Correlation between respiratory blood flow velocity variation and dynamic preload variables during coronary artery bypass surgery: A pilot observational study

Objectives To evaluate correlations between pressure-based dynamic preload indices and echocardiographic flow velocity variations during coronary artery bypass grafting. Design Prospective observational pilot study. Setting Single university hospital Patients Thirty adults undergoing elective coronary artery bypass grafting. Interventions Modified passive leg raising (PLR) at three intraoperative time points. Measurements and Main Results Mean arterial pressure increased after PLR at all three time points. In pooled analyses, stroke volume variation decreased from 13 ± 4% to 10 ± 4% and pulse pressure variation from 10 ± 2% to 7 ± 3% (both p < 0.05). Respiratory peak velocity variations at the left ventricular outflow tract and descending aorta did not change significantly. Pulse contour-derived cardiac output also did not change (5.1 ± 1.1 versus 5.1 ± 1.1 L/min; p = 0.71). Stroke volume variation and pulse pressure variation correlated strongly (r = 0.720), whereas correlations between pressure- and flow-derived indices were weak (r = 0.147–0.351). Conclusions Pressure-derived indices correlated only weakly with echocardiographic respiratory peak velocity variations in patients undergoing CABG. As forward flow did not measurably increase following modified PLR, the physiological significance of these weak correlations remains uncertain.