Extracorporeal carbon dioxide removal enhanced by lactic acid infusion in spontaneously breathing conscious sheep

Background: The authors studied the effects on membrane lung carbon dioxide extraction (VCO2ML), spontaneous ventilation, and energy expenditure (EE) of an innovative extracorporeal carbon dioxide removal (ECCO2R) technique enhanced by acidification (acid load carbon dioxide removal [ALCO2R]) via lactic acid. Methods: Six spontaneously breathing healthy ewes were connected to an extracorporeal circuit with blood flow 250 ml/min and gas flow 10 l/min. Sheep underwent two randomly ordered experimental sequences, each consisting of two 12-h alternating phases of ALCO2R and ECCO2R. During ALCO2R, lactic acid (1.5 mEq/min) was infused before the membrane lung. Caloric intake was not controlled, and animals were freely fed. VCO2ML, natural lung carbon dioxide extraction, total carbon dioxide production, and minute ventilation were recorded. Oxygen consumption and EE were calculated. Results: ALCO2R enhanced VCO2ML by 48% relative to ECCO2R (55.3 \ub1 3.1 vs. 37.2 \ub1 3.2 ml/min; P less than 0.001). During ALCO2R, minute ventilation and natural lung carbon dioxide extraction were not affected (7.88 \ub1 2.00 vs. 7.51 \ub1 1.89 l/min, P = 0.146; 167.9 \ub1 41.6 vs. 159.6 \ub1 51.8 ml/min, P = 0.063), whereas total carbon dioxide production, oxygen consumption, and EE rose by 12% each (223.53 \ub1 42.68 vs. 196.64 \ub1 50.92 ml/min, 215.3 \ub1 96.9 vs. 189.1 \ub1 89.0 ml/min, 67.5 \ub1 24.0 vs. 60.3 \ub1 20.1 kcal/h; P less than 0.001). Conclusions: ALCO2R was effective in enhancing VCO2ML. However, lactic acid caused a rise in EE that made ALCO2R no different from standard ECCO2R with respect to ventilation. The authors suggest coupling lactic acid-enhanced ALCO2R with active measures to control metabolism