Distribution of transpulmonary pressure during one-lung ventilation in pigs at different body positions.

. Global and regional transpulmonary pressure (P) during one-lung ventilation (OLV) is poorly characterized. We hypothesized that global and regional P and driving P (ΔP) increase during protective low tidal volume OLV compared to two-lung ventilation (TLV), and vary with body position. . In sixteen anesthetized juvenile pigs, intra-pleural pressure sensors were placed in ventral, dorsal, and caudal zones of the left hemithorax by video-assisted thoracoscopy. A right thoracotomy was performed and lipopolysaccharide administered intravenously to mimic the inflammatory response due to thoracic surgery. Animals were ventilated in a volume-controlled mode with a tidal volume (V) of 6 mL kg during TLV and of 5 mL kg during OLV and a positive end-expiratory pressure (PEEP) of 5 cmHO. Global and local transpulmonary pressures were calculated. Lung instability was defined as end-expiratory P<2.9 cmHO according to previous investigations. Variables were acquired during TLV (TLVsupine), left lung ventilation in supine (OLVsupine), semilateral (OLVsemilateral), lateral (OLVlateral) and prone (OLVprone) positions randomized according to Latin-square sequence. Effects of position were tested using repeated measures ANOVA. . End-expiratory P and ΔP were higher during OLVsupine than TLVsupine. During OLV, regional end-inspiratory P and ΔP did not differ significantly among body positions. Yet, end-expiratory P was lower in semilateral (ventral: 4.8 ± 2.9 cmHO; caudal: 3.1 ± 2.6 cmHO) and lateral (ventral: 1.9 ± 3.3 cmHO; caudal: 2.7 ± 1.7 cmHO) compared to supine (ventral: 4.8 ± 2.9 cmHO; caudal: 3.1 ± 2.6 cmHO) and prone position (ventral: 1.7 ± 2.5 cmHO; caudal: 3.3 ± 1.6 cmHO), mainly in ventral ( ≤ 0.001) and caudal ( = 0.007) regions. Lung instability was detected more often in semilateral (26 out of 48 measurements; = 0.012) and lateral (29 out of 48 measurements, < 0.001) as compared to supine position (15 out of 48 measurements), and more often in lateral as compared to prone position (19 out of 48 measurements, = 0.027). . Compared to TLV, OLV increased lung stress. Body position did not affect stress of the ventilated lung during OLV, but lung stability was lowest in semilateral and lateral decubitus position.