Evaluation of an autoregulatory ECMO system for total respiratory support in an acute ovine model

Extracorporeal membrane oxygenation (ECMO) has become a mainstay of therapy for patients suffering from severe respiratory failure. Ambulatory ECMO systems aim to provide long-term out-of-hospital respiratory support. As a patient's activity level changes, the required level of ECMO support varies with oxygen consumption and metabolic fluctuations. To compensate for such changes, an autoregulatory ECMO system (AR-ECMO) has been developed and its performance was evaluated as a proof of concept in an acute ovine model. The AR-ECMO system consists of a regular ECMO circuit and an electromechanical control system. A custom fuzzy logic control algorithm was implemented to adjust the blood flow and sweep gas flow of the ECMO circuit to meet the varying respiratory demand by utilizing two noninvasive sensors for venous oxyhemoglobin saturation and the oxygenator exhaust gas CO₂ concentration. Disturbance responses of the AR-ECMO to induced acute respiratory distress were assessed for six hours in four juvenile sheep cannulated with a veno-pulmonary artery ECMO configuration, including acute ventilator shutoff, ventilator step change (off-on-off), and forced desaturation. All sheep survived for the study duration. The AR-ECMO system was able to respond and maintain stable hemodynamics and physiological blood gas contents (SpO₂  = 96.3 % ± 4.29, pH 7.44 ± 0.09, pCO₂  = 38.9 ± 9.9 mm Hg, and pO₂ =237.9 ± 123.6 mm Hg) during simulated respiratory distress. Acceptable correlation between oxygenator exhaust gas CO₂ and oxygenator outlet pCO₂ were observed (R²  = 0.84). In summary, the AR-ECMO system successfully maintained physiologic control of peripheral oxygenation and carbon dioxide over the study period, utilizing only measurements taken directly from the ECMO circuit. The range of system response necessitates an adaptable system in the setting of variable metabolic demands. The ability of this system to respond to significant disturbances in ventilator support is encouraging. Future work to evaluate our AR-ECMO system in long-term, awake animal studies is necessary for further refinement.