地氟烷和七氟烷在稳态条件下对脑氧饱和度的影响

我们研究了七氟烷和地氟烷对局部脑组织氧饱和度（rSO2）的影响。22例经腹行子宫切除术的患者在稳态条件下以随机交叉的方式间隔30分钟吸入七氟烷和地氟烷各15分钟，维持脑电双频指数（bispectral index，BIS）值为40～50。另一组接受同样手术和麻醉的22例患者维持BIS值为20—30。在每种麻醉药15分钟的维持期间，每3分钟记录一次稳态条件下的rSO2、BIS、麻醉药吸入浓度和呼气末浓度、呼气末二氧化碳、SpO2、舒张压和收缩压以及心率。当BIS值维持于40～50或20—30时，两种麻醉药的rSO2均无差异。维持BIS值为40～50和20—30所需地氟烷和七氟烷的MACBIS值分别为1．0和1．2（P=0．004）及1．6和1．8（P〈0．001）。吸入1．6MAC地氟烷的rSO，值（71±13）高于1MAC时的rSO2值（66±10，P〈0．001），吸入1．8MAC七氟烷的rSO2值（72±11）高于1．2MAC时的rSO2值（66±13，P〈0．001）。因此，BIS值等效浓度的地氟烷或七氟烷的rSO，值相似，而提高两种麻醉药的吸入浓度均可增加rSO2值。     

Comparative pharmacodynamic modeling of the electroencephalography-slowing effect of isoflurane, sevoflurane, and desflurane.

BACKGROUND: The most common measure to compare potencies of volatile anesthetics is minimum alveolar concentration (MAC), although this value describes only a single point on a quantal concentration-response curve and most likely reflects more the effects on the spinal cord rather than on the brain. To obtain more complete concentration-response curves for the cerebral effects of isoflurane, sevoflurane, and desflurane, the authors used the spectral edge frequency at the 95th percentile of the power spectrum (SEF95) as a measure of cerebral effect. METHODS: Thirty-nine patients were randomized to isoflurane, sevoflurane, or desflurane groups. After induction with propofol, intubation, and a waiting period, end-tidal anesthetic concentrations were randomly varied between 0.6 and 1.3 MAC, and the EEG was recorded continuously. Population pharmacodynamic modeling was performed using the software package NONMEM. RESULTS: The population mean EC50 values of the final model for SEF95 suppression were 0.66+/-0.08 (+/- SE of estimate) vol% for isoflurane, 1.18+/-0.10 vol% for sevoflurane, and 3.48+/-0.66 vol% for desflurane. The slopes of the concentration-response curves were not significantly different; the common value was lambda = 0.86+/-0.06. The Ke0 value was significantly higher for desflurane (0.61+/-0.11 min(-1)), whereas separate values for isoflurane and sevoflurane yielded no better fit than the common value of 0.29+/-0.04 min(-1). When concentration data were converted into fractions of the respective MAC values, no significant difference of the C50 values for the three anesthetic agents was found. CONCLUSIONS: This study demonstrated that (1) the concentration-response curves for spectral edge frequency slowing have the same slope, and (2) the ratio C50(SEF95)/MAC is the same for all three anesthetic agents. The authors conclude that MAC and MAC multiples, for the three volatile anesthetics studied, are valid representations of the concentration-response curve for anesthetic suppression of SEF95.     

Comparative Pharmacodynamic Modeling of the Electroencephalography-slowing Effect of Isoflurane, Sevoflurane, and Desflurane

Background: The most common measure to compare potencies of volatile anesthetics is minimum alveolar concentration (MAC), although this value describes only a single point on a quantal concentration-response curve and most likely reflects more the effects on the spinal cord rather than on the brain. To obtain more complete concentration-response curves for the cerebral effects of isoflurane, sevoflurane, and desflurane, the authors used the spectral edge frequency at the 95th percentile of the power spectrum (SEF95) as a measure of cerebral effect.

Methods: Thirty-nine patients were randomized to isoflurane, sevoflurane, or desflurane groups. After induction with propofol, intubation, and a waiting period, end-tidal anesthetic concentrations were randomly varied between 0.6 and 1.3 MAC, and the EEG was recorded continuously. Population pharmacodynamic modeling was performed using the software package NONMEM.

