Gas viscosity effects in anesthesia.

The viscosity effects when carrier anesthetic gases are passed through ventilators can lead to significant alterations in ventilating volumes. This effect was studied in both experimental and clinical situations using the Bird anesthetic machine powered by a nitrous oxide-oxygen blender and fitted with a Wright gas-volume meter. Despite the fact that nitrous oxide is +/- 30% denser than oxygen, when it is used as the main carrier gas through the Bird anesthetic machine during automatic ventilation, the ventilating volumes increase although the settings on the machine remain unaltered. When the machine is slave to the spontaneous respiratory efforts of the patient this effect disappears. Oxygen is more viscous than nitrous oxide and this will explain the observed phenomena. It is suggested that it would be safer for patients if vaporizers and ventilators were calibrated with a 3:1 mixture of nitrous oxide and oxygen.