Serum Bicarbonate Levels Among Patients on Venovenous Extracorporeal Membrane Oxygenation for Acute Respiratory Distress Syndrome With and Without Kidney Replacement Therapy

Abstract

OBJECTIVES: For patients with acute respiratory distress syndrome (ARDS) receiving venovenous extracorporeal membrane oxygenation (ECMO) who develop acute kidney injury (AKI) requiring kidney replacement therapy (KRT), the inability to renally compensate for respiratory acidosis could result in increased sweep gas flow to normalize arterial pH. Our objective was to examine the relationship of serum bicarbonate levels, arterial pH, sweep gas flow, and Paco 2. DESIGN: This is a retrospective cohort study. We compared patients who received KRT while undergoing venovenous ECMO to patients who did not. SETTING: Vanderbilt University Medical Center, February 2019 to February 2022. PATIENTS: We examined data from adult patients receiving venovenous ECMO for ARDS. INTERVENTIONS: Values for serum bicarbonate, arterial pH, Paco 2, and sweep gas flow were collected daily from time of cannulation until the earlier of decannulation, 30 days, or death. MEASUREMENTS AND MAIN RESULTS: Of the 126 patients included, 53 (42.1%) received KRT and 73 (57.9%) did not. In patients who received KRT, mean serum bicarbonate levels remained between 22 and 28 mmol/L throughout the study period. Patients who did not receive KRT experienced an increase in mean serum bicarbonate levels over time up to 40 mmol/L (mean difference = –4.4 mmol/L [95% CI, –6.3 to –2.5 mmol/L]; p < 0.0001). Mean values for Paco 2 (–5.2 [95% CI, –8.8 to –1.7]; p = 0.004) and pH (–0.03 [95% CI, –0.03 to –0.02]; p < 0.0001) were lower in patients who received KRT than in patients who did not, despite higher sweep gas flow rates in patients who received KRT than in patients who did not (mean difference = 1.5 [95% CI, 0.8–2.3]; p < 0.001). CONCLUSIONS: ARDS patients on venovenous ECMO with preserved kidney function experience an increase in bicarbonate concentration over time, compared to patients with AKI on KRT. Whether this increase in bicarbonate concentration increases pH, decreases sweep gas flow requirements, and facilitate weaning from venovenous ECMO requires examination in future research.