Enhanced extracorporeal carbon dioxide removal by acidification and metabolic control.

BACKGROUND: Extracorporeal carbon dioxide removal (ECCO<inf>2</inf>R) promotes protective ventilation in patients with acute respiratory failure, but devices with high CO<inf>2</inf> extraction capacity are required for clinically relevant impact. This study evaluates three novel low-flow techniques based on dialysate acidification, also combined with renal replacement therapy, and metabolic control.

METHODS: Eight swine were connected to a low-flow (350 mL/min) extracorporeal circuit including a dialyzer with a closed-loop dialysate circuit, and two membrane lungs on blood (ML<inf>b</inf>) and dialysate (ML<inf>d</inf>), respectively. The following 2-hour steps were performed: 1) ML<inf>b</inf>-start (ML<inf>b</inf> ventilated); 2) ML<inf>bd</inf>-start (ML<inf>b</inf> and ML<inf>d</inf> ventilated); 3) HLac (lactic acid infusion before ML<inf>d</inf>); 4) HCl-NaLac (hydrochloric acid infusion before ML<inf>d</inf> combined with renal replacement therapy and reinfusion of sodium lactate); 5) HCl-βHB-NaLac (hydrochloric acid infusion before ML<inf>d</inf> combined with renal replacement therapy and reinfusion of sodium lactate and sodium 3-hydroxybutyrate). Caloric and fluid inputs, temperature, blood glucose and arterial carbon dioxide pressure were kept constant.

RESULTS: The total MLs CO<inf>2</inf> removal in HLac (130±25 mL/min), HCl-NaLac (130±21 mL/min) and HCl-βHB-NaLac (124±18 mL/min) were higher compared with ML<inf>bd</inf>-start (81±15 mL/min, P<0.05) and ML<inf>b</inf>-start (55±7 mL/min, P<0.05). Minute ventilation in HLac (4.3±0.9 L/min), HCl-NaLac (3.6±0.8 L/min) and HCl-βHB-NaLac (3.6±0.8 L/min) were lower compared to ML<inf>b</inf>-start (6.2±1.1 L/min, P<0.05) and ML<inf>bd</inf>-start (5.8±2.1 L/min, P<0.05). Arterial pH was 7.40±0.03 at ML<inf>b</inf>-start and decreased only during HCl-βHB-NaLac (7.35±0.03, P<0.05). No relevant changes in electrolyte concentrations, hemodynamics and significant adverse events were detected.

CONCLUSIONS: The three techniques achieved a significant extracorporeal CO<inf>2</inf> removal allowing a relevant reduction in minute ventilation with a sufficient safety profile.