Low-flow CO₂ removal integrated into a renal-replacement circuit can reduce acidosis and decrease vasopressor requirements

Abstract

Introduction: Lung-protective ventilation in patients with ARDS and multiorgan failure, including renal failure, is often paralleled with a combined respiratory and metabolic acidosis. We assessed the effectiveness of a hollow-fiber gas exchanger integrated into a conventional renal-replacement circuit on CO₂ removal, acidosis, and hemodynamics.

Methods: In ten ventilated critically ill patients with ARDS and AKI undergoing renal- and respiratory-replacement therapy, effects of low-flow CO₂ removal on respiratory acidosis compensation were tested by using a hollow-fiber gas exchanger added to the renal-replacement circuit. This was an observational study on safety, CO₂-removal capacity, effects on pH, ventilator settings, and hemodynamics.

Results: CO₂ elimination in the low-flow circuit was safe and was well tolerated by all patients. After 4 hours of treatment, a mean reduction of 17.3 mm Hg (-28.1%) pCO₂ was observed, in line with an increase in pH. In hemodynamically instable patients, low-flow CO₂ elimination was paralleled by hemodynamic improvement, with an average reduction of vasopressors of 65% in five of six catecholamine-dependent patients during the first 24 hours.

Conclusions: Because no further catheters are needed, besides those for renal replacement, the implementation of a hollow-fiber gas exchanger in a renal circuit could be an attractive therapeutic tool with only a little additional trauma for patients with mild to moderate ARDS undergoing invasive ventilation with concomitant respiratory acidosis, as long as no severe oxygenation defects indicate ECMO therapy.

Figure 1

Scheme of the renal circuit with implementation of a hollow-filter gas exchanger.

Figure 2

Clinical effects of low-flow CO₂ removal 4 and 24 hours after commencement of treatment. Graphs illustrate mean changes of values for pH (A), pCO₂(B), pO₂(C), tidal volume on respirator (D), norepinephrine dose at mg/h (E), and average changes in P_max on the ventilator (F).

Figure 3

Exemplary time courses for clinical effects of low-flow CO₂ removal in two patients. Patient 10 had acute pneumonia (A, B, C); patient 6 had cardiomyopathy and acute pneumonia (D, E, F) for pH, pCO₂, and norepinephrine dose, respectively.