Total arteriovenous CO₂ removal: Simplifying extracorporeal support for respiratory failure

Background. To reduce the complexity, complications, and cost of conventional extracorporeal membrane oxygenation, we have developed a technique of simplified arteriovenous extracorporeal CO₂ removal (AVCO₂R) with a low-resistance membrane gas exchanger for total CO₂ removal to provide lung rest in the setting of severe respiratory failure. Methods. We initially used AVCO₂R in healthy animals to quantify the gas exchange capabilities of the system and establish ventilator management protocols for the subsequent studies of AVCO₂R in a large animal model of respiratory failure secondary to a severe smoke inhalation injury. Results. In healthy sheep the maximum spontaneous arteriovenous flow ranged from 1,350 to 1,500 mL/min, whereas CO₂ removal plateaued at a blood flow of approximately 1,000 ml/min in which 112 ± 3 mL/min CO₂ was removed, allowing an 84% reduction in the minute ventilation of from 6.9 ± 0.8 L/min to 1.1 ± 0.4 L/min (p < 0.01) without triggering hypercapnia. A subsequent reduction in extracorporeal flow at a reduced minute volume led to the development of hypercapnia only if it decreased to less than 500 mL/min. We also applied AVCO₂R in mechanically ventilated sheep with a severe smoke inhalation injury and removed 95% (111 ± 4 mL/min) of the total CO₂ production. This allowed the minute ventilation to be reduced by 95% and the peak inspiratory pressures by 52% (both p < 0.05) over 6 hours and produced no adverse hemodynamic effects. The partial pressure of arterial oxygen was maintained above 100 mm Hg at a maximally reduced minute volume. The mean AVCO₂R flow was 1,213 ± 29 mL/min, averaging 27% ± 1% of the cardiac output. Conclusions. We conclude that AVCO₂R in a simple arteriovenous shunt is a less complicated technique than extracorporeal membrane oxygenation and is capable of total CO₂ removal that allows a significant reduction in the minute ventilation and peak airway pressure during severe respiratory failure.