Physiological effects of lateral steep positioning in critically ill patients suffering from acute respiratory distress syndrome (ARDS)

Introduction

Continuous rotation therapy (CRT) using specially designed beds is known to prevent respiratory complications in ventilated patients and to exert beneficial effects in patients suffering from respiratory failure due to acute lung injury (ALI) and/or ARDS. Little is known about the physiologic effects and potentially beneficial mechanisms of CRT. Moreover, data on the optimal setting of the turning angle and the duration of the pause in maximal lateral steep position are rare.

Methods

Twelve patients suffering from ALI and or ARDS were investigated. Patients were included if a pulmonary artery catheter had been placed and the decision to perform CRT had been taken. Patients were placed into a CRT positioning system (Rotorest, KCI, San Antonio, TX, USA) and the study was performed after 1–3 days of turning. In a first phase, oxygenation and hemodynamics were assessed during continuous turning in the supine and both maximal steep positions at an angle of 62°. In a second phase, the patients were positioned in both maximal steep positions for half an hour. Oxygenation and hemodynamics were assessed in the supine position and every 10 min during steep positioning. All patients were sedated and mechanically ventilated using a pressure-controlled mode. Ventilation parameters were not changed throughout the study period.

Results

Ten male and two female patients fulfilling the diagnostic criteria of ARDS were evaluated. The median age was 54 years (range 22–81 years). Ten patients tolerated prolonged lateral steep positioning well; in two patients the study had to be broken off prematurely in the left lateral position due to a decrease in blood pressure in one, and a decrease in arterial oxygen saturation in the other case. The results were comparable in both phases of the study. Overall, oxygenation did not change significantly with position but tended to deteriorate in lateral steep compared with in the supine position. Interindividual changes of oxygenation with different positions showed a high variability. Tidal volumes and lung compliance declined significantly in the lateral steep position compared with the supine position. The cardiac index and arterial blood pressure did not change significantly.

Conclusion

The beneficial effects of CRT are not due to recruitment of nonventilated lung areas. Steep positioning itself does not improve oxygenation. Continuous turning seems to exert beneficial effects due to other mechanisms. CRT should be performed without prolonged pauses in the maximal steep position.