ISSN:0003-3022    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0003-3022    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundThere are significant physiologic differences between spinal and epidural anesthesia. Consequently, these two types of regional anesthesia may influence thermoregulatory processing differently. Accordingly, in volunteers and in patients, we tested the null hypothesis that the core-temperature thresholds triggering thermoregulatory sweating, vasoconstriction, and shivering are similar during epidural and spinal anesthesia.MethodsSix male volunteers participated on three consecutive study days: epidural or spinal anesthesia were randomly assigned on the 1st and 3rd days (± T10 level); no anesthesia was given on the 2nd day. On each day, the volunteers were initially warmed until they started to sweat, and subsequently cooled by central venous infusion of cold fluid until they shivered. Mean skin temperature was kept constant near 36°C throughout each study. The tympanic membrane temperatures triggering a sweating rate of 40 g · m−2· h−1, a finger flow less than 0.1 ml/min, and a marked and sustained increase in oxygen consumption (± 30%) were considered the thermoregulatory thresholds for sweating, vasoconstriction, and shivering, respectively. Twenty-one patients were randomly assigned to receive epidural (n = 10) or spinal (n = 11) anesthesia for knee and calf surgery (± T10 level). As in the volunteers, the shivering threshold was defined as the tympanic membrane temperature triggering a sustained increase in oxygen consumption.ResultsThe thresholds and ranges were similar during epidural and spinal anesthesia in the volunteers. However, the sweating-to-vasoconstriction (interthreshold) range, the vasoconstriction-to-shivering range, and the sweating-to-shivering range all were significantly increased by regional anesthesia. The shivering thresholds in patients assigned to epidural and spinal anesthesia were virtually identical.ConclusionsComparable sweating, vasoconstriction, and shivering thresholds during epidural and spinal anesthesia suggest that thermoregulatory processing is similar during each type of regional anesthesia. However, thermoregulatory control was impaired during regional anesthesia, as indicated by the significantly enlarged interthreshold and sweating-to-shivering ranges.

ISSN:0003-3022    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundLower core temperatures than usual are required to trigger shivering during epidural and spinal anesthesia, but the etiology of this impairment remains unknown. In this investigation, we propose and test a specific mechanism by which a peripheral action of regional anesthesia might alter centrally mediated thermoregulatory responses. Conduction anesthesia blocks all thermal sensations; however, cold signals are disproportionately affected because at typical leg temperatures mostly cold receptors fire tonically. It thus seems likely that epidural and spinal anesthesia increase the leg temperature perceived by the thermoregulatory system. Because skin temperature reportedly contributes 5–20% to thermoregulatory control, increased apparent (as distinguished from actual) leg temperature would produce a complimentary decrease in the core temperature triggering thermoregulatory shivering. Accordingly, we tested the hypothesis that abnormal tolerance for hypothermia during epidural anesthesia coincides with an increase in apparent leg temperature. We defined apparent temperature as the leg-skin temperature required to induce a reduction in the shivering threshold comparable to that produced by epidural anesthesia.MethodsSix women were studied on 4 randomly ordered days: (1) leg-skin temperature near 32°C; (2) leg-skin temperature near 36°C; (3) leg-skin temperature near 38°C; and (4) epidural anesthesia without leg-warming (leg-skin temperature ± 34°C). At each designated leg temperature, core hypothermia sufficient to evoke shivering was induced by central venous infusion of cold fluid. Upper-body skin temperature was kept constant throughout. In each volunteer, linear regression was used to calculate the correlation between the shivering thresholds on the 3 nonepidural days and concurrent leg temperatures. The slope of these regression equations thus indicated the extent to which leg-warming increased thermoregulatory tolerance for core hypothermia, and was expressed as a percentage leg-skin and leg-tissue contribution to total thermal afferent input. The skin and tissue temperatures that would have been required to produce the observed shivering threshold during epidural anesthesia, the apparent temperatures, were then interpolated from the regression.ResultsThere was a good linear relation between the shivering threshold and leg-skin temperature (r2= 0.94 ± 0.06). The contribution of leg-skin temperature to the shivering threshold was 11 ± 3% of the total thermal input. Apparent leg-skin temperature during epidural anesthesia was 37.8 ± 0.5°C, which exceeded actual leg-skin temperature by ± 4°C. The contribution of leg-tissue temperature to the shivering threshold was 19 ± 7% of the total. Apparent leg-tissue temperature during epidural anesthesia was 37.1 ± 0.4°C, which exceeded actual leg-skin temperature by ± 2°C.ConclusionsBecause leg-skin contributed ± 11% to the shivering threshold, it is unlikely that the entire skin surface contributes at much less than 20%. These data suggest that the shivering threshold during epidural anesthesia is reduced by a specific mechanism, namely that conduction block significantly increases apparent (as distinguished from actual) leg temperature.

