Estimation of Halothane Tensions in Blood by Gas Chromatography

Abstract

THE concentration of anæsthetic in the brain depends, among other things, on the tension of the anæsthetic in arterial blood¹. At a given tension the concentration in the blood is proportional to the blood/gas partition coefficient. This shows considerable variation between individuals, and is likely to alter with changes in blood constituents (for example, blood lipids). Comparison of results expressed in terms of mass per unit volume^2,3 may therefore be misleading. For example, a blood sample equilibrated with 1 per cent halothane would have a tension of 7.13 mm mercury at 37° C and a concentration of 16.9 mg per cent (partition coefficient 2.3). The concentration in a sample of Ringer's solution with the same tension would be 6.2 mg per cent (partition coefficient 0.74). The method described here enables the tension of a volatile anæsthetic to be estimated from concentrations in a gas phase in equilibrium with the blood, and is a modification of the method described by Curry et al.⁴.