Splanchnic hemodynamics and gut mucosal-arterial PCO2 gradient during systemic hypocapnia

Abstract

The effects of hypocapnia [arterial PCO2 (P(CO2)) 15 Torr] on splanchnic hemodynamics and gut mucosal-arterial P(CO2) were studied in seven anesthetized ventilated dogs. Ileal mucosal and serosal blood flow were estimated by using laser Doppler flowmetry, mucosal PCO2 was measured continuously by using capnometric recirculating gas tonometry, and serosal surface PO2 was assessed by using a polarographic electrode. Hypocapnia was induced by removal of dead space and was maintained for 45 min, followed by 45 min of eucapnia. Mean Pa(CO2) at baseline was 38.1 ± 1.1 (SE) Torr and decreased to 13.8 ± 1.3 Torr after removal of dead space. Cardiac output and portal blood flow decreased significantly with hypocapnia. Similarly, mucosal and serosal blood flow decreased by 15 ± 4 and by 34 ± 7%, respectively. Also, an increase in the mucosal-arterial PCO2 gradient of 10.7 Torr and a reduction in serosal PO2 of 30 Torr were observed with hypocapnia (P < 0.01 for both). Hypocapnia caused ileal mucosal and serosal hypoperfusion, with redistribution of flow favoring the mucosa, accompanied by increased PCO2 gradient and diminished serosal PO2.