Anesthesia and analgesia
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Anesthesia and analgesia · Aug 2002
Case ReportsFalsely increased bispectral index values in a series of patients undergoing cardiac surgery using forced-air-warming therapy of the head.
Falsely increased bispectral index (BIS) values of >70 occur during forced-warm-air therapy in patients undergoing cardiac surgery. When forced-warm-air therapy for the head is used (as in ultra-fast-tracking cardiac patients), BIS interpretation needs careful examination. Falsely increased BIS values can easily be recognized when the warm-air flow is stopped. Within 2-3 min, BIS returns to a much lower, "true" value.
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Anesthesia and analgesia · Aug 2002
Characterization of the interactions between volatile anesthetics and neuromuscular blockers at the muscle nicotinic acetylcholine receptor.
Volatile anesthetics enhance the neuromuscular blockade produced by nondepolarizing muscle relaxants (NDMRs). The neuromuscular junction is a postulated site of this interaction. We tested the hypothesis that volatile anesthetic enhancement of muscle relaxation is the result of combined drug effects on the nicotinic acetylcholine receptor. The adult mouse muscle nicotinic acetylcholine receptor (alpha(2), beta, delta, epsilon) was heterologously expressed in Xenopus laevis oocytes. Concentration-effect curves for the inhibition of acetylcholine-induced currents were established for vecuronium, d-tubocurarine, isoflurane, and sevoflurane. Subsequently, inhibitory effects of NDMRs were studied in the presence of the volatile anesthetics at a concentration equivalent to half the concentration producing a 50% inhibition alone. All individually tested compounds produced rapid and readily reversible concentration-dependent inhibition. The calculated 50% inhibitory concentration values were 9.9 nM (95% confidence interval [CI], 8.4-11.4 nM), 43.4 nM (95% CI, 33.6-53.3 nM), 897 microM (95% CI, 699-1150 microM), and 818 microM (95% CI, 685-1001 microM) for vecuronium, d-tubocurarine, isoflurane, and sevoflurane, respectively. Coapplication of either isoflurane or sevoflurane significantly enhanced the inhibitory effects of vecuronium and d-tubocurarine, especially so at small concentrations of NDMRs. Volatile anesthetics increase the potency of NDMRs, possibly by enhancing antagonist affinity at the receptor site. This effect may contribute to the clinically observable enhancement of neuromuscular blockade by volatile anesthetics. ⋯ Isoflurane and sevoflurane enhance the receptor blocking effects of nondepolarizing muscle relaxants on nicotinic acetylcholine receptors.
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Anesthesia and analgesia · Aug 2002
The technical aspects of epidural steroid injections: a national survey.
Although epidural steroid injections (ESIs) are a common treatment for chronic pain conditions, it is not clear whether there is consensus on their technical aspects. The current literature suggests that variations in technical aspects may affect ESI outcomes. The goal of the survey was to help establish a standard frame of reference for the performance of ESIs. We analyzed survey results from 68 academic anesthesia programs and 28 private practices in the United States. The main finding in this survey is that there is no clear-cut consensus as to the ideal method to perform ESI. There is a wide variation among individual practices in almost every technical aspect of ESI. Private practices use significantly more fluoroscopy than academic centers. The large difference was found in the cervical region where 73% of private practices and only 39% of academic institutions polled perform the ESIs with fluoroscopic guidance (P = 0.005). A similar discrepancy was found in approaches to the epidural space after laminectomy where 61% of private practices, but only 15% of academic centers, use the transforaminal approach. The study results indicate that there is no consensus, and that there is a wide variation in current practices. ⋯ A national survey of practices performing epidural steroid injections was conducted. The purpose was to establish whether consensus exists on technical aspects of this procedure. The study results indicate that there is no consensus, and that there is a wide variation in current practices.
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Anesthesia and analgesia · Aug 2002
The mechanisms of intracranial pressure modulation by epidural blood and other injectates in a postdural puncture rat model.
The epidural blood patch is considered effective in treating postdural puncture headache. We have developed a postdural puncture model in rats for quantitative evaluation of the magnitude and duration of changes in cerebrospinal fluid (CSF) pressure in the cisterna magna in response to the administration of epidural blood or other moieties. This model was used to compare the efficacy of various methods of epidural injection for restoring and maintaining CSF pressure for up to 240 min. After lumbar dural puncture, CSF pressure declined 3.6 +/- 0.2 mm Hg. Epidural saline (100 microL) injected at the puncture site initially increased pressure by 7.2 +/- 0.7 mm Hg, but it rapidly (7.8 +/- 0.6 min) returned to postdural puncture baseline. A similar initial increase of CSF pressure was observed with equal volumes of all other epidural injectates, but the duration of pressure increase varied greatly. Hetastarch and dextran 40 produced results similar to saline. Only whole blood or fibrin glue consistently increased CSF pressure for the entire 240-min observation period. Whole blood mixed with anticoagulant or injected 20-mm cephalad to the puncture site did not sustain pressure. After laminectomy, direct application of blood or adhesive to the dural defect caused no pressure increase. Continuous infusion of saline after bolus could maintain pressure increase for 180 min, but within 60 min of stopping infusion, pressure returned to baseline. These results confirm the efficacy of the epidural administration of blood or fibrin glue to correct CSF hypotension after dural puncture and also provide insight into the mechanisms of intracranial pressure modulation. Sealing the dural defect does not effectively correct CSF pressure unless an epidural tamponade effect is also maintained. ⋯ A rat model was developed to evaluate different drugs that may be injected epidurally to treat postdural puncture headache. Epidural injection of blood or fibrin glue was the most effective method of maintaining increased cerebrospinal fluid pressure after dural puncture. Sealing the dural defect does not effectively correct cerebrospinal fluid pressure unless an epidural tamponade effect is maintained.
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Anesthesia and analgesia · Aug 2002
Randomized Controlled Trial Comparative Study Clinical TrialA comparison of 0.1% and 0.2% ropivacaine and bupivacaine combined with morphine for postoperative patient-controlled epidural analgesia after major abdominal surgery.
Ropivacaine (ROPI), which is less toxic and produces less motor block than bupivacaine (BUPI), seems attractive for epidural analgesia. Few data are available concerning dose requirements of epidural ROPI when combined with morphine. In this study, we compared the dose requirements and side effects of ROPI and BUPI combined with small-dose morphine after major abdominal surgery. Postoperatively, 60 patients were randomly allocated (double-blinded manner) to four groups: patient-controlled epidural analgesia with the same settings using 0.1% or 0.2% solution of ROPI or BUPI combined with an epidural infusion of 0.1 mg/h of morphine. Pain scores, side effects, motor block, and local anesthetic consumption were measured for 60 h. Pain scores and the incidence of side effects did not differ among the groups. Consumption of ROPI and BUPI were similar in both 0.1% groups. Doubling the concentration significantly reduced the consumption (milliliters) of BUPI (P < 0.05) but not of ROPI. Consequently, using ROPI 0.2% significantly increased the dose administered as compared with ROPI 0.1% (ROPI 0.1% = 314 +/- 151 mg and ROPI 0.2% = 573 +/- 304 mg at Hour 48; P < 0.05). Patient-controlled epidural analgesia with the 0.1% or 0.2% solution of ROPI or BUPI combined with epidural morphine resulted in comparable analgesia. As compared with ROPI 0.1%, the use of ROPI 0.2% increased consumption of local anesthetic without improving analgesia. ⋯ Small-dose (0.1%) ropivacaine and bupivacaine have similar potency and result in comparable analgesia and incidence of side effects.