A comparison of bolus versus continuous cardiac output in an experimental model of heart failure

Objective: The majority of studies examining cardiac output measurement hav e been done in physiologically stable models with low thermal background no ise. Research comparing continuous cardiac output (CCO) with bolus thermodi lution cardiac output (COTD) measures in human and animal models have repor ted high correlations, negligible bias, but large limits of agreement. The purpose of this project was to compare CCO with COTD measures in an experim ental model of heart failure where the cardiac output values were low and t he range was narrow. Design: A one-group experimental design with preintervention control measur es and repeated CCO and COTD measures across nine time points. Setting: Cardiovascular research laboratory. Subjects: Thirty dogs. Measures and Main Results: Univariate and multivariate versions of repeated -measures analysis were used to assess the influences of temperature, weigh t, and stage of the experimental protocol on CCO, COTD, and the differences between them. The two measures CCO and COTD were assessed for agreement by using methods proposed by Bland and Altman. Two hundred and fifty pairs of measurements were obtained during sinus rhythm. The range for COTD measure s was 0.5-4.67 L/min and for CCO measures 1.0-5.40 L/min. Of the 250 cardia c outputs estimated by the continuous method, 73.4% of the values were with in +/-15% of that estimated by the repetitive, single thermodilution method . The mean bias for the entire protocol was 0.01 (SD = 0.51) with a range o f 4.33 L/min. Conclusion: Agreement between the two measures may be the function of biolo gical variability, responses to anesthesia, and technique. Bland and Altman evaluation demonstrated low bias and precision and similar levels of agree ment when compared with previous studies in an experimental model where the cardiac output was low and the range was narrow.