OBJECTIVES: To compare the effect of semi-recumbent and sitting positions on gas exchange, respiratory mechanics and hemodynamics in patients weaning from mechanical ventilation. BACKGROUND: Upright positions are encouraged during rehabilitation of the critically ill but there effects have not been well described. METHODS: A prospective, randomized, cross-over trial was conducted. Subjects were passively mobilized from supine into a seated position (out of bed) and from supine to a semi-recumbent position (> 45 degrees backrest elevation in bed). Arterial blood gas (PaO2/FiO2, PaO2, SaO2, PaCO2 and A-a gradient), respiratory mechanics (Ve, Vt, RR, Cdyn, RR/Vt) and hemodynamic measurements (HR, MABP) were collected in supine and at 5 min and 30 min after re-positioning. RESULTS: Thirty-four intubated and ventilated subjects were enrolled. The angle of backrest inclination in sitting (67 +/- 5 degrees) was greater than gained with semi-recumbent positioning (50 +/- 5 degrees, p < 0.001). There were no clinically important changes in arterial blood gas, respiratory mechanic or hemodynamic values due to either position. CONCLUSIONS: Neither position resulted in significant changes in respiratory and hemodynamic parameters. Both positions can be applied safely in patients being weaned from ventilation.

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