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

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

Propofol and remifentanil effect-site concentrations estimated by pharmacokinetic simulation and bispectral index monitoring during craniotomy with intraoperative awakening for brain tumor resection

Different anesthetic techniques have been suggested for craniotomy with intraoperative awakening. We describe an asleep-awake-asleep technique with propofol and remifentanil infusions, with pharmacokinetic simulation to predict the effect-site concentrations and to modulate the infusion rates of both drugs, and bispectral index (BIS) monitoring. Five critical moments were defined: first loss of consciousness (LOC1), first recovery of consciousness (ROC1), final of neurologic testing (NT), second loss of consciousness (LOC2), and second recovery of consciousness (ROC2). At LOC1, predicted effect-site concentrations of propofol and remifentanil were, respectively, 3.6+/-1.2 microg/mL and 2.4+/-0.4 etag/mL. At ROC1, predicted effect-site concentrations of propofol and remifentanil were, respectively, 2.1+/-0.3 microg/mL and 1.8+/-0.3 etag/mL. At NT, predicted effect-site concentrations of propofol and remifentanil were, respectively, 0.9+/-0.3 microg/mL and 1.8+/-0.2 etag/mL. At LOC2, predicted effect-site concentrations of propofol and remifentanil were, respectively, 2.1+/-0.2 microg/mL and 2.5+/-0.2 etag/mL. At ROC2, predicted effect-site concentrations of propofol and remifentanil were, respectively, 1.2+/-0.5 microg/mL and 1.4+/-0.2 etag/mL (data are mean+/-SE). A significative correlation was found between BIS and predicted effect-site concentrations of propofol (r=0.547, P<0.001) and remifentanil (r=0.533, P<0.001). Multiple regression analysis between BIS and propofol and remifentanil predicted effect-site concentrations at the different critical steps of the procedure was done and found also significative (r=0.7341, P<0.001).     

The effect-site concentration of remifentanil blunting cardiovascular responses to tracheal intubation and skin incision during bispectral index-guided propofol anesthesia

We sought to determine the effect-site concentration of remifentanil blunting sympathetic responses to tracheal intubation and skin incision during bispectral index (BIS)-guided propofol anesthesia. Forty-one ASA physical status I-II patients, aged 20-65 yr and undergoing major abdominal surgery, were randomly assigned to one of two groups: tracheal intubation (group TI, n = 20) or skin incision (group SI, n = 21). All patients received a target-controlled infusion of propofol of 4 microg/mL, which was then adjusted to maintain a BIS value ranging between 40 and 50. The effect-site concentration of remifentanil blocking the sympathetic responses to tracheal intubation and skin incision in 50% of cases (Ce50) was determined using an up-and-down sequential allocation method. The mean (95% confidence interval [CI]) Ce50 of remifentanil was 5.0 ng/mL for TI (95% CI, 4.7-5.4 ng/mL) and 2.1 ng/mL for SI (95% CI, 1.4-2.8 ng/mL). This study shows that effect-site concentrations of remifentanil of 5 ng/mL and 2 ng/mL are effective in blunting sympathetic responses to tracheal intubation and skin incision in 50% of patients when combined with a BIS-guided target controlled infusion of propofol.     

Correlation of approximate entropy,bispectral index,and spectral edge frequency 95 (SEF95) with clinical signs of "anesthetic depth" during coadministration of propofol and remifentanil

