Carbon Monoxide Production from Desflurane, Enflurane, Halothane, Isoflurane, and Sevoflurane with Dry Soda Lime

Background : Previous studies in which volatile anesthetics were exposed to small amounts of dry soda lime, generally controlled at or close to ambient temperatures, have demonstrated a large carbon monoxide (CO) production from desflurane and enflurane, less from isoflurane, and none from halothane and sevoflurane. However, there is a report of increased CO hemoglobin in children who had been induced with sevoflurane that had passed through dry soda lime. Because this clinical report appears to be inconsistent with existing laboratory work, the authors investigated CO production from volatile anesthetics more realistically simulating conditions in clinical absorbers.

Methods : Each agent, 2.5 or 5% in 2 l/min oxygen, were passed for 2 h through a Drager absorber canister (bottom to top) filled with dried soda lime (Dragersorb 800). CO concentrations were continuously measured at the absorber outlet. CO production was calculated. Experiments were performed in ambient air (19-20[degrees]C). The absorbent temperature was not controlled.

Results : Carbon monoxide production peaked initially and was highest with desflurane (507 +/- 70, 656 +/- 59 ml CO), followed by enflurane (460 +/- 41, 475 +/- 99 ml CO), isoflurane (176 +/- 2.8, 227 +/- 21 ml CO), sevoflurane (34 +/- 1, 104 +/- 4 ml CO), and halothane (22 +/- 3, 20 +/- 1 ml CO) (mean +/- SD at 2.5 and 5%, respectively).     

地氟醚、七氟醚与安氟醚低流量麻醉临床观察

比较地氟醚、七氟醚、安氟醚用于低流麻醉时ＢＰ和ＨＲ改变,苏醒过程、不良反应以及药物费用。方法：４２例ＡＳＡＩⅠ－Ⅱ级择期腹部外科手术病人随机分成地氟醚,安氟醚和七氟醚三组。麻醉诱导后连接Ｃｉｃｅｒｏ麻醉机。降低新鲜气流,地氟醚和安氟醚为０．３－０．５Ｌ／ｍｉｎ,七氟醚为０．８－１．０Ｌ／ｍｉｎ,从回路呼出端向麻醉机回路内注入液吸入麻醉药４－５分钟内使三组病人呼气末麻醉药浓度达到１ＭＡＣ左右,即地氟     

七氟醚 异氟醚和安氟醚对离体兔胸主动脉环收缩功能的影响

目的：比较吸入麻醉药七氟醚、异氟醚和安氟醚对离体兔胸主动清脉环收缩功能的影响。方法：将取自２４只新西兰白兔的离体胸主动脉环随机分为七氟醚、异氟醚、安氟醚三组。衔用ＰＥ产生主动张力,稳定后分别吹入上述三种吸入麻醉药七氟醚记录不同浓度时的血管张力。结果：与基础值（麻醉药浓度为零时）相比,血管张力在三种吸入麻醉药２为１．０、１．５、２．０ＭＡＣ时均降低（Ｐ值分别小于０．０５、０．０５、０．０１）。安氟醚     

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.     

Desflurane, Sevoflurane, and Isoflurane Impair Canine Left Ventricular-Arterial Coupling and Mechanical Efficiency

Background: The effects of desflurane, sevoflurane, and isoflurane on left ventricular-arterial coupling and mechanical efficiency were examined and compared in acutely instrumented dogs.

Methods: Twenty-four open-chest, barbiturate-anesthetized dogs were instrumented for measurement of aortic and left ventricular (LV) pressure (micromanometer-tipped catheter), dP/dtmax, and LV volume (conductance catheter). Myocardial contractility was assessed with the end-systolic pressure-volume relation (Ees) and preload recruitable stroke work (Msw) generated from a series of LV pressure-volume diagrams. Left ventricular-arterial coupling and mechanical efficiency were determined by the ratio of Ees to effective arterial elastance (Ea; the ratio of end-systolic arterial pressure to stroke volume) and the ratio of stroke work (SW) to pressure-volume area (PVA), respectively.

