Effects of sevoflurane and propofol on evoked potentials during neurosurgical anesthesia

BACKGROUND: The effect of anesthetics on somatosensory evoked potential (SEP) and auditory brain stem response (ABR) has been a subject of intense reseach over the last two decades. In fact, volatile anesthetics have been repeatedly shown to decrease cortical amplitude in a dose-dependent fashion but the information regarding the effect of propofol is incomplete. The purpose of this study was to compare the effects of sevoflurane and propofol on evoked potentials during comparable depth of anesthesia guided by bispectral index (BIS). METHODS: Forty four patients scheduled for neurosurgery were studied. Anesthesia was maintained with intravenous propofol using target controlled infusion (TCI). We measured the change of amplitude and latency of SEP(N20-P25), ABR (V wave) and visual evoked potential (VEP: P100) at three sets of sevoflurane (0%, 1%, 2%) or propofol concentrations (effect site concentration of 1.5, 2.0, 3.0 microug x ml(-1)). BIS monitor was used to measure relative depth of hypnosis. RESULTS: With increasing concentrations of sevoflurane (0, 1% and 2%), SEP showed dose-related reduction in its amplitude, ABR produced less marked changes and VEP showed a significant reduction at 1%. VEP at the propofol concentration of 3.0 microg x ml(-1) was decreased significantly compared with the amplitude at 1.5 microg x ml(-1) concentration. No significant change was observed with SEP and ABR during the change of propofol dosages. BIS values were almost the same with each anesthetics. CONCLUSIONS: VEP was most strongly affected with anesthetics, and ABR showed less marked influence of sevoflurane and propofol. Propofol based TIVA technique would induce less change in evoked potentials than sevoflurane.     

Cardiac anesthesia induction by low target plasma concentration setting of propofol using target-controlled infusion

BACKGROUND: Propofol-anesthesia administerd using target-controlled infusion (TCI) has been proposed for cardiac surgery. But, moderate target concentration of propofol during induction using TCI has not been studied in detail. METHODS: Thirty patients scheduled for cardiac surgery under cardiopulmonary bypass (CPB) and TCI propofol anesthesia were randomly divided into two groups to receive a computer-controlled infusion of propofol with target concentrations of 1.5 or 2.0 micro/g x ml(-1) [1.5 microg x ml(-1) group (n=15) and 2.0 microg x ml(-1) group (n=15)]. Mean arterial pressure (MAP), heart rate (HR) and bispectral index scale (BIS) values were recorded at 5 time points during induction of anesthesia. RESULTS: MAP was significantly lower in 2.0 microg x ml(-1) group compared with 1.5 microg x ml(-1) group. In both groups, a rise of BIS value did not occur during tracheal intubation. CONCLUSIONS: We have demonstrated that propofol TCI at a target concentration of 1.5 microg x ml(-1) is effective for hemodynamic stability during induction of anesthesia in patients for cardiac surgery under CPB.     

The effect of nitrous oxide on the central nervous system evaluated by the bispectral index under various levels of propofol anesthesia

BACKGROUND: The effect of nitrous oxide either as a sole agent or with volatile anesthetic agents on the central nervous system has been well studied. However, it has not been clarified during various levels of propofol anesthesia. We therefore evaluated the effect of nitrous oxide on the central nervous system using bispectral index (BIS) and suppression ratio (SR) under various levels of propofol anesthesia. METHODS: Twelve patients were enrolled for the study. After the administration of subarachnoid block, propofol was infused using a stepped down series (effect site concentration of 5, 4, 3 microg x ml(-1)) for 20 minutes. After obtaining BIS and SR at each concentration, nitrous oxide was added. RESULTS: When 67% of nitrous oxide was added to the estimated effect site propofol concentration of 5 microg x ml(-1), BIS decreased and SR increased indicating that the nitrous oxide had a depressant effect on the central nervous system. On the other hand, nitrous oxide combined with 3 or 4 microg x ml(-1) of propofol did not cause significant changes in BIS and SR, suggesting that nitrous oxide did not have a suppressive effect. CONCLUSIONS: We conclude that nitrous oxide has different effects on BIS according to their basal propofol concentrations.     

