Risk of topical anesthetic-induced methemoglobinemia: a 10-year retrospective case-control study

Methemoglobinemia is a rare but serious disorder, defined as an increase in oxidized hemoglobin resulting in a reduction of oxygen-carrying capacity. Although methemoglobinemia is a known complication of topical anesthetic use, few data exist on the incidence of and risk factors for this potentially life-threatening disorder.

To examine the incidence of and risk factors for procedure-related methemoglobinemia to identify patient populations at high risk for this complication.

Retrospective study in an academic research setting.

Medical records for all patients diagnosed as having methemoglobinemia during a 10-year period were reviewed.

All cases of methemoglobinemia that occurred after the following procedures were included in the analysis: bronchoscopy, nasogastric tube placement, esophagogastroduodenoscopy, transesophageal echocardiography, and endoscopic retrograde cholangiopancreatography.

Comorbidities, demographics, concurrent laboratory values, and specific topical anesthetic used were recorded for all cases. Each case was compared with matched inpatient and outpatient cases.

In total, 33 cases of methemoglobinemia were identified during the 10-year period among 94,694 total procedures. The mean (SD) methemoglobin concentration was 32.0% (12.4%). The methemoglobinemia prevalence rates were 0.160% for bronchoscopy, 0.005% for esophagogastroduodenoscopy, 0.250% for transesophageal echocardiogram, and 0.030% for endoscopic retrograde cholangiopancreatography. Hospitalization at the time of the procedure was a major risk factor for the development of methemoglobinemia (0.14 cases per 10,000 outpatient procedures vs 13.7 cases per 10,000 inpatient procedures, P < .001).

The overall prevalence of methemoglobinemia is low at 0.035%; however, an increased risk was seen in hospitalized patients and with benzocaine-based anesthetics. Given the potential severity of methemoglobinemia, the risks and benefits of the use of topical anesthetics should be carefully considered in inpatient populations.