Objective: 

To assess the safety and efficacy of combining extracorporeal CO₂ removal with continuous renal replacement therapy in patients presenting with acute respiratory distress syndrome and acute kidney injury.

Design: 

Prospective human observational study.

Settings: 

Patients received volume-controlled mechanical ventilation according to the acute respiratory distress syndrome net protocol. Continuous venovenous hemofiltration therapy was titrated to maintain maximum blood flow and an effluent flow of 45 mL/kg/h with 33% predilution.

Patients: 

Eleven patients presenting with both acute respiratory distress syndrome and acute kidney injury required renal replacement therapy.

Interventions: 

A membrane oxygenator (0.65 m²) was inserted within the hemofiltration circuit, either upstream (n = 7) or downstream (n = 5) of the hemofilter. Baseline corresponded to tidal volume 6 mL/kg of predicted body weight without extracorporeal CO₂ removal. The primary endpoint was 20% reduction in PaCO₂ at 20 minutes after extracorporeal CO₂ removal initiation. Tidal volume was subsequently reduced to 4 mL/kg for the remaining 72 hours.

Measurements and Main Results: 

Twelve combined therapies were conducted in the 11 patients. Age was 70 ± 9 years, Simplified Acute Physiology Score II was 69 ± 13, Sequential Organ Failure Assessment score was 14 ± 4, lung injury score was 3 ± 0.5, and PaO₂/FIO₂ was 135 ± 41. Adding extracorporeal CO₂ removal at tidal volume 6 mL/kg decreased PaCO₂ by 21% (95% CI, 17–25%), from 47 ± 11 to 37 ± 8 Torr (p < 0.001). Lowering tidal volume to 4 mL/kg reduced minute ventilation from 7.8 ± 1.5 to 5.2 ± 1.1 L/min and plateau pressure from 25 ± 4 to 21 ± 3 cm H₂O and raised PaCO₂ from 37 ± 8 to 48 ± 10 Torr (all p < 0.001). On an average of both positions, the oxygenator’s blood flow was 410 ± 30 mL/min and the CO₂ removal rate was 83 ± 20 mL/min. The oxygenator blood flow (p <0.001) and the CO₂ removal rate (p = 0.083) were higher when the membrane oxygenator was placed upstream of the hemofilter. There was no safety concern.

Conclusions: 

Combining extracorporeal CO₂ removal and continuous venovenous hemofiltration in patients with acute respiratory distress syndrome and acute kidney injury is safe and allows efficient blood purification together with enhanced lung protective ventilation.