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

BACKGROUND: The bispectral (BIS) index is a pharmacodynamic measure of the effect of anesthesia on the central nervous system. The aim of this study was to investigate the relationship between BIS index and predicted plasma concentration of propofol delivered by target controlled infusion (TCI) during emergence in children. METHODS: With approval of IRB, 30 patients (2-7 years) were included in this study. Anesthesia was with TCI propofol 3-5 microg.ml(-1) and remifentanil 7.5 ng.ml(-1) to maintain BIS 40-60 and the propofol concentration was fixed at 3 microg.ml(-1) Remifentanil infusion was stopped 10 min before the end of surgery. BIS values were recorded after reducing propofol in decrement of 0.2 microg.ml(-1). BIS values were checked when spontaneous respiration occurred and children were able to obey a command (eye opening or hand grasping). RESULTS: Spearman's correlation analysis showed negative correlation between BIS and propofol plasma concentration (r = -0.559, P < 0.001). When respiration returned, mean BIS was 77.2 +/- 5.3 and propofol plasma concentration 1.6 +/- 0.3 microg.ml(-1) and when a verbal command was obeyed, BIS was 82.4 +/- 5.6 and propofol plasma concentration 1.5 +/- 0.3 microg.ml(-1). CONCLUSIONS: In preschool children, BIS moderately correlated with the predicted plasma concentration of propofol.     

The effect of two low-dose propofol infusions on the relationship between six-pulse transcranial electrical stimulation and the evoked lower extremity muscle response

BACKGROUND: Transcranial stimulation of the motor cortex using high-voltage electrical stimuli given in train is a method of monitoring the integrity of the motor pathways during thoracoabdominal aortic aneurysm surgery. The purpose of this study was to assess the relationship between the stimulus intensity and the corresponding amplitude of the myogenic motor evoked potential (tcMEP) in response to six-pulse transcranial electrical stimulation during two levels of low-dose propofol infusion and stable fentanyl/nitrous oxide anaesthesia. METHODS: Nine patients (37-78 yr) scheduled to undergo surgery on the thoracoabdominal aorta were studied. After achieving a stable anaesthetic state the output voltage was decreased with 50 V intervals from 350 V to 200 V during a target propofol infusion aimed at a plasma steady-state concentration of 0.7 microg x ml(-1) and increased with 50 V intervals from 200 V to 450 V during a target propofol infusion aimed at a plasma steady-state concentration of 1.4 microg x ml(-1). TcMEPs were recorded from the right tibialis anterior muscle. RESULTS: Doubling the target propofol infusion to 1.4 microg x ml(-1) resulted in a 30-50% decrease in tcMEP amplitude. The largest tcMEP amplitude using the six-pulse paradigm was found during a propofol infusion aimed at a plasma concentration of 0.7 microg x ml(-1) and demanded a stimulus output of 350 V, corresponding to a charge density of 7.5 microC x cm(-2) per phase. CONCLUSION: Doubling the target propofol infusion to 1.4 microg x ml(-1) provides less robust, but still recordable tcMEPs in response to six-pulse electrical stimulation. Safety guidelines are discussed.     