ISSN:0003-3022    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundSeveral cases of hypotension have been reported in patients who received angiotensin-converting enzyme inhibitors (ACEIs) before a surgical procedure, suggesting that interactions between ACEIs and anesthesia may be neither beneficial nor predictable. To determine if continuation of ACEI therapy until the morning of surgery leads to an unacceptable decrease in blood pressure on induction, we investigated 51 vascular surgical patients that were chronically treated for hypertension with either captopril or enalapril.MethodsAfter randomization, ACEI therapy was either continued until the morning of surgery or stopped at the time of the preanesthetic visit, at least 12 h (captopril) or 24 h (enalapril) before surgery. Each patient received a standardized anesthetic induction. If systolic blood pressure (monitored using a radial artery cannula) decreased to less than 90 mmHg in response to induction, ephedrine was administered.ResultsA marked decrease in plasma converting-enzyme activity was found in patients who received enalapril until the morning of the surgical procedure, and 100% of them required ephedrine after induction. In patients who received their usual dose of captopril on the morning of surgery, plasma converting-enzyme activity was reduced to a lesser extent (when compared with patients who received enalapril). Finally, in the patients in whom ACEI therapy, either enalapril or captopril, was stopped of the evening before surgery, the incidence of induction-induced hypotension was significantly less when enalapril or captopril therapy has been discontinued.ConclusionsThese data indicate that in hypertensive patients chronically treated with ACEIs, maintenance of therapy until the day of surgery may increase the probability of hypotension at induction.

ISSN:0003-3022    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundThe effects of epidurally administered alfentanil may be due in part to its uptake into the systemic circulation. Therefore we examined the systemic absorption kinetics after epidural injection of alfentanil.MethodsPharmacokinetics were determined using a stable isotope method in ten patients, undergoing lower abdominal surgery under general anesthesia. After epidural injection of 0.68 mg deuterium-labeled alfentanil (alfentanil-d5), 1 mg unlabeled alfentanil was administered over 1 h by an intravenous infusion. Blood samples were collected for 12 h. Concentrations of alfentanil and alfentanil-d5were measured by a combination of gas chromatography and mass fragmentography. The systemic absorption profiles of alfentanil-d5were determined by deconvolution of the plasma alfentanil-d5concentrations with the biexponential unit disposition functions, derived from the intravenous data. In addition, data were analyzed by moment analysis.ResultsThe mean (± SD) steady-state volume of distribution, total plasma clearance, elimination half-life and mean residence time, derived from the unlabeled alfentanil concentration-time data, were 43.2 ± 19.5 1, 418 ± 129 ml/min, 119 ± 34 min, and 103 ± 26 min, respectively. The absorption of alfentanil-d5was monophasic in most patients. The mean systemic availability and mean absorption time derived from the deconvolution data were 100 ± 17% and 114 ± 24 min. The values determined by moment analysis were 107 ± 18% and 112 ± 36 min, respectively.ConclusionsAfter epidural administration alfentanil is slowly absorbed into the general circulation. Resulting plasma concentrations are very low and do not contribute appreciably to the systemic opioid effect.

