Trendelenburg positioning after cardiac surgery: effects on intrathoracic blood volume index and cardiac performance

Abstract

Background and objective: The efficacy of the Trendelenburg position, a common first step to treat suspected hypovolaemia, remains controversial. We evaluated its haemodynamic effects on cardiac preload and performance in patients after cardiac surgery. Methods: Twelve patients undergoing mechanical ventilation of the lungs who demonstrated left ventricular 'kissing papillary muscles' by transoesophageal echocardiography, thus suggesting hypovolaemia, were positioned 30° head down for 15 min immediately after cardiac surgery. Cardiac output by thermodilution, central venous pressure, pulmonary artery occlusion pressure, left ventricular end-diastolic area by transoesophageal echocardiography and intrathoracic blood volume by thermo- and dye dilution were determined before, during and after this Trendelenburg manoeuvre. Results: Trendelenburg's manoeuvre was associated with increases in central venous pressure (9 ± 2 to 12 ± 3 mmHg) and pulmonary artery occlusion pressure (8 ± 2 to 11 ± 3 mmHg). The intrathoracic blood volume index increased slightly (dye dilution from 836 ± 129 to 872 ± 112 mL m−2; thermodilution from 823 ± 129 to 850 ± 131 mL m−2) as did the left ventricular end-diastolic area index (7.5 ± 2.1 to 8.1 ± 1.7 cm2 m−2), whereas mean arterial pressure and the cardiac index did not change significantly. After supine repositioning, the cardiac index decreased significantly below baseline (3.0 ± 0.6 versus 3.5 ± 0.8 L min−1 m−2) as did mean arterial pressure (76 ± 12 versus 85 ± 11 mmHg), central venous pressure (8 ± 2 mmHg) and pulmonary artery occlusion pressure (6 ± 4 mmHg). The intrathoracic blood volume index and left ventricular end-diastolic area index did not differ significantly from baseline. Conclusions: Trendelenburg's manoeuvre caused only a slight increase of preload volume, despite marked increases in cardiac-filling pressures, without significantly improving cardiac performance.