Peep titration based on the open lung approach during one lung ventilation in thoracic surgery: a physiological study

BACKGROUND: During thoracic surgery in lateral decubitus, one lung ventilation (OLV) may impair respiratory mechanics and gas exchange. We tested a strategy based on an open lung approach (OLA) consisting in lung recruitment immediately followed by a decremental positive-end expiratory pressure (PEEP) titration to the best respiratory system compliance (C(RS)) and separately quantified the elastic properties of the lung and the chest wall. Our hypothesis was that this approach would improve gas exchange. Further, we were interested in documenting the impact of the OLA on partitioned respiratory system mechanics. METHODS: In thirteen patients undergoing upper left lobectomy we studied lung and chest wall mechanics, transpulmonary pressure (P(L)), respiratory system and transpulmonary driving pressure (ΔP(RS) and ΔP(L)), gas exchange and hemodynamics at two time-points (a) during OLV at zero end-expiratory pressure (OLV(pre-OLA)) and (b) after the application of the open-lung strategy (OLV(post-OLA)). RESULTS: The external PEEP selected through the OLA was 6 ± 0.8 cmH(2)O. As compared to OLV(pre-OLA), the PaO(2)/FiO(2) ratio went from 205 ± 73 to 313 ± 86 (p = .05) and C(L) increased from 56 ± 18 ml/cmH(2)O to 71 ± 12 ml/cmH(2)O (p = .0013), without changes in C(CW). Both ΔP(RS) and ΔP(L) decreased from 9.2 ± 0.4 cmH(2)O to 6.8 ± 0.6 cmH(2)O and from 8.1 ± 0.5 cmH(2)O to 5.7 ± 0.5 cmH(2)O, (p = .001 and p = .015 vs OLV(pre-OLA)), respectively. Hemodynamic parameters remained stable throughout the study period. CONCLUSIONS: In our patients, the OLA strategy performed during OLV improved oxygenation and increased C(L) and had no clinically significant hemodynamic effects. Although our study was not specifically designed to study ΔP(RS) and ΔP(L), we observed a parallel reduction of both after the OLA. TRIAL REGISTRATION: TRN: ClinicalTrials.gov, NCT03435523, retrospectively registered, Feb 14 2018.