Nitrous oxide is widely used in anesthesia and critical care medicine. The effect of nitrous oxide on diaphragm contractility in humans is unknown. We evaluated the effect of a 50% nitrous oxide-50% oxygen mixture on diaphragm contractility in healthy adult volunteers. The sniff transdiaphragmatic pressure (Sn Pdi) and the twitch transdiaphragmatic pressure (Tw Pdi) elicited by bilateral supramaximal phrenic nerve stimulation were measured before during and after inhalation of a mixture of 50% nitrous oxide and 50% oxygen. Sn Pdi decreased by 15.4% during nitrous oxide inhalation, with a value of 136 +/- 21 cm H(2)O before nitrous oxide and a value of 115 +/- 27 cm H(2)O during nitrous oxide inhalation (P = 0.03). Similarly, Tw Pdi decreased from 21.2 +/- 1.8 cm H(2)O before nitrous oxide inhalation to 16.9 +/- 4.1 cm H(2)O during nitrous oxide inhalation (P = 0.03). The effect of nitrous oxide was totally abolished 20 min after its discontinuation. Nitrous oxide has a short-acting suppressant effect on the pressure generating capacity of the diaphragm in healthy humans.
Implications: We investigated whether nitrous oxide (a common component of gas anesthesia) reduces diaphragm strength in humans. Diaphragm strength is reduced by nitrous oxide but the effect wears off within 20 min of administration. Caution is advised when using nitrous oxide without anesthesiologist supervision in patients at risk of ventilatory failure