The Science Journal of the American Association for Respiratory Care

2002 OPEN FORUM Abstracts

METHEMOGLOBINEMIA IN HOSPITALIZED PATIENTS: A CASE SERIES

Sreekumar Subramanian, MD, Austin E. Delacruz, Jr., B.A, RRT, RPFT, Perinatal-Pediatric Specialist* and Rafaello Goeting, CRT, RCP. Departments of Respiratory Therapy and Surgery, David Grant U.S. Air Force Medical Center, Travis Air Force Base California, USA

Purpose: Methemoglobinemia refers to the oxidation of ferrous (Fe2+) iron to ferric (Fe3+) iron within the hemoglobin molecule, which occurs following oxidative stresses. The subsequent impairment in oxygen transport may lead to progressive hypoxia and death. Early identification of this complication is often confounded by falsely normal diagnostic testing. The purpose of this report is to review the etiology, pathophysiology and clinical management of this uncommon, but highly dangerous condition.

Methods: The database of all arterial blood gas analyses at David Grant U.S. Air Force Medical Center from 1998-2001 was reviewed to identify all patients with elevated methemoglobin (MetHb) levels.5 patients were identified with levels >10%. Their charts have been reviewed, with particular attention to any predisposing factors, treatment and clinical outcome.

Results: The mean methemoglobin level was 25% (normal 0-1.5%). In our series, topical benzocaine spray was the most common offending agent (4/5 patients). The reason for benzocaine use were: bronchoscopy and intubation (3 patients), and nasogastric tube placement (1 patient). In symptomatic patients, the threshold for instituting therapy is a level of 20% MetHb, with a lower threshold of 10% for patients with significant cardiac or pulmonary history. Asymptomatic patients generally do not require treatment for MetHb level less than 30%. The treatment of choice for acute, severe methemoglobinemia is intravenous 1% methylene blue, at a dose of 1-2 mg/kg.

Conclusions: Methemoglobinemia is a rare complication encountered by various clinicians. Diagnosis requires a high index of suspicion, because pulse oximetry often gives near normal readings. Definitive diagnosis requires co-oximetry. Prompt treatment is essential to optimize outcome.

Clinical Implications: Early recognition of this condition, and administration of methylene blue can be lifesaving in severe cases.

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