John Collins Warren and his act of conscience: a brief narrative of the trial and triumph of a great surgeon.
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On examination of the correspondence among the principals involved, as well as the original patent application being prepared by Morton, it has become possible to reconstruct some of the remarkable details attending the first use of ether anesthesia at the Massachusetts General Hos pital in the autumn of 1846. At the time that Warren invited Morton to demonstrate the use of his "ethereal vapor" for anesthesia in a minor operation on Oct. 16, 1846, the exact chemical composition of the agent used was being held secret by Morton; Warren was clearly disturbed by this unethical use of a secret "nostrum." When the time arrived 3 weeks later for its possible use for a serious "capital" operation, Warren employed a simple stratagem of public confrontation to discover from Morton the true nature of the substance to be used. On being informed that it was pure unadulterated sulfuric ether, not some mysterious new discovery labeled "Letheon," Warren gave approval for its first use in a "capital" operation (low thigh amputation) on Nov. 7, 1846. Despite this revelation to the immediate participants, a veil of secrecy continued to surround the substance for many months, an anomalous situation evidently traceable to Morton's desire for personal reward from the discovery. It was this matter of secrecy, rather than priority for its discovery, that surrounded the early use of ether anesthesia with controversy and recrimination both in this country and abroad. (+info)
A neomorphic syntaxin mutation blocks volatile-anesthetic action in Caenorhabditis elegans.
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The molecular mechanisms underlying general anesthesia are unknown. For volatile general anesthetics (VAs), indirect evidence for both lipid and protein targets has been found. However, no in vivo data have implicated clearly any particular lipid or protein in the control of sensitivity to clinical concentrations of VAs. Genetics provides one approach toward identifying these mechanisms, but genes strongly regulating sensitivity to clinical concentrations of VAs have not been identified. By screening existing mutants of the nematode Caenorhabditis elegans, we found that a mutation in the neuronal syntaxin gene dominantly conferred resistance to the VAs isoflurane and halothane. By contrast, other mutations in syntaxin and in the syntaxin-binding proteins synaptobrevin and SNAP-25 produced VA hypersensitivity. The syntaxin allelic variation was striking, particularly for isoflurane, where a 33-fold range of sensitivities was seen. Both the resistant and hypersensitive mutations decrease synaptic transmission; thus, the indirect effect of reducing neurotransmission does not explain the VA resistance. As assessed by pharmacological criteria, halothane and isoflurane themselves reduced cholinergic transmission, and the presynaptic anesthetic effect was blocked by the resistant syntaxin mutation. A single gene mutation conferring high-level resistance to VAs is inconsistent with nonspecific membrane-perturbation theories of anesthesia. The genetic and pharmacological data suggest that the resistant syntaxin mutant directly blocks VA binding to or efficacy against presynaptic targets that mediate anesthetic behavioral effects. Syntaxin and syntaxin-binding proteins are candidate anesthetic targets. (+info)
Causes of nitrous oxide contamination in operating rooms.
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BACKGROUND: To reduce the ambient concentration of waste anesthetic agents, exhaust gas scavenging systems are standard in almost all operating rooms. The incidence of contamination and the factors that may increase the concentrations of ambient anesthetic gases have not been evaluated fully during routine circumstances, however. METHODS: Concentrations of nitrous oxide (N2O) in ambient air were monitored automatically in 10 operating rooms in Kagoshima University Hospital from January to March 1997. Ambient air was sampled automatically from each operating room, and the concentrations of N2O were analyzed every 22 min by an infrared spectrophotometer. The output of the N2O analyzer was integrated electronically regarding time, and data were displayed on a monitor in the administrative office for anesthesia supervisors. A concentration of N2O > 50 parts per million was regarded as abnormally high and was displayed with an alarm signal. The cause of the high concentration of N2O was then sought. RESULTS: During the 3-month investigation, N2O was used in 402 cases. Abnormally high concentrations of N2O were detected at some time during 104 (25.9%) of those cases. The causes were mask ventilation (42 cases, 40.4% of detected cases), unconnected scavenging systems (20 cases, 19.2%), leak around uncuffed pediatric endotracheal tube (13 cases, 12.5%), equipment leakage (12 cases, 11.5%), and others (17 cases, 16.4%). CONCLUSIONS: N2O contamination was common during routine circumstances in our operating rooms. An unconnected scavenging system led to the highest concentrations of N2O recorded. Proper use of scavenging systems is necessary if contamination by anesthetic gas is to be limited. (+info)
Effects of anticholinergics on postoperative vomiting, recovery, and hospital stay in children undergoing tonsillectomy with or without adenoidectomy.