ISSN:0003-3022    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundThe rate of administration of an intravenous anesthetic induction agent is an important variable determining the total dose required to reach a given endpoint, such as loss of consciousness (LOC). The influence of infusion rate on the dose-response relationship has not been described rigorously. In this study we characterized the effect of different thiopental infusion rates on the times and doses required to reach a clinical (induction) endpoint.MethodsFifty-six healthy, nonpremedicated men, aged 19–59 yr, were randomly assigned to receive one of seven different thiopental infusion rates (40, 60, 75, 150, 300, 600, and 1,200 mg/min). The infusion was continued until the patient dropped a held object, indicating LOC. The infusion rates were selected using a simulation which predicted the relationship between the rate of administration and cumulative dose administered at the time of LOC. Average population pharmacokinetic parameters from a three-compartment thiopental model were combined with an effect-site rate constant for thiopental equilibration of 0.58 min−1and a median effect-site concentration of 13.8 mg/1 from previously published pharmacokinetic and pharmacodynamic models for thiopental. This derived model was used to predict the total amount of thiopental required, at each infusion rate, to produce LOC.ResultsThe observed median effective doses for infusion rates of 40–150 mg/min were similar and ranged from 296 to 318 mg. Dose requirements increased significantly with increasing infusion rates greater than 150 mg/min; median effective doses for infusion rates of 300, 600, and 1,200 mg/min were significantly different from each other (436, 555, and 711 mg, respectively). The original simulation underestimated the observed thiopental doses at all but the lowest infusion rate. A new simulation was performed using a recently developed combined pharmacokinetic-pharmacodynamic model. This model incorporated a four-compartment thiopental pharmacokinetic model with quantal dose-response data to derive an effect-site rate constant for thiopental equilibration of 0.29 min−1and a median effect-site concentration for LOC of 11.3 mg/1. The median thiopental doses predicted by this new simulation under the extreme conditions of a 30-fold range of infusion rates were within 13% of the observed doses.ConclusionsIn this study we quantified the relationship between the rate of thiopental administration and the resultant cumulative thiopental dose necessary to produce LOC. This study validated a novel pharmacokinetic-pharmacodynamic model based on a four-compartment pharmacokinetic model and infusion quantal dose-response data. Finally, we demonstrated that thiopental dose-response relationships are dependent on drug administration rate, and found that the ability to predict this dependence accurately is influenced by the pharmacokinetics, pharmacodynamics, and median effectsite concentration used to simulate the dose-response relationships.

ISSN:0003-3022    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundMost techniques for measuring cerebral blood flow (CBF) can not be performed rapidly enough to detect sudden changes in CBF. However, measurement of internal jugular bulb (IJB) blood velocity may offer real-time information on changes in CBF. In the current study, we measured IJB blood velocity and CBF in anesthetized humans.MethodsIn protocol 1, IJB blood velocity was continuously measured using an intravascular Doppler catheter during cardiac surgery under hypothermic cardiopulmonary bypass (CPB). CBF values obtained with a Kety-Schmidt method using inhalation of 30% argon in oxygen gas were compared with concurrent IJB blood velocity values in ten patients. A 3-French intravascular Doppler catheter was placed in the right IJB, and CBF measurements were made before CPB, in a stable hypothermic period during CPB, at rewarming during CPB, and after CPB. In protocol 2, dimensions of right IJB were observed before and during CPB using an intravascular rotating A scan ultrasonic catheter (5-French) in three patients.ResultsIJB blood velocity responded quickly to changes in arterial pressure or body temperature during CPB. The percent change in IJB blood velocity relative to pre-CPB value showed a good linear correlation with the percent change in CBF (%CBF = 0.87 X %IJB velocity + 17,r= 0.87). The mean difference between percent changes in CBF and IJB blood velocity was −5.6% and the standard deviation was 16%. Despite a large reduction in arterial pressure or IJB pressure, there were no significant changes in the IJB dimension.ConclusionsThe results suggest that IJB blood velocity may represent a clinically useful monitor of changes in CBF in anesthetized humans.

