Comparison of a supra-sternal cardiac output monitor (USCOM) with the pulmonary artery catheter

Cardiac output (CO) cannot reliably be estimated by clinical examination. We aimed to measure the agreement between CO measurements using a supra-sternal Doppler monitor (USCOM, Coffs Harbour, Australia) and the pulmonary artery catheter (PAC). The study was conducted in the intensive care unit of a tertiary teaching hospital. All patients with PAC in situ were eligible. Simultaneous CO readings were taken when clinically indicated. Investigators and clinicians were blinded to each other's results. The CO values used were the mean of three consecutive supra-sternal Doppler readings for patients with a sinus rhythm and seven for atrial fibrillation, and the mean of three thermodilution curves with acceptable form and values within 10% of each other for the PAC. Agreement was measured using both the paired t-test to calculate bias and limits of agreement and the intraclass correlation (ICC) coefficient. Ninety-four subjects were enrolled. From 89 subjects, 250 paired comparisons were obtained. USCOM monitor readings were unobtainable in five patients. Mean supra-sternal Doppler CO was 5.5 litre min(-1). Bias was -0.09 litre min(-1) and levels of agreement were +/- 2.92 litre min(-1) when compared with PAC. ICC was 0.46 (95% CI 0.36-0.56), and mean percentage difference was 19 (IQR 6-31)%. In our subjects, there was poor agreement between CO measurements done with the supra-sternal Doppler monitor and PAC.