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BACKGROUND: Nausea and vomiting are the most frequent problems after minor ambulatory surgical procedures. The agents used to induce and maintain anesthesia may modify the incidence of emesis. When neuromuscular blockade is antagonized with anticholinesterases, atropine or glycopyrrolate is used commonly to prevent bradycardia and excessive oral secretions. This study was designed to evaluate the effect of atropine and glycopyrrolate on postoperative vomiting in children. METHODS: Ninety-three patients undergoing tonsillectomy with or without adenoidectomy were studied. After inhalation induction of anesthesia with nitrous oxide, oxygen, and halothane, anesthesia was maintained with a nitrous oxide-oxygen mixture, halothane, morphine, and atracurium. Patients were randomized to receive, in a double-blinded manner, either 15 microg/kg atropine or 10 microg/kg glycopyrrolate with 60 microg/kg neostigmine to reverse neuromuscular blockade. Patient recovery, the incidence of postoperative emesis, antiemetic therapy, and the duration of postoperative hospital stay were assessed. RESULTS: There were no significant differences in age, gender, weight, or discharge time from the postanesthesia care unit or the hospital between the groups. Twenty-four hours after operation, the incidence of vomiting in the atropine group (56%) was significantly less than in the glycopyrrolate group (81%; P<0.05). There was no significant difference between the atropine and glycopyrrolate groups in the number of patients who required antiemetics or additional analgesics. CONCLUSIONS: In children undergoing tonsillectomy with or without adenoidectomy, reversal of neuromuscular blockade with atropine and neostigmine is associated with a lesser incidence of postoperative emesis compared with glycopyrrolate and neostigmine. (+info)
Functional brain imaging during anesthesia in humans: effects of halothane on global and regional cerebral glucose metabolism.
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BACKGROUND: Propofol and isoflurane anesthesia were studied previously with functional brain imaging in humans to begin identifying key brain areas involved with mediating anesthetic-induced unconsciousness. The authors describe an additional positron emission tomography study of halothane's in vivo cerebral metabolic effects. METHODS: Five male volunteers each underwent two positron emission tomography scans. One scan assessed awake-baseline metabolism, and the other scan assessed metabolism during halothane anesthesia titrated to the point of unresponsiveness (mean +/- SD, expired = 0.7+/-0.2%). Scans were obtained using a GE2048 scanner and the F-18 fluorodeoxyglucose technique. Regions of interest were analyzed for changes in both absolute and relative glucose metabolism. In addition, relative changes in metabolism were evaluated using statistical parametric mapping. RESULTS: Awake whole-brain metabolism averaged 6.3+/-1.2 mg x 100 g(-1) x min(-1) (mean +/- SD). Halothane reduced metabolism 40+/-9% to 3.7+/-0.6 mg x 100 g(-1) x min(-1) (P< or =0.005). Regional metabolism did not increase in any brain areas for any volunteer. The statistical parametric mapping analysis revealed significantly less relative metabolism in the basal forebrain, thalamus, limbic system, cerebellum, and occiput during halothane anesthesia. CONCLUSIONS: Halothane caused a global whole-brain metabolic reduction with significant shifts in regional metabolism. Comparisons with previous studies reveal similar absolute and relative metabolic effects for halothane and isoflurane. Propofol, however, was associated with larger absolute metabolic reductions, suppression of relative cortical metabolism more than either inhalational agent, and significantly less suppression of relative basal ganglia and midbrain metabolism. (+info)
Clinical isoflurane metabolism by cytochrome P450 2E1.
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BACKGROUND: Some evidence suggests that isoflurane metabolism to trifluoroacetic acid and inorganic fluoride by human liver microsomes in vitro is catalyzed by cytochrome P450 2E1 (CYP2E1). This investigation tested the hypothesis that P450 2E1 predominantly catalyzes human isoflurane 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. METHODS: Twenty-two elective surgery patients who provided institutionally-approved written informed consent were randomized to receive disulfiram (500 mg orally, N = 12) or nothing (controls, N = 10) the evening before surgery. All patients received a standard isoflurane anesthetic (1.5% end-tidal in oxygen) for 8 hr. Urine and plasma trifluoroacetic acid and fluoride concentrations were quantitated in samples obtained for 4 days postoperatively. RESULTS: Patient groups were similar with respect to age, weight, gender, duration of surgery, blood loss, and delivered isoflurane dose, measured by cumulative end-tidal isoflurane concentrations (9.7-10.2 MAC-hr). Postoperative urine excretion of trifluoroacetic acid (days 1-4) and fluoride (days 1-3) was significantly (P<0.05) diminished in disulfiram-treated patients. Cumulative 0-96 hr excretion of trifluoroacetic acid and fluoride in disulfiram-treated patients was 34+/-72 and 270+/-70 micromoles (mean +/- SD), respectively, compared to 440+/-360 and 1500+/-800 micromoles in controls (P<0.05 for both). Disulfiram also abolished the rise in plasma metabolite concentrations. CONCLUSIONS: Disulfiram, a selective inhibitor of human hepatic P450 2E1, prevented 80-90% of isoflurane metabolism. These results suggest that P450 2E1 is the predominant P450 isoform responsible for human clinical isoflurane metabolism in vivo. (+info)
Potassium channel-mediated hyperpolarization of mesenteric vascular smooth muscle by isoflurane.
