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[Nitrous oxide in combination anesthesia. Quantitative aspects of the effect of nitrous oxide]
1Institut für Anaesthesiologie und Intensivmedizin, Leopoldina-Krankenhauses Schweinfurt.
Unlabelled:
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)
Insights
Nitrous oxide (N2O) significantly reduces the required concentration of halothane during surgery. This study found that 70% N2O lowered the mean intraoperative concentration (MIC) of halothane by 28% compared to nitrogen (N2).
Area of Science:
- Anesthesiology
- Pharmacology
- Surgical Research
Background:
- The Minimal Alveolar Concentration (MAC) quantifies inhalational anesthetic potency but is established only at skin incision.
- The effect of nitrous oxide (N2O) on anesthetic requirements throughout an entire operation remains largely uncharacterized.
Purpose of the Study:
- To determine the Mean Intraoperative Concentration (MIC) of halothane when combined with 70% N2O versus 70% N2.
- To evaluate the impact of N2O on halothane requirements for the complete duration of surgical procedures.
Main Methods:
- A prospective, randomized study involving 40 ASA I-II patients undergoing hysterectomies.
- Patients received standardized premedication, IV induction with thiopental, and neuromuscular blockade with alcuronium.
- Post-induction, patients were randomized to receive halothane in either 30% O2/70% N2 (n=20) or 30% O2/70% N2O (n=20); MIC was calculated from end-expiratory halothane concentrations.
Main Results:
- Biometric data and patient conditions were comparable between the two groups.
- The Mean Intraoperative Concentration (MIC) of halothane was significantly lower in the N2O group (0.52 +/- 0.01 vol%) compared to the N2 group (0.72 +/- 0.014 vol%).
- This represents a 28% reduction in halothane requirement when using 70% N2O.
Conclusions:
- Combining 70% nitrous oxide with halothane substantially decreases the required intraoperative concentration of halothane.
- N2O demonstrates significant anesthetic-sparing effects throughout the entire surgical procedure, not just at incision.