High- versus Low-Flow Extracorporeal Respiratory Support in Experimental Hypoxemic Acute Lung Injury

Rationale: In the EOLIA (ECMO to Rescue Lung Injury in Severe ARDS) trial, oxygenation was similar between intervention and conventional groups, whereas (V) over dot(E) was reduced in the intervention group. Comparable reductions in ventilation intensity are theoretically possible with low-flow extracorporeal CO2 removal (ECCO2R), provided oxygenation remains acceptable. Objectives: To compare the effects of ECCO2R and extracorporeal membrane oxygenation (ECMO) on gas exchange, respiratory mechanics, and hemodynamics in animal models of pulmonary (intratracheal hydrochloric acid) and extrapulmonary (intravenous oleic acid) lung injury. Methods: Twenty-four pigs with moderate to severe hypoxemia (PaO2:F-IO2 <= 150 mm Hg) were randomized to ECMO (blood flow 50-60 ml/kg/min), ECCO2R (0.4 L/min), or mechanical ventilation alone. Measurements and Main Results: (V) over dot(O2), (V) over dot(CO2), gas exchange, hemodynamics, and respiratory mechanics were measured and are presented as 24-hour averages. Oleic acid versus hydrochloric acid showed higher extravascular lung water (1,424 +/- 419 vs. 574 +/- 195 ml; P < 0.001), worse oxygenation (Pa-O2:F-IO2 = 125 +/- 14 vs. 151 +/- 11 mm Hg; P, 0.001), but better respiratory mechanics (plateau pressure 27 +/- 4 vs. 30 +/- 3 cm H2O; P= 0.017). Both models led to acute severe pulmonary hypertension. In both models, ECMO (3.7 +/- 0.5 L/min), compared with ECCO2R (0.4 L/min), increased mixed venous oxygen saturation and oxygenation, and improved hemodynamics (cardiac output= 6.0 +/- 61.4 vs. 5.2 +/- 1.4 L/min; P= 0.003). (V) over dot(O2) and (V) over dot(CO2), irrespective of lung injury model, were lower during ECMO, resulting in lower Pa-CO2 and (V) over dot(E) but worse respiratory elastance compared with ECCO2R (64 +/- 27 vs. 40 +/- 8 cm H2O/L; P<0.001). Conclusions: ECMO was associated with better oxygenation, lower (V) over dot(O2), and better hemodynamics. ECCO2R may offer a potential alternative to ECMO, but there are concerns regarding its effects on hemodynamics and pulmonary hypertension.