Non-invasive Estimation of Cardiac Output in Critical Care Patients

Objective.This study was carried out to compare cardiac output measurements determined by thermodilution and by Portapres, a non-invasive system. Design, patients and setting.Eighty-seven non-invasive blood pressure measurements were performed in 46 patients in our critical care unit utilising the new, non-invasive Portapres system. Cardiac output values were obtained from these blood pressure values using an aortic impendance model and compared to cardiac output values estimated by the thermodilution technique.Measurements and main results.Statistically significant (p< 0.01) differences (2.3 l/min; limits of agreement ±  5l/min) were noted between invasive and non-invasive cardiac output measurements. Differences in measured cardiac outputs increased for patients receiving catecholamine therapy, in patients with hemodynamic instability(e.g., sepsis and cardiac insufficiency), in patients with artificial ventilation, in patients with long duration of intensive care, in younger(<60 yr) patients and in women. We found no influence of the body mass index (BMI) on the accuracy of Portapres results. In only one single subgroup,10 patients with pulmonary diseases, Portapres measurements were not statistically significant different from reference results. Conclusions.To date, Portapres measurements cannot replace thermodilution cardiac output estimations. Fluctuations of finger arterial perfusion due to hemodynamic instability, hypothermia and catecholamines may be responsible for problems of Portapres use in critically ill patients.