Propofol suppresses the cortical somatosensory evoked potential in rats

The dose-response curve for the effect of volatile anesthetics on the somatosensory evoked potential (SEP) is well described, but for propofol, the large dose segment of the curve is undefined. We describe the effect of increasing plasma concentrations of propofol on cortical SEPs in 18 rats. After surgical preparation under ketamine anesthesia, a remifentanil infusion was begun at 2.5, 5, or 10 microg x kg(-1) x min(-1). After 20 min, the propofol infusion was initiated at 20 mg x kg(-1) x h(-1) and was increased to 40, 60, and 80 mg x kg(-1) x h(-1) at 20-min intervals. SEP was recorded before remifentanil infusion, before propofol infusion rate changes, and 30 min after discontinuing propofol infusion. In six additional rats, the plasma concentrations of propofol after each 20-min infusion were measured using gas chromatography. Remifentanil did not have a significant effect, but propofol significantly depressed the SEP amplitude and prolonged the latency at infusion rates of 40 mg x kg(-1) x h(-1) and more. Propofol's effect was dose-dependent, but even at 80 mg x kg(-1) x h(-1) with an estimated plasma concentration of 31.6 +/- 3.4 microg/mL (10.8 50% effective concentration), a measurable response was present in 44.5% of rats. These results suggest that even at large doses, propofol and remifentanil provide adequate conditions for SEP monitoring. IMPLICATIONS: Rats demonstrate dose-dependent somatosensory evoked potential (SEP) suppression with propofol but not with remifentanil. However, SEP suppression by 50% occurred only at large (1.5 EC(50)) concentrations of propofol, and a measurable SEP was present in 8 of 18 rats, even at 10.8 EC(50).     

Anesthetic management with propofol during pheochromocytoma resection under bispectral index monitoring

In three patients undergoing pheochromocytoma resection under propofol/fentanyl anesthesia, bispectral index (BIS) was monitored for assessment of hypnotic effect. In two patients, arterial blood concentrations of propofol were measured by high performance liquid chromatography (HPLC), and compared with those of the estimated blood concentrations. Until resection of the tumor, propofol was infused at a rate of 10 mg x kg(-1) x hr(-1). After resection of the tumor, propofol dosage was reduced to 3-6 mg x kg(-1) x hr(-1), keeping the BIS values around 60. Rapid infusion of fluid and norepinephrine was required to maintain blood pressure after removal of the tumor in two patients. In one patient, blood pressure was maintained well without rapid infusion of fluid or vasopressor. Arterial blood concentration of propofol after resection of the tumor was equal to the estimated blood concentration (3.04 vs 3.02 microg x ml(-1)) in a patient without rapid infusion of fluid. In a patient with rapid infusion of fluid, the arterial blood concentration was lower than the estimated blood concentration (2.59 vs 3.58 microg x ml(-1)). The anesthetic depth can not be estimated accurately by hemodynamic changes in the patients undergoing pheochromocytoma resection. BIS monitoring should be recommended for adjustment of propofol dosage after pheochromocytoma resection.     

Noxious stimuli do not modify myogenic motor evoked potentials by electrical stimulation during anesthesia with propofol-based anesthesia

PURPOSE: To investigate whether motor evoked potentials (MEP) to transcranial electrical stimulation under constant blood propofol concentration are affected by the arousing effect of surgical noxious stimuli. METHODS: Twenty patients who underwent elective spinal surgery were studied. Patients were anesthetized with 50% nitrous oxide in oxygen, fentanyl, and propofol to maintain the bispectral index (BIS) score around 50. MEP in response to a multipulse transcranial electrical stimulation at stimulus sites of C3-C4 were recorded over the right abductor pollicis brevis muscle. Changes of peak-to-peak amplitude and onset latency of MEP, BIS score before and after surgical stimuli were evaluated. Propofol plasma concentration was measured at the same time points. RESULTS: Both MEP amplitude and latency did not change significantly after surgical stimuli although BIS increased significantly (48 +/- 6 to 58 +/- 5; P < 0.05). Plasma propofol concentration was maintained at the same level between the two measurement points (3.3 +/- 0.7 to 3.3 +/- 0.7 micro g*mL(-1)). There was no relation between BIS change and changes of MEP amplitude and latency, and propofol plasma concentration. CONCLUSION: MEP to the transcranial electrical stimulation under a constant and clinically appropriate blood propofol concentration are not affected by surgical noxious stimuli.     

