Extra-corporeal membrane oxygenation (ECMO) is an important therapy for severe respiratory failure. However, comprehensive understanding of the interplay between the membrane and native lungs is limited. Herein, we introduce the concept of relative gas exchange. In this study, data was collected from a subset of four experiments conducted in a porcine model of lung injury. The animals were mechanically ventilated under general anesthesia and underwent venovenous ECMO (VV ECMO) at 0, 6, 12, or 18 cmH2O of positive end-expiratory pressure (PEEP) over a 15-hour period. Blood gas analysis was performed on arterial and venous blood, as well as on ECMO drainage and return. Oxygen uptake and carbon dioxide removal, as well as the contribution of the membrane lung to overall gas exchange ratio r were calculated. Blood gas measurements in the four measurement sites were as follows: pH 7.37 (IQR, 0.107), pco2 57.4 mmHg (IQR, 20.9), and po2 88.0 mmHg (IQR, 439.0). Relative contribution of ECMO on oxygen uptake rO2 (at PEEP0: 36.80 %, PEEP6: 52.5 %, PEEP12: 38.0 %, PEEP18: 81.0 %) and carbon dioxide removal rCO2 (at PEEP0: 51.9 %, PEEP6: 44.9 %, PEEP12: 57.6 %, PEEP18: 49.0 %) respectively. All PEEP levels showed similar rco2 values, yet for PEEP = 18 cmH2O, sweep gas flow was substantially lower: PEEP0: 3.25 l/min (IQR, 0.5), PEEP6/PEEP12: 3.25 l/min (IQR, 1.0), PEEP18: 1.5 l/min (IQR, 1.0). With similar ECMO blood flow of 2.22 ml/min (IQR, 0.265), the membrane lung had a higher contribution to oxygen uptake in the experiment at PEEP18: 81.0 % (IQR, 16.0) compared to the other PEEP levels: 44.0 % (IQR, 14.6). In this study, the concept of relative gas exchange between native and membrane lung for VV ECMO is introduced for the first time. The results observed, which were derived from a fairly small study population, are consistent with existing knowledge regarding ventilatory and ECMO settings and their contribution to total gas exchange.

Clinical Relevance—This study introduces the novel concept of relative gas exchange balance between native and membrane lung. If substantiated, this concept could lead to considerable improvements in the precise management of gas exchange, weaning strategies and the patient outcome when receiving ECMO therapy.