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Effects of PEEP on oxygenation and respiratory mechanics during one-lung ventilation.

BACKGROUND
One-lung ventilation-related hypoxaemia (OLV-RH) can occur in patients with healthy lungs. In this case, PEEP frequently improves oxygenation. The aim of this study was to determine, in a healthy lung model of OLV, whether the increase in PEEP improved oxygenation and whether the mechanisms involved include both inspiratory lung recruitment and an end-expiratory lung volume increase. Since inhaled nitric oxide (iNO) may have a synergistic effect on oxygenation in the case of PEEP-induced recruitment, their association was also tested.


METHODS
Twenty pigs were studied during open-chest, left OLV. Arterial blood gases and haemodynamic variables were measured at different levels of PEEP (0, 5, 10 and 15 cm H(2)O) applied in random order with or without iNO 4 p.p.m. Pressure-volume curves were measured at each level of PEEP.


RESULTS
PEEP(5) and PEEP(10) improved Pa(O(2))/FI(O(2)) ratio (P<0.005) and shunt (P<0.005) regardless of the presence of iNO. PEEP(15) improved oxygenation and shunt only when it was associated with iNO (P<0.001). Whereas PEEP(5), PEEP(10) and PEEP(15) were associated with a significant increase in end-expiratory volume (P<0.001), only PEEP(5) and PEEP(10) were associated with continuous lung volume recruitment (P<0.01). Moreover, PEEP(15) induced a significant decrease in linear compliance (P<0.001).


CONCLUSIONS
In a healthy porcine lung model of OLV-RH, moderate PEEP can improve oxygenation. This effect implies both expiratory and inspiratory pulmonary recruitment. Co-administration of 4 p.p.m. iNO was ineffective.