IMPACT OF LACTIC ACID AND GLUCOSE SOLUTION INFUSIONS ON CO2 PRODUCTION: PRELIMINARY DATA FROM AN EXPERIMENTAL STUDY IN PIGS

INTRODUCTION. The infusion of lactic acid at the inlet of an artificial lung has proved to be an effective and safe technique to increase extracorporeal CO2 removal [1]. However, lactic acid is an energetic substrate and his metabolism produces CO2. OBJECTIVES. The aim of this study was to assess the total CO2 production (VCO2) during the infusion of lactic acid or glucose solutions while maintaining a constant caloric intake. METHODS. Four pigs (44.9 ± 5 kg) were sedated and mechanically ventilated. A 50 % glucose solution was administered for 4 h (*88 kcal/h); during the next 4 h 2.5 mEq/min of lactic acid (*44 kcal/h) and 50 % glucose solution at 22 ml/h (*44 kcal/h) were infused. This step was repeated three times for each pig with a two-hour stop between each step. Every hour VCO2 and arterial lactate were determined. Blood glucose level was kept constant (target = 100 mg/dl) titrating intravenous insulin infusion. RESULTS. VCO2 during lactic acid + glucose infusion increased by about 6–7 % compared to the infusion of glucose alone (200 ± 25 ml/min vs. 186 ± 24 ml/min, p.05, see Figure 1); blood glucose did not differ between the 2 groups (respectively 101 ± 12 vs. 103 ± 8). The arterial lactate was always lower than 3 mmol/L. A slight increase in total VCO2 during lactic acid infusion may be explained by the difference (*3.6 %) between the moles of CO2 produced by complete oxidation of amounts of glucose and lactate of equal caloric intake. CONCLUSIONS. When lactic acid infusion is used to enhance extracorporeal CO2 removal, a decrease of the caloric input equivalent to the metabolic load of the infused lactate would allow to maintain a nearly constant total production of CO2.