Results: The population mean EC50 values of the final model for SEF (95) suppression were 0.66 +/- 0.08 (+/- SE of estimate) vol% for isoflurane, 1.18 +/- 0.10 vol% for sevoflurane, and 3.48 +/- 0.66 vol% for desflurane. The slopes of the concentration-response curves were not significantly different; the common value was [Greek small letter lambda] = 0.86 +/- 0.06. The Ke0 value was significantly higher for desflurane (0.61 +/- 0.11 min-1), whereas separate values for isoflurane and sevoflurane yielded no better fit than the common value of 0.29 +/- 0.04 min (-1). When concentration data were converted into fractions of the respective MAC values, no significant difference of the C50 values for the three anesthetic agents was found.     

Bispectral index and regional cerebral oxygen saturation during propofol/N2O anesthesia

PURPOSE: A study was undertaken to compare the influence of midazolam, isoflurane, and aminophylline (which may antagonize anesthetic action) on bispectral index (BIS) and regional cerebral oxygen saturation (rSO(2)) during propofol/N(2)O anesthesia, and to test the hypothesis that the drug-induced changes in BIS values are accompanied by a change in rSO(2). METHODS: General anesthesia was administered to 36 patients with a continuous infusion of propofol to maintain a BIS value of 40 +/- 5. After baseline recordings, patients were randomly assigned to receive either midazolam, isoflurane, or aminophylline. Bispectral index values, rSO(2) using near-infrared spectroscopy, and hemodynamic parameters were recorded for 60 min. RESULTS: Midazolam (0.05 mg x kg(-1)) significantly decreased the BIS from 47.8 +/- 5.4 to 35.0 +/- 4.5 at five minutes after injection (P < 0.001 vs control) during propofol anesthesia, whereas the rSO(2) was unchanged. Similarly, isoflurane (1.1% end-tidal) decreased the BIS from 42.5 +/- 7.5 to 27.8 +/- 6.9 (P < 0.001) without affecting rSO(2). In contrast, aminophylline (3 mg.kg(-1)) was associated with an increase in BIS from 41.6 +/- 2.1 to 48.3 +/- 9.2 at five minutes after injection (P < 0.05) without affecting rSO(2). CONCLUSIONS: Midazolam or isoflurane-induced decreases in the BIS during propofol anesthesia were not accompanied by a decrease in rSO(2). Aminophylline significantly increased the BIS score during propofol anesthesia, suggesting that aminophylline can antagonize, at least in part, the sedative actions of propofol.     

七氟醚、异氟醚和地氟醚对神经外科手术患者经颅电刺激运动诱发电位的影响

目的 比较七氟醚、异氟醚和地氟醚对神经外科手术患者经颅电刺激运动诱发电位(MEPs)的影响.方法 择期行神经外科手术患者60例,年龄18～64岁,ASA分级Ⅰ或Ⅱ级.随机分为3组(n=20):七氟醚组、异氟醚组和地氟醚组.监测BIS值和经颅电刺激MEPs.调节七氟醚、异氟醚和地氟醚吸入浓度,使其呼气末浓度分别达到0.50、0.75、1.00和1.30 MAC,每一浓度均维持15 min,视为稳态呼气末浓度.于给予吸入麻醉药前(基础状态)和达到各稳态呼气末浓度(T1-4)时,记录MEPs的波幅和潜伏期以及BIS值.记录MEPs波形记录失败情况.结果 与七氟醚组和异氟醚组比较,地氟醚组T1.2时波幅和BIS值降低,T1-4时潜伏期延长(P＜0.05);七氟醚组和异氟醚组各指标比较差异无统计学意义(P＞0.05).七氟醚组、异氟醚和地氟醚组基础状态、T1、T2时的记录失败率均为0;T3时记录失败率分别为0、5%和20%,三组比较差异无统计学意义(P＞0.05);T4时记录失败率分别为5%、20%和45%,与七氟醚组和异氟醚组比较,地氟醚组记录失败率升高(P＜0.05);七氟醚组和异氟醚组比较差异无统计学意义(P＞0.05).结论 地氟醚对神经外科手术患者经颅电刺激MEPs的抑制作用强于七氟醚和异氟醚.术中行MEPs监测时,七氟醚和异氟醚适宜的呼气末浓度为1.00 MAC,地氟醚为0.75～1.00 MAC.     

The bispectral index system in pediatrics--is it related to the end-tidal concentration of inhalation anesthetics?

