[Clinical studies on the narcotic effects of nitrous oxide (author's transl)]

In 340 male and 450 female patients of various age the depth of anaesthesia acquired during induction with nitrous oxide (75%) and oxygen (25%) was investigated by means of clinical methods. Premedication consisted of atropine (0,1 mg/1o kg body weight) in 26% and atropine plus pethidine (or morphine) in 74% of the patients, respectively of the total, 2.4% of the patients failed to enter the analgesic-amnestic level, determined as I-3, while 97.6% occupied and more than 50% of the patients surpassed it. Thus the MAC of nitrous oxide in man seems to be 75 volume per cent or less. The depth of anaesthesia varied significantly with duration of inhalation (p smaller than 0.001). Up to five minutes of inhalation 5% of the patients failed to arrive at I-3, while 95% reached this plane and 46% surpassed it. After more than five minutes of inhalation the corresponding values were 1%, 99% and 56%, respectively. Significantly deeper levels of anaesthesia were acquired by females than by males (p smaller than 0.001) during the initial 10 minutes of inhalation. After that time sexual differences disappeared. Patients of good physical condition reached deeper planes of anaesthesia than bad risk cases (p smaller than 0.001). The use of analgesics as premedicants reduced the effectiveness of nitrous oxide, as compared to premedicated patients with atropine alone (p smaller than 0.01 in men and p smaller than 0.05 in women). Adults below 30 years of age entered the stages II and III-1 significantly less frequently than older patients (p smaller than 0.01), whereas children (up to 14 years of age) reached those stages significantly more frequently than adult patients in general (p smaller than 0.01).