A Method for the Determination of Cyclopro- Pane, Ethylene, and Nitrous Oxide in Blood with the Van Slyke-neill Manometric Apparatus*

The dctcrmination of anesthetic gases in blood taken from patients during anesthesia has been reported in several instances (l-3). In each case, however, reservation has been made as to the accuracy of the results because of errors in the vacuum extraction method. The principal source of error has been that the volume of gas determined was not corrected for unextracted gas. This technical difficulty was recognized by the authors cited and the error which was introduced was probably of insufficient magnitude to alt,er the interpretation of their results significantly. It is felt by the authors of this paper, howcvcr, that there is a need for a method by which anesthetic gases can be accurately determined on a single sample without detracting from the accuracy of analysis for carbon dioxide and oxygen. The determination of blood gases by the Van Slyke-Neil1 manometric method (4) is based on the principle of extracting the gases from the blood and reagent in a partial vacuum. The gases are separated by absorption with specific reagents, and the volume per cent of the gas in the original blood sample is calculated from the resulting differences in pressures read on the manometer at constant volume. A correction must bc made, however, for the unextracted gas in the liquid. This is accomplished by the factor 1 + (&‘&/(A S)) where A S is the volume at which extraction takes place, and S the volume of the liquid. The cr’ is equivalent to X, or the Ost-