ISSN:0003-3022    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

BackgroundAfter upper abdominal surgery, patients have been observed to have alterations in respiratory movements of the rib cage and abdomen and respiratory shifts in pleural and abdominal pressure that suggest dysfunction of the diaphragm. The validity of making such deductions about diaphragm function from these observations is open to discussion.MethodsIn eight adult patients, American Society of Anesthesiologists physical status 2, scheduled for elective cardiac surgery, we measured respiratory rate, tidal volume, rib cage and abdominal cross-section changes, and esophageal (Pes) and gastric (Pga) pressures preoperatively, 1 day postoperatively, and 5 days postoperatively. These data were analyzed in detail by following the variables through each respiratory cycle.ResultsMean Delta Pga/Delta Pesdecreased from 0.73 preoperatively to -0.56 1 day postoperatively and recovered to 0.47 5 days postoperatively. Plots of Pesagainst Pgaand rib cage against abdominal expansion (Konno-Mead diagrams) were constructed. Six patients showed a postoperative pattern of breathing similar to that seen in patients who have undergone abdominal surgery: a decrease in the ratio of delta Pga/delta Pesand a shift toward rib cage expansion, with an increase in breathing rate and a decrease in tidal volume. This change was accomplished in most cases by the use of abdominal muscles in expiration with an increase in inspiratory intercostal muscle action without an increase in diaphragm activation, that is, a shift in the normal balance of respiratory muscle use in favor of muscles other than the diaphragm. A different ventilatory pattern was observed in the other two patients, consisting of minimal rib cage excursion and a large abdominal excursion. In these cases tidal volume was generated largely by contraction and relaxation of abdominal muscles with probable reduction in diaphragm activity. In addition, five patients exhibited positive changes in Pesat the end of inspiration that corresponded to closure of the upper airway, relaxation of inspiratory muscles, and subsequent opening of the airway with sudden exhalation, producing a grunt.ConclusionsIndirect measurements of respiratory muscle action based on pressure and chest wall motion are easier than are assessments based on implanted electromyogram electrodes and sonomicrometers that measure electric activity and muscle length, respectively, directly. Interpretation requires numerous assumptions and detailed analysis of phase relations among the variables. In patients after thoracic surgery, however, these measurements strongly point to a shift in the distribution of motor output toward muscles other than the diaphragm.

ISSN:0003-3022    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

BackgroundComputer-assisted target controlled infusions (TCI) result in prediction errors that are influenced by pharmacokinetic variability among and within patients. it is uncertain whether the selection of a propofol pharmacokinetic parameter set significantly influences drug concentrations and clinical acceptability.MethodsThirty patients received similar propofol TCI regimens after being randomly allocated to one of three parameter sets. Arterial and venous concentrations were measured and prediction errors calculated from pooled and intrasubject data.ResultsArterial propofol concentrations in the Dyck group revealed greater bias (mean 43%) than did those in the Marsh (-1%) and Tackley (-3%) groups. The Dyck group also showed greater inaccuracy (mean:47%) than the Marsh (29%) and Tackley (24%) groups. There was little tendency for measured concentrations to vary from targeted values over time (divergence). Variability about an observed mean in individual patients (wobble) was low. Venous propofol concentrations were initially much less than arterial concentrations, but this difference decreased over time.ConclusionsAlthough it may be preferable to administer propofol TCI by using a locally derived parameter set, it is acceptable to use a model from elsewhere. The Marsh and Tackley models produced equally good performance and are appropriate for propofol TCI within the range of 3-6 micro gram/ml. The Dyck model was less accurate at maintaining anesthetic concentrations, possibly because it was derived from low concentrations. Concentrations in blood, the most sensitive indicators of performance, demonstrated differences among the parameter sets. Clinically, TCI worked well, and by clinical criteria, the choice of pharmacokinetic model did not appear to make a difference.

