Determinations of cardiac output are essential to the management of patients in cardiogenic shock and those undergoing open-heart surgery. Because of this growing demand for better methods, the thermal dilution technique has been developed for clinical use. Saline at room temperature is injected via the subclavian vein, and the temperature change is recorded by the thermistor in the pulmonary artery and cardiac output is read off immediately. Cardiac outputs can be determined as frequently as every 20 seconds, using saline injections of 7 to 10 cc for each determination. Consistency is in the range of less than 100-cc differences between sequential determinations. Many seriously ill patients have had cardiac outputs determined with this method. This experience has demonstrated that the thermal dilution technique is very reliable, and that it can be used in acute clinical situations with ease and excellent reproducibility.
Ellis RJ, Gold J, Rees JR, Lillehei CW. Computerized Monitoring of Cardiac Output by Thermal Dilution. JAMA. 1972;220(4):507–511. doi:10.1001/jama.1972.03200040029006
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