Background
Recently, USCOM technique (Ultrasound Cardiac Output Monitor), using advanced Doppler method to assess cardiac output (CO), has become clinically available. However, this technique requires validation in different categories of patients. The aim of our study was to evaluate the accuracy of USCOM compared to prepulmonary thermodilution in patients after off-pump coronary artery bypass grafting (OPCAB).

Methods
We enrolled 14 patients who underwent elective OPCAB into an ongoing prospective observational study. The measurements of cardiac index (CI) based on USCOM (CIUSCOM) and CI determined by thermodilution using pulmonary artery catheter (CITD) were performed at seven stages during postoperative period. We calculated Spearman’s rho coefficient to assess the correlation between CIUSCOM and CITD. The agreement between methods was evaluated using Bland-Altman analysis with percentage error calculation using overall pairs of data and separately during mechanical ventilation (4 stages) and after tracheal extubation (3 stages). 


Results
Totally, 98 pairs of data were collected. We found significant correlation between CIUSCOM and CITD  in overall data (rho = 0.524, p < 0.01) and during mechanical ventilation (rho = 0.683, p < 0.01), but there was no correlation during spontaneous breathing (rho = 0.043, p = 0.79). Bland–Altman analysis revealed bias between CIUSCOM and CITD  of -1.09 L/min/m2 with limits of agreement of ± 1.18 L/min/m2 and percentage error of 63%. In a subgroup of stages during mechanical ventilation the intermethod bias was -1.16 L/min/m2 with limits of agreement of ± 1.15 L/min/m2 and percentage error of 67%, in a subgroup after tracheal extubation the bias was -1.00 L/min/m2 with limits of agreement of ± 1.23 L/min/m2 and percentage error of 59%.

Conclusions
Despite significant correlation between CIUSCOM and CITD during mechanical ventilation after off-pump coronary surgery, USCOM demonstrates poor accuracy with underestimation of CO compared to thermodilution technique both before and after tracheal extubation.


02 / Ultrasound-based monitoring of cardiac output after off-pump coronary artery bypass grafting