Toxic methemoglobinemia caused by topical anesthetic given before transesophageal echocardiography.

Transesophageal echocardiography was performed on a patient with critical aortic stenosis and severe three-vessel coronary artery disease. Immediately after the procedure the patient experienced marked cyanosis (oxygen saturation of 53%) secondary to methemoglobinemia (methemoglobin saturation of 45%). Toxic methemoglobinemia was thought to be caused by topical anesthetic. He responded dramatically to treatment with intravenous methylene blue. Toxic methemoglobinemia should be suspected in unexplained cyanosis occurring after transesophageal echocardiography and other endoscopic procedures during which potentially causative agents have been used.