Methemoglobinemia in patients undergoing esophagogastroduodenoscopy: a randomized controlled trial.

Background: Methemoglobinemia is a potentially life-threatening complication of local anesthetic sprays employed in upper endoscopy. There is limited information available on the incidence of this complication, and no prospective trial has ever undertaken to evaluate subclinical levels of methemoglobinemia.

Objective: To evaluate the incidence of subclinical methemoglobinemia in patients exposed to anesthetic spray.

Methods: Subjects were randomized to a "spray" or "no-spray" group. Subjects in the "spray" group received a 1-second benzocaine spray before upper endoscopy. All subjects in both groups were monitored with a noninvasive co-oximetry device capable of detecting methemoglobin levels in real time.

Results: 401 subjects were enrolled (209 in the study group, 192 in the control group); mean peak methemoglobin concentrations were 0.82% (CI 0.74-0.90%, SD 0.57%) and 0.80% (CI 0.73-0.86%, SD 0.46%) respectively. There was no statistically significant difference between the two groups (p = 0.69). Only 3 (1.4%) subjects in the study group and 2 (1%) subjects in the control group had a peak methemoglobin concentration >2%.

Conclusions: In this randomized clinical trial, no significant elevation of methemoglobin concentration was observed in any subject. Final analysis failed to demonstrate any statistically significant difference between the two groups.