BACKGROUND: Several studies relating electroencephalogram parameter values to clinical endpoints using a single (mostly hypnotic) drug at relatively low levels of central nervous system depression (sedation) have been published. However, the usefulness of a parameter derived from the electroencephalogram for clinical anesthesia largely depends on its ability to predict the response to stimuli of different intensity or painfulness under a combination of a hypnotic and an (opioid) analgesic. This study was designed to evaluate the predictive performance of spectral edge frequency 95 (SEF95), BIS, and approximate entropy for the response to increasingly intense stimuli under different concentrations of both propofol and remifentanil in the therapeutic range. METHODS: Ten healthy male and ten healthy female volunteers were studied during coadministration of propofol and remifentanil. After having maintained a specific target concentration for 10 min, the depth of sedation-anesthesia was assessed using the responsiveness component of the Observer's Assessment of Alertness/Sedation (OAA/S) rating scale, which was modified by adding insertion of a laryngeal mask and laryngoscopy. The electroencephalogram derived parameters approximate entropy, bispectral index, and SEF95 were recorded just before sedation level was assessed. RESULTS: The prediction probability values for approximate entropy were slightly, but not significantly, better than those for bispectral index, SEF95, and the combination of drug concentrations. A much lower prediction ability was observed for tolerance of airway manipulation than for hypnotic endpoints. CONCLUSION: Approximate entropy revealed informations on hypnotic and analgesic endpoints using coadministration of propofol and remifentanil comparable to bispectral index, SEF95, and the combination of drug concentrations.     

Hypnotic endpoints vs. the bispectral index, 95% spectral edge frequency and median frequency during propofol infusion with or without fentanyl

Hypnotic endpoints and/or EEG variables, e.g. bispectral index, 95% spectral edge frequency and median frequency, have been studied to monitor anaesthetic (hypnotic) depth during total intravenous anaesthesia. In this study, the relation between the hypnotic endpoints of unresponsiveness to verbal commands, loss of eyelash reflex and body movement response to mechanical nasal membrane stimulation vs. bispectral index, 95% spectral edge frequency and median frequency during propofol anaesthesia with or without fentanyl is presented. Forty-two patients were randomly assigned to receive either propofol infusion, 30 mg kg-1 h-1 (n = 22), or propofol infusion, 30 mg kg-1 h-1 + fentanyl bolus, 2 micrograms kg-1 i.v. (n = 20). Bispectral index, 95% spectral edge frequency and median frequency and propofol doses were monitored and recorded at unresponsiveness to verbal commands, loss of eyelash reflex and inhibition of nasal body movement response. The bispectral index values were significantly higher in the propofol + fentanyl compared with the propofol group, i.e. 74.7 +/- 10.9, 73.1 +/- 10.5 and 47.1 +/- 9.2 vs. 65.8 +/- 9.8, 59.6 +/- 10 and 33.8 +/- 5.7 at unresponsiveness to verbal commands, loss of eyelash reflex and inhibition of nasal body movement response respectively. Doses of propofol for achieving the hypnotic endpoints were significantly lower in the propofol + fentanyl compared with the propofol group. Plasma propofol concentrations at inhibition of nasal body movement response were lower in the propofol + fentanyl compared with the propofol group (9.2 +/- 2.0 micrograms mL-1 vs. 14.1 +/- 4.2 micrograms mL-1). Our results suggest that fentanyl pretreatment potentiates the effects of propofol and achieves the hypnotic endpoints at higher bispectral index values and lower propofol doses and concentrations (measured at inhibition of nasal body movement response).     

Clinical variables related to propofol effect-site concentrations at recovery of consciousness after neurosurgical procedures

Target controlled infusion (TCI) systems and computer data acquisition software are increasingly used in anesthesia. It was hypothesized that the use of such systems might allow retrieval of information useful to anticipate the effect-site concentrations of propofol at which patients would recover from anesthesia. The goal of the study was to identify variables related to propofol effect-site concentrations at recovery of consciousness (ROC). Sixteen patients with a Glasgow of 15, ASA 1 or 2, subjected to neurosurgical procedures, received TIVA with TCI propofol and remifentanil. Data were collected every 5 seconds from Datex AS3 and Aspect A200XP (BIS). Effect-site TCI was used for propofol (initial effect target 5.0 microg/ml) and for remifentanil (initial plasma target 2.5 ng/ml). All clinical events were noted. Variables possibly related to propofol effect-site concentration at ROC were selected. Data are expressed as mean +/- SD. Effect-site propofol concentration at ROC was 1.3 +/- 0.5 microg/ml. A positive correlation was found between propofol effect-site concentration at ROC and: age (49.3 +/- 17 years) (P = 0.003); mean remifentanil dose during surgery (0.11 +/- 0.05 microg/kg/min) (P = 0.003); mean propofol dose during surgery (0.12 +/- 0.03 mg/kg/min) (P = 0.046); and remifentanil effect-site concentration at ROC (2.85 +/- 2.06 ng/ml) (P = 0.002). Propofol effect-site concentrations were not correlated with: weight, height, LBM, duration of anesthesia, minimum BIS at induction (30.4 +/- 6.8), time till minimum BIS (4.7 +/- 2.2 min), mean and median BIS during surgery (38.2 +/- 4.5 and 37.8 +/- 5.3). BIS-related variables were not useful as ROC predictors. Only drug variables and age correlated with propofol effect-site concentrations at ROC.     

