Associations between changes in oxygenation, dead space and driving pressure induced by the first prone position session and mortality in patients with acute respiratory distress syndrome.

BACKGROUND

Outcome prediction in acute respiratory distress syndrome (ARDS) is challenging, especially in patients with severe hypoxemia. The aim of the current study was to determine the prognostic capacity of changes in PaO/FiO, dead space fraction (V/V) and respiratory system driving pressure (ΔP) induced by the first prone position (PP) session in patients with ARDS.

METHODS

This was a post hoc analysis of the conveniently-sized 'Molecular Diagnosis and Risk Stratification of Sepsis' study (MARS). The current analysis included ARDS patients who were placed in the PP. The primary endpoint was the prognostic capacity of the PP-induced changes in PaO/FiO, V/V, and ΔP for 28-day mortality. PaO/FiO, V/V, and ΔP was calculated using variables obtained in the supine position before and after completion of the first PP session. Receiving operator characteristic curves (ROC) were constructed, and sensitivity, specificity positive and negative predictive value were calculated based on the best cutoffs.

RESULTS

Ninety patients were included; 28-day mortality was 46%. PP-induced changes in PaO/FiO and V/V were similar between survivors non-survivors [+83 (+24 to +137) +58 (+21 to +113) mmHg, and -0.06 (-0.17 to +0.05) -0.08 (-0.16 to +0.08), respectively]. PP-induced changes in ΔP were different between survivors non-survivors [-3 (-7 to 2) 0 (-3 to +3) cmHO; P=0.03]. The area under the ROC of PP-induced changes in ΔP for mortality, however, was low [0.63 (95% confidence interval (CI), 0.50 to 0.75]; PP-induced changes in ΔP had a sensitivity and specificity of 76% and 56%, and a positive and negative predictive value of 60% and 73%.

CONCLUSIONS

Changes in PaO/FiO, V/V, and ΔP induced by the first PP session have poor prognostic capacities for 28-day mortality in ARDS patients.