Administration of nitrous oxide in normal subjects. Evaluation of systems of gas delivery for their clinical use and hemodynamic effects.

Nitrous oxide (concentrations of 30 to 50%) was administered to 22 healthy volunteer subjects via nasal prongs, rebreathing mask, and an airlines mask to assess the efficiency of systems of delivery and the hemodynamic effects. The end-expired concentration of nitrous oxide, expressed as a percentage of the inspired concentration of nitrous oxide, was 19% for nasal prongs, 34% for the rebreathing mask, and 95% for the airlines mask (most accurate delivery). The pulse rate fell from a mean of 79+/-3 beats per minute to 67+/-2 with nasal prongs, to 64+/-2 with the rebreathing mask, and to 64+/-2 with the airlines mask. Both systolic and diastolic pressures fell from means of 122+/-4 and 74+/-2 mm Hg, respectively, to 98+/-3 mm Hg and 64+/-2 mm Hg, respectively, with the airlines apparatus. The fall in systolic blood pressure (slope, -0.79) exceeded that in the diastolic (slope, -0.35). In additional eight normal subjects, administration of 30% nitrous oxide via airlines mask produced identical changes in blood pressure and pulse rate, but there was no effect from 30 minutes of administration of 30% nitrous oxide on the end-systolic volume index, cardiac index, ejection fraction, normalized wall velocity determined echocardiographically, ejection time, or the ratio of preejection period to ejection time.