The Haldane effect of rabbit blood under different acid-base conditions

The Haldane effect (HE), i.e. the difference in plasma pH of oxygenated and deoxygenated blood, was investigated in rabbits over a wide range of respiratory (PCO2 2.7 to 8.0 kPa) and metabolic (BE +5 to -15 mM) acid-base conditions and compared to cats, dogs and humans. Even under standard conditions (PCO2 = 5.3 kPa, BE = O mM) and normalized to the same Hb-concentration, the HE-induced pH-difference was distinctly greater in rabbits, cats and dogs (about 0.045) than in humans (0.034 - 0.039). During respiratory and metabolic acid-base changes, the HE-induced delta pH was inversely related to PCO2 and BE. The dependency of the Haldane effect on the acid-base status can be estimated by means of a linear inverse relationship between delta pH and lgHCO3-, as originally proposed for human blood by v. Mengden et al., 1969. Correspondingly, the regression analysis of the present experimental Haldane effect data of rabbits, cats and dogs, yielded highly linear correlations as well as characteristic species-related regression coefficients. Additionally considering the influence of the Hb-concentration, a most useful tool for quantitative estimation of the Haldane effect is thus available. This is of practical importance, e.g. when determining the arterial PCO2 indirectly by the Astrup method. However, Haldane corrections based only on human blood data available so far, would lead to an underestimation of the Haldane effect in common laboratory animals. If the appropriate Haldane shift of pH for a species is not considered, the resulting PCO2 may be erroneous by up to several 100 Pa, particularly in the range of metabolic acidosis.