Blood-gas tension measurement in anaesthesia by bubble equilibration and mass spectrometry.

If a small bubble gas is equilibrated with a volume of blood the partial pressures of the components of the bubble after equilibration approximate to the original tensions in the blood. A method is described in which the bubble is analysed by a respiratory mass spectrometer connected to a mini-computer. The normal respiratory monitoring function of the mass spectrometer need be interrupted for only 20 s for each sample and the complete equilibration and analysis procedure takes only 3 min. Theoretical studies, experimental tests and records of experimental usage show that, in a subject anaesthetized with halothane in nitrous and oxygen, tension can be measured with an overall SD of 5% for carbon dioxide and halothane and, certain reservations, an SD of about 3% for nitrous oxide.