The effect of Trendelenburg and modified trendelenburg positions on cardiac output, blood pressure, and oxygenation: a preliminary study.

BACKGROUND

Although we have insufficient knowledge about the effects of Trendelenburg positions on various hemodynamic parameters, these positions are frequently used to influence cardiac output and blood pressure in critically ill patients.

OBJECTIVES

To determine the effect of Trendelenburg and modified Trendelenburg positions on five dependent variables: cardiac output, cardiac index, mean arterial pressure, systemic vascular resistance, and oxygenation in critically ill patients.

METHODS

In this preliminary study subjects were 23 cardiac surgery patients (mean age, 55; SD, 8.09) who had a pulmonary artery catheter for cardiac output determination and who were clinically stable, normovolemic and normotensive. Baseline measurements of the dependent variables were taken in the supine position. Patients were then placed in 10 degrees Trendelenburg or 30 degrees modified Trendelenburg position. The dependent variables were measured after 10 minutes in each position. A 2-period, 2-treatment crossover design with a preliminary baseline measurement was used.

RESULTS

Five subjects were unable to tolerate Trendelenburg position because of nausea or pain in the sternal incision. In the 18 who were able to tolerate both position changes, no statistically significant changes were found in the five dependent variables. Changes in systemic vascular resistance over time approached statistical significance and warrant further study.

CONCLUSIONS

This preliminary study does not provide support for Trendelenburg positions as a means to influence hemodynamic parameters such as cardiac output and blood pressure in normovolemic and normotensive patients.