[Nitrous oxide in combination anesthesia. Quantitative aspects of the effect of nitrous oxide].
Minimal Alveolar Concentration (MAC) defines the anesthetic potency of nitrous oxide (N2O) combined with an inhalational anesthetic only for the moment of skin incision. For the complete operation, the proportional action of N2O is unknown. This prospective, randomized study reports the mean intraoperative concentration (MIC) of halothane with and without 70% N2O in combination with premedication, i.v. induction, and muscle relaxation for the duration of operation.


METHODS
Forty ASA I-II patients scheduled for hysterectomies gave informed consent. All patients received atropine 0.5 mg, promethazine and pethidine 1 mg/kg i.m. 30-45 min prior to anesthesia, i.v. induction with thiopental, and neuromuscular blockade with alcuronium at the beginning of the operation. Post-induction, patients received randomized halothane in 30% O2/70% N2 (group 1, n = 20) or in 30% O2/70% N2O (group 2, n = 20). In the course of this observation (before induction and up to 15 min after extubation), the following parameters were measured (Table 1): arterial pressure (AP), heart rate (HR), plasma concentrations of growth hormone, prolactin, and cortisol in central venous blood, esophageal temperature, "train-of-four" ratio, and expiratory CO2 concentration. MIC had been computed from the integral of end-expiratory halothane concentration during the course of the operation.


RESULTS
Biometric data and concomitant conditions were equivalent within the two groups (Table 2). MIC halothane was 0.72 +/- 0.014 vol% in group 1 (O2/N2) and 0.52 +/- 0.01 vol% in group 2 (O2/N2O).(ABSTRACT TRUNCATED AT 250 WORDS)
Rothhammer
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Institut für Anaesthesiologie und Intensivmedizin, Leopoldina-Krankenhauses Schweinfurt.
D000769:Anesthesia, Inhalation; D001794:Blood Pressure / Q000187:drug effects; D001831:Body Temperature / Q000187:drug effects; D002986:Clinical Trials as Topic; D004359:Drug Therapy, Combination; D013006:Growth Hormone / Q000097:blood; D006221:Halothane; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D009609:Nitrous Oxide / Q000494:pharmacology; D011388:Prolactin / Q000097:blood; D011446:Prospective Studies; D011897:Random Allocation; D012119:Respiration / Q000187:drug effects
D011388:Prolactin; D013006:Growth Hormone; D009609:Nitrous Oxide; D006221:Halothane; D006854:Hydrocortisone
Lachgas in der Kombinationsnarkose. Quantitative Aspekte des Wirkanteils von N2O.