Case Presentation:
A 19‐month‐old male with a history of neonatal spontaneous pneumothorax presented with cyanosis. He was in his usual state of health when, on the day of presentation, he began whimpering and coughing. Soon thereafter his mother was unable to wake him, his lips turned blue and he became “floppy like a rag doll”, whereupon his mother sought medical attention. There was no clear ingestion history, though earlier that day he was found chewing on a breath spray container. In addition, he had just spent 20 minutes lying on the freshly shampooed carpet of the hotel room his family was living in. His only medication was a topical teething analgesic. On initial physical exam, he was afebrile with a blood pressure of 111/64 mmHg, a pulse of 150 beats per minute, a respiratory rate of 30 breaths per minute and an oxygen saturation of 94% on supplemental oxygen via 100% non‐rebreather mask. He was in severe distress, was drowsy but arousable and his skin appeared blue. Work of breathing was normal and his lungs were clear to auscultation bilaterally. Laboratories revealed a hemoglobin of 11.7g/dl, a bicarbonate of 16mmol/L and a negative urine drug screen. An arterial blood gas showed a pH of 7.26, a partial pressure of carbon dioxide of 40.4 mmHg, a partial pressure of oxygen of 12.2 mmHg, and a methemoglobin level of 57.5%. Following treatment with methylene blue his color, oxygen saturation and methemoglobin level normalized.
Discussion:
Methemoglobinemia occurs when there is an increase in the amount of methemoglobin in the blood, causing a left shift in the oxygen dissociation curve. It can be acquired or congential. Acquired forms can be caused by environmental agents such as aniline dyes, aminophenol and phenylhydroxylamine or medications such as nitrates, dapsone, chloroquine, sulfonamides, lidocaine and benzocaine, the offending agent in this case. Patients with mild to moderate methemoglobinemia can present with headache, fatigue, shortness of breath, and cyanosis. At higher levels, respiratory depression, mental status changes, seizures, shock or death may occur. Clinical suspicion must be high to diagnose this potentially lethal condition which should be in the differential diagnosis when a patient presents with cyanosis that does not respond to oxygen therapy. A careful exposure history must be obtained to elicit potential offending agents. Recently attention has been paid to over‐the‐counter teething agents containing benzocaine. In 2011, the Food and Drug Administration issued a warning recommending that parents and caregivers not use benzocaine products for children younger than 2 years, except under the advice and supervision of a health care professional.
Conclusions:
Anticipatory guidance should be given to parents of teething children about the risks of oral anesthetics as they are a potential cause of methemoglobinemia.