In the Protective Ventilation in Cardiac Surgery (PROVECS) randomized, controlled trial, an open-lung ventilation strategy did not improve postoperative respiratory outcomes after on-pump cardiac surgery. In this prespecified subanalysis, the authors aimed to assess the regional distribution of ventilation and plasma biomarkers of lung epithelial and endothelial injury produced by that strategy.
Perioperative open-lung ventilation consisted of recruitment maneuvers, positive end-expiratory pressure (PEEP) = 8 cm H2O, and low-tidal volume ventilation including during cardiopulmonary bypass. Control ventilation strategy was a low-PEEP (2 cm H2O) low-tidal volume approach. Electrical impedance tomography was used serially throughout the perioperative period (n = 56) to compute the dorsal fraction of ventilation (defined as the ratio of dorsal tidal impedance variation to global tidal impedance variation). Lung injury was assessed serially using biomarkers of epithelial (soluble form of the receptor for advanced glycation end-products, sRAGE) and endothelial (angiopoietin-2) lung injury (n = 30).
Eighty-six patients (age = 64 ± 12 yr; EuroSCORE II = 1.65 ± 1.57%) undergoing elective on-pump cardiac surgery were studied. Induction of general anesthesia was associated with ventral redistribution of tidal volumes and higher dorsal fraction of ventilation in the open-lung than the control strategy (0.38 ± 0.07 vs. 0.30 ± 0.10; P = 0.004). No effect of the open-lung strategy on the dorsal fraction of ventilation was noted at the end of surgery after median sternotomy closure (open-lung = 0.37 ± 0.09 vs. control = 0.34 ± 0.11; P = 0.743) or in extubated patients at postoperative day 2 (open-lung = 0.63 ± 0.18 vs. control = 0.59 ± 0.11; P > 0.999). Open-lung ventilation was associated with increased intraoperative plasma sRAGE (7,677 ± 3,097 pg/ml vs. 6,125 ± 1,400 pg/ml; P = 0.037) and had no effect on angiopoietin-2 (P > 0.999).
In cardiac surgery patients, open-lung ventilation provided larger dorsal lung ventilation early during surgery without a maintained benefit as compared with controls at the end of surgery and postoperative day 2 and was associated with higher intraoperative plasma concentration of sRAGE suggesting lung overdistension.
The optimal ventilatory strategy for patients undergoing on-pump cardiac surgery remains controversial
The authors previously reported a randomized, controlled trial comparing an open-lung strategy consisting of low tidal volumes, moderate levels of positive end-expiratory pressure, recruitment maneuvers, and ventilation during cardiopulmonary bypass versus European-based conventional management (low positive end-expiratory pressure, low tidal volumes, no ventilation during bypass) in 488 low-risk patients, which failed to show a difference in the incidence of postoperative pulmonary complications
A prespecified substudy monitored a subset of those patients with electrical impedance tomography to assess dorsal versus ventral distribution of ventilation and serially assessed biomarkers of potential epithelial (soluble form of the receptor for advanced glycation end-products) or endothelial (angiopoietin-2) lung injury
After induction, tidal volume was redistributed to ventral regions with a statistically significant higher dorsal fraction of ventilation in the open-lung group
However, this effect was transient with no differences noted at the end of surgery or in extubated patients at postoperative day 2
Significantly higher intraoperative levels of soluble form of the receptor for advanced glycation end-products were noted in the open-lung group, suggestive of epithelial damage from lung overdistention