Relationship between gas exchange response to prone position and lung recruitability during acute respiratory failure.
ABSTRACT To clarify whether the gas exchange response to prone position is associated with lung recruitability in mechanically ventilated patients with acute respiratory failure.
In 32 patients, gas exchange response to prone position was investigated as a function of lung recruitability, measured by computed tomography in supine position.
No relationship was found between increased oxygenation in prone position and lung recruitability. In contrast, the decrease of PaCO(2) was related with lung recruitability (R(2) 0.19; P = 0.01). Patients who decreased their PaCO(2) more than the median value (-0.9 mmHg) had a greater lung recruitability (19 +/- 16 vs. 8 +/- 6%; P = 0.02), higher baseline PaCO(2) (48 +/- 8 vs. 41 +/- 11 mmHg; P = 0.07), heavier lungs (1,968 +/- 829 vs. 1,521 +/- 342 g; P = 0.06) and more non-aerated tissue (1,009 +/- 704 vs. 536 +/- 188 g; P = 0.02) than those who did not.
During prone position, changes in PaCO(2), but not in oxygenation, are associated with lung recruitability which, in turn, is associated with the severity of lung injury.
Article: Prone position.[Show abstract] [Hide abstract]
ABSTRACT: Prone position can prevent ventilator-induced lung injury in acute respiratory distress syndrome (ARDS) patients receiving conventional mechanical ventilation and, hence, may have the potential to improve survival from this basis. Even though no single randomized controlled trial has proven benefit on patient outcome until recently, two meta-analyses, one on grouped data and the other on individual data, have shown that patients with PaO2/FIO2 ratio less than 100 mmHg at the time of inclusion did benefit from prone position. As a fifth trial completed recently has shown a significant reduction in mortality in patients with severe and confirmed ARDS from using prone position, the purpose of this review is to revisit prone positioning in ARDS in the light of these new findings. In this trial done in patients with severe ARDS severity criteria (PaO2/FIO2 ratio less than 150 mmHg with positive end expiratory pressure of 5 cmH2O or more, FIO2 of 60% or more and tidal volume around 6 ml/kg predicted body weight) confirmed 12-24 h after the onset of ARDS, the day 28 mortality in the supine group (229 patients) was 32.8 versus 16% in the prone group (237 patients) (P < 0.001). Significant reduction in mortality was confirmed at day 90. From the combined results of the two meta-analyses and the last randomized controlled trial, there is a very strong signal to use prone position in patients with severe ARDS, as early as possible and for long sessions.Current opinion in critical care 12/2013; · 3.18 Impact Factor
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ABSTRACT: In the prone position, CT-scan densities redistribute from dorsal to ventral as the dorsal region tends to re-expand while the ventral zone tends to collapse. Although gravitational influence is similar in both positions, dorsal recruitment usually prevails over ventral de-recruitment, due to the need for the lung and its confining chest wall to conform to the same volume. The final result of proning is that the overall lung inflation is more homogeneous from dorsal to ventral than in the supine position with more homogeneously distributed stress and strain. As the distribution of perfusion remains nearly constant in both postures, proning usually improves oxygenation. Animal experiments clearly show that prone positioning delays or prevents ventilation-induced lung injury, likely due in large part to more homogeneously distributed stress and strain. Over the last 15 years, five major trials have been conducted to compare prone and supine position in ARDS regarding survival advantage. The sequence of trials enrolled patients who were progressively more hypoxemic, exposure to prone position was extended from 8 to 17 hours/day, and lung protective ventilation was more rigorously applied. Single patient and meta-analyses drawing from the four major trials showed significant survival benefit in patients with PaO2/FiO2 lower than 100. The latest PROSEVA trial confirmed these benefits in a formal randomized study. The bulk of data indicates that in severe ARDS, carefully performed prone positioning offers an absolute survival advantage of 10-17%, making this intervention highly recommended in this specific population subset.American Journal of Respiratory and Critical Care Medicine 10/2013; · 11.04 Impact Factor
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ABSTRACT: In patients with acute respiratory distress syndrome (ARDS), in supine position, there is a decrease of inflation along the sternum vertebral axis, up to lung collapse. In 1991 we published a report showing that, in ARDS patients, shifting from supine to prone position led immediately to the inversion of the inflation gradient and to a redistribution of densities from dorsal to ventral lung regions. This led to a "sponge model" as a wet sponge, similar to a heavy edematous lung, squeezes out the gas in the most dependent regions, due to the weight-related increase of the compressive forces. The sponge model accounts for density distribution in prone position, for which the unloaded dorsal regions are recruited, while the loaded ventral region, collapses. In addition, the sponge model accounts for the mechanism through which the positive end-expiratory pressure acts as counterforce to oppose the collapsing, compressing forces. The final result of proning was that the inversion of gravitational forces, together with other factors such as lung-chest wall shape-matching and the heart weight led to a more homogeneous distribution of inflation throughout the lung parenchyma. This is associated with oxygenation improvement as the dorsal recruitment, for anatomical reasons, prevails on the ventral de-recruitment. The more homogeneous distribution of inflation (i.e. of stress and strain) decreases/prevents the ventilator-induced lung injury, as consistently shown in animal experiments. Finally, and a series of clinical trials led to the conclusion that in patients with severe ARDS, the prone position provides a significant survival advantage.European Journal of Intensive Care Medicine 09/2013; · 5.17 Impact Factor