Percutaneous extracorporeal arteriovenous carbon dioxide removal improves survival in respiratory distress syndrome: A prospective randomized outcomes study in adult sheep

Objective: Arteriovenous carbon dioxide removal (AVCO₂R) uses a simple arteriovenous shunt for CO₂ removal to minimize barotrauma/volutrauma from mechanical ventilation. We performed a prospective randomized outcomes study of AVCO₂R in our new, clinically relevant model of respiratory distress syndrome. Methods: Adult sheep (n = 18) received an LD₅₀ severe smoke inhalation and 40% third-degree burn. When respiratory distress syndrome developed (PaO₂/FIO₂ < 200 at 40 to 48 hours), animals were randomized to the AVCO₂R (n = 9) or sham group (n = 9) for 7 days. Ventilator management protocols mandated reductions in minute ventilation, first tidal volume to peak inspiratory pressure less than 30 cm H₂O, then respiratory rate when PaCO₂ was less than 40 mm Hg. Pao₂ was kept above 60 mm Hg by adjusting FIO₂. When FIO₂ was 0.21, animals were weaned. Results: The study required 2946 animal-hours of critical care with 696 AVCO₂R hours. One died in each group during model development. AVCO₂R flow from 820 mL/min to 970 mL/min (11% to 14% cardiac output) removed CO₂ at a rate of 92 to 116 mL/min (mean 103 mL/min; 93%-97% of CO₂ production). Heart rate, mean arterial pressure, cardiac output, and pulmonary arterial wedge pressure remained relatively constant. Within 48 hours, AVCO₂R allowed significant ventilator reductions versus baseline in the following measurements: tidal volume (420 to 270 mL), peak inspiratory pressure (25 to 14 cm H₂O), minute ventilation (13 to 5 L/min), respiratory rate (26 to 16 breaths/min), and FIO₂ (0.88 to 0.35). Ventilator-free days with AVCO₂R were 3.9 versus 0.2 (P < .01) for sham animals, and ventilator-dependent days with AVCO₂R were 2.4 versus 6.2 (P < .01) for the 3 sham survivors. All 8 AVCO₂R animals and 3 of 8 sham animals survived 7 days after randomization. Conclusions: Percutaneous AVCO₂R achieved significant reduction in airway pressures, increased ventilator-free days, decreased ventilator-dependent days, and improved survival in a sheep model of respiratory distress syndrome.