The effect of nitrous oxide on the oxyhaemoglobin dissociation curve

The influence of nitrous oxide on the oxyhaemoglobin dissociation curve (ODC) was studied using blood from twenty healthy patients. When the blood samples were exposed to 50 per cent N2O during the determination of the ODC, a left shift was observed and the P50 was decreased by 1.06 kPa (8 mmHg). This shift cannot be explained by temperature, pH, PCO2, or 2,3-DPG effects. Following exposure of the blood to N2O-free gases, the shift disappeared rapidly, and a normal P50 (3.46 kPa) (26 mmHg) was reobtained. In keeping with this reversibility, blood samples taken before and during 45 minutes of N2O-curare anaesthesia showed identical dissociation curves to those which had been obtained during the in vitro N2O exposure experiment.