BACKGROUND AND GOAL OF STUDY: Bispectral Index (BIS) has been used in adults to measure depth of anesthesia using various protocols. Though less investigated in children, there is growing evidence that bispectral index seems adequately calibrated for monitoring the depth of isoflurane and sevoflurane anesthesia in pediatric patients. A range of BIS scores (40-60) has been seen to be an indicator for an acceptable level of hypnosis and anesthesia. Davidson and Czarnecki have reported that, at an end-tidal concentration of 1 MAC, the BIS for halothane was significantly greater than isoflurane (56.5 +/- 8.1 vs. 35.9 +/- 8.5). The explanation given is the fact that the volume concentration of the MAC value is inversely related to the BIS value. Accordingly, it is expected that the BIS value at 1 MAC of desflurane must be less than halothane and isoflurane. MATERIALS AND METHODS: This is a clinical cross-over, prospective, randomized double blinded study. 90 pediatric patients scheduled for below umbilical surgery, under general and caudal analgesia, were allocated into 4 study groups. The BIS values at a relatively equipotent doses of the previously mentioned agents were compared with each other in the same group and between other groups. RESULTS: At a relatively equipotent doses, the mean BIS value for halothane {60.4 +/- 5.6} was significantly higher than isoflurane {45.5 +/- 9.2} and desflurane {38.5 +/- 9.2} P<0.001). Equivalent end-tidal doses of different inhalational anesthetics do not necessarily have the same effects on cortical and sub-cortical functions and consequently on EEG. Conclusion: The use of a relatively equipotent end-tidal concentration of different inhalational agents may result in different BIS values.     

Bispectral index values at sevoflurane concentrations of 1% and 1.5% in lower segment cesarean delivery

Inadequate hypnosis in the absence of opioid analgesia may account for the increased incidence of awareness in cesarean delivery. An end-tidal concentration of 0.5 MAC isoflurane in 50% nitrous oxide (N(2)O) during cesarean delivery resulted in bispectral index (BIS) values >60, the threshold below which consciousness is unlikely. Our aim was to determine the BIS values achieved with the equivalent end-tidal concentration of sevoflurane and to determine if a larger concentration would consistently maintain BIS values <60. Twenty ASA physical status I-II parturients were randomized to receive an end-tidal concentration of either 1% sevoflurane or 1.5% sevoflurane delivered in 50% N(2)O throughout surgery. Thiopental 4 mg/kg was used for anesthetic induction. Morphine 0.1-0.15 mg/kg was administered only after delivery. Mean BIS values in the period between skin incision and neonatal delivery were 61 (95% confidence interval, 57-64) in the 1% sevoflurane group, versus 42 (95% confidence interval, 37-47) in the 1.5% sevoflurane group. BIS values were significantly different between groups at skin incision, uterine incision, delivery, and 10 min after delivery, but not thereafter. Indices of maternal and neonatal outcome were similar between groups. IMPLICATIONS: Bispectral index (BIS) values <60 are consistent with a high probability of unconsciousness. An end-tidal concentration of 1.5% sevoflurane maintained BIS values <60 during cesarean delivery, whereas 1% did not. Adverse effects were not seen with the use of larger concentrations of sevoflurane.     

The relationship between end-tidal isoflurane concentration and electroencephalographic bispectral index during isoflurane/epidural anesthesia

We studied the effects of increases in isoflurane concentration on the bispectral index (BIS) in 16 patients undergoing lower abdominal surgery during isoflurane/epidural anesthesia. In 8 patients, the lungs were ventilated with an air/oxygen mixture (inspired oxygen fraction 0.33) [N(-) group], and in another 8 patients, the lungs were ventilated with 66% nitrous oxide in oxygen [N(+) group]. During surgery, patients received 1.0 MAC (1.15%) end-tidal isoflurane and the BIS was recorded after 10 min of unchanged end-tidal concentration. After this, we increased the end-tidal concentration of isoflurane by 0.2 MAC to 1.8 MAC. At each concentration step, the BIS was recorded again after 10 min of unchanged end-tidal concentration. At isoflurane concentration < 1.4 MAC, the BIS did not change with increasing isoflurane concentration in both groups (BIS values = about 40). In N (-) group, the BIS decreased in all patients at isoflurane concentration > 1.6 MAC. The mean BIS values were 22 (SD 18) at 1.6 MAC and 2(4) at 1.8 MAC, respectively. In N (+) group, the BIS decreased in four patients at isoflurane concentration > 1.6 MAC, and the BIS did not decrease at 1.8 MAC in another four patients. The mean BIS values were 27 (17) at 1.6 MAC and 21(21) at 1.8 MAC. The present data suggest that BIS may not correlate with anesthetic effect of isoflurane at isoflurane concentration > 1.0 MAC.     

