ISSN:0003-3022    

出版商:OVID    

年代:1997

数据来源: OVID

ISSN:0003-3022    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

BackgroundCricoid cartilage pressure induced to prevent pulmonary aspiration from regurgitation of gastric contents has been recommended, and its efficacy requires a force greater than 40 Newtons. For regurgitation to occur, both an increase in gastric pressure and relaxation of the lower esophageal sphincter (LES) are necessary. However, the effect of cricoid cartilage pressure on the LES is unknown. This study evaluated the effects of cricoid cartilage pressure on LES in human volunteers.MethodsLower esophageal sphincter and esophageal barrier pressures (which equals LES pressure‐gastric pressure) were measured using a manometric method in eight unanesthetized volunteers (4 men, 4 women) classified as American Society of Anesthesiologists physical status 1. The force applied to the cricoid cartilage was measured continuously, and LES pressure was recorded at a cricoid force of 20 and 40 Newtons.ResultsCricoid pressure decreased LES pressure from 24 +/‐ 3 mmHg to 15 +/‐ 4 mmHg at a force of 20 Newtons (P < 0.05) and to 12 +/‐ 4 mmHg with a force of 40 Newtons (P < 0.01).ConclusionsThese findings may explain the occurrence of pulmonary aspiration before tracheal intubation despite application of cricoid cartilage pressure.

ISSN:0003-3022    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

BackgroundPrevious studies have reported conflicting results concerning the influence of age and gender on the pharmacokinetics and pharmacodynamics of fentanyl, alfentanil, and sufentanil. The aim of this study was to determine the influence of age and gender on the pharmacokinetics and pharmacodynamics of the new short‐acting opioid remifentanil.MethodsSixty‐five healthy adults (38 men and 27 women) ages 20 to 85 y received remifentanil by constant‐rate infusion of 1 to 8 micro gram [centered dot] kg sup ‐1 [centered dot] min sup ‐1 for 4 to 20 min. Frequent arterial blood samples were drawn and assayed for remifentanil concentration. The electroencephalogram was used as a measure of drug effect. Population pharmacokinetic and pharmacodynamic modeling was performed using the software package NONMEM. The influence of volunteer covariates were analyzed using a generalized additive model. The performances of the simple (without covariates) and complex (with covariates) models were evaluated prospectively in an additional 15 healthy participants ages 41 to 84 y.ResultsThe parameters for the simple three‐compartment pharmacokinetic model were V1= 4.98 l, V2= 9.01 l, V3= 6.54 l, Cl1= 2.46 l/min, Cl2= 1.69 l/min, and Cl3= 0.065 l/min. Age and lean body mass were significant covariates. From the ages of 20 to 85 y, V1and Cl1decreased by approximately 25% and 33%, respectively. The parameters for the simple sigmoid Emaxpharmacodynamic model were ke0= 0.516 min sup ‐1, E0= 20 Hz, Emax= 5.62 Hz, EC50= 11.2 ng/ml, and gamma = 2.51. Age was a significant covariate of EC50and ke0, with both decreasing by approximately 50% for the age range studied. The complex pharmacokinetic‐pharmacodynamic model performed better than did the simple model when applied prospectively.ConclusionsThis study identified (1) an effect of age on the pharmacokinetics and pharmacodynamics of remifentanil; (2) an effect of lean body mass on the pharmacokinetic parameters; and (3) no influence of gender on any pharmacokinetic or pharmacodynamic parameter.