Clinical assessment of target-controlled infusion of propofol during monitored anesthesia care

PURPOSE: To determine the plasma concentrations of propofol required to achieve different levels of sedation during monitored anesthesia care. METHODS: Sixty ASA I-II, 18-65 yr-old patients, received a target-controlled continuous iv infusion of propofol. The target plasma concentration of propofol (Cpt) was initially set at 0.4 microg x ml(-1). Two minutes after calculated equilibrium between plasma and effect-site concentrations, the Cpt of propofol was increased by 0.2 microg x ml(-1) steps until the patient showed no reaction to squeezing the trapezius. The level of sedation was assessed immediately before each increase in propofol Cpt using the Observer's Assessment of Alertness/Sedation (OAA/S) scale. RESULTS: The Cpt of propofol required to induce lethargic response to name was 1.3 microg x ml(-1) (5 degrees and 95 degrees percentiles: 1.0 - 1.8 microg x ml(-1)), to obtain response after loud and repeated calling name was 1.7 microg x ml(-1) (1.2 - 2.2 microg x ml(-1)), to obtain response after prodding or shaking was 2.0 microg x ml(-1) (1.6 - 2.6 microg x ml(-1)), to obtain response after squeezing the trapezius was 2.4 microg x ml(-1) (1.8 - 3.0 microg x ml(-1)). Patients showed no response after squeezing the trapezius at 2.8 microg x ml(-1) (2.0 - 3.6 microg x ml(-1)). Correlation between Cpt propofol and sedation scores were r = 0.76, P < 0.0001. CONCLUSIONS: Target-controlled infusion of propofol provided easy and safe management of intraoperative sedation, allowing fast and predictable deepening in the level of sedation, while minimizing systemic side effects of intravenous sedation due to the minimal risk of overdosing the drug.     

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.     

Variation of bispectral index under TIVA with propofol in a paediatric population

BACKGROUND: In this prospective observational study, we aim to explore the relationship between age and bispectral index (BIS) values at different plasma concentrations of propofol. METHODS: Fifty children aged from 3 to 15 yr were included. Anaesthesia was induced using a target-controlled infusion of propofol with the Kataria pharmacokinetic model together with a bolus of remifentanil followed by a continuous infusion rate at 0.2 microg kg(-1) min(-1). Target plasma propofol concentration was initially stabilized to 6 microg ml(-1) and continued for 6 min. The target was then decreased and stabilized to 4 microg ml(-1) and then to 2 microg ml(-1). BIS values, plasma propofol concentration, and EEG were continuously recorded. In order to explore the relationship between variations in propofol concentration and the EEG bispectrum, we used a multiple correspondence analysis (MCA). Results are shown in median (range). RESULTS: We found no statistical difference between BIS values with propofol 6 microg ml(-1) [23 (12-40)] and 4 microg ml(-1) [28 (9-67)]. At 2 microg ml(-1), BIS was significantly different [52 (24-71)], but a significant correlation between the age of children and BIS values was found (r2=0.66; P<0.01). There was little change in children's position between 6 and 4 microg ml(-1) in the structure model of the MCA. From 4 to 2 microg ml(-1), the position of children moved only on axis 2. CONCLUSIONS: These results showed the difficulty to interpret BIS values because of the absence of significant change for higher plasma propofol concentration variation or because of the link with age for the lower plasma concentration.     

The relationship between bispectral index and targeted propofol concentration is biphasic in patients with major burns

BACKGROUND: Many pathophysiologic alterations in major burns can cause changes in the distribution of, and perhaps response to, drugs commonly used in anesthesia practice. This study was conducted to assess changes in bispectral index (BIS) caused by increasing the target propofol effect-site concentration during a target-controlled infusion (TCI) in major burns. METHODS: Eighteen patients, ASA physical status 2 or 3, aged from 20 to 55 years old, weighing 50-70 kg, with major burns, scheduled for elective early escharectomy less than a week after injury were recruited. A further 18 ASA physical status class 1 or 2, non-burns, age, sex- and weight-matched adult patients scheduled for elective surgery under general anesthesia were recruited as controls. During anesthesia induction, target propofol effect-site concentrations were increased by increments of 0.5 microg ml(-1) up to 4.5 microg ml(-1). The BIS responses to each target concentration using TCI were compared in both groups. RESULTS: In the burns group, significantly greater BIS values relating to increasing propofol TCI were noted at deeper anesthesia when compared with controls; at > or =3.5 microg ml(-1); mean BIS remained at a plateau of about 50. Patients with burns had higher cardiac indices, and lower hemoglobin and albumin concentrations than the controls. They consumed more vecuronium to maintain the same degree of neuromuscular blockade than the controls. CONCLUSIONS: In major burns, the final biphasic BIS responses appeared to be determined by numerous other variables such as BIS algorithm, TCI performance, and altered propofol pharmacokinetics and pharmacodynamics. According to our results the importance of an individually tailored approach, including careful anesthetic titration, based upon the patient's clinical condition and responses can not be overemphasized.     