BIS监测异丙酚复合瑞芬太尼全麻患儿麻醉深度的准确性

目的 评价脑电双频谱指数(BIS)监测异丙酚复合瑞芬太尼全麻患儿麻醉深度的准确性.方法 择期手术患儿60例,ASA Ⅰ或Ⅱ级,年龄3～8岁,体重14～40kg,随机分为4组(n=15),人室后开放手背静脉,稳定5 min.C组静脉输注0.9%生理盐水0.2 ml·kg-1·h-1;R1组、R2组和R3组分别静脉输注瑞芬太尼0.1、0.3或0.5 μg·kg-1·min-1,瑞芬太尼或生理盐水输注10 min开始靶控输注异丙酚,起始效应室浓度为1 μg/ml,逐渐递增至2、3、4μg/ml.分别于稳定5min、瑞芬太尼静脉输注10min、异丙酚效应室浓度达到l、2、3、4μg/ml稳定1 min及意识消失时记录BIS和警觉,镇静(OAA/S)评分;记录意识消失时间.采用logistic回归法计算意识消失时的BIS50、BIS95和意识消失时异丙酚的EC50、EC95.BIS与OAA/S评分、异丙酚效应室浓度作直线相关分析.结果 C组、R1.组、R2组和R3组BIS与OAA/S评分均呈正相关,r分别为0.89、0.90、0.87、0.82(P<0.05);BIS与异丙酚效应室浓度均呈负相关,r分别为-0.87、-0.90、-0.87、-0.92(P<0.05);与C组比较,其余3组患儿意识消失时异丙酚效应室浓度降低,意识消失时间缩短,R2组和R3组意识消失时BIS升高,BIS50和BIS95升高,异丙酚EC50和EC95降低(P<0.05);与R1组比较,R2组BIS50和BIS95升高,R3组异丙酚EC50和EC95降低(P<0.05).结论 瑞芬太尼复合异丙酚麻醉下,采用BIS监测患儿麻醉深度存在一定局限性.     

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

BACKGROUND: Two opioid regimens, computer-simulated to provide optimal general anesthesia in combination with propofol, were compared using clinical criteria. METHODS: Fifty patients undergoing thyroid surgery were blindly, prospectively and randomly allocated to receive either (a) i.v. remifentanil (1.5 micro g kg-1, followed by 0.2 micro g kg-1 min-1) or (b) i.v. sufentanil (0.2 micro g kg-1 followed by 0.2 micro g kg-1 h-1). Remifentanil infusion was stopped at the last skin suture. Sufentanil infusion was stopped 30 min before the end of surgery. Intravenous propofol was titrated to keep BIS at 50+/-5. Remifentanil and sufentanil groups were compared with regards to (a) propofol delivery, (b) hemodynamic and recovery variables, and (c) effect-site propofol levels during a steady-state period for effect-site remifentanil and sufentanil levels. P<0.05 was significant. RESULTS: Groups were similar in demographic data; types and durations of surgery; total propofol consumption; and response, extubation and emergence times. During the steady-state period for the opioid delivery, the remifentanil and sufentanil effect-site levels were 5.3 ng ml-1 and 0.18 ng ml-1, respectively (potency ratio=30). In both opioid groups, in accordance with previous computer-simulations, the effect-site propofol concentrations remained (a) within a narrow range unaffected by surgical stimuli, (b) significantly smaller in the remifentanil group than in the sufentanil group, but (c) smaller than expected from previous computer-simulations. More patients required ephedrine following induction of anesthesia in the remifentanil compared with the sufentanil group. CONCLUSIONS: The present clinical trial conducted in thyroid surgery is consistent with previous computer-simulated opioid-propofol combinations with respect to intraoperative and recovery variables. Effect-site propofol ranges were, however, lower than expected.     

