Intraoperative detection of methemoglobinemia in a patient given benzocaine spray to relieve discomfort from a nasogastric tube: a case report.

A 27-year-old man who had 2 admissions 1 month apart for abdominal surgery had a high methemoglobin (MHb) level secondary to liberal use of benzocaine oral spray. A co-oximetry level for MHb of greater than 0.30 proportion of total hemoglobin (30.1%) was detected intraoperatively. The patient was successfully treated with methylene blue intravenously and recovered uneventfully. When the arterial blood gas with a normal partial pressure of oxygen is inconsistent with a low pulse oximeter reading and with the physical appearance of the patient, methemoglobinemia should be considered as a differential diagnosis. This case illustrates the acquired form of methemoglobinemia. Adequate oxygen delivery to the tissues in the body is compromised when MHb overwhelms the capacity of the red blood cells to carry oxygen. If methemoglobinemia is left untreated, it may be fatal.