ISSN:0003-3022    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

BackgroundRopivacaine is a new amide local anesthetic structurally similar to bupivacaine and mepivacaine. Previous studies showed that ropivacaine has a similar clinical effect as bupivacaine with regard to sensory anesthesia and slightly less motor blockade than bupivacaine. Ropivacaine appears to be less cardiotoxic and arrhythmogenic than bupivacaine. The clinical and pharmacokinetic effects of 0.5% ropivacaine (5 mg/ml) versus 0.5% bupivacaine (5 mg/ml) when used epidurally for elective cesarean section were investigated.MethodsUsing a randomized, double-blind study design, 60 ASA physical status 1 or 2 term parturients presenting for elective cesarean section received either 0.5% bupivacaine (150 mg) or 0.5% ropivacaine (150 mg) epidurally in appropriate fractionated doses over a 10-min period. Onset, duration, and regression of sensory and motor blockade were noted until complete resolution was observed. Quality of intraoperative anesthesia and abdominal wall muscle relaxation were noted. Maternal plasma concentrations of local anesthetic were determined before anesthetic administration and 5, 10, 20, 30, and 60 min and 2, 3, 6, 8, 12, and 24 h after drug injection in 20 subjects. Umbilical cord blood was obtained at time of delivery for acid-base values and determination of the free and total plasma concentration of local anesthetic. Neonates also were examined for neurobehavioral assessments by Scanlon's and Neurologic and Adaptive Capacity Scores at 2 and 24 h after delivery.ResultsAll patients received satisfactory anesthesia for operation. The onset, duration, and regression of sensory blockade were similar for both groups. Onset of degree 1 and 2 motor blockade was faster, and duration of degree 1 motor block was longer in the group receiving bupivacaine. Hemodynamic sequelae were similar between groups. All neonates had 5-min Apgar scores of 7 or greater and normal acid-base values and neurobehavioral assessments. Pharmacokinetic analysis showed that the Cmaxwas similar for both drugs (1.3 plus/minus 0.09 for ropivacaine and 1.1 plus/minus 0.09 micro gram/ml for bupivacaine). The T1/2 of the terminal decline in plasma concentration was shorter for ropivacaine versus bupivacaine (5.2 plus/minus 0.60 versus 10.9 plus/minus 1.08 h, respectively; P < 0.01). The free (i.e., unbound) concentrations of ropivacaine were approximately twice those of bupivacaine in both maternal and neonatal blood at the time of delivery. The ratio of umbilical vein to maternal vein concentration of unbound drug was 0.72 for ropivacaine and 0.69 for bupivacaine.ConclusionsRopivacaine, 0.5%, epidurally provided satisfactory and similar sensory anesthesia compared to 0.5% bupivacaine for elective cesarean section. The Cmaxwas similar for both drugs, although the terminal half-life of ropivacaine was significantly shorter, and the blood concentrations of free ropivacaine were significantly greater than that for bupivacaine. These values were less than concentrations shown to be toxic in animals.

ISSN:0003-3022    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

BackgroundPremedication with oral clonidine may improve the quality and duration of lidocaine spinal anesthesia, but this effect has not been examined in a quantitative fashion.MethodsEight volunteers received 50 mg lidocaine (1.5% dextrose free) both with and without 0.2 mg oral clonidine 1.5 h before spinal anesthesia in a randomized, double-blind, placebo-controlled, crossover fashion. Sensory block was assessed by pinprick, transcutaneous electric stimulation equivalent to surgical incision, and duration of tolerance to pneumatic thigh tourniquet. Motor block at the quadriceps and gastrocnemius muscles was assessed by isometric force dynamometry. Episodes of bradycardia, hypotension, and sedation were recorded.ResultsRegression of pinprick was unchanged with clonidine. However, duration of tolerance to electric stimulation was increased at the knee (28 plus/minus 24 min) and ankle (31 plus/minus 28 min) with clonidine (P < 0.05). The duration of tolerance to tourniquet-induced pain was increased with clonidine (14 plus/minus 12 min; P < 0.05). The duration of motor block was increased at the quadriceps (20 plus/minus 13 min) and gastrocnemius (33 plus/minus 24 min) muscle groups with clonidine (P < 0.05). Although clonidine decreased systolic blood pressure (13 plus/minus 4 mmHg, P < 0.003) and heart rate (13 plus/minus 5 beats/min; P = 0.02), no subjects had hypotension or bradycardia. The incidence of sedation was greater with clonidine than with plain lidocaine (50% vs. 0%, P < 0.04).DiscussionPremedication with oral clonidine prolonged sensory and motor block from lidocaine spinal anesthesia. The exact mechanism whereby oral clonidine prolongs spinal anesthesia remains to be determined.