ISSN:0003-3022    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

BackgroundThe pharmacokinetics and pharmacodynamics of remifentanil were studied in 65 healthy volunteers using the electroencephalogram (EEG) to measure the opioid effect.[1]In a companion article, the authors developed complex population pharmacokinetic and pharmacodynamic models that incorporated age and lean body mass (LBM) as significant covariates and characterized intersubject pharmacokinetic and pharmacodynamic variability. In the present article, the authors determined whether remifentanil dosing should be adjusted according to age and LBM, or whether these covariate effects were overshadowed by the interindividual variability present in the pharmacokinetics and pharmacodynamics.MethodsBased on the typical pharmacokinetic and pharmacodynamic parameters, nomograms for bolus dose and infusion rates at each age and LBM were derived. Three populations of 500 individuals each, ages 20, 50, and 80 yr, were simulated base on the interindividual variances in model parameters as estimated by the NONMEM software package. The peak EEG effect in response to a bolus, the steady‐state EEG effect in response to an infusion, and the time course of drug effect were examined in each of the three populations. Simulations were performed to examine the time necessary to achieve a 20%, 50%, and 80% decrease in remifentanil effect site concentration after a variable‐length infusion. The variability in the time for a 50% decrease in effect site concentrations was examined in each of the three simulated populations. Titratability using a constant‐rate infusion was also examined.ResultsAfter a bolus dose, the age‐related changes in V1and ke0nearly offset each other. The peak effect site concentration reached after a bolus dose does not depend on age. However, the peak effect site concentration occurs later in elderly individuals. Because the EEG shows increased brain sensitivity to opioids with increasing age, an 80‐yr‐old person required approximately one half the bolus dose of a 20‐yr old of similar LBM to reach the same peak EEG effect. Failure to adjust the bolus dose for age resulted in a more rapid onset of EEG effect and prolonged duration of EEG effect in the simulated elderly population. The infusion rate required to maintain 50% EEG effect in a typical 80‐yr‐old is approximately one third that required in a typical 20‐yr‐old. Failure to adjust the infusion rate for age resulted in a more rapid onset of EEG effect and more profound steady‐state EEG effect in the simulated elderly population. The typical times required for remifentanil effect site concentrations to decrease by 20%, 50%, and 80% after prolonged administration are rapid and little affected by age or duration of infusion. These simulations suggest that the time required for a decrease in effect site concentrations will be more variable in the elderly. As a result, elderly patients may occasionally have a slower emergence from anesthesia than expected. A step change in the remifentanil infusion rate resulted in a rapid and predictable change of EEG effect in both the young and the elderly.ConclusionsBased on the EEG model, age and LBM are significant demographic factors that must be considered when determining a dosage regimen for remifentanil. This remains true even when interindividual pharmacokinetic and pharmacodynamic variability are incorporated in the analysis.

ISSN:0003-3022    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

BackgroundGlossopharyngeal nerve (GPN) blocks may provide reliable analgesia for awake direct laryngoscopy, although this has not been evaluated prospectively. This study was designed to determine if GPN blocks provide a superior route of local anesthetic administration for awake direct laryngoscopy as measured by hemodynamic, gag, and subjective pain responses.MethodsA prospective, randomized, single‐blinded, crossover design was used. All participants (n = 11) were anesthesiologists. Three routes of local anesthetic administration were evaluated: 2 min of 2% viscous lidocaine swish and gargle (S&G); S&G combined with 10% lidocaine spray (S&G/spray); and S&G combined with 1% lidocaine bilateral GPN blocks (S&G/block; anterior tonsillar pillar method). Five minutes after the local anesthetic was administered, laryngoscopy was performed and sustained for 20 s. Noninvasive hemodynamic measurements and serum lidocaine concentrations were determined. Visual analogue scale scores and a poststudy questionnaire were used to assess participants' ability to tolerate local anesthetic administration and laryngoscopy and their choice for use in clinical practice.ResultsNo significant hemodynamic changes were observed, although there was a modest increase (< 15%) in heart rate in the S&G/block group in the first minute after laryngoscopy. Serum lidocaine concentrations were higher (P < 0.05) in the S&G/block group at 5 and 10 min (0.5 +/‐ 0.1 and 1.0 +/‐ 0.2 micro gram/ml) compared with the S&G group. Participants' visual analogue scale scores, which assessed their ability to tolerate laryngoscopy, showed that S&G (5.4 +/‐ 0.9) resulted in more discomfort (P < 0.05) than either S&G/spray (3.5 +/‐ 0.9) or S&G/block (3.3 +/‐ 0.7). The laryngoscopist's visual analogue scale scores, which assessed the ease of visualization, revealed a trend (P < 0.08) toward less coughing and gagging with S&G/spray (1.8 +/‐ 0.9) compared with S&G (4.0 +/‐ 1.3) and S&G/block (3.7 +/‐ 1.1). Oropharyngeal discomfort lasting 24 h or more was reported by 91% of participants after S&G/block, whereas no participant reported oropharyngeal discomfort after S&G or S&G/spray. Significantly more participants (73%) indicated their preference for using S&G/spray in future clinical practice compared with S&G (P < 0.01) and S&G/block (P <0.05).ConclusionsGlossopharyngeal nerve blocks do not provide a superior route of local anesthetic administration for awake direct laryngoscopy. Two minutes of 2% viscous lidocaine S&G followed by 10% lidocaine spray was the anesthetic route preferred by participants and laryngoscopists.

