Prolonged enteral fast with parenteral nutrition decreases PCO2 and flow volume in portal vein: its association with bile secretion.

In an attempt to clarify metabolic events during an enteral fast with parenteral nutrition (PN), changes in blood gas distribution and blood flow in the portal vein, and in bile secretion and hepatic blood flow were investigated in dogs. Dogs were maintained on glucose 25 kcal/kg/day for 7 days. In group I, 8 dogs received orally 10 kcal/kg/day and parenterally 15 kcal/kg/day. In group II, 8 dogs had no oral intake and the total calories were provided by PN for the same interval. On the 7th day, the difference in PCO2 between abdominal aorta and portal vein (A-P DCO2) and the concentration of total bile acids in the bile (TBAC) decreased in group II. The values of A-P DCO2 and TBAC were -5.9 +/- 1.2 mm Hg, 35.4 +/- 9.6 mmol/l in group I and -1.2 +/- 1.0 mm Hg, 18.7 +/- 7.3 mmol/l in group II. These decreases in group II were statistically significant (p < 0.01). Portal venous blood flow significantly decreased in group II, as compared to the levels in group I; however, hepatic blood flow, as estimated by the indocyanine green clearance rate, showed no significant decrease. After the 7-day study in group II, saline containing CO2 at high pressure was administered into the mesenteric vein to achieve gradation of A-P DCO2. Gradation of A-P DCO2 from -1.3 to -5.9 mmHg resulted in an increase in the secretion in TBAC and bicarbonate in the bile from 14.0 to 30.0 mmol/l and from 10.3 to 19.5 mmol/l, respectively. We tentatively conclude that portal hypocapnea plays a role in decreasing bile secretion during the enteral fast with PN administration.