Results: Desflurane, sevoflurane, and isoflurane reduced heart rate, mean arterial pressure, and left ventricular systolic pressure. All three anesthetics caused similar decreases in myocardial contractility and left ventricular afterload, as indicated by reductions in Ees, Msw, and dP/dtmax and Ea, respectively. Despite causing simultaneous declines in Ees and Ea, desflurane decreased Ees /Ea (1.02+/-0.16 during control to 0.62+/-0.14 at 1.2 minimum alveolar concentration) and SW/PVA (0.51+/-0.04 during control to 0.43+/-0.05 at 1.2 minimum alveolar concentration). Similar results were observed with sevoflurane and isoflurane.     

Enflurane, Isoflurane and the Eye

The intra-ocular pressure was monitored in ophthalmological patients in whom nitrous oxide/oxygen anaesthesia was supplemented with an inspired concentration of 1% enflurane (10 patients) or 0.7% isoflurane (10 patients). These concentrations are proportionate to 0.6 MAC in oxygen. Both agents caused a significant decrease in intra-ocular pressure, enflurane by a mean of 3.1 mmHg (0.4 kPa) and isoflurane by 2.1 mmHg (0.3 kPa). There was no significant difference between agents. Isoflurane offers an alternative to enflurane in surgery when intra-ocular pressure is of importance.     

Effect of the Physical Properties of Isoflurane, Sevoflurane, and Desflurane on Pulmonary Resistance in a Laboratory Lung Model

Background: Airway resistance depends not only on an airway's geometry but also on flow rate, and gas density and viscosity. A recent study showed that at clinically relevant concentrations, the mixtures of volatile agents with air and oxygen and oxygen-nitrogen affected the density of the mixture. The goal of the current study was to investigate the effect of different minimum alveolar concentrations (MACs) of three commonly used volatile agents, isoflurane, sevoflurane, and desflurane, on the measurements of airway resistance.

Methods: A two-chamber fixed-resistance test lung was connected to an anesthesia machine using the volume control mode of ventilation. Pulmonary resistance was calculated at baseline (25% oxygen in air); at 1.0, 1.5, and 2.0 MAC; and also at the same concentrations, 1.2% and 4%, of isoflurane, sevoflurane, and desflurane mixtures with 25% oxygen in air. The analysis of variance test for repeated measures and probabilities for post hoc Tukey and least significant difference tests were used.

Results: Isoflurane affected pulmonary resistance only at 2 MAC. Sevoflurane caused a significant increase of pulmonary resistance at 1.5 and 2 MAC, whereas desflurane caused the greatest increase in pulmonary resistance at all MAC values used. At 1.2% concentration, no difference from the baseline resistance was observed, whereas at 4%, the three agents produced similar increases of pulmonary resistance.     

The Effect of Sevoflurane and Desflurane on Upper Airway Reactivity

Background: Although bronchial reactivity can be assessed by changes in airway resistance, there is no well-accepted measure of upper airway reactivity during anesthesia. The authors used the stimulus of endotracheal tube cuff inflation and deflation to assess changes in airway reactivity in patients anesthetized with sevoflurane and desflurane.

Methods: Sixty-four patients classified as American Society of Anesthesiologists physical status I or II participated in this randomized, double-blind study. Patients were anesthetized with either sevoflurane or desflurane at 1.0 and 1.8 minimum alveolar concentration (MAC). The trachea was stimulated by inflating the endotracheal tube cuff. A blinded observer assessed the severity of patient response to the stimulus and changes in hemodynamic variables. The process was repeated at the second MAC treatment condition.

Results: At 1.0 MAC, patients anesthetized with desflurane had a more intense response and a greater likelihood of significant coughing and associated hemodynamic changes (both at P < 0.05). At 1.8 MAC, sevoflurane and desflurane both suppressed clinically significant responses to tracheal stimulation. Interrater reliability was excellent for this measure of upper airway reactivity (P < 0.001).     

In Vitro Effects of Desflurane, Sevoflurane, Isoflurane, and Halothane in Isolated Human Right Atria

Background: Direct myocardial effects of volatile anesthetics have been studied in various animal species in vitro. This study evaluated the effects of equianesthetic concentrations of desflurane, sevoflurane, isoflurane, and halothane on contractile parameters of isolated human atria in vitro.

Methods: Human right atrial trabeculae, obtained from patients undergoing coronary bypass surgery, were studied in an oxygenated (95% O2-5% CO2) Tyrode's modified solution ([Ca2+]o = 2.0 mM, 30[degrees]C, stimulation frequency 0.5 Hz). The effects of equianesthetic concentrations (0.5, 1, 1.5, 2, and 2.5 minimum alveolar concentration [MAC]) of desflurane, sevoflurane, isoflurane, and halothane on inotropic and lusitropic parameters of isometric twitches were measured.

