Measurement of cardiac output (CO) is often performed in the assessment of critically ill patients with undifferentiated shock. Doppler echocardiography has been shown to be a reliable method for estimating cardiac output when images are acquired by cardiac sonographers and interpreted by cardiologists. However, few studies have assessed the accuracy of CO measurements by Doppler echocardiography performed by non-cardiac intensivists. The purpose of this study was to compare the accuracy of CO measurements by Doppler echocardiography performed by non-cardiac intensivists vs. measurements by pulmonary artery catheter (PAC). METHODS: A prospective observational study of critically ill patients with a PAC in place was conducted. Patients in sinus rhythm and without severe mitral or aortic regurgitation were included. Two non-cardiac intensivists who were not caring for the patients and were blinded to the patients' clinical and hemodynamic data performed transthoracic goal-directed echocardiograms on all subjects. Stroke volume (SV) was calculated using a 3-beat average of the Left Ventricular Outflow Tract (LVOT) Velocity Time Integral measured by pulsed-wave Doppler and the 2-dimensional diameter of the LVOT, and CO was calculated by multiplying SV by heart rate. Simultaneously, ICU-trained nurses obtained 3 different PAC-CO measurements by thermodilution, which were subsequently averaged. Association analysis was performed using linear regression and Pearson correlation. RESULTS: Eighty-six simultaneous PAC-CO and Echo-CO measurements were obtained in 32 consecutive patients. The patients' mean age was 66 years and most common comorbidities included acute coronary syndrome (50%), respiratory failure on mechanical ventilation (37%), and post-cardiac surgery (87%). Most patients (56%) had a left ventricular ejection fraction (LVEF) <40%, and the average LVEF was 31%. A strong correlation between Echo-CO and PAC-CO was seen (Pearson correlation R¼0.89; p<0.001). The linear regression coefficient was 1.09 (95%CI 0.97-1.21; p<0.001) with an R2 of 0.79, suggesting a strong linear correlation. Both mechanically ventilated patients (n¼50) and those breathing spontaneously (n¼36) had a strong Echo-CO to PAC-CO correlation (R¼0.83 and 0.92, respectively; p<0.001 for both subgroups). CONCLUSIONS: Cardiac output measured by non-cardiac intensivists using goal-directed echocardiography had a strong correlation with gold standard measurements by thermodilution using a pulmonary artery catheter. CLINICAL IMPLICATIONS: Noninvasive measurement of cardiac output in critically ill patients using Doppler echocardiography is an accurate technique when performed by non-cardiac intensivists.