ISSN:0003-3022    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

BackgroundMinimum alveolar concentration (MAC) is decreased in pregnancy, but it is not known how quickly after delivery MAC returns to normal. We measured the MAC of isoflurane in a group of women undergoing elective tubal ligation after delivery.MethodsAfter delivery, 20 patients underwent inhalational induction of anesthesia with isoflurane and tracheal intubation. MAC was determined in each patient by observing the response to a 10-s, 50-Hz, 80-mA transcutaneous tetanic electric stimulus to the ulnar nerve at various concentrations of isoflurane. The end-tidal concentration of isoflurane was kept constant for at least 10 min before each stimulus, and the concentration of isoflurane was ultimately varied in steps of 0.05 vol% until we obtained a sequence of three alternate responses: move-not move-move or not move-move-not move. The MAC for each subject was taken as the mean of the two concentrations just permitting and just preventing movement. A venous blood sample was taken immediately before induction of anesthesia for measurement of progesterone concentration. MAC was compared with time after delivery and plasma progesterone concentrations by Kendall's rank correlation.ResultsThere was a positive correlation between MAC and the time after delivery (P < 0.001). The median MAC of isoflurane was 0.775 vol% (range 0.675-0.775 vol%) in five women 24-36 h postpartum. MAC was more variable, 0.825 vol% (0.675-0.975 vol%) in nine women 36-72 h postpartum, whereas six patients more than 72 h postpartum had a MAC of 1.125 vol% (1.025-1.175 vol%). The correlation between MAC and plasma progesterone concentration was almost statistically significant (P = 0.060).ConclusionsThe MAC of isoflurane was reduced in women 24-36 h postpartum and gradually increased to normal values by 72 h postpartum.

ISSN:0003-3022    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

BackgroundThe minimum alveolar concentration (MAC) of volatile anesthetics is decreased during pregnancy, but MAC in the early postpartum period has not been reported. The aim of this study was to determine the MAC of isoflurane and to evaluate the relation between MAC and serum progesterone and beta-endorphin in patients after delivery.MethodsEight patients undergoing elective bilateral tubal ligation during general anesthesia in the early postpartum period (< 12 h postpartum) and eight patients undergoing this procedure in the late postpartum period (12-25 h postpartum) were studied. Eight patients undergoing bilateral tubal ligation more than 6 weeks after delivery served as control subjects. Anesthesia was induced with propofol and maintained with isoflurane in oxygen to a steady end-tidal concentration of 0.8-1.0 vol% for 10 min. Reaction to a standardized electric stimulation applied to the forearm was graded as positive (gross or delayed movement) or negative. By using the bracketing technique, the concentration of isoflurane was increased or decreased by 0.1 vol%, depending on the positive or negative responses.ResultsThe MAC (mean plus/minus SD) in patients in the early postpartum period was significantly less (0.75 plus/minus 0.17 vol%) than that in control subjects (1.04 plus/minus 0.12 vol%; P < 0.01) and that in patients in the late postpartum period (0.95 plus/minus 0.2 vol%; P < 0.05). The difference in MAC values between late postpartum and control was not significant (P > 0.05). There was an inverse correlation between progesterone concentration postpartum and time after delivery (r = -0.527; P = 0.036), but no relation between beta-endorphin and time after delivery (r = 0.089; P = 0.744). There was no correlation between plasma progesterone or beta-endorphin and MAC by multiple regression (r = 0.166; P = 0.950).ConclusionsIsoflurane MAC remains 28% less than normal within the 1st 12 h postpartum and then returns to normal 12-25 h after delivery.

