Effects of thoraco-pelvic supports during prone position in patients with acute lung injury/acute respiratory distress syndrome: a physiological study

INTRODUCTION: This study sought to assess whether the use of thoraco-pelvic supports during prone positioning in patients with acute lung injury/acute respiratory distress syndrome (ALI/ARDS) improves, deteriorates or leaves unmodified gas exchange, hemodynamics and respiratory mechanics. METHODS: We studied 11 patients with ALI/ARDS, sedated and paralyzed, mechanically ventilated in volume control ventilation. Prone positioning with or without thoraco-pelvic supports was applied in a random sequence and maintained for a 1-hour period without changing the ventilation setting. In four healthy subjects the pressures between the body and the contact surface were measured with and without thoraco-pelvic supports. Oxygenation variables (arterial and central venous), physiologic dead space, end-expiratory lung volume (helium dilution technique) and respiratory mechanics (partitioned between lung and chest wall) were measured after 60 minutes in each condition. RESULTS: With thoraco-pelvic supports, the contact pressures almost doubled in comparison with those measured without supports (19.1 +/- 15.2 versus 10.8 +/- 7.0 cmH2O, p < or= 0.05; means +/- SD). The oxygenation-related variables were not different in the prone position, with or without thoraco-pelvic supports; neither were the CO2-related variables. The lung volumes were similar in the prone position with and without thoraco-pelvic supports. The use of thoraco-pelvic supports, however, did lead to a significant decrease in chest wall compliance from 158.1 +/- 77.8 to 102.5 +/- 38.0 ml/cmH2O and a significantly increased pleural pressure from 4.3 +/- 1.9 to 6.1 +/- 1.8 cmH2O, in comparison with the prone position without supports. Moreover, when thoraco-pelvic supports were added, heart rate increased significantly from 82.1 +/- 17.9 to 86.7 +/- 16.7 beats/minute and stroke volume index decreased significantly from 37.8 +/- 6.8 to 34.9 +/- 5.4 ml/m2. The increase in pleural pressure change was associated with a significant increase in heart rate (p= 0.0003) and decrease in stroke volume index (p= 0.0241). CONCLUSION: The application of thoraco-pelvic supports decreases chest wall compliance, increases pleural pressure and slightly deteriorates hemodynamics without any advantage in gas exchange. Consequently, we stopped their use in clinical practice.