Safety and Efficacy of Combined Extracorporeal CO2 Removal and Renal Replacement Therapy in Patients With Acute Respiratory Distress Syndrome and Acute Kidney Injury: The Pulmonary and Renal Support in Acute Respiratory Distress Syndrome Study

Abstract

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 m) 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.

Figure 1.

Individual changes in Paco₂ between baseline and 20 min after ECCo₂R initiation (p < 0.001) at constant tidal volume (6 mL/kg predicted body weight).

Figure 2.

Time course of Paco₂ (A) and pH (B) during the study period; *p < 0.05 vs baseline; †p < 0.05 vs 20 min (M20); £p < 0.05 vs 1 hr (H1).

Figure 3.

Time course of tidal volume (V_T; A), minute ventilation (B), plateau pressure (P_plat; C), and positive end-expiratory pressure (PEEP; D) during the study period; *p < 0.05 vs baseline; †p < 0.05 vs 20 min (M20). .VE = minute ventilation.

Figure 4.

Time course of the total rate of Co₂ elimination (total Vco₂) with respective contribution of the Vco₂ by the natural lung and the Vco₂ by the membrane oxygenator; p = NS for total Vco₂ (Tables 4 and 5 for Vco_2Lung and Vco_2Oxy variations, respectively). Note that the total Vco₂ increased at 20 min (M20) due to additional Co₂ removal provided by the membrane oxygenator. Also note that the total Vco₂ decreased at 1 hr (H1) due to the reduction of tidal volume from 6 to 4 mL/kg predicted body weight, with values similar to baseline.

Figure 5.

Time course of the oxygenator blood flow (A) and Co₂ removal rate by the membrane oxygenator (B) during the study period according to the position of the membrane oxygenator within the renal replacement therapy circuit (upstream of hemofilter [HF] or downstream of HF); *p < 0.05 between positions; †p < 0.05 vs 20 min (M20); £p < 0.05 vs 1 hr (H1).