Results: Isoflurane, sevoflurane, and desflurane induced a moderate concentration-dependent decrease in active isometric force, which was significantly lower than that induced by halothane. In the presence of adrenoceptor blockade, the desflurane-induced decrease in peak of the positive force derivative and time to peak force became comparable to those induced by isoflurane. Halothane induced a concentration-dependent decrease in time to half-relaxation and a contraction-relaxation coupling parameter significantly greater than those induced by isoflurane, sevoflurane and desflurane.     

Renal Responses to Low-flow Desflurane, Sevoflurane, and Propofol in Patients

Background: The contributing factors that result in significant, postoperative proteinuria and glucosuria after low-flow isoflurane and sevoflurane anesthesia are unknown. The present study compared renal responses after anesthesia with desflurane (negligible metabolism), sevoflurane, or intravenous propofol.

Methods: Informed consent was obtained from 52 patients with American Society of Anesthesiologists physical status I-III (aged 36-81 yr). Patients with diabetes or renal insufficiency were excluded. Desflurane (n = 20) or sevoflurane (n = 22), without nitrous oxide, was given at 1 l/min fresh gas flow for elective surgical procedures lasting more than 2 h; 10 patients received propofol without nitrous oxide as the primary anesthetic. Blood and urine chemistries were obtained before surgery. Blood and 24-h urine collections were obtained for 3 days after surgery and were analyzed for liver and renal indices.

Results: Length of surgery averaged ~ 300 min (range, 136-750 min), minimum alveolar concentration-hour averaged 4.3 (range, 1.2-11.0), and infusion rates of propofol were 99-168 [mu]g [middle dot] kg-1 [middle dot] min-1. Plasma creatinine concentration did not change, plasma blood urea nitrogen decreased significantly, and significant increases in urine glucose, protein, and albumin occurred similarly in all groups. Mean (+/- SD) postoperative urine glucose values for day 1 after desflurane, sevoflurane, and propofol were 1.4 +/- 3.0, 1.1 +/- 2.1, and 1.9 +/- 2.6 g/d (normal, < 0.5 g/d). The average daily protein/creatinine ratios for postoperative days 2-3 after desflurane, sevoflurane, and propofol were 240 +/- 187, 272 +/- 234, and 344 +/- 243 (normal,< 150 mg/g). Regardless of anesthetic, there were significantly greater urine protein concentrations after surgical procedures in central versus peripheral regions.     

Concentration-Effect Relations, Prediction Probabilities (Pk), and Signal-to-noise Ratios of Different Electroencephalographic Parameters during Administration of Desflurane, Isoflurane, and Sevoflurane in Rats

Background: The authors investigated the suitability of different electroencephalographic parameters to quantify the anesthetic effect of desflurane, isoflurane, and sevoflurane in rats.

Methods: Ten male Sprague-Dawley rats were anesthetized in a randomized crossover design with maximum values of 11% desflurane, 2.1% isoflurane, and 3.5% sevoflurane. The electroencephalogram was recorded with implanted electrodes and a wireless telemetry system. Concentration-effect relations and signal-to-noise ratios were determined for the approximate entropy and for the median frequency and the spectral edge frequency, which were modified to account for spikes and burst suppression. The prediction probability Pk with respect to the response to a painful stimulus was determined.

Results: All drugs produced deep anesthesia with burst suppression and no response at the highest concentrations. The occurrence of spikes and burst suppression made a modification of median frequency and spectral edge frequency necessary to obtain Pk values greater than 0.5 and monotonic sigmoid concentration-effect relations. The Pk values were between 0.89 and 0.98, with significantly higher values for modified median frequency and spectral edge frequency during desflurane and sevoflurane. The signal-to-noise ratios were between 3.0 and 6.4 dB, with significantly better values for modified spectral edge frequency and approximate entropy during sevoflurane.     

