Comparison of continuous thermodilution and bolus cardiac output measurements in septic shock

OBJECTIVE: To compare continuous (CCO) and bolus (BCO) thermodilution cardiac output measurement techniques over a wide range of cardiac outputs and blood temperatures in a septic sheep model. DESIGN AND SETTING: Prospective experimental study in a university intensive care laboratory. SUBJECTS: Thirty-five anesthetized sheep. INTERVENTIONS: Pulmonary artery catheters allowing measurement of CCO and BCO were placed through the external jugular vein. Cecal ligation and perforation was performed to induce septic shock. In 14 sheep two femoral venous catheters were placed and connected to a hemofiltration system to alter blood temperature. MEASUREMENTS: CCO and BCO were measured every hour during the experiment. Three 10-ml bolus injections of iced normal saline were given through a closed injectate system and then averaged. The CCO readings were collected just before the BCO measurements. The relationship between CCO and BCO was assessed using Bland and Altman's method. RESULTS: In 465 paired data the temperature ranged between 34.0 degrees and 40.9 degrees C, CCO between 1.4 and 17.0 l/min, and BCO between 1.1 and 17.4 l/min. There was a highly significant correlation between CCO and BCO ( r=0.97). The bias (difference between CCO and BCO) was -0.19 l/min, the SD of the difference 0.45 l/min, and the limits of agreement -1.08/0.71 l/min. There were also highly significant correlations between CCO and BCO at the different temperatures (extreme values: 34.0-34.9 degrees C, r=0.90; 40.0-40.9 degrees C, r=0.98). CONCLUSIONS: Thermodilution measurements of CCO are reliable, when compared to BCO measurements, over a large range of cardiac outputs and blood temperatures.