Assessment of depth of anesthesia and postoperative respiratory recovery after remifentanil- versus alfentanil-based total intravenous anesthesia in patients undergoing ear-nose-throat surgery

BACKGROUND: The authors investigated whether total intravenous anesthesia (TIVA) with precalculated equipotent infusion schemes for remifentanil and alfentanil would ensure appropriate analgesia and that remifentanil would result in better recovery characteristics. METHODS: Forty consenting patients (classified as American Society of Anesthesiologists physical status I-III) scheduled for microlaryngoscopy were randomized to receive, in a double-blind manner, either remifentanil (loading dose 1 microg/kg; maintenance infusion, 0.25 microg x kg(-1) x min-1) or alfentanil (loading dose, 50 microg/kg; maintenance infusion, 1 microg x kg(-1) x min-1) as the analgesic component of TIVA. They were combined with propofol (loading dose, 2 mg/kg; maintenance infusion, 100 microg x kg(-1) min(-1)). To insure an equal state of anesthesia, the opioids were titrated to maintain heart rate and mean arterial pressure within 20% of baseline, and propofol was titrated to keep the bispectral index (BIS) less than 60. Neuromuscular blockade was achieved with succinylcholine. Drug dosages and the times from cessation of anesthesia to extubation, verbal response, recovery of ventilation, and neuropsychological testing, orientation, and discharge readiness were recorded. RESULTS: Demographics, duration of surgery, and anesthesia were similar between the two groups. Both groups received similar propofol doses. There were no difference in BIS values preoperatively (mean, 96), intraoperatively (mean, 55), and postoperatively (mean, 96). Recovery of BIS and times for verbal response did not differ. At 20, 30, and 40 min after terminating the opioid infusion, the peripheral oxygen saturation and respiratory rate were significantly higher in the remifentanil group compared with the alfentanil group. CONCLUSIONS: When both the hypnotic and analgesic components of a TIVA-based anesthetic are administered in equipotent doses, remifentanil provides a more rapid respiratory recovery, even after brief surgical procedures, compared with alfentanil.     

A-line, bispectral index, and estimated effect-site concentrations: a prediction of clinical end-points of anesthesia

Autoregressive modeling with exogenous input of middle-latency auditory evoked potentials (A-Line AEP index, AAI) has been developed for monitoring depth of anesthesia. We investigated the prediction of recovery and dose-response relationship of desflurane and AAI or bispectral index (BIS) values. Twenty adult men scheduled for radical prostatectomy were recruited. To minimize opioid effects, analgesia was provided by a concurrent epidural in addition to the general anesthetic. Electrodes for AAI and BIS monitoring and a headphone for auditory stimuli were applied. Propofol and remifentanil were used for anesthetic induction. Maintenance of anesthesia was with desflurane only. For comparison to AAI and BIS monitor parameters, pharmacokinetic models for desflurane and propofol distribution and effect-site concentrations were used to predict clinical end-points (Prediction probability P(K)). Patients opened their eyes at an AAI value of 47 +/- 20 and a BIS value of 77 +/- 14 (mean +/- sd), and the prediction probability for eye opening was P(K) = 0.81 for AAI, P(K) = 0.89 for BIS, and P(K) = 0.91 for desflurane effect-site concentration. The opening of eyes was best predicted by the calculated desflurane effect-site concentration. The relationship between predicted desflurane effect-site concentration versus AAI and BIS was calculated by nonlinear regression analysis (r = 0.75 for AAI and r = 0.80 for BIS). The correlation between BIS and clinical end-points of anesthesia or the desflurane effect-compartment concentration is better than for the AAI.     

