(P72) A Case of Acquired Methemoglobinemia from Chronic Orajel Use

Chief Complaint : Patient is a 21-year-old Caucasian female who presented secondary to acute respiratory distress, palpitations and cyanosis.

History of Present Illness : Patient is a 21-year-old female with a past medical history of depression and migraines, who presented to the emergency department with acute respiratory insufficiency and notable peripheral and central cyanosis. Patient was post-op day 3 from a routine laparoscopic salpingectomy, which was completed with no complications. Patient subsequently noted the onset of a generalized headache, non-productive cough and palpitations. She additionally noted progressively worsening cyanosis of her hands and feet, as well as her lips.
It was discovered that the patient was using three tubes of oral benzocaine daily for the past year, secondary to ongoing dentalgia. Patient had been asymptomatic from her use until undergoing general anesthesia, during which she did receive lidocaine as well.

Pertinent Physical Exam: Patient’s initial triage vital signs demonstrated hypoxia with an oxygen saturation of 85%, for which she was initially placed on 2L oxygen via nasal cannula. Patient was noted to be tachypneic with positive accessory muscle use. Patient was pale in appearance, with mild conjunctival pallor and cyanosis of the lips. Patient was additionally noted to have digital cyanosis of her upper extremities. Lung auscultation demonstrated bilateral symmetric breath sounds, however the patient was noted to have rapid, shallow respirations. Patient was additionally noted to be tachycardic, with EKG demonstrating sinus tachycardia. Blood pressure was within normal limits.

Pertinent Laboratory Data: Patient’s laboratory studies demonstrated a methhemoglobin level of 27. An arterial blood gas was obtained which demonstrated a pH of 7.425, PCO2 34.1, PO2 205, bicarbonate of 22.4. Bedside cardiac ultrasound did not demonstrate any sizable pericardial effusion or tamponade. Portable upright chest x-ray demonstrated mild pneumoperitoneum from her recent surgery, however no acute intrathoracic pathology. CT PE did not reveal acute thoracic pathology however did redemonstrate pneumoperitoneum. CT abdomen pelvis with contrast revealed postoperative changes including mild scattered pneumoperitoneum and emphysema.

Case Discussion: Our patient presented with hypoxemia and peripheral cyanosis, consistent with a diagnosis of methemoglobinemia. She remained persistently at an oxygen saturation of 85% despite intervention with supplemental oxygen with 15L nonrebreather. Poison control was contacted and recommended administration of 1 mg/kg dose Methylene Blue with repeat methemoglobin levels 30 minutes after administration and again in 6 hours. Patient was noted to have symptomatic improvement within an hour of treatment.

Methemoglobinemia is a known rare complication of topical and local anesthetic use. It is most commonly acquired through exposure to drugs which cause indirect oxidation of Fe (II) to Fe (III). In a 10-year retrospective case control study published in JAMA in 2013, 94,694 cases were assessed which used topical anesthetics and found that a total of 33 cases of
methemoglobinemia were identified, with a prevalence of 0.035%. The pathophysiology of methemoglobinemia is more often a result of secondary causes, rather than congenital etiologies. The oxidized ferrous component of hemoglobin is converted to the ferric state which results in an increased oxygen affinity leading to a decrease in oxygen unloading and decreased delivery to peripheral tissues, which is best exhibited by a leftward shift on the oxyhemoglobin dissociation curve.

This case illustrates the importance of increasing awareness of the presentation, diagnosis and management of methemoglobinemia as a rare hemoglobinopathy which can present in a similar manner to cardiac and respiratory causes of acute hypoxemia.

References and Acknowledgements (Optional): 1. Chowdhary S, Bukoye B, Bhansali AM, et al. Risk of Topical Anesthetic–Induced Methemoglobinemia: A 10-Year Retrospective Case-Control Study. JAMA Intern Med. 2013;173(9):771–776.

2. Taleb, M., Ashraf, Z., Valavoor, S. et al. Evaluation and Management of Acquired Methemoglobinemia Associated with Topical Benzocaine Use. Am J Cardiovasc Drugs 13, 325–330 (2013).

3. Umbreit J. Methemoglobin—it’s not just blue: a concise review. Am J Hematol. 2007;82(2):134–44.