Anesthesiology
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Comparative Study
Potency determination for vecuronium (ORG NC45): comparison of cumulative and single-dose techniques.
To compare two methods of estimating the potency of neuromuscular relaxants of medium duration, the authors determined the potency of vecuronium (ORG NC45) using cumulative dose-response (CDR) techniques, and compared these data with published values from our group obtained using the single bolus technique. During 60% N2O-halothane anesthesia, patients received 10 micrograms/kg vecuronium; additional incremental doses of vecuronium, 5 micrograms/kg, were given when no change occurred in the height of three successive twitches. Using these dose-response data, the authors determined least-squares regression lines and ED20, ED50, and ED80. ⋯ All potency estimates by CDR were larger than those obtained by the single bolus dose technique. It was concluded that, for vecuronium, a medium duration neuromuscular relaxant, CDR yields potency estimates which are larger than those obtained by the traditional single bolus dose technique. Because the single bolus dose technique is the accepted method for construction of dose-response curves, the authors recommended that CDR not be used for potency determination of muscle relaxants of medium and short duration such as vecuronium.
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Epinephrine-induced arrhythmias were studied in 14 dogs (Group 1) anesthetized with halothane alone (1.09% end-tidal), and on another occasion, at the same halothane concentration following intravenous thiopental (20 mg/kg). Surface (Lead II), catheter His bundle and high right atrial electrocardiograms, and airway and femoral arterial pressures were recorded. Graded doses of epinephrine (EPI-least dose 0.25 microgram . kg-1 . min-1) were infused over five minutes, but terminated sooner if ventricular tachycardia occurred (maximal sensitization). ⋯ The authors concluded that with halothane and increasing EPI dose, sensitization constitutes a spectrum of arrhythmias, beginning with atrial and progressing to severe ventricular arrhythmias. Thiopental reduces the EPI dose needed for AVD and ventricular, but not atrial, arrhythmias. It also reduces the EPI dose discrepancies for atrial and ventricular arrhythmias.
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Edrophonium's onset and duration of antagonism (n = 26) and atropine requirement (n = 24) were determined under conditions of d-tubocurarine (dTc) neuromuscular blockade and halothane, nitrous oxide anesthesia. Results are compared with previous work in our laboratory on neostigmine and pyridostigmine under similar conditions. dTc was administered by continuous infusion to maintain a 90% depression of muscle twitch tension. Edrophonium (0.03-1.0 mg/kg) was injected as an iv bolus in combination with atropine (0.5 mg). dTc infusion was continued until a stable 90% depression of muscle twitch tension was reestablished. ⋯ In equiantagonistic doses, the duration of antagonism by edrophonium (66 min) did not differ from neostigmine (76 min), but was shorter than pyridostigmine. Edrophonium required one-half the amount of atropine as did neostigmine to prevent bradycardia. The authors concluded that edrophonium has a more rapid onset than neostigmine and an equivalent duration of antagonism, and requires less atropine to prevent bradycardia.
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Randomized Controlled Trial Comparative Study Clinical Trial
Comparative evaluation of intravenous agents for rapid sequence induction--thiopental, ketamine, and midazolam.
The pharmacologic effects of ketamine, midazolam, and a midazolam-ketamine combination were compared with thiopental for rapid induction of general anesthesia. Thiopental, 4 mg/kg, 1.5 mg/kg ketamine, 0.3 mg/kg midazolam, or 0.15 mg/kg midazolam, and 0.75 mg/kg ketamine, were administered intravenously in a randomized fashion to 80 patients undergoing emergency surgery. Adequacy of induction, hemodynamic changes, and postoperative effects were assessed during and after a standardized induction-maintenance anesthetic technique. ⋯ Thus, midazolam effectively attenuated both the cardiostimulatory responses and unpleasant emergence reactions associated with ketamine. The author concludes that both midazolam and the midazolam-ketamine combination are safe and effective induction agents for emergency surgery, which may offer an advantage over thiopental in situations where hemodynamic stability is crucial. Furthermore, midazolam effectively attenuates the side effects of ketamine.