ISSN:0003-3022    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

BackgroundAlthough ischemic injury to the spinal cord is a well‐known complication of aortic surgery, no metabolic markers have been identified as predictors of an adverse outcome. This study evaluated the effect of cerebrospinal fluid (CSF) drainage, with and without distal femoral perfusion or moderate hypothermia on blood and CSF lactate concentrations and CSF pressure during thoracoabdominal aortic aneurysm surgery.MethodsThree nonconcurrent groups of patients were studied prospectively: patients with normal body temperature (35 degrees Celsius) but without distal femoral bypass (n = 6), patients with normal body temperature with bypass (n = 7), and patients with hypothermia (30 degrees Celsius) and bypass (n = 8). In all patients, CSF pressure was recorded before, during, and after aortic cross‐clamping. During the surgical repair, CSF drainage was performed using a 4‐Fr intrathecal silicone catheter. Blood and CSF lactate concentrations were measured throughout the operation.ResultsSignificant increases in blood (490%) and CSF (173%) lactate concentrations were observed during and after thoracic aortic occlusion in patients with normothermia and no bypass (P < 0.02 and 0.05, respectively). Distal perfusion attenuated the increase in both blood and CSF lactate (P < 0.01), and a further reduction was achieved with hypothermia of 30 degrees Celsius (P < 0.001). Patients who became paraplegic showed a greater increase in CSF lactate concentrations after aortic clamp release compared with those who suffered no neurological damage (275% vs. 123% of baseline; P < 0.05). Increased CSF pressure of 42–60% (P < 0.005) was noted soon after thoracic aortic occlusion, both with and without distal femoral bypass.ConclusionsIncremental reductions in CSF lactate concentrations were achieved using distal femoral bypass and hypothermia. The reduction in CSF lactate correlated with the methods used to protect the spinal cord during thoracoabdominal aortic aneurysm surgery and was associated with better outcome. Decompression by distal bypass of the hemodynamic overload caused by aortic occlusion was insufficient to eliminate the acute increase in CSF pressure. Cerebrospinal fluid lactate measurements during high aortic surgery may accurately represent the spinal cord metabolic balance.

ISSN:0003-3022    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

BackgroundThe results from studies of muscle relaxants show wide variations among institutions. The authors hypothesized that some of this variability could be explained by differences in duration of nerve stimulation before drug administration (stabilization period).MethodsTrain‐of‐four stimulation was applied every 12 s to both ulnar nerves and adductor pollicis twitch tension was measured in anesthetized participants given 30 micro gram/kg vecuronium. In phase 1, the stabilization period was > 30 min for both extremities. In phases 2–4, stabilization period was 20 min for one extremity and 2 min for the other. In addition, in phase 3, a 2‐s 50‐Hz tetanus initiated the 2‐min stimulation period; in phase 4, duration of tetanus was 5 s. Twitch recovery was recorded until stable for more than 15 min. Time to 25% recovery (clinical duration) was calculated based on two indices: predrug and final (recovery) twitch tension. Values for onset and clinical duration were compared by paired parametric and nonparametric tests.ResultsIn phase 1, predrug and recovery twitch tension were similar in each extremity, and onset and clinical duration did not differ between extremities, permitting paired comparisons in remaining studies. In phase 2, onset was more rapid with 20‐min of prestimulation. With 20‐min prestimulation, predrug and recovery twitch tension were similar; with 2‐min prestimulation, recovery twitch tension exceeded predrug values. When referenced to predrug twitch tension, clinical duration was shorter with 2‐min, than with 20‐min prestimulation. Initiating stimulation with 2‐s or 5‐s 50‐Hz tetani (phases 3, 4) abolished differences between extremities in onset and recovery.ConclusionsWith only train‐of‐four stimulation (no tetani), onset and clinical duration vary with duration of prestimulation, suggesting that a brief period of predrug stimulation is inadequate. However, lengthy prestimulation may be impractical in clinical studies. Tetanic stimulation for 2 or 5 s obviates the need for prolonged stabilization during studies of muscle relaxants.

