A 2 year-old boy presents to the emergency department with cyanosis and pulse oxygenation of 82% on ambient air that did not appear to be responding to oxygen. He was recently prescribed Orajel (benzocaine 20%) for teething pain. During blood draw, the nurse notedthe color appears to be chocolate-brown. This child did not have any previous medical problems and was well before he started to use this medication.
What is the diagnosis?
What is the mechanism?
Methemoglobin (MethB) is a form of hemoglobin where the deoxygenated hem moiety is oxidized from the ferrous iron (Fe2+) state to the ferric ion (Fe3+) state. Benzocaine is an anesthetic metabolized by plasma cholinesterase to phenylhydroxylamine and nitrobenzene. These two metabolites induce an oxidative stress on the RBC causing the oxidation of ferrous iron to ferric iron. This process overwhelms the cells natural ability to reduce the oxidized ferric iron to oxygen-carrying ferrous iron thereby producing methemoglobinemia. It is suggested that as little as 15 to 25 mg/kg benzocaine is capable of inducing MethB and producing cyanosis. Infants less than 3 months of age maybe more susceptible to anesthetic induced
MethB due to their limited enzymes.
How do you diagnose the patient?
Suspected patient with MethB should have his/her venous blood gas measured for methemoglobin.
How would you treat this patient?
MethB levels less than 20% generally do not require specific treatment except for removal of the causative agent. Symptomatic patients with level > 20% should receive intravenous Methylene Blue at a doses of 1 to 2 mg/kg over 5 min.
CAUTION: Although rare patients with G6PD deficiency may develop hemolysis when treated with methylene blue.
Can this child be discharged home?
Benzocaine has a rapid onset of action. Initial effects can occur within minutes and a duration of action of 15-20 min. The gel formulation may last several hours. Therefore this child can be safely discharged home after short observation period if signs and symptoms do not recur after treatment.
Dapsone, Nitroprusside, Phenacetin, Suflonamides, Anesthetics (prilocain, lidocaine, bupivicaine), sodium
nitrite, Phenazopyridine (Pyridium), Quinones (chloroquine, primaquine), Acetonitrile (nail remover),
Napthalene (mothball), Volatile nitrites, Chlorates.
No comments:
Post a Comment