ISSN:0003-3022    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

BackgroundSevoflurane has low blood and tissue solubility and is metabolized to free fluoride and hexafluoroisopropanol (HFIP). Although sevoflurane uptake and distribution and fluoride formation have been described, the pharmacokinetics of HFIP formation and elimination are incompletely understood. This investigation comprehensively characterized the simultaneous disposition of sevoflurane, fluoride, and HFIP.MethodsTen patients within 30% of ideal body weight who provided institutional review board-approved informed consent received sevoflurane (2.7% end-tidal, 1.3 MAC) in oxygen for 3 h after propofol induction, after which anesthesia was maintained with propofol, fentanyl, and nitrous oxide. Sevoflurane and unconjugated and total HFIP concentrations in blood were determined during anesthesia and for 8 h thereafter. Plasma and urine fluoride and total HFIP concentrations were measured during and through 96 h after anesthetic administration. Fluoride and HFIP were quantitated using an ion-selective electrode and by gas chromatography, respectively.ResultsThe total sevoflurane dose, calculated from the pulmonary uptake rate, was 88.8 plus/minus 9.1 mmol. Sevoflurane was rapidly metabolized to the primary metabolites fluoride and HFIP, which were eliminated in urine. HFIP circulated in blood primarily as a glucuronide conjugate, with unconjugated HFIP less or equal to 15% of total HFIP concentrations. In blood, peak unconjugated HFIP concentrations were less than 1% of peak seroflurane concentrations. Apparent renal fluoride and HFIP clearances (mean plus/minus SE) were 51.8 plus/minus 4.5 and 52.6 plus/minus 6.1 ml/min, and apparent elimination half-lives were 21.4 plus/minus 2.8 and 20.1 plus/minus 2.6 h, respectively. Renal HFIP and net fluoride excretion were 4,300 plus/minus 540 and 3,300 plus/minus 540 micro mol. Compared with the estimated sevoflurane uptake, 4.9 plus/minus 0.5% of the dose taken up was eliminated in the urine as HFIP. For fluoride, 3.7 plus/minus 0.4% of the sevoflurane dose taken up was eliminated in the urine, which, because a portion of fluoride is sequestered in bone, corresponded to approximately 5.6% of the sevoflurane dose metabolized to fluoride.ConclusionsSevoflurane was rapidly metabolized to fluoride and HFIP, which was rapidly glucuronidated and eliminated in the urine. The overall extent of sevoflurane metabolism was approximately 5%.