Forty-hertz midlatency auditory evoked potential activity predicts wakeful response during desflurane and propofol anesthesia in volunteers.

BACKGROUND: Suppression of response to command commonly indicates unconsciousness and generally occurs at anesthetic concentrations that suppress or eliminate memory formation. The authors sought midlatency auditory evoked potential indices that successfully differentiated wakeful responsiveness and unconsciousness. METHODS: The authors correlated midlatency auditory evoked potential indices with anesthetic concentrations permitting and suppressing response in 22 volunteers anesthetized twice (5 days apart), with desflurane or propofol. They applied stepwise increases of 0.5 vol% end-tidal desflurane or 0.5 microg/ml target plasma concentration of propofol to achieve sedation levels just bracketing wakeful response. Midlatency auditory evoked potentials were recorded, and wakeful response was tested by asking volunteers to squeeze the investigator's hand. The authors measured latencies and amplitudes from raw waveforms and calculated indices from the frequency spectrum and the joint time-frequency spectrogram. They used prediction probability (PK) to rate midlatency auditory evoked potential indices and concentrations of end-tidal desflurane and arterial propofol for prediction of responsiveness. A PK value of 1.00 means perfect prediction and a PK of 0.50 means a correct prediction 50% of the time (e.g., by chance). RESULTS: The approximately 40-Hz power of the frequency spectrum predicted wakefulness better than all latency or amplitude indices, although not all differences were statistically significant. The PK values for approximately 40-Hz power were 0.96 during both desflurane and propofol anesthesia, whereas the PK values for the best-performing latency and amplitude index, latency of the Nb wave, were 0.86 and 0.88 during desflurane and propofol (P = 0.10 for -40-Hz power compared with Nb latency), and for the next highest, latency of the Pb wave, were 0.82 and 0.84 (P < 0.05). The performance of the best combination of amplitude and latency variables was nearly equal to that of approximately 40-Hz power. The approximately 40-Hz power did not provide a significantly better prediction than anesthetic concentration; the PK values for concentrations of desflurane and propofol were 0.91 and 0.94. Changes of 40-Hz power values of 20% (during desflurane) and 16% (during propofol) were associated with a change in probability of nonresponsiveness from 50% to 95%. CONCLUSIONS: The approximately 40-Hz power index and the best combination of amplitude and latency variables perform as well as predictors of response to command during desflurane and propofol anesthesia as the steady-state concentrations of these anesthetic agents. Because clinical conditions may limit measurement of steady-state anesthetic concentrations, or comparable estimates of cerebral concentration, the approximately 40-Hz power could offer advantages for predicting wakeful responsiveness.     

Recovery from rocuronium by sugammadex does not affect motor evoked potentials

Motor evoked potential (MEP) monitoring has been employed to detect the spinal cord injury during spinal, neurosurgical and cardiovascular operations. Muscle relaxants diminish the amplitude of MEP because MEP is the picture of electromyogram. In 5 cases undergoing MEP monitoring, we examined the effect of rocuronium followed by the administration of sugammadex on MEP Anesthesia was induced with propofol (target controlled infusion 3.0-3.5 microg x ml(-1)) and remifentanil 0.15-0.3 microg x kg(-1) x min(-1), and the trachea was intubated with the use of rocuronium 0.6 mg x kg(-1) without any muscle rigidity, bucking and laryngospasm. General anesthesia was maintained by total intravenous anesthesia using propofol and remifentanil with no muscle relaxants. Immediately after the tracheal intubation, sugammadex 4 mg x kg(-1) was intravenously given. The amplitude of MEP was measured just before the administration of rocuronium, immediately after the tracheal intubation, and 1, 2, 3, 5 min following the administration of sugammadex. Sugammadex restored the MEP amplitude, deteriorated by rocuronium, in 3 to 5 min to the level of non-paralytic muscles. In one case, it took 8 min to restore the MEP of hemiparetic leg. Taking these findings into consideration, it is likely that rocuronium might not affect the MEP when reversed by sugammadex, and should be safe for smooth tracheal intubation in patients who need MEP monitoring.     