The effects of sevoflurane, isoflurane and desflurane on QT interval of the ECG

BACKGROUND AND OBJECTIVE: To determine if there is any significant difference between the effects of desflurane, isoflurane and sevoflurane on the QT interval, QT dispersion, heart rate corrected QT interval and QTc dispersion of the electrocardiogram. METHODS: The study was conducted in a prospective, double blind and randomized manner in a teaching hospital. Ninety ASA I patients, aged 16-50 yr, undergoing general anaesthesia for noncardiac surgery were studied. RESULTS: There was no significant change in QT intervals during the study in any group (P > 0.05). QT dispersion in the sevoflurane group 49+/-14 ms vs. 37+/-10 ms; in the desflurane group 55+/-16 and 62+/-21 ms vs. 35+/-14 ms and in the isoflurane group 54+/-26 and 59+/-24 ms vs. 42+/-19 ms were significantly increased at 3 and 10 min after 1 MAC of steady end-tidal anaesthetic concentration compared with baseline values (P < 0.05). QTc values in the sevoflurane group were 444+/-24 and 435+/-2 1ms vs. 413+/-19 ms (P < 0.05), in the isoflurane group were 450+/-26 and 455+/-34 ms vs. 416+/-34 ms (P < 0.05), in the desflurane group were 450+/-26 and 455+/-34 ms vs. 416+/-34 ms (P < 0.05) at 3 and 10 min after reaching 1 MAC of anaesthetic concentration and significantly increased compared with baseline values. QTc dispersion increased significantly with sevoflurane 62+/-14 ms vs. 45+/-16 ms (P < 0.05); isoflurane 70+/-36 ms at 3 min and 75+/-36 ms at 10 min after reaching 1 MAC of anaesthetic concentration vs. 50+/-24 ms (P < 0.05); desflurane 67+/-25 ms at 3 min and 74+/-27 ms at 10 min after 1 MAC concentration vs. 41+/-22 ms (P < 0.05). CONCLUSION: Sevoflurane, isoflurane and desflurane all prolonged QTd, QTc and QTcd but there were no significant intergroup differences.     

Epidural lidocaine decreases sevoflurane requirement for adequate depth of anesthesia as measured by the Bispectral Index monitor

BACKGROUND: Epidural anesthesia potentiates sedative drug effects and decreases minimum alveolar concentration (MAC). The authors hypothesized that epidural anesthesia also decreases the general anesthetic requirements for adequate depth of anesthesia as measured by Bispectral Index (BIS). METHODS: After premedication with 0.02 mg/kg midazolam and 1 microg/kg fentanyl, 30 patients aged 20-65 yr were randomized in a double-blinded fashion to receive general anesthesia with either intravenous saline placebo or intravenous lidocaine control (1-mg/kg bolus dose; 25 microg x kg(-1) x min(-1)). A matched group was prospectively assigned to receive epidural lidocaine (15 ml; 2%) with intravenous saline placebo. All patients received 4 mg/kg thiopental and 1 mg/kg rocuronium for tracheal intubation. After 10 min of a predetermined end-tidal sevoflurane concentration, BIS was measured. The ED50 of sevoflurane for each group was determined by up-down methodology based on BIS less than 50 (MAC(BIS50)). Plasma lidocaine concentrations were measured. RESULTS: The MAC(BIS50) of sevoflurane (0.59% end tidal) was significantly decreased with lidocaine epidural anesthesia compared with general anesthesia alone (0.92%) or with intravenous lidocaine (1%; P < 0.0001). Plasma lidocaine concentrations in the intravenous lidocaine group (1.9 microg/ml) were similar to those in the epidural lidocaine group (2.0 microg/ml). CONCLUSIONS: Epidural anesthesia reduced by 34% the sevoflurane required for adequate depth of anesthesia. This effect was not a result of systemic lidocaine absorbtion, but may have been caused by deafferentation by epidural anesthesia or direct rostral spread of local anesthetic within the cerebrospinal fluid. Lower-than-expected concentrations of volatile agents may be sufficient during combined epidural-general anesthesia.     

