METHEMOGLOBINEMIA AFTER ENDOSCOPY

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METHEMOGLOBINEMIA AFTER ENDOSCOPY

• Max Bayard, MD
• Fred Tudiver, MD
• Jeff Farrow, MD

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Case Report

• 26 Year Old White Woman
• Cyanotic ½ hour after esophagogastroduodenoscopy
  (EGD)
• Sent to ER
• CXR normal
• V/Q scan normal
• CBC normal
• Chemistry Panel normal

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Case Report

• Arterial Blood Gas Analysis
• pH 7.349
• pCO2 40.8 mm Hg
• pO2 97.5 mm Hg
• HCO3 21.8 mEq/dL
• Oxygen Saturation by pulse oximetry
• 83

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Case Report

• Arterial blood for methemoglobin
• 23.6 (normal lt 1)
• Patient admitted to ICU
• IV Methylene Blue given
• 3 hours later methemoglobin was nondetectable
• Patient discharged the following day with no ill
  effects

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PATHOLOGY

• Methemoglobin is produced naturally by the body
  when iron component of heme molecule is oxidized
  from the ferrous (Fe2) state to the ferric
  (Fe3) state. Ferric state does not have
  significant oxygen-carrying capacity.
• Oxidizing agents, such as benzocaine, can cause
  change from ferrous to ferric state.
• Susceptible individuals can develop excessive
  production of methemoglobinemia.

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PATHOLOGY

• May be caused by a variety of oxidizing agents
  including
• Topical anesthetics
• Benzocaine spray
• EMLA cream
• Metoclopramide
• Nitrates
• Sulfonamides
• Others

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INCIDENCE OF METHEMOGLOBINEMIA

• Recent study of incidence in patients undergoing
  transesophageal echocardiogram (TEE) with
  benzocaine topical spray was 0.1.
• Has occurred in these and other clinical
  situations
• EGD
• TEE
• Orogastric tube placement
• Intubation when topical benzocaine used
• IV nitroglycerine use and inhaled nitrous oxide

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CLINICAL FINDINGS

• Correlate with the levels of methemoglobin
• 10 concentrationcyanosis
• 30-50 concentrationfatigue, confusion,
  tachypnea
• gt50 concentrationcoma, seizures, arrhythmias,
  acidosis
• gt70 concentrationfrequently fatal
• Symptoms may be worse in an anemic patient

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DIAGNOSIS

• Arterial blood gas analysis with co-oximetry is
  necessary to confirm diagnosis
• Filter paper test at bedside can help
  differentiate deoxyhemoglobin from methemoglobin

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THE PEARL

• Key finding in an abnormal hemoglobin, such as
  methemoglobinemia is a mismatch between the pO2
  and the SaO2.
• Our patient
• PO2 was 97.5 mm Hg
• SaO2 was 83
• Based on above oxygen pressure, saturation should
  have been in the upper 90s

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TREATMENT

• Methemoglobin levels less than 20 will generally
  resolve without treatment
• 20-30 with symptoms or anyone gt30, treatment is
  with methylene blue at 1-2 mg/kg over 5 minutes.
  Dose may be repeated in one hour if necessary.
• Patients with G6PD deficiency should not receive
  methylene blue, but should have exchange
  transfusion.
• Patient needs to be warned to avoid potential
  exposure to other oxidating medications.

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SUMMARY

• Methemoglobinemia is a rare, but potentially
  life-threatening complication of the use of
  certain oxidizing medications
• Anecdotally, many are unaware of this
  complication
• Look for a mismatch between the pO2 and the SaO2