Amplitudes and intrapatient variability of myogenic motor evoked potentials to transcranial electrical stimulation during ketamine/N2O- and propofol/N2O-based anesthesia

The aim of the current study was to investigate whether there are differences in amplitudes and intrapatient variability of motor evoked potentials to five pulses of transcranial electrical stimulation between ketamine/N2O- and propofol/N2O-based anesthesia. Patients in the propofol group (n = 13) and the ketamine group (n = 13) were anesthetized with 50% N2O in oxygen, fentanyl, and 4 mg/kg/hr of propofol or 1 mg/kg/hr of ketamine, respectively. The level of neuromuscular blockade was maintained at an M-response amplitude of approximately 50% of control. Motor evoked potentials in response to multipulse transcranial electrical stimulation were recorded from the right adductor pollicis brevis muscle, and peak-to-peak amplitude and onset latency of motor evoked potentials were evaluated. To estimate intrapatient variability, the coefficient of variation (standard deviation/mean x 100%) of 24 consecutive responses was determined. Motor evoked potential amplitudes in the ketamine group were significantly larger than in the propofol group (mean, 10th-90th percentile: 380 microV, 129-953 microV; 135 microV, 38-658 microV, respectively; P <.05). There were no significant differences in motor evoked potential latency (mean +/- standard deviation: 20.9 +/- 2.2 msec and 21.4 +/- 2.2 msec, respectively) and coefficient of variation of amplitudes (median [range]: 32% [22-42%] and 26% [18-41%], respectively) and latencies (mean +/- standard deviation: 2.1 +/- 0.7% and 2.1 +/- 0.7%, respectively) between the ketamine and propofol groups. In conclusion, intrapatient variability of motor evoked potentials to multipulse transcranial stimulation is similar between ketamine/N2O- and propofol/N2O-based anesthesia, although motor evoked potential amplitudes are lower during propofol/N2O-based anesthesia than ketamine/N2O-based anesthesia.     

Narcotrend monitoring allows faster emergence and a reduction of drug consumption in propofol-remifentanil anesthesia

BACKGROUND: The Narcotrend is a new electroencephalographic monitor designed to measure depth of anesthesia, based on a six-letter classification from A (awake) to F (increasing burst suppression) including 14 substages. This study was designed to investigate the impact of Narcotrend monitoring on recovery times and propofol consumption in comparison to Bispectral Index (BIS) monitoring or standard anesthetic practice. METHODS: With institutional review board approval and written informed consent, 120 adult patients scheduled to undergo minor orthopedic surgery were randomized to receive a propofol-remifentanil anesthetic controlled by Narcotrend, by BIS(R), or solely by clinical parameters. Anesthesia was induced with 0.4 micro x kg-1 x min-1 remifentanil and a propofol target-controlled infusion at 3.5 microg/ml. After intubation, remifentanil was reduced to 0.2 micro x kg-1 x min-1, whereas the propofol infusion was adjusted according to clinical parameters or to the following target values: during maintenance to D(0) (Narcotrend) or 50 (BIS); 15 min before the end of surgery to C(1) (Narcotrend) or 60 (BIS). Recovery times were recorded by a blinded investigator, and average normalized propofol consumption was calculated from induction and maintenance doses. RESULTS: The groups were comparable for demographic data, duration of anesthesia, and mean remifentanil dosages. Compared with standard practice, patients with Narcotrend or BIS monitoring needed significantly less propofol (standard practice, 6.8 +/- 1.2 mg x kg-1 x h-1 vs. Narcotrend, 4.5 +/- 1.1 mg x kg-1 x h-1 or BIS(R), 4.8 +/- 1.0 mg x kg-1 x h-1; P < 0.001), opened their eyes earlier (9.3 +/- 5.2 vs. 3.4 +/- 2.2 or 3.5 +/- 2.9 min), and were extubated sooner (9.7 +/- 5.3 vs. 3.7 +/- 2.2 or 4.1 +/- 2.9 min). CONCLUSIONS: The results indicate that Narcotrend and BIS monitoring are equally effective to facilitate a significant reduction of recovery times and propofol consumption when used for guidance of propofol titration during a propofol-remifentanil anesthetic.     