安氟醚,异氟醚对肝酶水平的影响

以氧化亚氮吸入麻醉为对照，对血清肝酶值的变化为依据，估价安氟醚，异醚对肝酶的影响。４６例成人（均无肝胆疾患，肝酶血清均在正常范围，不包括肝胆手术）分为安氟醚组，异氟醚组和氧化亚氮组，在麻醉前及手术后，１，４，１０ｄ抽静脉血检测ＧＰＴ，ＧＯＴ和ＬＤＨ值，结果：安氟醚，异氟醚术后转氨酶均较术前有所增加，安氟醚组对照组比较无显著性差异（Ｐ＞０．１以上）；异氟醚组与对照组相比，术后４ｄ，１０ｄ，ＧＰＴ有显     

代氟醚和安氟醚低流量循环密闭吸入全麻的临床观察

使用低流量循环密闭回路内注入给药法，比较１ＭＡＣ代氟醚和安氟醚各１４例维持全麻时循环动力苏醒情况和不良反应。结果；代氟醚在维持阶段对心血管系统的抑制较安氟醚为轻，很可能和代氟醚能使交感神经兴奋性增加有关。     

Isoflurane and Enflurane in Long Anaesthesias for Plastic Microsurgery

Isoflurane and enflurane as main anaesthetics at 0.5-0.7% end-tidal concentrations in 70% N2O/30% O2 supplemented with fentanyl maintained smooth basal anaesthesia in ASA I-II patients during long (6-11 h) plastic surgery (n = 7 + 6) as well as during shorter (2-4 h) operations (n = 5 + 5). There were no statistically significant differences in haemodynamic parameters between isoflurane and enflurane patients, although mean arterial pressure was somewhat lower and heart rate higher in the isoflurane patients during the course of long anaesthesias. Both isoflurane and enflurane patients had to be given extra colloids and occasionally vasodilators to maintain peripheral temperature during the long anaesthesias. No clinically adverse renal or hepatic effects were seen, but the liver enzyme activities of four isoflurane and enflurane patients increased after the long anaesthesias. The highest serum inorganic fluoride concentration was 44 mumol/l in the enflurane patients and 5.6 mumol/l in the isoflurane patients.     

The Magnitude and Time Course of Vecuronium Potentiation by Desflurane Versus Isoflurane

Background: Preliminary studies suggest that desflurane and isoflurane potentiate the action of muscle relaxants equally. However, variability between subjects may confound these comparisons. A crossover study was performed in volunteers on the ability of desflurane and isoflurane to potentiate the neuromuscular effect of vecuronium, to influence its duration of action, and on the magnitude and time course of reversal of potentiation when anesthesia was withdrawn.

Methods: Adductor pollicis twitch tension was monitored in 16 volunteers given 1.25 MAC desflurane on one occasion, and 1.25 MAC isoflurane on another. In eight subjects, vecuronium bolus dose potency was determined using a two-dose dose-response technique; the vecuronium infusion dose requirement to achieve 85% twitch depression also was determined. Also in these subjects, the magnitude and time course of spontaneous neuromuscular recovery were determined when the anesthetic was withdrawn while maintaining a constant vecuronium infusion. In the other eight subjects, the time course of action of 100 micro gram/kg vecuronium was determined.

Results: Vecuronium's ED50 and infusion requirement to maintain 85% twitch depression were 20% less during desflurane, compared to isoflurane, anesthesia; vecuronium plasma clearance was similar during the two anesthetics. After 100 micro gram/kg vecuronium, onset was faster and recovery was longer during desflurane anesthesia. When the end-tidal anesthetic concentration was abruptly reduced from 1.25 to 0.75 MAC, twitch tension increased similarly ([nearly equal] 15% of control), and time for the twitch tension to reach 90% of the final change was similar ([nearly equal] 30 min) with both anesthetics. Decreasing anesthetic concentration from 0.75 to 0.25 MAC increased twitch tension by 46 plus/minus 10% and 25 plus/minus 7% of control (mean plus/minus SD, P < 0.001) with desflurane and isoflurane, respectively; 90% response times for these changes were 31 plus/minus 10 min and 18 plus/minus 7 min (P < 0.05), respectively.     

