Potential interference by hydroxocobalamin on cooximetry hemoglobin measurements during cyanide and smoke inhalation treatments

Study objective: Concentrated aqueous solutions of hydroxocobalamin (OHCob) are administered intravenously for cyanide poisoning victims, many of whom also have concurrent smoke inhalation. Because of its intense light absorbance in visible wavelengths (absorption peak at 532 nm), we investigate potential interference effects of OHCob on total hemoglobin concentration (tHb), carboxyhemoglobin (COHb), methemoglobin (MetHb), and oxyhemoglobin (Hb-O-2) cooximetry measurement values in blood. Methods: In vivo cooximetry measurements were conducted with 3 specific pathogen-free white New Zealand rabbits (3.80 +/- 0.21 kg) during the intravenous infusion of OHCob (625 mg during a 100-minute period). Resultant changes in tHb, Hb-O-2, COHb, and MetHb values were measured and correlated with respect to estimated in vivo OHCob concentrations. In vitro measurements were conducted with rabbit blood to confirm in vivo measurements. Results: The introduction of OHCob clearly interfered with the cooximetry measurements of each of the hemoglobin component fractions in whole blood and resulted in altered measurement values from the baseline values. The presence of OHCob in blood interferes with cooximetry measurements of COHb, MetHb, and Hb-O-2. The increase in measured COHb fraction with increasing concentrations of OHCob was most notable. Conclusion: The presence of OHCob in blood interferes with cooximetry measurements of COHb, MetHb, and Hb-O-2. These effects need to be considered during OHCob treatment of cyanide poisoning, particularly in smoke inhalation victims with potential for concurrent carbon monoxide exposure, because it may lead to potentially erroneous reported COHb levels.