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GENERAL ARTICLES

Inhaling Nitrous Oxide Reduces the Induction Dose Requirements of Propofol

Department of Anaesthesia and Surgical Intensive Care, Singapore General Hospital, Singapore

Address correspondence and reprint requests to Dr. N. C. Hwang, Department of Anaesthesia and Surgical Intensive Care, Singapore General Hospital, Outram Rd., Singapore 169608.

Inhaling nitrous oxide (N₂O) before propofol induction appears to decrease propofol usage. To investigate the efficacy of N₂O as a component of the drugs used to induce anesthesia, the effect of inhaling a N₂O:oxygen (O₂) mixture on the dose of propofol required to induce anesthesia was determined in a double-blinded manner. We randomized 117 unpremedicated patients scheduled for elective surgery into three groups. Group FN received 1 µg/kg fentanyl and breathed 4 L/min N₂O + 2 L/min O₂. Group PN received placebo and breathed 4 L/min N₂O + 2 L/min O₂. Group FO received 1 µg/kg fentanyl and breathed 6 L/min O₂. Propofol was infused at 20 mg/min after 1 min of gas mixture inhalation, and the infusion stopped when there was loss of response to verbal command. The mean (SD) propofol dose was 0.75 (0.30), 0.84 (0.26), and 1.33 (0.51) mg/kg, and the induction time 133 (57), 142 (47), and 226 (78) s for Groups FN, PN, and FO, respectively. We conclude that inhalation of 66% N₂O in O₂ 1 min before the IV induction of anesthesia with propofol at 20 mg/min, reduces the induction dose of propofol by 44% and decreases the time required for the induction of anesthesia (P < 0.001).

Implications: This prospective, randomized, double-blinded study shows that the inhalation of nitrous oxide can reduce the dose of propofol required to induce anesthesia. The technique leads to good induction conditions with reduced usage of propofol.