Does epidural anesthesia have general anesthetic effects? A prospective, randomized, double-blind, placebo-controlled trial

BACKGROUND: Clinically, patients require surprisingly low end-tidal concentrations of volatile agents during combined epidural-general anesthesia. Neuraxial anesthesia exhibits sedative properties that may reduce requirements for general anesthesia. The authors tested whether epidural lidocaine reduces volatile anesthetic requirements as measured by the minimum alveolar concentration (MAC) of sevoflurane for noxious testing cephalad to the sensory block. METHODS: In a prospective, randomized, double-blind, placebo-controlled trial, 44 patients received 300 mg epidural lidocaine (group E), epidural saline control (group C), or epidural saline-intravenous lidocaine infusion (group I) after premedication with 0.02 mg/kg midazolam and 1 microg/kg fentanyl. Tracheal intubation followed standard induction with 4 mg/kg thiopental and succinylcholine 1 mg/kg. After 10 min or more of stable end-tidal sevoflurane, 10 s of 50 Hz, 60 mA tetanic electrical stimulation were applied to the fifth cervical dermatome. Predetermined end-tidal sevoflurane concentrations and the MAC for each group were determined by the up-and-down method and probit analysis based on patient movement. RESULTS: MAC of sevoflurane for group E, 0.52+/-0.18% (+/- 95% confidence interval [CI]), differed significantly from group C, 1.18+/-0.18% (P < 0.0005), and from group I, 1.04+/-0.18% (P < 0.001). The plasma lidocaine levels in groups E and I were comparable (2.3+/-1.0 vs. 3.0+/-1.2 microg/ml +/- SD). CONCLUSIONS: Lidocaine epidural anesthesia reduced the MAC of sevoflurane by approximately 50%. This MAC sparing is most likely caused by indirect central effects of spinal deafferentation and not to systemic effects of lidocaine or direct neural blockade. Thus, lower concentrations of volatile agents than those based on standard MAC values may be adequate during combined epidural-general anesthesia.     

The dynamic relationship between end-tidal sevoflurane and isoflurane concentrations and bispectral index and spectral edge frequency of the electroencephalogram.

BACKGROUND: Inhalational anesthetics produce dose-dependent effects on electroencephalogram-derived parameters, such as 95% spectral edge frequency (SEF) and bispectral index (BIS). The authors analyzed the relationship between end-tidal sevoflurane and isoflurane concentrations (FET) and BIS and SEF and determined the speed of onset and offset of effect (t1/2k(e0)). METHODS: Twenty-four patients with American Society of Anesthesiologists physical status I or II were randomly assigned to receive anesthesia with sevoflurane or isoflurane. Several transitions between 0.5 and 1.5 minimum alveolar concentration were performed. BIS and SEF data were analyzed with a combination of an effect compartment and an inhibitory sigmoid Emax model, characterized by t1/2k(e0), the concentration at which 50% depression of the electroencephalogram parameters occurred (IC50), and shape parameters. Parameter values estimated are mean +/- SD. RESULTS: The model adequately described the FET-BIS relationship. Values for t1/2k(e0), derived from the BIS data, were 3.5 +/- 2.0 and 3.2 +/- 0.7 min for sevoflurane and isoflurane, respectively (NS). Equivalent values derived from SEF were 3.1 +/- 2.4 min (sevoflurane) and 2.3 +/- 1.2 min (isoflurane; NS). Values of t1/2k(e0) derived from the SEF were smaller than those from BIS (P < 0.05). IC50 values derived from the BIS were 1.14 +/- 0.31% (sevoflurane) and 0.60 +/- 0.11% (isoflurane; P < 0.05). CONCLUSIONS: The speed of onset and offset of anesthetic effect did not differ between isoflurane and sevoflurane; isoflurane was approximately twice as potent as sevoflurane. The greater values of t1/2k(e0) derived from the BIS data compared with those derived from the SEF data may be related to computational and physiologic delays.     

