[Toxic methemoglobinemia following the postoperative ingestion of 4,4-diaminodiphenylsulfone (DADPS)--on the differential diagnosis of cyanosis].

Blood gas analysis devices routinely used in clinical practice measure pH, pCO2 and pO2 directly, while all other values they specify are calculated on the basis of nomograms. In the presence of higher concentrations of biologically useless forms of haemoglobin, calculation of the haemoglobin saturation (% O2 Hb) leads to a clinically relevant false assessment of oxygen availability. A case is described in which toxic methemoglobinaemia occurred postoperatively after resumption of long-term medication with 150 mg 4,4-diaminodiphenylsulfone (DADPS). Increasing methaemoglobin values up to maximal 17.7% at a total haemoglobin of 11.3 g/dl correlated with the symptoms of cyanosis and respiratory distress. This symptom complex, which is not atypical postoperatively, could not be clarified by differential diagnosis with the aid of cardiac output measurements and arterial blood gas analyses. The cardiac index amounted to 4.1 l/m2 at a pulmonary capillary wedge pressure of 8 mmHg; the arterial partial oxygen pressure was between 16 and 19 kPa. Only the differential determination of oxihaemoglobin, CO-haemoglobin and methaemoglobin with an oximeter yielded evidence of severe arterial hypoxaemia and made therapy possible.