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BACKGROUND: A primary source of calcium (Ca2+) necessary for excitation contraction in vascular smooth muscle (VSM) is influx via voltage-dependent Ca2+ channels. Thus, force generation in VSM is coupled closely to resting transmembrane potential, which itself is primarily a function of potassium conductance. Previously, the authors reported that volatile anesthetics hyperpolarize VSM of small mesenteric resistance arteries and capacitance veins. The current study was designed to determine whether isoflurane-mediated hyperpolarization is the result of specific effects on one or more of four types of potassium channels known to exist in VSM. METHODS: Transmembrane potentials (Em) were recorded from in situ mesenteric capacitance and resistance vessels in Sprague-Dawley rats weighing 250-300 g. In separate experiments, selective inhibitors of each of four types of potassium channels known to exist in VSM were administered in the superfusate of the vessel preparations to assess their effects on isoflurane-mediated hyperpolarization. RESULTS: Resting VSM Em ranged from -38 to -43 mV after local sympathetic denervation. Isoflurane produced a significant hyperpolarization (2.7-4.3 mV), whereas each potassium channel inhibitor significantly depolarized (2.8-8.5 mV) the VSM. Both 100 nM iberiotoxin (inhibitor of high conductance calcium-activated potassium channels) and 1 microM glybenclamide (inhibitor of adenosine triphosphatase-sensitive potassium channels) significantly inhibited VSM hyperpolarization induced by 1 MAC (minimum alveolar concentration) levels of inhaled isoflurane (0.1-0.9 mV Em change, which was not significant). In contrast, isoflurane hyperpolarized the VSM significantly despite the presence of 3 mM 4 aminopyridine (inhibitor of voltage-dependent potassium channels) or 10 microM barium chloride (an inhibitor of inward rectifier potassium channels) (3.7-8.2 mV change in VSM Em). CONCLUSIONS: These results suggest that isoflurane-mediated hyperpolarization (and associated relaxation) of VSM can be attributed in part to an enhanced (or maintained) opening of calcium-activated and adenosine triphosphate-sensitive potassium channels but not voltage-dependent or inward rectifier potassium channels. (+info)
Effects of isoflurane anesthesia on pulmonary vascular response to K+ ATP channel activation and circulatory hypotension in chronically instrumented dogs.
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BACKGROUND: The objective of this study was to evaluate the effects of isoflurane anesthesia on the pulmonary vascular responses to exogenous adenosine triphosphate-sensitive potassium (K+ ATP) channel activation and circulatory hypotension compared with responses measured in the conscious state. In addition, the extent to which K+ ATP channel inhibition modulates the pulmonary vascular response to circulatory hypotension in conscious and isoflurane-anesthetized dogs was assessed. METHODS: Fifteen conditioned, male mongrel dogs were fitted with instruments for long-term monitoring to measure the left pulmonary vascular pressure-flow relation. The dose-response relation to the K+ ATP channel agonist, lemakalim, and the pulmonary vascular response to circulatory hypotension were assessed in conscious and isoflurane-anesthetized (approximately 1.2 minimum alveolar concentration) dogs. The effect of the selective K+ ATP channel antagonist, glibenclamide, on the pulmonary vascular response to hypotension was also assessed in conscious and isoflurane-anesthetized dogs. RESULTS: Isoflurane had no effect on the baseline pulmonary circulation, but it attenuated (P<0.05) the pulmonary vasodilator response to lemakalim. Reducing the mean systemic arterial pressure to approximately 50 mm Hg resulted in pulmonary vasoconstriction (P<0.05) in the conscious state, and this response was attenuated (P<0.05) during isoflurane. Glibenclamide had no effect on the baseline pulmonary circulation, but it potentiated (P<0.05) the pulmonary vasoconstrictor response to hypotension in conscious and isoflurane-anesthetized dogs. CONCLUSIONS: These results indicate that K+ ATP-mediated pulmonary vasodilation and the pulmonary vasoconstrictor response to hypotension are attenuated during isoflurane anesthesia. Endogenous K+ ATP channel activation modulates the pulmonary vasoconstrictor response to hypotension in the conscious state, and this effect is preserved during isoflurane anesthesia. (+info)