CONTINUOUS VERSUS INTERMITTENT CARDIAC-OUTPUT MEASUREMENT IN CARDIAC SURGICAL PATIENTS UNDERGOING HYPOTHERMIC CARDIOPULMONARY BYPASS

Objective: Continuous thermodilution cardiac output (CCO) measurement was clinically evaluated in patients who underwent coronary revascular ization using hypothermic low-flow, low-pressure cardiopulmonary bypas s (CPB). Design: Prospective study. Setting: University hospital setti ng. Participants: 30 cardiac surgical patients. interventions: CCO was correlated to standard bolus cardiac output (ICO) obtained at end-exp iration. Interventions: CCO was correlated to standard bolus thermodil ution cardiac output (ICO) obtained at end-expiration. Measurements an d Main Results: Measurements were taken at selected time points (n = 1 8) before anesthesia induction, before CPB, and 5 minutes to 12 hours after CPB. A total of 540 data pairs were thus obtained. ICO ranged fr om 1.9 to 9.9 L/min, CCO from 1.5 to 9.9 L/min. Correlation between IC O and CCO was highly significant (r = 0.872; p < 0.01), accompanied by an excellent accuracy (bias -0.0213 L) and precision (0.59 L) before CPB and more than 45 minutes after CPB. However, during the first 45 m inutes after CPB, there was no correlation (r = 0.273) between ICO and CCO, and ICO tended to be relatively high, whereas CCO measurements s howed relatively low values. During the first 45 minutes after hypothe rmic CPB, but not during the ensuing time period, central blood temper ature decreased, which may be interpreted as a lack of thermal equilib ration between central and peripheral compartments. It is hypothesized that thermal instability in combination with increased respiratory va riations in pulmonary artery blood temperature caused inhomogenous rew arming of different body sites and might be the main reason for the la ck of correlation between ICO and CCO. Conclusions: Despite an excelle nt correlation, accuracy, and precision between CCO and ICO before CPB and more than 45 minutes after hypothermic CPB, a lack of correlation in the early phase after CPB has been found. Further investigation is needed to elucidate tire underlying cause of these findings and to cl arify whether ICO or CCO or both fail to represent the real cardiac ou tput up to 45 minutes after weaning from hypothermic CPB. Copyright (C ) 1995 by W.B. Saunders Company