CO2 induced acute respiratory acidosis and brain tissue intracellular pH:: a 31P NMR study in swine

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 P-31 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, O-2 saturation and HCO(3)(-)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.