Cardiac output is classically measured using thermodilution, which requires a pulmonary artery catheter (PAC). Pulmonary artery catheters are invasive and, as highlighted in 2 posts last month on AA2day (post 1; post 2), have multiple risks. The Nexfin determines cardiac output by analyzing the arterial pulse contour using an inflatable finger cuff. In the article “Noninvasive Continuous Cardiac Output by the Nexfin Before and After Preload-Modifying Maneuvers: A Comparison with Intermittent Thermodilution Cardiac Output,” Dr. Serban Ion Bubenek-Turconi, “Prof. C. C. Iliescu” Institute for Cardiovascular Diseases, Bucharest, Romania, and coauthors compared cardiac output measured using thermodilution with cardiac output measured using the Nexfin device in 28 patients before and after they had undergone elective on-pump cardiac surgery, and before and after a preload challenge or a passive leg-raising maneuver was indicated.
The majority of patients (18) received moderate doses of inotropic therapy and/or low-dose vasopressor therapy. There was 70% correlation in the cardiac outputs measured using thermodilution or the Nexfin, and 100% concordance between changes in cardiac output. Percentage error was almost 40%, though changes in cardiac output in response to preload modifications were tracked reliably.
In the accompanying editorial titled “Alea Iacta Est: A New Approach to Cardiac Output Monitoring?”, Dr. Michael Imhoff, Department for Medical Informatics, Biometrics and Epidemiology, Ruhr-University Bochum, Dortmund, Germany, noted that the study was excellent but “that measurement errors of up to 40% are not acceptable, if one wants to do protocol-driven hemodynamic therapy, and that we need to intensify our quest for less harmful but reliable methods to measure CO. We may need to be more cautious about the results of validation studies with such technologies.”
Indeed, more study is needed. However, technology that non-invasively measures cardiac output is an important advance in monitoring patient.