Bispectral index-guided administration of anaesthesia: comparison between remifentanil/propofol and remifentanil/isoflurane

BACKGROUND AND OBJECTIVE: The bispectral index of the electroencephalogram is a measure of the hypnotic component of anaesthesia and can be used to guide the administration of anaesthesia. This study compares bispectral index-guided anaesthesia with remifentanil and either propofol or isoflurane. METHODS: Eighty consenting patients were randomly assigned to two groups. Following induction with propofol and remifentanil, anaesthesia was maintained with remifentanil/propofol or remifentanil/isoflurane. Remifentanil infusion rates were guided by haemodynamic responses--maintaining mean arterial pressure and heart rate within 20% of baseline. Propofol and isoflurane administration was guided using the bispectral index (45-60). Thirty minutes before the end of surgery, morphine was administered (0.15 mg kg(-1) intravenously). Fifteen minutes before end of surgery, propofol and isoflurane were reduced (bispectral index 60-75). At the end of surgery, the anaesthetic agents were discontinued. Groups were compared for recovery, remifentanil doses and signs of inadequate anaesthesia using the chi2-test and ANOVA (P < 0.05). RESULTS: The duration of surgery was longer in the propofol/remifentanil group (121 +/- 53 versus 94 +/- 40 min). Recovery data were not different between groups. The remifentanil infusion rate was significantly lower with additional isoflurane (0.18 +/- 0.06 microg kg(-1) min(-1)) than with additional propofol (0.31 +/- 0.20 microg kg(-1) min(-1)). The propofol infusion rate was 123 +/- 48 microg kg(-1) min(-1); isoflurane concentration was 0.66 +/- 0.13%. CONCLUSIONS: Bispectral index-guided anaesthesia with remifentanil plus propofol or isoflurane results in the absence of postoperative recall and a fast recovery with both drug combinations. In our patients, at comparable bispectral index-levels, haemodynamic control requires higher doses of remifentanil with propofol than with isoflurane.     

Median EEG frequency is more sensitive to increases in sympathetic activity than bispectral index.

Sympathetic heart rate variability is correlated with the increase in plasma catecholamines during rapid opioid detoxification. We evaluated whether the bispectral index, median frequency, or 95% spectral edge of the electroencephalogram are sensitive to the sympathetic response seen during reversal of opioid dependence. Eight patients undergoing rapid opioid detoxification gave informed consent. Two-channel frontal electroencephalogram was measured. Sympathetic heart rate variability was measured in 256 second segments by Fourier transform of continuous heart rate and the low frequency segment (0.02-0.13 Hz) analyzed for sympathetic function. Patients were anesthetized with propofol infusion. After a 30-60 min steady state, naloxone was infused intravenously at a rate of 25 mg/30 min, followed by an infusion of 1 mg/hr. During induction of anesthesia, sympathetic heart rate variability decreased from 1.80 to 0.3, bispectral index from 86 to 47, median frequency from 10.2 to 3.4, spectral edge from 23.5 to 16.7 (all P<.05). During naloxone infusion, the median percent increase in sympathetic heart rate variability was 487% (P<.05), median frequency increased 163% (P<.05), bispectral index (10%), and spectral edge (7%) did not significantly change. The increase in median frequency was delayed compared to sympathetic heart rate variability and median frequency remained elevated after sympathetic heart rate variability returned to anesthetized baseline in 5 of 8 cases. Our results show that median frequency and sympathetic heart rate variability increase during opioid detoxification, but the time course of each response is different. Median frequency is a more sensitive electroencephalogram indicator of opioid reversal than bispectral index or spectral edge.     

Correlation of Approximate Entropy, Bispectral Index, and Spectral Edge Frequency 95 (SEF95) with Clinical Signs of Anesthetic Depth during Coadministration of Propofol and Remifentanil

Background: Several studies relating electroencephalogram parameter values to clinical endpoints using a single (mostly hypnotic) drug at relatively low levels of central nervous system depression (sedation) have been published. However, the usefulness of a parameter derived from the electroencephalogram for clinical anesthesia largely depends on its ability to predict the response to stimuli of different intensity or painfulness under a combination of a hypnotic and an (opioid) analgesic. This study was designed to evaluate the predictive performance of spectral edge frequency 95 (SEF95), BIS, and approximate entropy for the response to increasingly intense stimuli under different concentrations of both propofol and remifentanil in the therapeutic range.

