Direct read-out of cardiac output by means of the fiberoptic indicator dilution method

The feasibility of determining cardiac output by the indicator dilution principle, without the need for any calculation or the withdrawal of blood, was studied in 15 patients and 3 dogs. A total of 150 curves were utilized and good agreement found between the “direct” reading obtained from a cardiac output “meter” and the result derived from more conventional indicator dilution calculations. Cardiac outputs were studied with varying heart rates, samplings, and injection sites, and varied from 1 to 16 L. per minute. The advantages of the method lie in its speed, the use of a conventional indicator (indocyanine green), the ease of calibration which is accomplished with only 3 ml. of blood, and the absence of the need for repeated withdrawal of arterial blood samples.