异氟醚和地氟醚对罗库溴铵肌松作用的影响

目的：观察１．０ＭＡＣ异氟醚或地氟醚对罗库溴铵增效作用的影响。方法：选择１８例择期手术病人随机分为地氟醚和异氟醚组，每组在静脉诱导麻醉后，先测得维持９０％肌松并达到稳定后罗库溴铵的注射速率，然后吸入异氟醚或地氟醚，使呼气末浓度为１．０ＭＡＣ，再调整罗库溴铵的注入速率，维持９０％的肌松，观察吸入全麻后罗库溴铵的注射速率随时间变化的趋势。结果：异氟醚、地氟醚均显著降低了罗库溴铵的注入速率，且随吸入时间     

Direct Cerebral Vasodilatory Effects of Sevoflurane and Isoflurane

Background: The effect of volatile anesthetics on cerebral blood flow depends on the balance between the indirect vasoconstrictive action secondary to flow-metabolism coupling and the agent's intrinsic vasodilatory action. This study compared the direct cerebral vasodilatory actions of 0.5 and 1.5 minimum alveolar concentration (MAC) sevoflurane and isoflurane during an propofol-induced isoelectric electroencephalogram.

Methods: Twenty patients aged 20-62 yr with American Society of Anesthesiologists physical status I or II requiring general anesthesia for routine spinal surgery were recruited. In addition to routine monitoring, a transcranial Doppler ultrasound was used to measure blood flow velocity in the middle cerebral artery, and an electroencephalograph to measure brain electrical activity. Anesthesia was induced with propofol 2.5 mg/kg, fentanyl 2 [mu]g/kg, and atracurium 0.5 mg/kg, and a propofol infusion was used to achieve electroencephalographic isoelectricity. End-tidal carbon dioxide, blood pressure, and temperature were maintained constant throughout the study period. Cerebral blood flow velocity, mean blood pressure, and heart rate were recorded after 20 min of isoelectric encephalogram. Patients were then assigned to receive either age-adjusted 0.5 MAC (0.8-1%) or 1.5 MAC (2.4-3%) end-tidal sevoflurane; or age-adjusted 0.5 MAC (0.5-0.7%) or 1.5 MAC (1.5-2%) end-tidal isoflurane. After 15 min of unchanged end-tidal concentration, the variables were measured again. The concentration of the inhalational agent was increased or decreased as appropriate, and all measurements were repeated again. All measurements were performed before the start of surgery. An infusion of 0.01% phenylephrine was used as necessary to maintain mean arterial pressure at baseline levels.

Results: Although both agents increased blood flow velocity in the middle cerebral artery at 0.5 and 1.5 MAC, this increase was significantly less during sevoflurane anesthesia (4 +/- 3 and 17 +/- 3% at 0.5 and 1.5 MAC sevoflurane; 19 +/- 3 and 72 +/- 9% at 0.5 and 1.5 MAC isoflurane [mean +/- SD]; P < 0.05). All patients required phenylephrine (100-300 [mu]g) to maintain mean arterial pressure within 20% of baseline during 1.5 MAC anesthesia.     

Initial Contractile Response of Isolated Rat Heart Cells to Halothane, Enflurane, and Isoflurane

Background: In several beating cardiac muscle preparations, a short-lived increase in twitch tension or amplitude has been observed when they were exposed abruptly to solutions containing halothane or enflurane. As exposure to the anesthetics was continued, the expected negative inotropic effect became evident after the short-lived increase in twitch. No such increase in twitch has been reported during exposure to isoflurane. It has been hypothesized that this short-lived increase in twitch is caused by an enhancement of calcium release from the sarcoplasmic reticulum, but other mechanisms have not been excluded.

Methods: Freshly isolated, single rat ventricular cells were stimulated to beat at room temperature and abruptly exposed to solutions containing halothane (0.25-0.64 mM), enflurane (0.69-1 mM), or isoflurane (0.31-0.54 mM). During these exposures, twitch amplitude was measured and intracellular calcium concentration was followed using the calcium-sensitive dye indo-1. In some experiments, the whole-cell patch-clamp technique was used to measure membrane current. In addition, in several cells the sarcoplasmic reticulum calcium content was assessed through the response to brief pulses of caffeine.

Results: Both the twitch amplitude and the intracellular calcium transient were increased temporarily in cells abruptly exposed to halothane or enflurane. No such behavior was found with isoflurane. After continued exposure to all three agents, both the twitch amplitude and the calcium transient were less than control. During the beats exhibiting an increase in twitch, no alteration in the relation between cell length (twitch amplitude) and the intracellular calcium transient was found compared with control conditions. In addition, the temporary increase in twitch amplitude occurred in cells contracting under voltage-clamp control when halothane was introduced, and it was not associated with any increase in the calcium current. The sarcoplasmic reticulum calcium content at the time of the halothane-induced increase in twitch also was not increased.