Effects of body temperature on accuracy of continuous cardiac output measurements

Intermittent measurement of cardiac output is routine in the critically ill surgical patient. A new catheter allows real-time continuous measurement o f cardiac output. This study evaluated the impact of body temperature varia tion on the accuracy of these measurements compared to standard intermitten t bolus thermodilution technique. This prospective study in a university ho spital surgical intensive care unit included 20 consecutive trauma patients . Data were collected with pulmonary artery catheters, which allowed both c ontinuous (COC) and bolus (COB) thermodilution measurements. The catheter w as placed through either the subclavian or internal jugular vein. Measureme nts for COB were performed using a bolus (10 cm(3)) of ice-cold saline with a closed-injectate delivery system at end-expiration. Computer-generated c urves were created on a bedside monitor, and the average of three measureme nts within 10% of one another was used as COB. COC was determined as the av erage of the displayed CO before and after thermodilution CO measurements. Body temperature was measured from the pulmonary artery catheter and was gr ouped as less than or equal to 36.5 degrees C, 36.6-38.4 degrees C, and >38 .5 degrees C. COB and COC were compared for agreement by plotting the mean of the differences (COB - COC) between the methods. The differences were pl otted against the average of each pair and analyzed with linear regression. One hundred seventy-eight paired measurements were made over a period of 1 to 3 days. CO ranged from 3.7 to 15.5 L/min. Eighty-one percent of measure ments were at a temperature of 36.5-38.4 degrees C. Approximately 7% of mea surements were at a temperature below 36.5 degrees C and 11.2% were in pati ents with a core temperature above 38.5 degrees C. Correlation between the two techniques was 0.96, 0.91, and 0.82 for temperatures of less than or eq ual to 36.5 degrees C, 36.6-38.4 degrees C, and greater than or equal to 38 .5 degrees C, respectively. In conclusion, the COC measurements correlate w ell with COB in trauma patients with a core temperature less than or equal to 38.5 degrees C. The accuracy degraded at higher temperatures, which may be related to the smaller signal-to-noise ratio at elevated body temperatur es.