Methemoglobinemia and transesophageal echo

Area of Science:

• Cardiology
• Pharmacology
• Hematology

Background:

• Methemoglobin (MHb) is the ferric (Fe3+) oxidized form of Hemoglobin (Hb), impairing oxygen transport.
• Methemoglobinemia, an elevation in MHb, causes tissue hypoxia and shifts the oxygen-Hb dissociation curve leftward.
• Topical anesthetics, like benzocaine, can induce methemoglobinemia, a rare but serious adverse effect.

Observation:

• A patient developed acute hypoxemia (O2 saturation drop from 100% to 86%) after topical benzocaine use for a medical procedure.
• Clinical signs included pallor and cyanosis, with arterial blood gas analysis revealing dark, chocolate-colored blood.
• Suspected methemoglobinemia was confirmed by elevated MHb levels (30.1%).

Findings:

• Empirical treatment with Methylene Blue (1 mg/kg) rapidly resolved the patient's methemoglobinemia and hypoxemia.
• The case highlights the association between topical benzocaine and methemoglobinemia.
• Arterial blood gas results confirmed severe hypoxemia (O2 sat 69%) secondary to methemoglobinemia.

Implications:

• Prompt recognition and treatment of methemoglobinemia are essential to prevent severe cardiopulmonary compromise, neurological sequelae, and death.
• This case underscores the importance of considering methemoglobinemia in patients with unexplained hypoxemia after exposure to agents like benzocaine.
• Methylene Blue is an effective antidote for drug-induced methemoglobinemia, rapidly restoring oxygen-carrying capacity.