Abstract 19165: Improving Accuracy of Cardiac Output Estimates Using the Fick Principle - Oxygen versus Carbon Dioxide
Introduction: The Fick principle is frequently used to estimate cardiac output (CO) in critically ill patients. These data are used to guide patient management and to estimate vascular resistance. Oxygen-based Fick (FickO2) has been shown to systematically overestimate CO. The substitution of all O2 parameters with CO2 parameters may improve the accuracy of Fick.
Objective: To compare CO as measured by (1) FickO2, (2) carbon dioxide-based Fick (FickCO2), and (3) aortic flow probe at varying O2 and CO2 tensions.
Methods: Yorkshire swine (n=8, 29-30kg) were anesthetized, intubated, and paralyzed. Instrumentation included a femoral arterial and pulmonary arterial catheters, myocardial tissue PO2 probe (Oxford Optronix), and a transit time flow probe (Transonic, Inc) placed on the aortic root via sternotomy. Indexed oxygen consumption (VO2) and carbon dioxide production (VCO2) were continuously measured (E-CAiOVX module, GE Healthcare). In separate experiments, PaO2 was varied between 100-650 mmHg, and PaCO2 between 20-80 mmHg in graded fashion. FickCO2 was calculated based on VCO2 and the veno-arterial CO2 content difference (A). Data were compared between each group to flow probe by Bland Altman analysis.
Results: FickO2 consistently overestimated cardiac index (CI) (bias 1.3 L/min/m2, SD of bias 0.75), and did so in proportion to FiO2 (B). This overestimation was explained by a correlation with both tissue PO2 and SvO2 with FiO2 (P<0.001, linear regression). FickCO2 estimated CO more accurately at all PaO2 values (C) (bias -0.02 L/min/m2, SD of bias 0.84). Extremes of PaCO2 caused minimal error in FickCO2 (D) (bias -0.18 L/min/m2, SD of bias 0.82).
Conclusion: FickCO2 is more accurate than FickO2 within a range of clinically relevant ranges of PaO2 and PaCO2. FickCO2 utilizes VCO2, clinically easier variable to measure than VO2. FickCO2 may represent a translatable method for CO estimation in critically ill patients.
- Congenital heart disease
- Congenital heart surgery, pediatric
- Pediatric cardiac intensive care
- Stroke volume
Author Disclosures: D.A. Perry: None. L.M. Thomson: None. A.R. Moore: None. A.K. Kaza: None. J.N. Kheir: None.
- © 2016 by American Heart Association, Inc.