High precision mixing of anesthetic gases based on a new principle.

A machine has been constructed for mixing O2 and N2O. It consists of: (a) a proportional pressure and thereby flow regulator at the inlets for O2 and N2O; (b) a digital gas mixer which determines the gas mixture; and (c) a rotameter to measure the outlet flow. The contents of mixtures obtained from the machine were measured with a quadropole mass spectrometer (at 2 and 5 1 min--1 with downstream pressures of 500 and 3000 Pa). The mean numeric difference between desired and registered vol% O2 varied between 0.3 and 0.5 vol% at the four conditions tested. The maximal deviation was 1.2 vol%. Five conventional machines in daily use at the hospital were also tested. The mean numeric difference for these machines varied between 1.1 and 2.7 vol% O2. The maximum deviation was 7.4 vol%.