ISSN:0003-3022    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

BackgroundDue to potential neurologic sequelae, the risk:benefit ratio of thoracic epidural analgesia is controversial. Surprisingly, however, few available data address neurologic complications. The incidence of neurologic complications occurring after thoracic epidural catheterization was studied in patients scheduled for abdominal or abdominothoracic surgery.MethodsA total of 4,185 patients were studied, including 2,059 during the prospective phase of the study and 2,126 during the retrospective phase. After thoracic epidural catheterization, all patients received general anesthesia. Patients' neurologic status was assessed by an anesthesiologist using clinical criteria after operation and after epidural catheter removal. If neurologic complications were suspected, a neurologist was consulted. The incidence of specific complications was compared for different thoracic puncture sites: upper (T3/4–6/7), mid (T7/8–8/9), and lower (T9/10–11/12) catheter insertion levels.ResultsThe overall incidence of complications after thoracic epidural catheterization was 3.1% (n = 128). This included dural perforation (0.7%; n = 30); unsuccessful catheter placement (1.1%; n = 45); postoperative radicular type pain (0.2%; n = 9), responsive to catheter withdrawal in all cases; and peripheral nerve lesions (0.6%; n = 24), 0.3% (n = 14) of which were peroneal nerve palsies probably related to surgical positioning or other transient peripheral nerve lesions (0.2%; n = 10). No signs suggesting epidural hematoma were recognized, and there were no permanent sensory or motor defects attributable to epidural catheterization. Unintentional dural perforation was observed significantly more often in the lower (3.4%) than in the mid (0.9%), or upper (0.4%) thoracic region. A single patient experienced severe respiratory depression after receiving epidural buprenorphine but recovered without sequelae.ConclusionsThoracic epidural catheterization for abdominal and thoracoabdominal surgery is not associated with a high incidence of serious neurologic complications. In fact, the incidence of puncture‐ and catheter‐related complications is less in the mid and upper than in lower thoracic region, and the predicted maximum risk for permanent neurologic complications (upper bound of the 95% confidence interval) is 0.07%.

ISSN:0003-3022    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

BackgroundAnesthetic induction and maintenance with propofol are associated with decreased blood pressure that is, in part, due to decreased peripheral resistance. Several possible mechanisms whereby propofol could reduce peripheral resistance include a direct action of propofol on vascular smooth muscle, an inhibition of sympathetic activity to the vasculature, or both. This study examined these two possibilities in humans by measuring the forearm vascular responses to infusions of propofol into the brachial artery (study 1) and by determining the forearm arterial and venous responses to systemic (intravenous) infusions of propofol after sympathetic denervation of the forearm by stellate blockade (study 2).MethodsBilateral forearm venous occlusion piethysmography was used to examine forearm vascular resistance (FVR) and forearm vein compliance (FVC). Study 1 used infusion of intralipid (time control) and propofol at rates between 83 and 664 micro gram/min into the brachial artery of 11 conscious persons and compared responses to arterial infusions of sodium nitroprusside (SNP) at 0.3, 3.0, and 10 micro gram/min. Venous blood from the infusion arm was assayed for plasma propofol concentrations. In study 2, after left stellate block (12 ml 0.25% bupivacaine + 1% lidocaine), six participants were anesthetized and maintained with propofol infusions of 125 and 200 micro gram [centered dot] kg sup ‐1 [centered dot] min sup ‐1. Simultaneous right forearm (unblocked) blood flow dynamics served as the time control. In three additional conscious participants, intrabrachial artery infusions of SNP and nitroglycerin, both at 10 micro gram/min, were performed before and after stellate blockade of the left forearm to determine whether the sympathetically denervated forearm vessels could dilate beyond the level produced by denervation alone.ResultsIn study 1, infusion of intralipid or propofol into the brachial artery did not change FVR or FVC. Sodium nitroprusside significantly decreased FVR in a dose‐dependent manner by 22 +/‐ 5%, 65 +/‐ 3%, and 78 +/‐ 2% (mean +/‐ SEM) but did not change FVC. During the incremental propofol infusions, plasma propofol concentrations increased from 0.2 to 10.1 micro gram/ml and averaged 7.4 +/‐ 1.1 micro gram/ml during the highest infusion rate. In study 2, stellate ganglion blockade decreased FVR by 50 +/‐ 6% and increased FVC by 58 +/‐ 10%. Propofol anesthesia at 125 and 200 micro gram [centered dot] kg sup ‐1 [centered dot] min sup ‐1 progressively reduced mean arterial pressure. In the arm with sympathetic denervation, FVR and FVC showed no further changes during propofol anesthesia, whereas in the control arm FVR significantly decreased by 41 +/‐ 9% and 42 +/‐ 7%, and FVC increased significantly by 89 +/‐ 27% and 85 +/‐ 32% during 125 and 200 micro gram [centered dot] kg sup ‐1 [centered dot] min sup ‐1 infusions of propofol, respectively. In the three additional conscious participants, intraarterial infusion of SNP and nitroglycerin (TNG) after the stellate blockade resulted in a further decrease of FVR and a further increase of FVC.ConclusionsIn contrast to SNP infusions, propofol infusions into the brachial artery of conscious persons caused no significant vascular responses, despite the presence of therapeutic plasma concentrations of propofol within the forearm. The effects of propofol anesthesia on FVR and FVC are similar to the effects of sympathetic denervation by stellate ganglion blockade. Thus the peripheral vascular actions of propofol appear to be due primarily to an inhibition of sympathetic vasoconstrictor nerve activity.

ISSN:0003-3022    

出版商:OVID    

年代:1997

数据来源: OVID