Trendelenburg versus PASG Application???Hemodynamic Response in Man

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Abstract
Diminished venous return is the primary determinant of reduced cardiac output in hemorrhagic hypoperfusion. In this study the hemodynamic response of two therapies commonly employed to increase venous return in hemorrhagic hypoperfusion—pneumatic antishock garment (PASG) application and Trendelenburg (TREND) positioning—were compared in normovolemic man. Five patients had PASG pressure of 20 mm Hg compared with 10° Trendelenburg, eight patients had 20 and 40 mm Hg PASG application compared with 10° Trendelenburg. PASG application at both 20 and 40 mm Hg resulted in a significant increase in CVP (11.1 ± 1.9 baseline to 16.0 ± 2.7 PASG 40; p < 0.01) left atrial pressure (LAP) (10.1 ± 1.3 baseline to 14.4 ± 1.8 PASG 20; p < 0.01) pulmonary capillary wedge pressure (PCWP) (11.6 ± 2.0 baseline to 16.8 ± 3.4 PASG 40; p < 0.01) and esophageal pressure (Pes) (5.0 ± 0.8 baseline to 8.6 ± 0.9 PASG 40; p < 0.01). However, transmural right and left atrial pressure (RATP, LATP) and cardiac index (CI) were unchanged. Ten degrees of Trendelenburg resulted in no increase in CVP, PCWP, RATP, or LATP, but CI (2.67 ± 0.07 baseline to 2.82 ±0.1 TREND; p p < 0.01) was significantly less in Trendelenburg compared to PASG at 40 mm Hg. The data demonstrate that elevation in CVP, LAP, and PCWP following PASG application is secondary to an increase in intrathoracic pressure (as measured by Pes). The elevation in CVP inhibits venous return and does not allow for an increase in CI following compression of the lower extremities and abdomen. Trendelenburg positioning increased CI without elevating intrathoracic pressure. The increase in CI with Trendelenburg argues that Trendelenburg positioning increases venous return without other significant hemodynamic alteration. We conclude that Trendelenburg is superior to PASG application in promoting venous return in normovolemic man, an effect expected to be similar in hypovolemia.