Temperatures in soda lime during degradation of desflurane, isoflurane, and sevoflurane by desiccated soda lime

Rarely, fire and patient injury result from the degradation of sevoflurane by desiccated Baralyme. The present investigation sought to determine whether high temperatures also arose with sevoflurane use in the presence of desiccated soda lime. We desiccated soda lime by directing a 10 L/min flow of oxygen through fresh absorbent. Using 1140 +/- 30 g (mean +/- sd) of this desiccated absorbent, we filled a single standard absorber canister placed in a standard anesthetic circuit to which we directed a 6 L/min flow of oxygen containing 1.5 minimum alveolar concentration (MAC) desflurane or sevoflurane, or 3.0 MAC desflurane, isoflurane, or sevoflurane (with and without concurrent delivery of 200 mL/min carbon dioxide). In an additional test, 2 canisters (rather than a single canister) containing desiccated absorbent were used and 3.0 MAC sevoflurane was applied. A 3-L reservoir bag served as a surrogate lung, and we ventilated this lung with a minute ventilation of 10 L/min. With desflurane at 1.5 MAC or 3.0 MAC or isoflurane at 3.0 MAC temperatures increased in 20 to 40 min to a peak of 30 degrees C to 45 degrees C and then declined. With 1.5 or 3.0 MAC sevoflurane, temperatures increased to approximately 90 degrees C, after which temperatures declined. Concurrent delivery of carbon dioxide and sevoflurane did not increase the peak temperatures reached. The use of 2 canisters increased the duration but not the peak of increased temperature reached with 3.0 MAC sevoflurane. No fires resulted from degradation of any anesthetic.     

Relationship between minimum alveolar concentration and electroencephalographic bispectral index as well as spectral edge frequency 95 during isoflurane/epidural or sevoflurane/epidural anesthesia]

To investigate the relationship between minimum alveolar concentration (MAC) and electroencephalographic variables, we measured the bispectral index (BIS) and the spectral edge frequency 95 (SEF 95) in 17 patients undergoing elective surgery during isoflurane/epidural (n = 8) or sevoflurane/epidural (n = 9) anesthesia. Patients received 2.0 MAC end-tidal concentrations of isoflurane or sevoflurane, and the BIS and the SEF 95 were recorded after 15 min of an unchanged end-tidal concentration. The concentration of the inhalational agent was decreased to 1.2 MAC, and measurements were repeated again. During isoflurane anesthesia, the BIS increased significantly (3.6 +/- 3.9 at 2.0 MAC, 43.5 +/- 9.2 at 1.2 MAC [mean +/- SD]). In contrast, the BIS did not change significantly during sevoflurane anesthesia (35.3 +/- 8.4 at 2.0 MAC, 42.8 +/- 6.1 at 1.2 MAC). There were significant differences in the BIS and the SEF 95 at 2.0 MAC between isoflurane and sevoflurane groups. In contrast, the BIS and the SEF 95 showed no difference at 1.2 MAC between the groups. These findings suggest that different inhalational anesthetics may have different effects on the BIS and the SEF 95.     

Recovery and Kinetic Characteristics of Desflurane and Sevoflurane in Volunteers after 8-h Exposure, including Kinetics of Degradation Products

Background: Desflurane and sevoflurane permit speedier changes in anesthetic partial pressures than do older halogenated anesthetics. The authors determined the kinetic characteristics of desflurane and sevoflurane and those of compound A [CH2 F-O-C(= CF2)(CF3)], a nephrotoxic degradation product of sevoflurane.

Methods: Volunteers received 1.25 minimum alveolar concentration of desflurane or sevoflurane, each administered for 8 h in a fresh gas inflow of 2 l/min. Inspired (FI) and end-tidal (FA) concentrations of anesthetic and compound A were measured during administration, and FA relative to FAO (the last end-tidal concentration during administration) during elimination. The indices of recovery were also measured.

Results: The ratio FI /FA rapidly approached 1.0, with values greater for sevoflurane (desflurane 1.06 +/- 0.01 vs. sevoflurane 1.11 +/- 0.02, mean +/- SD). The ratio FA /FI for compound A was approximately 0.8. The FA /FAO ratio decreased slightly more rapidly with desflurane than with sevoflurane, and objective measures indicated faster recovery with desflurane: The initial response to command (14 +/- 4 min vs. 28 +/- 8 min [means +/- SD]) and orientation (19 +/- 4 vs. 33 +/- 9 min) was quicker, and recovery was faster as defined by results of the Digit Symbol Substitution, P-deletion, and Trieger tests. Desflurane produced less vomiting (1 [0.5, 3]; median [quartiles] episodes) than did sevoflurane (5 [2.5, 7.5] episodes). The FA /FAO ratio for compound A decreased within 5 min to a constant value of 0.1.     

