INFLUENCE OF HYPERBILIRUBINEMIA ON THE ME ASUREMENT OF OXYGENATED HEMOGLOBIN (O2HB), CARBOXYHEMOGLOBIN (COHB) AND METHEMOGLOBIN (METHB) BY MULTIWAVELENGTH OXIMETERS

Oximetric measurements are influenced by several mechanisms. Severe ja undice is one of these mechanisms with some clinical interest. In the literature it is pointed out that a high bilirubin concentration may f alsify oximetric measurements and is often accompanied by elevated COH b levels. The reason for this phenomenon is thought to be an interfere nce in the absorption spectra of haemoglobin derivatives and bilirubin [2, 3, 4, 10]. In our investigation we attempted to answer the follow ing questions: 1. How do multiwavelength oximeters measure haemoglobin derivatives in different bilirubin concentrations? 2. Do different mu ltiwavelength oximeters give different concentrations of haemoglobin d erivatives? Methods. In 13 patients who developed postoperative jaundi ce on the intensive care unit, O2Hb, COHb and MetHb were measured in m ixed venous blood with two multiwavelength oximeters (OSM3, Radiometer ; CO 2500, Ciba-Coming). Bilirubin concentration was measured by the D PD (dichlorphenyldiazonium) method in the central laboratory of our ho spital. Results. With increasing bilirubin concentrations, both oximet ers measured increasing O2Hb values; the OSM3 consistently showed high er O2Hb concentrations than the CO 2500, with a maximal difference of 2.8% (Fig. 3). Regarding COHb, we saw clear increases in the values wi th increasing bilirubin concentrations (Fig. 4). The CO 2500 showed hi gher COHb values than the OSM3 (average 1.54 +/- 0.3 %). The findings regarding MetHb differed. The CO 2500 showed increasing MetHb values a s the bilirubin concentration increased (Fig. 5). All measurements exc eeded normal values above a bilirubin concentration of 17 mg/dl. The O SM3, however, measured constant MetHb values which did not depend on j aundice. Conclusions. 1. The in vitro measurement of haemoglobin deriv ates by multiwavelength oximeters is influenced by hyperbilirubinaemia . This is caused by an interference between the light absorption spect ra of the haemoglobin derivates and of bilirubin and by the increasing development of endogenous CO in the haem metabolism during severe jau ndice (Fig. 7). 2. With increasing bilirubin levels, a lower O2Hb is m easured with the CO 2500 than with the OSM3. 3. We also see increasing COHb values with rising bilirubin concentrations. 4. With increasing bilirubin levels the MetHb concentration measured with the CO 2500 ris es, while the OSM3 gives constant MetHb values. 5. In severe jaundice the O2Hb values measured with multiwavelength oximeters are not identi cal with the real blood concentration of this haemoglobin derivative. In this situation multiwavelength oximeters cannot be used as a refere nce method for in vivo oximetric systems such as pulse oximeters or fi breoptic pulmonary artery catheters.