News (Page 71)

Benzocaine-induced methemoglobinemia: Discussion (Part 3)


Small infants are at increased risk because they have markedly lower levels of cytochrome-b5 reductase and fetal hemoglobin is more easily oxidized to MHg . The activity of some enzymes involved in these processes is less efficient in the elderly. Methemoglobinemia has also been reported in dialysis patients and may be a result of chloramine toxicity due to inadequate removal by hemodialysis filters.

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Benzocaine-induced methemoglobinemia: Discussion (Part 2)

The congenital form of methemoglobinemia is most common in Alaskan Native Americans and individuals of Inuit descent . MHg levels in individuals with this congenital form of methemoglobinemia are usually between 15% and 30% of total hemoglobin, and individuals are normally asymptomatic except for varying degrees of persistent cyanosis. Another form of congenital methemoglobinemia occurs in individuals who display an aberrant form of hemoglobin (HbM),…

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Benzocaine-induced methemoglobinemia: Discussion (Part 1)

Clinical decision-making algorithm

MHg has an impaired O2 binding capacity and is unable to carry O2 from the lungs to metabolically active tissue. Furthermore, the oxidation of one subunit of the hemoglobin tetramer to MHg prevents the remaining normal subunits from unloading their bound O2, causing an additional leftward shift in the O2 dissociation curve. In the case of ben-zocaine, a toxic metabolite N-hydroxy derivative is thought to…

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Benzocaine-induced methemoglobinemia: Case presentations (Part 5)

Arterial blood gas analysis revealed an MHg level of 18.8% (normal 0.0% to 1.5%). A total of 50 mg (approximately 1 mg/kg) of methylene blue was administered by direct intravenous push over 5 min. Repeat blood gases 90 min later showed resolution of the methemoglobinemia (MHg 1.2%), and she was completely asymptomatic. She was transferred back to the medical ward 3.5 h following the administration…

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Benzocaine-induced methemoglobinemia: Case presentations (Part 4)

persistent nausea

Case 2 A 22-year-old woman was admitted to hospital for investigation of persistent nausea, vomiting and weight loss of 7 kg. She had undergone an appendectomy two months earlier but was otherwise healthy and was only taking antiemetics. An endoscopy performed one month earlier in a local hospital revealed gastritis and duodenitis. The day after admission she developed coffee ground hematemesis and a repeat gastroscopy…

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Benzocaine-induced methemoglobinemia: Case presentations (Part 3)

Following methylene blue administration, her O2 saturation by pulse oximetry fell further to approximately 65%, indicating that the methylene blue likely interfered with the ability of pulse oximetry to accurately assess O2 saturation. In addition, within a few minutes of its administration, the patient experienced significant nausea and vomiting, a noted side effect of methylene blue treatment. This was successfully treated with ondansetron (4 mg…

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Benzocaine-induced methemoglobinemia: Case presentations (Part 2)

peripheral and central cyanosis

The patient was found to have profound peripheral and central cyanosis. Her cardiac and respiratory exams were normal. Her blood pressure was 107/73 mmHg, heart rate was 96 beats/min and O2 saturation by pulse oximetry was 82% to 89% on 100% O2 by a nonrebreathing mask. Her chest and cardiovascular exam were normal but she was dyspneic, drowsy and confused. Flumazenil (0.2 mg intravenously) and…

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Benzocaine-induced methemoglobinemia: Case presentations (Part 1)

Case 1 A 60-year-old woman who had a cardiac transplant for cardiomyopathy three years ago was undergoing an upper endoscopy for investigation of microcytic anemia. Her past medical history was significant for lupus erythematosus and chronic renal insufficiency (creatinine 212 pmol/L). Her medications included cyclosporine, mycophenolate mofetil, omeprazole, enalapril maleate, pravastatin sodium, diltiazem hydrochloride, epoetin alfa and etidronate sodium.

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Benzocaine-induced methemoglobinemia


Methemoglobinemia is a serious and potentially fatal complication that can occur with the use of benzocaine-containing anesthetics and a wide variety of other pharmacological agents. Due to the routine use of benzocaine as a topical anesthetic during endoscopy, all endoscopists should be aware of this reaction. Methemoglobinemia arises when an exogenous substance, such as benzocaine, oxidizes the iron moiety of hemoglobin from a ferrous to…

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Medical practitioners careers (Part 8)

Strategy #1 Remember that success in your professional and personal life will be largely dependent on your capacity to deal with people. Dr Jean Gray, in a talk delivered to a Canadian Society for Clinical Investigation Symposium, eloquently presented this point of view, with which I strongly agree. She pointed out that those with whom you work will all have strengths and weaknesses and it…

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