异丙酚和异氟醚对全麻手术病人脑干听觉诱发电位影响的比较

目的 比较异丙酚和异氟醚对全麻手术病人脑干听觉诱发电位(BAEP)的影响.方法 择期拟行全麻手术的病人30例,年龄20～50岁,体重44～75 kg,ASA分级Ⅰ或Ⅱ级,随机分为2组(n=15):异丙酚组(P组)和异氟醚组(I组).监测SpO2、PETCO2、BAEP和BIS.麻醉诱导:P组靶控输注异丙酚,血浆靶浓度6μg/kg,I组吸入3%异氟醚,两组静脉注射维库溴铵0.1 mg/kg,气管插管后行机械通气,维持PETCO235～40 mm Hg,SpO298%～100%.P组靶控输注异丙酚,I组吸入异氟醚维持麻醉.分别于麻醉诱导前(T0)、气管插管后BIS达70并维持5 min(T1)和BIS达50并维持5 min(T2)时,记录Ⅰ波、Ⅲ波、Ⅴ波的潜伏期、Ⅰ-Ⅲ、Ⅲ-Ⅴ、Ⅰ-Ⅴ的峰间期.结果 P组Ⅰ波、Ⅲ波、Ⅴ波的潜伏期和Ⅰ-Ⅲ、Ⅲ-Ⅴ、Ⅰ-Ⅴ的峰间期组内比较差异无统计学意义(P＞0.05);与T0时比较,I组T1时Ⅰ波、Ⅲ波、Ⅴ波的潜伏期和Ⅰ-Ⅲ、Ⅲ-Ⅴ、Ⅰ-Ⅴ的峰间期差异无统计学意义(P＞0.05),T2时Ⅲ波、Ⅴ波的潜伏期和Ⅰ-Ⅲ、Ⅲ-Ⅴ、Ⅰ-Ⅴ的峰间期延长(P＜0.05或0.01);与T1时比较,I组T2时Ⅲ波、Ⅴ波的潜伏期和Ⅰ-Ⅲ、Ⅰ-Ⅴ的峰间期延长(P＜0.05或0.01);与P组比较,I组T2时Ⅴ波潜伏期和Ⅰ-Ⅴ峰间期延长(P＜0.05).结论 与异氟醚相比,等效剂量的异丙酚对全麻手术病人BAEP的影响更小,提示其对脑干功能的抑制作用更小.

