The prognostic value of the change of oxygenation index after starting prone position ventilation in ARF

Introduction

In acute respiratory failure, classified as acute lung injury (ALI) or the more severe acute respiratory distress syndrome (ARDS), prone position ventilation (PPV) can improve oxygenation by recruiting alveoli situated in dorsal-dependent regions of the lung and by alteration of the ventilation/perfusion ratio. The aim of our study is to analyze the prognostic value of the change of oxygenation after starting prone position ventilation in ARF.

Methods

We studied 110 consecutive patients with an ARF, n = 18 with ALI and n = 92 with ARDS, at a mean age of 66 ± 13 (SE) years in a clinical followup design at a surgical ICU in a university hospital, who met the criteria of the American European consensus definition. All patients were ventilated intermittent in the SP and in the PP (135° left/right-side-position) for at least 6 hours per day for supportive treatment of ARF. Data collection included, apart from baseline characteristics, the individual oxygenation index. We compared the individual oxygenation index (PaO₂/FiO₂) before and after the start of prone position with the SPSS^® Mann–Whitney test and the data set of each patient with outcome.

Results

PPV was well tolerated in all n = 110 patients and showed a significant increase of PaO₂/FiO₂ ratio in n = 106 within the first 6 hours of PPV (SP 149 ± 0.52 vs PP 230 ± 0.73 mmHg [mean ± SEM]). In the remaining four cases there was a positive effect within the first 24 hours. The surviving patients (n = 43) and the patients who survived 28 days, but died in further course, showed a median increase of oxygenation index of +50.00 and +65.67 mmHg, respectively, after 24 hours of ventilation in the prone position. The patients who died within the first 7 days in ICU showed a median deterioration of -11.46 mmHg. Patients who died after 8–28 days after starting PPV showed a median improvement of +29.92 mmHg after the first 24 hours of ventilation in the prone position.

Conclusion

Our results show that in patients with an acute respiratory failure who are ventilated in the prone position the extent of functional recruitment as a result of the body position change is of prognostic value. Patients with an improvement of the oxygenation index of 50 mmHg and more within the first 24 hours after starting prone position ventilation have a better prognosis than patients with a slight increase or even a deterioration. A less improvement of oxygenation index seems to increase the risk to die in the course of acute respiratory failure. Thus, patients with a high risk of change for the worse can be identified in good time and lead to more interventional approaches for treatment of acute respiratory failure.