Simultaneous computer-calculated carbon dioxide and oxygen direct Fick and dye dilution measurements of cardiac output in dogs.

Cardiac output was measured by both indocyanine green dye dilution and the direct Fick method using computer-calculated values for oxygen consumption and carbon dioxide excretion in eight mechanically ventilated dogs anesthetized with pentobarbital, with either tubocurarine or succinylcholine intravenous drip for neuromuscular relaxation. Sequential measurements were made during the anesthesia and in response to pharmacologically induced increased cardiac output using doxapram hydrochloride (1.5 mg/kg) given intravenously. The purpose of this project was to investigate the accuracy and reliability of the direct Fick measurements during anesthesia using computer-calculated measurements of pulmonary gas exchange and, since, these measurements have not been reported in detail previously, to establish tentative control values for future projects. The correlation of dye and direct Fick measurements of cardiac output during the first hour after induction of anesthesia was very good (r = 0.85 for all dye-carbon dioxide Fick values; r = 0.83 for all dye-oxygen Fick values.