Abstract

A patient with hemoglobin-H (Hb-H) disease developed an acute hemolytic crisis after treatment with trimethoprim and sulfamethoxazole. Despite her poor clinical condition and profound anemia (Hb, 2.7 g/dL), pulse oximetry continued to demonstrate a high O2 saturation percentage. Manipulation of Beer's law shows that anemia theoretically should not affect pulse oximetry values. The literature describes the effects of dyshemoglobinopathies such as carboxyhemoglobinemia and methemoglobinemia on O2 saturation percentage measured by pulse oximetry, but the effect of genetic hemoglobinopathies on pulse oximetry values is largely unreported. Because most hemoglobinopathies do not significantly change the protein-heme electronic interaction, the values of O2 saturation percentage determined through pulse oximetry should remain clinically valid. Hb-H is an exception to this generalization; as in patients with carboxyhemoglobinemia, pulse oximetry measurements showing high O2 saturation percentage do not correspond to high levels of oxygen available for delivery to tissues.