[Role of P50 in resuscitation (author's transl)]

The amount of oxygen made available to the tissues of the body depends essentially upon pulmonary gas exchanges, cardiac output and its regional distribution, haemoglobin concentration and also upon the oxygen affinity of the haemoglobin molecule. That a standard oxyhaemoglobin dissociation curve faithfully describes oxygen loading and unloading both in healthy subjects and in those suffering from pathological process has come under attack. Beside the effect of pH, PCO2 and temperature, the oxyhaemoglobin dissociation curve can be modified by alterations of other factors (concentration of 2,3-diphosphoglycerate, hormones, drugs). Although the shifts of the oxyhaemoglobin dissociation curve, expressed by variations of P50 may seem minute, the effect of these shifts, expressed in terms of the "functional value of haemoglobin" are very large. Assessment of the intensive care patient must take into account the effect of alterations of the oxyhaemoglobin dissociation curve which can either increase or diminish tissue oxygenation.