Optimal PEEP during one-lung ventilation with capnothorax: An experimental study

Background One-lung ventilation (OLV) with induced capnothorax carries the risk of severely impaired ventilation and circulation. Optimal PEEP may mitigate the physiological perturbations during these conditions. Methods Right-sided OLV with capnothorax (16 cm H2O) on the left side was initiated in eight anesthetized, muscle-relaxed piglets. A recruitment maneuver and a decremental PEEP titration from PEEP 20 cm H2O to zero end-expiratory pressure (ZEEP) was performed. Regional ventilation and perfusion were studied with electrical impedance tomography and computer tomography of the chest was used. End-expiratory lung volume and hemodynamics were recorded and. Results PaO2 peaked at PEEP 12 cm H2O (49 +/- 14 kPa) and decreased to 11 +/- 5 kPa at ZEEP (P < 0.001). PaCO2 was 9.5 +/- 1.3 kPa at 20 cm H2O PEEP and did not change when PEEP step-wise was reduced to 12 cm H2O PaCO2. At lower PEEP, PaCO2 increased markedly. The ventilatory driving pressure was lowest at PEEP 14 cm H2O (19.6 +/- 5.8 cm H2O) and increased to 38.3 +/- 6.1 cm H2O at ZEEP (P < 0.001). When reducing PEEP below 12-14 cm H2O ventilation shifted from the dependent to the nondependent regions of the ventilated lung (P = 0.003), and perfusion shifted from the ventilated to the nonventilated lung (P = 0.02). Conclusion Optimal PEEP was 12-18 cm H2O and probably relates to capnothorax insufflation pressure. With suboptimal PEEP, ventilation/perfusion mismatch in the ventilated lung and redistribution of blood flow to the nonventilated lung occurred.