Solubility characteristics of the ideal agent for measurement of cardiac output by soluble gas uptake methods.

Measurements of the rate of uptake of soluble gases such as nitrous oxide or acetylene has been used as the basis of a method of cardiac output estimation since 1912. Using theoretical models of single, multiple and rebreathing techniques of cardiac output measurement, we determined the effect of solubility in blood and lung tissue on the changes in the final expired concentration of the gas. Decreasing lung tissue solubility increased the sensitivity of all three models to cardiac output changes. When the lung tissue/blood partition coefficient was 1, the optimum blood/gas partition coefficients were 2.6 for the single-breath model, 4.1 for the three breath-model and 3.5 for the rebreathing model. A selection of gases, including volatile anaesthetic agents was studied using the same models. Under most conditions, enflurane approximated most closely to the requirements for an ideal agent for use in this technique of cardiac output measurement.