The Effect of Acute Respiratory Acidosis on the Proportion: Total Splanchnic Perfusion/Cardiac Output, and the Alteration in this Proportion by Two Anaesthetics

Eight dogs were anaesthetized and ventilated. Respiratory acidosis with variations in the pH (range: 7.49 to 7.05) were brought about by changes in the dead space of the apparatus. The pH-related changes in cardiac output (Q), and total splanchnic perfusion (Q_sp1) were studied during anaesthesia with mebumal natrium (NFN) N₂O-O₂-gallamoni jodidum (NFN) (“basic anaesthesia”), and after the addition of 1 % halothane (inspiratory). Similar relationships were demonstrated in the systemic circulation between pH changes and changes in the cardiac output, pulse pressure, and total peripheral resistance during both types of anaesthesia; whereas the pulse frequency and the mean aorti cpressure were not significantly correlated to changes in pH. Q_sp1 was different during the two types of anaesthesia. Under “basic anaesthesia,” the pH-related changes in Q and Q_sp1 were opposite and of varying magnitude. Their mutual relation: the fraction of cardiac output perfusing the splanchnic area, was Q_sp1/Q= -2.28 + 0.34×pH (r = 0.69, N = 28, P<0.001). After the addition of halothane, no correlation could be demonstrated between Q_sp1/Q and changes in pH. The changes in Q and Q_sp1 were in the same direction and of the same relative magnitude, with an average of Q_sp1/Q = 0.21. In agreement with this, no changes could be demonstrated in the total splanchnie resistance (R_sp1) during halothane anaesthesia in relation to the provoked pH changes, while R_sp1 under “basic anaesthesia” showed a slight rise with falling pH in the majority of dogs (six out of eight). The pressure in the portal vein (P_vp) appeared to rise with a falling pH. For both types of anaesthesia, the AP_vp (kPa) = -0.97 × δpH (r = 0.79, N = 34, P<0.001).