Abstract
The authors present a case of methemoglobinemia due to accidental industrial exposure to nitric oxide gas. The patient showed severe generalized cyanosis on admission, although he had no other clinical symptoms. The arterial blood was chocolate-colored, and the concentration of arterial methemoglobin (Met-Hb) was as high as 45%. The serum and urine NO3- concentrations were 23 and 1, 443μg/ml, respectively. Continuous positive airway pressure (CPAP) mask therapy gradually decreased the concentration of Met-Hb. This was accelerated by intravenous methylene blue administration of 0.5mg/kg for 10 minutes. Arterial (SpO2) and mixed venous (SxO2) Hb-oxygen saturations were monitored using a pulse-oximeter and oximetric Swan-Ganz catheter, respectively. Blood samples were intermittently drawn to measure HbO2 (A) and HbO2 (V), by hemoximeter (Radiometer OSM-3). Pulseoximetry and mixed venous-oximetry could not differentiate Met-Hb from HbO2 or deoxy-Hb and overestimated HbO2 (A) and HbO2 (V) because they utilized only two light lengths. As the concentration of Met-Hb decreased, this overestimation was improved. When methemoglobinemia was severe, the assessment of Hb-oxygen saturation misrepresented the actual values of HbO2 (A) and HbO2 (V).
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