Changing from Isoflurane to Desflurane toward the End of Anesthesia Does Not Accelerate Recovery in Humans

Background: In an attempt to combine the advantage of the lower solubilities of new inhaled anesthetics with the lesser cost of older anesthetics, some clinicians substitute the former for the latter toward the end of anesthesia. The authors tried to determine whether substituting desflurane for isoflurane in the last 30 min of a 120-min anesthetic would accelerate recovery.

Methods: Five volunteers were anesthetized three times for 2 h using a fresh gas inflow of 2 l/min: 1.25 minimum alveolar concentration (MAC) desflurane, 1.25 MAC isoflurane, and 1.25 MAC isoflurane for 90 min followed by 30 min of desflurane concentrations sufficient to achieve a total of 1.25 MAC equivalent ("crossover"). Recovery from anesthesia was assessed by the time to respond to commands, by orientation, and by tests of cognitive function.

Results: Compared with isoflurane, the crossover technique did not accelerate early or late recovery (P > 0.05). Recovery from isoflurane or the crossover anesthetic was significantly longer than after desflurane (P < 0.05). Times to response to commands for isoflurane, the crossover anesthetic, and desflurane were 23 +/- 5 min (mean +/- SD), 21 +/- 5 min, and 11 +/- 1 min, respectively, and to orientation the times were 27 +/- 7 min, 25 +/- 5 min, and 13 +/- 2 min, respectively. Cognitive test performance returned to reference values 15-30 min sooner after desflurane than after isoflurane or the crossover anesthetic. Isoflurane cognitive test performance did not differ from that with the crossover anesthetic at any time.     

Cerebrovascular reactivity to carbon dioxide is preserved during hypocapnia in children anesthetized with 1.0 MAC, but not with 1.5 MAC desflurane

PURPOSE: Maintenance of cerebrovascular reactivity to CO(2) (CCO(2)R) is important during neurosurgical anesthesia. This study was designed to determine the effect of different desflurane concentrations on CCO(2)R in children. METHODS: Children undergoing urological surgery were enrolled. Anesthesia was induced with sevoflurane in air/oxygen. After intubation, sevoflurane was switched to desflurane. Analgesia was provided with an epidural neuraxial block. Mechanical ventilation was adjusted to an initial EtCO(2) of 30 mmHg. Exogenous CO(2) was used to achieve an EtCO(2) of 40 and 50 mmHg. Patients were randomized to the sequence of desflurane concentration (1.0 and 1.5 MAC) and the EtCO(2). Transcranial Doppler was used to measure middle cerebral artery blood flow velocity (Vmca). Five minutes were allowed to reach steady state after each change in EtCO(2) and 15 min after changing the desflurane concentration. RESULTS: Sixteen patients were studied. The mean age and weight were 3.5 +/- 1.5 yr and 14.4 +/- 3.1 kg, respectively. Mean arterial pressure remained stable throughout the study, while at an EtCO(2) of 50 mmHg, heart rate decreased at both desflurane concentrations (P < 0.05). At 1.0 MAC, Vmca increased from 30 to 40 mmHg (P < 0.05), but not from 40 to 50 mmHg EtCO(2). At 1.5 MAC, Vmca increased between 30 and 50 mmHg (P < 0.05). CONCLUSION: CCO(2)R is preserved during hypocapnia in children anesthetized with 1.0 MAC, but not with 1.5 MAC desflurane. The lack of further increase in Vmca at higher EtCO(2) concentrations implies that desflurane may cause significant cerebral vasodilatation in children. This may have important implications in children with reduced intracranial compliance.     

Sevoflurane decreases bispectral index values more than does halothane at equal MAC multiples

