Ventilation-perfusion distribution and shunt fraction during one-lung ventilation: effect of different inhaled oxygen levels

Ventilation with higher fraction of inspired oxygen (F(I)O2) is one of the commonly-chosen strategies executed for treatment of hypoxemia during one lung ventilation (OLV) for thoracic surgery. In this study, we investigated the effect of F(I)O2 on pulmonary ventilation-perfusion (VA/Q) distribution during OLV. Six pigs, weighing 27 to 34 kg, were selected for this study. Following by a steady-state period, randomized administrations of F(I)O2 with 0.4, 0.6 and 1.0 were performed for 30 minutes at the right lateral decubitus position during OLV, while hemodynamic data and lung mechanics were simultaneously monitored. The VA/Q distributions of the lung(s) were assessed by the multiple inert gas elimination technique (MIGET). PaO2 at F(I)O2 of 100% was significantly reduced in OLV compared with two-lung ventilation (TLV) (522 +/- 104 vs. 653 +/- 21 mmHg; P < 0.001) at right lateral decubitus position. MIGET algorithms demonstrated a wider VA/Q distribution during OLV at F(I)O2 of 40%, as compared with distribution during TLV at F(I)O2 of 100%, but a bimodal perfusion distribution shifted to lower VA/Q component during OLV at F(I)O2 of 100%. There was an increase of pulmonary shunting in OLV, as compared with TLV at F(I)O2 of 100% (1.94 +/- 2.2% vs. 9.5 +/- 9.7%; P < 0.01). In addition, OLV caused a significant increase in the dispersion of perfusion at F(I)O2 of 100% (0.62 +/- 0.20 vs. 0.44 +/- 0.23; P < 0.01), but ventilation showed no denoting changes (1.06 +/- 0.20 vs. 0.98 +/- 0.35; P > 0.01). During OLV with right lateral decubitus position, there were no significant changes in the pulmonary shunt, the dispersion of perfusion and ventilation at different F(I)O2. OLV resulted in an increase in pulmonary shunting and heterogeneity compared with TLV. Furthermore, the PaO2 decreased during OLV regardless of the postural changes. At different F(I)O2, there were no significant changes in the pulmonary shunt, the dispersion of perfusion and ventilation during OLV with right lateral decubitus posture.