Comparison of three methods for cardiac output determination in cats.

Cardiac output (CO) was measured in sodium pentobarbital-anesthetized cats over a wide range of blood flow rates. In 10 cats, CO was measured simultaneously, using Fick determination and thermodilution techniques. Echocardiography was used to estimate contractility of the heart by measuring percentage change in minor diameter and velocity of circumferential fiber shortening. These indices were compared with CO by the other techniques. Echocardiographic equations used for CO determination in man were evaluated for reliability in the cat. Thermodilution and Fick determination correlated best with low CO (r = 0.89) and less with intermediate (r = 0.69) and high (r = 0.75) CO. Percentage change in minor diameter and velocity of circumferential fiber shortening correlated with thermodilution measurements of the cardiac index (r = 0.71 and r = 0.84, respectively). The value of echocardiography for CO estimation was questionable, using existing equations. Fick determination of CO was more inconsistent and was more prone to technical error than was thermodilution.