CO 2 induced acute respiratory acidosis and brain tissue intracellular pH: a 31 P NMR study in swine

Abstract

High concentration carbon dioxide (CO₂) is used to promote pre-slaughter anaesthesia in swine and poultry, as well as short-lasting surgical anaesthesia and euthanasia in laboratory animals. Questions related to animal welfare have been raised, as CO₂ anaesthesia does not set in momentarily. Carbon dioxide promotes anaesthesia by lowering the intracellular pH in the brain cells, but the dynamics of the changes in response to a high concentration of CO₂ is not known. Based on ³¹P NMR spectroscopy, we describe CO₂-induced changes in intracellular pH in the brains of five pigs inhaling 90% CO₂ in ambient air for a period of 60 s, and compare the results to changes in arterial blood pH, P_CO2, O₂ saturation and HCO₃ ^- concentration. The intracellular pH paralleled the arterial pH and P_CO2 during inhalation of CO₂; and it is suggested that the acute reaction to CO₂ inhalation mainly reflects respiratory acidosis, and not metabolic regulation as for example transmembrane fluxes of H⁺/HCO₃ ^-. The intracellular pH decreased to approximately 6.7 within the 60 s inhalation period, and the situation was metabolically reversible after the end of CO₂ inhalation. The fast decrease in intracellular pH supports the conclusion that high concentration CO₂ leads to anaesthesia soon after the start of inhalation.