At the minimum alveolar concentration (MAC) of inhaled anesthetics, 50% of subjects move in response to noxious stimulation. Similarly, at MAC-awake, 50% of subjects respond appropriately to command. The bispectral index (BIS) nominally measures the effect of anesthetics on wakefulness or consciousness. We postulated that the use of halothane with a larger MAC-awake/MAC ratio than sevoflurane would produce higher BIS values at comparable levels of MAC. We studied 33 unpremedicated patients anesthetized by inhalation, 18 with sevoflurane and 15 with halothane. We measured BIS before and during anesthesia at 1 MAC, both before and after tracheal intubation facilitated by fentanyl and rocuronium and then at 1.5 MAC. BIS measurements were made after meeting steady-state conditions. No surgery was performed during this study. BIS values in awake patients did not differ between the sevoflurane and halothane groups (96 +/- 2 and 96 +/- 2, mean +/- sd, respectively). At 1 MAC without and with neuromuscular blockade and at 1.5 MAC, BIS values for patients anesthetized with halothane (54 +/- 7, 56 +/- 7, and 49 +/- 7, respectively) exceeded those for patients anesthetized with sevoflurane (34 +/- 6, 34 +/- 6, and 29 +/- 5, respectively) (P < 0.0001). This finding adds to other evidence indicating that BIS is drug specific.     

Ventilatory Response to Hypoxia in Humans: Influences of Subanesthetic Desflurane

Background: At low dose, the halogenated anesthetic agents halothane, isoflurane, and enflurane depress the ventilatory response to isocapnic hypoxia in humans. In the current study, the influence of subanesthetic desflurane (0.1 minimum alveolar concentration [MAC]) on the isocapnic hypoxic ventilatory response was assessed in healthy volunteers during normocapnia and hypercapnia.

Methods: A single hypoxic ventilatory response was obtained at each of 4 target end-tidal partial pressure of oxygen concentrations: 75, 53, 44, and 38 mmHg, before and during 0.1 MAC desflurane administration. Fourteen subjects were tested at a normal end-tidal partial pressure of carbon dioxide (43 mmHg), with 9 subjects tested at an end-tidal carbon dioxide concentration of 49 mmHg (hypercapnia). The hypoxic sensitivity (S) was computed as the slope of the linear regression of inspired minute ventilation (VI) on (100 - SP O2). Values are mean +/-SE.

Results: Sensitivity was unaffected by desflurane during normocapnia (control: S = 0.45+/-0.071 *symbol* min *symbol* sup -1 *symbol* % sup -1 vs. 0.1 MAC desflurane: S = 0.43+/-0.09 1 *symbol* min sup -1 *symbol* % sup -1). With hypercapnia S decreased by 30% during desflurane inhalation (control: S = 0.74+/-0.091 *symbol* min sup -1 *symbol* %1 vs. 0.1 MAC desflurane: S = 0.53+/-0.06 1 *symbol* min sup -1 *symbol* % sup -1; P < 0.05).     

Sevoflurane increases lumbar cerebrospinal fluid pressure in normocapnic patients undergoing transsphenoidal hypophysectomy.

BACKGROUND: The data on the effect of sevoflurane on intracranial pressure in humans are still limited and inconclusive. The authors hypothesized that sevoflurane would increase intracranial pressure as compared to propofoL METHODS: In 20 patients with no evidence of mass effect undergoing transsphenoidal hypophysectomy, anesthesia was induced with intravenous fentanyl and propofol and maintained with 70% nitrous oxide in oxygen and a continuous propofol infusion, 100 microg x kg(-1) x min(-1). The authors assigned patients to two groups randomized to receive only continued propofol infusion (n = 10) or sevoflurane (n = 10) for 20 min. During the 20-min study period, each patient in the sevoflurane group received, in random order, two concentrations (0.5 times the minimum alveolar concentration [MAC] and 1.0 MAC end-tidal) of sevoflurane for 10 min each. The authors continuously monitored lumbar cerebrospinal fluid (CSF) pressure, blood pressure, heart rate, and anesthetic concentrations. RESULTS: Lumbar CSF pressure increased by 2+/-2 mmHg (mean+/-SD) with both 0.5 MAC and 1 MAC of sevoflurane. Cerebral perfusion pressure decreased by 11+/-5 mmHg with 0.5 MAC and by 15+/-4 mmHg with 1.0 MAC of sevoflurane. Systolic blood pressure decreased with both concentrations of sevoflurane. To maintain blood pressure within predetermined limits (within+/-20% of baseline value), phenylephrine was administered to 5 of 10 patients in the sevoflurane group (range = 50-300 microg) and no patients in the propofol group. Lumbar CSF pressure, cerebral perfusion pressure, and systolic blood pressure did not change in the propofol group. CONCLUSIONS: Sevoflurane, at 0.5 and 1.0 MAC, increases lumbar CSF pressure. The changes produced by 1.0 MAC sevoflurane did not differ from those observed in a previous study with 1.0 MAC isoflurane or desflurane.