 1 minute of being unresponsive and continued to obtain increments of propofol. Vital signs were stable in all patients even during oversedation. Eighteen patients were talkative, and 17 complained of pain along the vein. Operating conditions were good in 38, fair in 12, and poor in 2. The majority, 48 patients, were relaxed, and 47 were willing to undergo the sedation technique again. Ten had total, 22 had partial, and 20 had no amnesia.

CONCLUSIONS

Relaxed patients, good operating conditions, and quick recovery of oversedated patients without unstable vital signs provide evidence that propofol has favorable pharmacokinetic and pharmacodynamic properties for patient-controlled sedation. This study also highlights the importance of close monitoring of patients during patient-controlled sedation.

Potential inhibition of cytochrome P450 3A4 by propofol in human primary hepatocytes

AIM: Hepatic cytochrome P450 isoenzymes constitute a superfamily of hemoproteins that play a major role in the metabolism of endogenous compounds and in the detoxification of xenobiotic molecules. P450 3A4 is one of the most important forms in human being, and mediates the metabolism of around 70% of therapeutic drugs and endogenous compounds. Propofol, a widely used intravenous anesthetic drug, is known to inhibit cytochrome P450 activities in isolated rat hepatocytes. The goal of this study was to evaluate the potential efficacy of propofol on P450 3A4 in a dose-dependent manner to understand its drug-drug interaction.

METHODS: Hepatocytes were isolated from liver specimens from hepatic angioma patients undergone hepatic surgery. Primary incubated hepatocytes were treated with 0, 0.01, 0.05, 0.1, 0.5, and 1.0 mM propofol for 24 hours. P450 3A4 activity was measured with Nash’s colorimetry. The protein expression was assessed by Western blot analysis.

RESULTS: A dose-dependent inhibitory effect of propofol was observed in cytochrome P450 3A4 activity. A minimal dosage of propofol (0.01 mM) induced a significant inhibition of P450 3A4 activity, although its regular dosages (0.01-0.1 mM) showed no inhibitory effect on the cellular protein expression of P450 3A4.

CONCLUSION: Propofol may be a potential CYP3A4 inhibitor as this anesthetic can inhibit isoenzyme activity significantly and reduce the metabolic rate of CYP3A4 substrates. This inhibition occurs at post-expression level, and concentration of propofol used clinically does not affect CYP3A4 protein expression. propofol may thus induce drug interaction of cytochrome P450 3A4 activity at the dosage used clinically.