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 H 2 O) on the left side was initiated in eight anesthetized, muscle‐relaxed piglets. A recruitment maneuver and a decremental PEEP titration from PEEP 20 cm H 2 O 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 PaO 2 peaked at PEEP 12 cm H 2 O (49 ± 14 kP a) and decreased to 11 ± 5 kP a at ZEEP ( P < 0.001). Pa CO 2 was 9.5 ± 1.3 kP a at 20 cm H 2 O PEEP and did not change when PEEP step‐wise was reduced to 12 cm H 2 O Pa CO 2. At lower PEEP , Pa CO 2 increased markedly. The ventilatory driving pressure was lowest at PEEP 14 cm H 2 O (19.6 ± 5.8 cm H 2 O) and increased to 38.3 ± 6.1 cm H 2 O at ZEEP ( P < 0.001). When reducing PEEP below 12‐14 cm H 2 O 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 H 2 O 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.