Methods: Ten healthy male and ten healthy female volunteers were studied during coadministration of propofol and remifentanil. After having maintained a specific target concentration for 10 min, the depth of sedation-anesthesia was assessed using the responsiveness component of the Observer's Assessment of Alertness/Sedation (OAA/S) rating scale, which was modified by adding insertion of a laryngeal mask and laryngoscopy. The electroencephalogram derived parameters approximate entropy, bispectral index, and SEF95 were recorded just before sedation level was assessed.

Results: The prediction probability values for approximate entropy were slightly, but not significantly, better than those for bispectral index, SEF95, and the combination of drug concentrations. A much lower prediction ability was observed for tolerance of airway manipulation than for hypnotic endpoints.     

Nitrous oxide prevents movement during orotracheal intubation without affecting BIS value

We sought to determine whether the addition of nitrous oxide (N(2)O) to an anesthetic with propofol and remifentanil modifies the bispectral index (BIS) during the induction of anesthesia and orotracheal intubation. Thirty ASA physical status I or II patients were randomly allocated to receive either 50% air in oxygen (control group) or 60%-70% N(2)O in oxygen (N(2)O group) that was commenced via a mask simultaneously with the induction of anesthesia. Anesthesia was performed in all the patients with IV propofol at the target effect compartment site concentration of 4 microg/mL throughout the study. A target-controlled infusion (TCI) of remifentanil was initiated 3 min after the TCI of propofol and maintained at the effect-site concentration of 4 ng/mL until the end of the study. After loss of consciousness, and before the administration of vecuronium 0.1 mg/kg, a tourniquet was applied to one arm and inflated to a value more than the systolic blood pressure. An examiner, blinded to the presence of N(2)O, sought to detect any gross movement within the first minute after tracheal intubation, which was performed 10 min after remifentanil TCI began. Inspired and expired oxygen, N(2)O, and carbon dioxide were continuously monitored. A BIS value was generated every 10 s. Arterial blood pressure and heart rate (HR) were measured noninvasively every minute. Measures of mean arterial pressure (MAP), HR, and BIS were obtained before the induction, before the start of the remifentanil TCI, before laryngoscopy, and 5 min after intubation. No significant intergroup differences were seen in BIS, HR, and MAP throughout the study. Maximum changes in BIS, HR, and MAP with intubation were significant (P < 0.01) for both groups but comparable. Six patients in the control group and none in the N(2)O group moved after intubation (P < 0.05). IMPLICATIONS: We demonstrated that 0.6 minimal alveolar concentration of nitrous oxide combined with a potent anesthetic and an opioid prevents movement after orotracheal intubation without affecting the bispectral index. This demonstrates that the bispectral index is not a useful neurophysiologic variable to monitor the level of anesthesia when nitrous oxide is added to a general anesthetic regimen using propofol and remifentanil.     

Brain tumors may alter the relationship between bispectral index values and propofol concentrations during induction of anesthesia

STUDY OBJECTIVE: To compare propofol-predicted effect-site concentrations (PropCe) and bispectral index (BIS) of the electroencephalogram during induction of anesthesia in patients with small brain tumors and to analyze BIS and PropCe at loss of consciousness (LOC). DESIGN: Prospective investigation. SETTING: Operating theater of a university hospital. PATIENTS: 26 ASA physical status I and II patients, 13 of whom were scheduled for nontumor spinal surgeries, and the other 13, for brain surgery for small brain tumor removal. INTERVENTIONS: Anesthesia was induced with a propofol 1% constant infusion rate of 200 mL/h until LOC. MEASUREMENTS: BIS, PropCe, heart rate, and mean arterial pressure were analyzed at the beginning of the propofol infusion and every 30 seconds during induction. MAIN RESULTS: The BIS values were significantly higher in patients with brain tumors in the period from 150 to 210 seconds, with PropCe similar to patients without brain tumors. Loss of consciousness occurred 3.6 +/- 0.8 minutes in patients without brain tumors and 3.9 +/- 0.7 minutes in patients with brain tumors. No differences were observed between groups in the time to LOC (3.6 +/- 0.8 in group 1 vs 3.9 +/- 0.7 in group 2) or in BIS at LOC (48.7 +/- 11.4 in group 1 vs 58.6 +/- 21.7 in group 2). CONCLUSIONS: For similar propofol concentrations, patients with small brain tumors show higher BIS values on induction of anesthesia with propofol.     

