Mobilizing Carbon Dioxide Stores. An Experimental Study

Abstract Rationale Understanding the physiology of CO2 stores mobilization is a prerequisite for intermittent extracorporeal CO2 removal (ECCO2R) in patients with chronic hypercapnia. Objectives To describe the dynamics of CO2 stores. Methods Fifteen pigs (61.7 ± 4.3 kg) were randomized to 48 hours of hyperventilation (group “Hyper,” n = 4); 48 hours of hypoventilation (group “Hypo,” n = 4); 24 hours of hypoventilation plus 24 hours of normoventilation (group “Hypo-Baseline,” n = 4); or 24 hours of hypoventilation plus 24 hours of hypoventilation plus ECCO2R (group “Hypo-ECCO2R,” n = 3). Forty-eight hours after randomization, the current V. e was reduced by 50% in every pig. Measurements and Main Results We evaluated V. co2, V. o2, and metabolic V. co2 (V. o2 times the metabolic respiratory quotient). Changes in the CO2 stores were calculated as V. co2 − metabolic V̇co2. After 48 hours, the CO2 stores decreased by 0.77 ± 0.17 l kg−1 in group Hyper and increased by 0.32 ± 0.27 l kg−1 in group Hypo (P = 0.030). In group Hypo-Baseline, they increased by 0.08 ± 0.19 l kg−1, whereas in group Hypo-ECCO2R, they decreased by 0.32 ± 0.24 l kg−1 (P = 0.197). In the second 24-hour period, in groups Hypo-Baseline and Hypo-ECCO2R, the CO2 stores decreased by 0.15 ± 0.09 l kg−1 and 0.51 ± 0.06 l kg−1, respectively (P = 0.002). At the end of the experiment, the 50% reduction of V. e caused a PaCO2 rise of 9.3 ± 1.1, 32.0 ± 5.0, 16.9 ± 1.2, and 11.7 ± 2.0 mm Hg h−1 in groups Hyper, Hypo, Hypo-Baseline, and Hypo-ECCO2R, respectively (P < 0.001). The PaCO2 rise was inversely related to the previous CO2 stores mobilization (P < 0.001). Conclusions CO2 from body stores can be mobilized over 48 hours without reaching a steady state. This provides a physiological rationale for intermittent ECCO2R in patients with chronic hypercapnia.