Arterial and Mixed Venous Blood Gas Status during Apnoea of Intubation — Proof of the Christiansen-Douglas-Haldane Effect in Vivo

Abstract

The Christiansen-Douglas-Haldane effect, in short the Haldane effect, describes the dependence of the CO2 binding of blood on the degree of oxygenation of haemoglobin. Under the physiological conditions of an ‘open’ system between blood and alveoli the partial pressure of arterial C02 (PaCO2), must be less than that of mixed venous blood (P[Formula: see text]CO2). During the unphysiological conditions of a ‘closed’ system, e.g. hyperoxic apnoea, i.e. continuous oxygen uptake without CO2 delivery by the lungs, the Paco2 will not only approximate the P[Formula: see text]CO2 but will even exceed it. Without the Haldane effect, rapid adjustment of Paco2 to P[Formula: see text]CO2 would be expected during apnoea due to the lack of CO2 excretion. If however, as undertaken in this study, ongoing oxygenation (high alveolar Po2 (PACO2) with concomitant lack of C02 delivery (apnoea, i. e. the C02 concentration remains constant) lead to a continuing sufficient oxygenation of blood during its passage through the lung capillaries, then this leads to a rightwards shift of the CO2 binding curve — the Haldane effect. The resulting increase in Pco2 as shown here actually leads to an arterial-mixed venous CO2 partial pressure difference (a[Formula: see text]DPco2) of 2.8±1.8 mmHg. The results described substantiate for the first time the existence of the Haldane effect under clinical conditions.