ISSN:0003-3022    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundFlumazenil, a benzodiazepine antagonist, reverses midazolam-induced sedation and amnesia. We designed a double-blind study to evaluate the effects of flumazenil on patient outcome when flumazenil was used to reverse large or small doses of midazolam as part of standardized monitored anesthesia care.MethodsNinety-nine healthy consenting women undergoing breast biopsy procedures with local anesthesia were randomly assigned to one of four treatment groups: group 1, propofol-placebo (control); group 2, propofol-flumazenil; group 3, midazolam-placebo; or group 4, midazolam-flumazenil. All patients received intravenous midazolam 2 mg and intravenous fentanyl 50 μg, followed by an infusion of either propofol 25–150 μg-kg−1. min−1or midazolam 0.5–4 μg · kg−1. min−1. At the end of the operation, patients were intravenously administered either 10 ml saline (groups 1 and 3) or flumazenil 1 mg in 10 ml saline (groups 2 and 4). Amnesia was assessed by determining recall of pictures shown before and after the procedure. Subjective feelings of sedation, anxiety, clumsiness, and fatigue were evaluated using 100-mm visual analogue scales preoperatively and at 30-min intervals in the recovery room. Cognitive function was assessed using the digit-symbol substitution test at similar intervals. Early recovery was evaluated by the ability of the patients to be transferred directly from the operating room to the step-down unit, as well as by times to ambulation and discharge. A standardized questionnaire and telephone interview were used to assess “resedation” and other postdischarge side effects.ResultsFlumazenil (1 mg) enhanced early recovery and picture recall after high-dose (group 4) but not low-dose (group 2) midazolam. Only 32% of patients in group 3 were transferred directly to the step-down unit compared with 85% in group 4 (P< 0.05). Flumazenil significantly improved visual analogue scale and digit-symbol substitution test scores at the 30− and 60-min testing intervals (P< 0.05). At the 90-min interval, there were no significant differences between groups 3 and 4. Compared with group 3 (84 ± 22 min), patients in groups 1, 2, and 4 were ready for discharge significantly earlier (60 ± 23, 65 ± 21, and 67 ± 27 min, respectively) (P< 0.05). However, 33% of the patients in group 4 reported resedation after discharge (vs.0–8% in the other three study groups) (P< 0.05).ConclusionsEarly recovery after breast biopsy procedures with midazolam sedation and flumazenil reversal is similar to recovery after propofol sedation. However, the beneficial effects of flumazenil were apparent only during the first 60 min after the procedure and resedation after discharge is an important consideration in the outpatient setting.

ISSN:0003-3022    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

BackgroundSevoflurane reacts with soda lime, generating degradation products. The concentrations of sevoflurane degradation products in a low-flow circuit have been reported for anesthesia times of less than 5 h. In this study, sevoflurane degradation products generated during low-flow anesthesia exceeding 10 h were examined.MethodsSixteen patients received sevoflurane anesthesia with a fresh gas flow rate of 11/min. In eight patients, soda lime was used as the CO2absorbent; in the other eight patients, Baralyme was used. During anesthesia, the concentrations of degradation products in the circuit, the temperature of the CO2absorbent, inspired and end-tidal sevoflurane concentrations, and the volume of CO2eliminated by the patient were measured. Gas was sampled from the inspiratory limb of the circuit and analyzed by gas chromatography.ResultsTwo degradation products, CF2=C(CF3)—O—CH2F (compound A) and CH3OCF2CH(CF3)OCH2F (compound B), were detected. In the soda lime group, the individual maximum concentration of compound A was 23.6 ± 2.9 (12.0–37.4) ppm. In the Baralyme group, the concentration was 32.0 ± 2.3 (23.5–41.3) ppm. The individual maximum concentration of compound A in the Baralyme group was significant higher than that in the soda lime group. Compound B was detected in two patients, reaching a maximum concentration of 0.2 ppm. The end-tidal sevoflurane concentration, temperature of the CO2absorbent, and volume of CO2eliminated by the patient were the same in both groups.ConclusionsThe degradation products detected were at low concentrations in long-duration, low-flow anesthesia with sevoflurane. Baralyme produced higher concentrations of degradation products than soda lime.

ISSN:0003-3022    

出版商:OVID    

年代:1994

数据来源: OVID