HEMODYNAMICS DURING INHALATION OF A 50-PERCENT NITROUS-OXIDE-IN-OXYGEN MIXTURE WITH AND WITHOUT HYPOVOLEMIA

Background: Inhalation of a gas mixture containing 50% nitrous oxide i n oxygen (N2O/O-2) is widely used for pain relief in emergency situati ons, which may also be associated with blood loss. The aim of this stu dy was to evaluate the haemodynamic effects of this gas mixture in nor mo- and hypovolaemic subjects. Methods: Six healthy males were studied during inhalation of N2O/O-2 before and after withdrawal of 900 ml of blood. On each occasion, we measured systemic and pulmonary arterial pressures, cardiac output, blood gases, extravascular lung water, and the blood flow and oxygen consumption in the whole body, liver and kid neys. Results: Inhalation of N2O/O-2 reduced the stroke volume and inc reased peripheral resistance. Oxygen uptake decreased in the liver (-3 0%) and in the whole body (-23%). Blood withdrawal reduced the pulmona ry arterial and central venous pressures (-30 to -50%) and further dec reased stroke volume and the blood flows to the liver and the kidney ( -15%). The extravascular lung water tended to increase both during inh alation of N2O/O-2 and during hypovolaemia. Conclusion: N2O/O-2 aggrav ated the hypokinetic circulation induced by hypovolaemia. However, the oxygen consumption decreased only during inhalation of N2O/O-2 This o pens up the possibility that the cardiodepression associated with N2O/ O-2 is caused by a change in metabolic demands. (C) Acta Anaesthesiolo gica Scandinavica 41 (1997).