Abstract：

Objective To compare the effects of propofol versus isoflurane on brainstem auditory evoked potential (BAEP) and explore the difference in the effects of the two anesthetics on the brainstem. Methods Thirty ASA Ⅰ or Ⅱ patients aged 20-50 yr without heating disorder, scheduled for elective surgery performed under general anesthesia were randomly divided into 2 groups (n = 15 each): propofol group (group P) and isoflurane group (group Ⅰ). SpO2, PET CO2, BIS and BAEP were continuously monitored before and during anesthesia. Anesthesia was induced by propofol administered by TCI or isoflurane inhalation. Tracheal intubation was facilitated with vecuronium. The patients were mechanically ventilated. PET CO2 was maintained at 35-40 mm Hg and SpO2 at 98%-100%. After intubation BIS was maintained at 70 and 50 respectively ,the latency of the wave Ⅰ , Ⅱ and Ⅴ and the inter-peak latency (IPL) betwecn wave Ⅰ -Ⅲ , Ⅲ-Ⅴ and Ⅰ -Ⅴ were recorded.Results In group P there was no significant difference in the latency of the wave Ⅰ , Ⅲ and Ⅴ and the IPL between wave Ⅰ - Ⅲ , Ⅲ - Ⅴ and Ⅰ - Ⅴ between the baseline before anesthesia and at BIS 70 and 50. In group Ⅰ the latency of wave Ⅲ and Ⅴ and the IPL between wave Ⅰ - Ⅲ , Ⅲ - Ⅴ and Ⅰ - Ⅴ were significantly longer at BIS 50 than the baseline before anesthesia, while the latency of wave Ⅲ and Ⅴ and the IPL between wave Ⅰ -Ⅲ andⅠ -Ⅴ at BIS 50 were significantly longer than that at BIS 70. At BIS 50 the latency of wave Ⅴ and the IPL between wave Ⅰ -Ⅴ were significantly longer in group Ⅰ than in group P. Conclusion At comparable depth of anesthesia propofol exerts less depressant effects on BAEP indicating less depression of brainstem.     

The influence of intermittent hemodialysis (HD) on bispectral index (scale) (BIS) and serum propofol concentration under postoperative intravenous sedation

We experienced a case of postoperative intravenous sedation with propofol during intermittent hemodialysis (HD), and investigated the correlation between the clinical sedation level based on bispectral index scale (BIS) together with Ramsay score, and the serum concentration of propofol. One adult oral cancer patient (carcinoma of the lower gingiva) with end-stage renal dysfunction needing HD was selected for this study. The day after operation, HD was commenced under intravenous sedation with propofol. Clinical sedation level was assessed using BIS and Ramsay score, and serum propofol concentrations were determined in arterial blood samples. Serum concentrations were measured every 15 times until 51 hours after operation. The initial dose of propofol was set at 3.5 mg x kg(-1) x h(-1) on the basis of clinical symptoms. According to BIS and Ramsay score, sedation level decreased lineally for 1 hour after commencement of HD. In contrast, serum propofol concentration incresed from 1.71 microg x ml(-1) to 2.21 microg x ml(-1). Total serum concentration of propofol was enhanced during HD because of dialytic dehydration, but, according to BIS and Ramsay scores, the possibility was suggested that the fraction of albmin-unbound propofol with pharmacological activities was eliminated or absorbed by membrane during HD.     

Bispectral index decreased to "10" during propofol anesthesia despite the appropriate serum concentration of propofol

We report a case showing a bispectral index (BIS) value "10" during anesthesia maintained with propofol. Vital signs of the patient including blood pressure and heart rate were stable and the depth of anesthesia was considered as adequate. The serum concentration of propofol measured later was 2.5 and 2.2 microg ml(-1) when BIS indicated 10 and 35, respectively. The age of patient was 81 and the BIS values in elderly might decrease in accordance with the reduction of brain function.     

The relationship between the respiratory parameters under spontaneous breathing and effect site propofol concentrations

BACKGROUND: The prediction of the hypnotic states is useful to maintain the adequate anesthesia. During propofol anesthesia, the respiratory depression has been documented in a dose-dependent manner. Therefore, we investigated whether the respiratory depression under the spontaneous breathing reflected the estimated effect site propofol concentrations (Cp) in a dose-dependent fashion. METHODS: We enrolled 12 patients for elective lower limb surgery under combined subarachnoid anesthesia and propofol sedation. The respiratory parameters and BIS were measured at the Cp of 5 microg x ml(-1) followed by the 0.5 microg x ml(-1) decrements until the patients' movement. Effective indices to predict patients' movement were determined by receiver-operator characteristics. RESULTS: The significant correlations within a particular patient between the respiratory parameters and Cp were observed, although those were not between the patients. An EtCO2 of 53 mmHg or greater represents a clinically determinant condition for non-movement of the patients. CONCLUSIONS: We concluded that the respiratory parameters during spontaneous breathing were useful indices to predict the changes in the effect site propofol concentrations and to maintain the adequate anesthetic levels.