Correlation Between Respiratory Blood Flow Velocity Variation and Dynamic Preload Variables During Coronary Artery Bypass Surgery: A Pilot Observational Study.

Abstract

Objectives: To evaluate correlations between pressure-based dynamic preload indices and echocardiographic flow velocity variations during coronary artery bypass grafting (CABG).

Design: Prospective observational pilot study.

Setting: Single university hospital.

Participants: Thirty adults undergoing elective CABG.

Interventions: Modified passive leg raising (PLR) at 3 intraoperative time points.

Measurements and main results: Mean arterial pressure increased after PLR at all 3 time points. In pooled analyses, stroke volume variation decreased from 13% ± 4% to 10% ± 4% and pulse pressure variation decreased from 10% ± 2% to 7% ± 3% (both p < 0.05). Respiratory peak velocity variations in 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 L/min v 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.