Cardiac Output Determination by Thermodilution Technique: The Method of Choice in Low Flow States

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Abstract
The validity of the thermodilution technique of determining cardiac output in low flow states was investigated. The simultaneous determinations attained by the thermodilution method were compared to those made by microsphere dilution and electromagnetic flow transducer methods. Measurements were carried out in 5 awake miniature swine (10-14 kg) by chronically implanted ascending aortic flow transducer and left atrial catheters. A Swan-Ganz thermodilution catheter and a femoral arterial catheter were placed on the morning of the study. Four simultaneous cardiac output determinations were carried out in each animal using the 3 techniques. The first 2 measurements were made during normotension and the last 2 during graded, stable hypovolemic shock (mean arterial pressure, 75 and 50 mm Hg). Simultaneous measurements (34) of cardiac output were carried out using thermodilution and flow transducer methods. No significant difference occurred among the cardiac outputs derived by any of the 3 methods used, during normotension or shock. Linear regression analysis showed excellent correlation between thermodilution and each of the other methods. Thermodilution evidently is an accurate, repeatable technique for measurement of cardiac output in low flow states, including shock, thus widening its applicability in experimental models.