The effect of ketamine on clinical endpoints of hypnosis and EEG variables during propofol infusion

BACKGROUND: We studied the effect of variable doses of ketamine on the endpoints of hypnosis, e.g., unresponsiveness to verbal commands (UVC), loss of eyelash reflex (LER), and inhibition of body movement response with or without sneezing to nasal membrane stimulation (INBMR), and processed EEG variables, e.g., bispectral index (BIS), 95% spectral edge frequency (SEF) and median frequency (MF) during propofol infusion. METHODS: Forty-eight patients received either propofol infusion, 30 mg.kg-1.h-1 (Group P; n = 12) or ketamine bolus, 0.25, 0.5 or 0.75 mg i.v., followed by propofol infusion, 30 mg.kg-1.h-1 + variable dose ketamine infusion, 0.25, 0.5 or 0.75 mg.kg-1.h-1 (Groups PK0.25, PK0.5 and PK0.75; n = 12 each) until UVC, LER and INBMR. BIS, 95% SEF and MF values were monitored and recorded at the endpoints of hypnosis. Propofol and ketamine concentrations were measured at INBMR. RESULTS: Propofol infusion, 30 mg.kg-1.h-1, induced UVC, LER and INBMR at BIS: 65 +/- 2, 63 +/- 9 and 33 +/- 7; 95% SEF: 17 +/- 3, 17 +/- 4 and 14 +/- 3; and MF values of 5 +/- 2, 5 +/- 3 and 3 +/- 2, respectively. With adjunctive ketamine (Groups PK0.5 and PK0.75), the hypnotic endpoints were achieved at higher BIS and 95% SEF values and lower propofol doses and concentrations as compared to Groups P and PK0.25 (9.9 +/- 5.8 and 9.4 +/- 3.4 vs. 13.4 +/- 4.5 and 14 +/- 5.8 micrograms.ml-1). CONCLUSIONS: Our results suggest additive interaction between propofol and ketamine (Groups PK0.5 and PK0.75) for achieving the hypnotic endpoints; however, ketamine did not depress the EEG variables in proportion to its hypnotic effect. The paradoxically higher BIS and 95% SEF values at the hypnotic endpoints may be due to lower propofol concentrations and/or no effect of ketamine on the EEG variables.     

Bispectral index in patients with target-controlled or manually-controlled infusion of propofol

In this prospective, randomized study we compared bispectral index (BIS), hemodynamics, time to extubation, and the costs of target-controlled infusion (TCI) and manually-controlled infusion (MCI) of propofol. Forty patients undergoing first-time implantation of a cardioverter-defibrillator were included. Anesthesia was performed with remifentanil (0.2-0.3 micro g. kg(-1). min(-1)) and propofol. Propofol was used as TCI (plasma target concentration, 2.5-3.5 micro g/mL; n = 20) or MCI (3.0-4.0 mg. kg(-1). h(-1); n = 20). BIS, heart rate, and arterial blood pressure were measured at six data points: T1, before anesthesia; T2, after intubation; T3, after skin incision; T4, after first defibrillation; T5, after third defibrillation; and T6, after extubation. There were no significant hemodynamic differences between the two groups. BIS was significantly lower at T3 and T4 in the TCI group than in the MCI group. The mean dose of propofol was larger in TCI patients (5.8 +/- 1.4 mg. kg(-1). h(-1)) than in the MCI patients (3.7 +/- 0.6 mg. kg(-1). h(-1)) (P < 0.05), whereas doses of remifentanil did not differ. Time to extubation did not differ between the two groups (TCI, 13.7 +/- 5.3 min; MCI, 12.3 +/- 3.5 min). One patient in the MCI group had signs of intraoperative awareness without explicit memory after first defibrillation (BIS before shock, 49; after shock, 83). Costs were significantly less in the MCI group (34.83 US dollars) than in the TCI group (39.73 US dollars). BIS failed to predict the adequacy of anesthesia for the next painful stimulus. IMPLICATIONS: In this prospective, randomized study, bispectral index (BIS), hemodynamics, time to extubation, and costs of target-controlled infusion (TCI) and manually-controlled infusion of propofol were compared. TCI increased the amount of propofol used. BIS failed to predict the adequacy of anesthesia for the next painful stimulus.     