ISSN:0003-3022    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

BackgroundSevoflurane is metabolized to free fluoride and hexafluoroisopropanol (HFIP). Cytochrome P450 2E1 is the major isoform responsible for sevoflurane metabolism by human liver microsomes in vitro. This investigation tested the hypothesis that P450 2E1 is predominantly responsible for sevoflurane metabolism in vivo. Disulfiram, which is converted in vivo to a selective inhibitor of P450 2E1, was used as a metabolic probe for P450 2E1.MethodsTwenty-one patients within 30% of ideal body weight, who provided institutional review board-approved informed consent and were randomized to receive disulfiram (500 mg oral, n = 11) or nothing (control, n = 10) the night before surgery, were evaluated. All patients received sevoflurane (2.7% end-tidal, 1.3 MAC) in oxygen for 3 h after propofol induction. Thereafter, sevoflurane was discontinued, and anesthesia was maintained with propofol, fentanyl, and nitrous oxide. Blood sevoflurane concentrations during anesthesia and for 8 h thereafter were measured by gas chromatography. Plasma and urine fluoride and total (unconjugated plus glucuronidated) HFIP concentrations were measured by an ion-selective electrode and by gas chromatography, respectively, during anesthesia and for 96 h postoperatively.ResultsPatient groups were similar with respect to age, weight, sex, case duration, and intraoperative blood loss. The total sevoflurane dose, measured by cumulative end-tidal sevoflurane concentrations (3.7 plus/minus 0.1 MAC-h; mean plus/minus SE), total pulmonary uptake, and blood sevoflurane concentrations, was similar in both groups. In control patients, plasma fluoride and HFIP concentrations were increased compared to baseline values intraoperatively and postoperatively for the first 48 and 60 h, respectively. Disulfiram treatment significantly diminished this increase. Plasma fluoride concentrations increased from 2.1 plus/minus 0.3 micro Meter (baseline) to 36.2 plus/minus 3.9 micro Meter (peak) in control patients, but only from 1.7 plus/minus 0.2 to 17.0 plus/minus 1.6 micro Meter in disulfiram-treated patients (P < 0.05 compared with control patients). Peak plasma HFIP concentrations were 39.8 plus/minus 2.6 and 14.4 plus/minus 1.1 micro Meter in control and disulfiram-treated patients (P < 0.05), respectively. Areas under the plasma fluoride- and HFIP-time curves also were diminished significantly to 22% and 20% of control patients, respectively, by disulfiram treatment. Urinary excretion of fluoride and HFIP was similarly significantly diminished in disulfiram-treated patients. Cumulative 96-h fluoride and HFIP excretion in disulfiram-treated patients was 1,080 plus/minus 210 and 960 plus/minus 240 micro mol, respectively, compared to 3,950 plus/minus 560 and 4,300 plus/minus 540 micro mol in control patients (P < 0.05).ConclusionsDisulfiram, an effective P450 2E1 inhibitor, substantially decreased fluoride ion and HFIP production during and after sevoflurane anesthesia. These results suggest that P450 2E1 is a predominant P450 isoform responsible for human sevoflurane metabolism in vivo.

ISSN:0003-3022    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

BackgroundAlthough a positive inotropic effect of hypertonic saline has been demonstrated in isolated cardiac tissue as well as in animal preparations, no information exists about a possible positive inotropic action of hypertonic saline in humans. The aim of this investigation was to determine whether a clinically relevant positive inotropic effect can be demonstrated in humans.MethodsTwenty-six patients without cardiovascular disease were randomized to receive 4 ml/kg of either 7.2% hypertonic saline/6% hetastarch or 6% hetastarch (control) at a rate of 1 ml *symbol* kg sup -1 *symbol* min sup -1 while under general endotracheal anesthesia. Transesophageal echocardiography was used to evaluate left ventricular function. Arterial pressure, heart rate, and left ventricular end-systolic and end-diastolic diameter, area, and wall thickness were measured immediately before and after administration of either solution. Fractional area change, end-systolic wall stress, and the area under the end-systolic pressure-length relationship curve (ESPLRarea) were calculated. ESPLRareawas used to assess left ventricular contractility.ResultsAdministration of hypertonic saline/hetastarch resulted in a significant decrease of mean arterial pressure and end-systolic wall stress from 77 plus/minus 14 (mean plus/minus SD) to 64 plus/minus 17 mmHg (P < 0.01) and from 52 plus/minus 14 to 32 plus/minus 11 103dyne/cm2(P > 0.01), respectively. End-diastolic area and fractional area change increased from 16.5 plus/minus 2.9 to 21.7 plus/minus 3.3 cm2(P < 0.01) and from 0.53 plus/minus 0.07 to 0.70 plus/minus 0.06 (P < 0.01), respectively, whereas there was only a minor change of ESPLRareafrom 38 plus/minus 13 to 44 plus/minus 13 mmHg.cm (P < 0.05).ConclusionsThe apparent improvement of left ventricular systolic function in response to hypertonic saline/hetastarch is caused mainly by the combined effect of increased left ventricular preload and reduced left ventricular afterload. A possible positive inotropic action of hypertonic saline/hetastarch is not likely to be clinically relevant.

ISSN:0003-3022    

出版商:OVID    

年代:1995

数据来源: OVID