Respiratory Dialysis—A Novel Low Bicarbonate Dialysate to Provide Extracorporeal Co2 Removal

Objectives

We designed a novel respiratory dialysis system to remove Co₂ from blood in the form of bicarbonate. We aimed to determine if our respiratory dialysis system removes Co₂ at rates comparable to low-flow extracorporeal Co₂ removal devices (blood flow < 500 mL/min) in a large animal model.

Design

Experimental study.

Setting

Animal research laboratory.

Subjects

Female Yorkshire pigs.

Interventions

Five bicarbonate dialysis experiments were performed. Hypercapnia (Pco₂ 90–100 mm Hg) was established in mechanically ventilated swine by adjusting the tidal volume. Dialysis was then performed with a novel low bicarbonate dialysate.

Measurements and Main Results

We measured electrolytes, blood gases, and plasma-free hemoglobin in arterial blood, as well as blood entering and exiting the dialyzer. We used a physical-chemical acid-base model to understand the factors influencing blood pH after bicarbonate removal. During dialysis, we removed 101 (±13) mL/min of Co₂ (59 mL/min when normalized to venous Pco₂ of 45 mm Hg), corresponding to a 29% reduction in Paco₂ (104.0 ± 8.1 vs 74.2 ± 8.4 mm Hg; p < 0.001). Minute ventilation and body temperature were unchanged during dialysis (1.2 ± 0.4 vs 1.1 ± 0.4 L/min; p = 1.0 and 35.3°C ± 0.9 vs 35.2°C ± 0.6; p = 1.0). Arterial pH increased after bicarbonate removal (7.13 ± 0.04 vs 7.21 ± 0.05; p < 0.001) despite no attempt to realkalinize the blood. Our modeling showed that dialysate electrolyte composition, plasma albumin, and plasma total Co₂ accurately predict the measured pH of blood exiting the dialyser. However, the final effluent dose exceeded conventional doses, depleting plasma glucose and electrolytes, such as potassium and phosphate.

Conclusions

Bicarbonate dialysis results in Co₂ removal at rates comparable with existing low-flow extracorporeal Co₂ removal in a large animal model, but the final dialysis dose delivered needs to be reduced before the technique can be used for prolonged periods.