腹腔镜结直肠手术中滴定靶控输注麻醉的应用

目的探讨以脑电双频指数（B1S）和收缩压为滴定目标、以丙泊酚复合瑞芬太尼滴定靶控输注静脉麻醉对腹腔镜结直肠手术中麻醉用药量和麻醉深度的影响。方法选择60例择期腹腔镜结直肠手术患者为研究对象,采用丙泊酚复合瑞芬太尼滴定靶控输注静脉麻醉,以BIS维持40～60、收缩压波动不超过基础值的20％为目标,滴定调节两种药物的血浆靶浓度,当BIS与收缩压的变化趋势出现矛盾时首先调节SBP。记录不同时间点的BIS、血压及麻醉药血浆靶控浓度等。结果麻醉诱导后血压基本平稳,BIS维持在60以内,其中在人工气腹建立后和Trendelenburg体位期间,BIS低至35。40之间：整个麻醉过程中患者均无术中知晓。麻醉期间存在手术刺激时,丙泊酚和瑞芬太尼血浆靶浓度的95％C1分别为2．55～2．65mg／L和4．09～4．26μg／L,其中丙泊酚的血浆靶浓度所推荐剂量。结论在腹腔镜结直肠手术中,以BIS结合收缩压为目标进行丙泊酚复合瑞芬太尼滴定靶控输注静脉麻醉,可维持有的麻醉深度,并减少麻醉药的用量。     

Clinical usefulness of remifentanil

Anesthesia with remifentanil can be induced either with slow bolus administration (1 microg x kg(-1) for over 60 sec) or with starting the continuous infusion (0.5-1 microg x kg(-1) x hr(-1)) combined with a standard hypnotic agent (i.e. propofol, thiamylal, sevoflurane or isoflurane). According to the patient's requirement observing hemodynamics, the infusion rate of remifentanil should be titrated after tracheal intubation. Because of the rapid onset and short duration of its action, the infusion rate can be increased or decreased safely. Remifentanil is an effective agent in obtunding the stress response to tracheal intubation and surgery. Due to its synergistic effect with hypnotic agents, sevoflurane, isoflurane or propofol, it should be reduced carefully to prevent excessive depth of anesthesia. BIS values should be monitored closely. Remifentanil seems to be as potent as fentanyl. Prior to emergence from general anesthesia using remifentanil, postoperative pain management should be considered. NSAIDs or a long acting opioid could be administered.     

The effect of cigarette smoking on the hypnotic efficacy of propofol

The bispectral index (BIS) was used to examine the hypnotic efficacy of propofol in 25 smokers (20 cigarettes/day for 2 years) and 24 matched non-smokers (same gender, age, height, weight). BIS was recorded at baseline, at four incremental effect-site concentrations of propofol and at loss of consciousness. Compared with non-smokers, smokers were found to have higher BIS values at baseline (mean (SD)) (97 (1) vs 98 (1)), at 0.7 microg x ml(-1) (95 (3) vs 97 (1)) and at 1.1 microg x ml(-1) (89 (6) vs 94 (4)), p = 0.0099, and they lost consciousness at higher propofol concentrations (2.0 (0.4) vs 2.4 (0.8) microg x ml(-1)), p = 0.03, and at lower BIS values (66 (10) vs 60 (10)), p = 0.04. The hypnotic efficacy of propofol is reduced when used at low effect-site concentrations in smokers. This phenomenon may have some impact on the management of smokers undergoing sedation using target controlled infusion systems.