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Questions and Answers
What is a likely symptom when methemoglobin levels are between 25% and 50%?
What is a likely symptom when methemoglobin levels are between 25% and 50%?
- Chest pain (correct)
- Seizures
- Profound acidosis
- Delirium
At what methemoglobin level typically results in death?
At what methemoglobin level typically results in death?
- Exactly 100%
- Below 25%
- Between 50%–70%
- Above 70% (correct)
Which device can accurately measure methemoglobin levels?
Which device can accurately measure methemoglobin levels?
- Blood gas analyzer
- Co-oximeter (correct)
- Greater than 85% pulse oximeter
- Standard pulse oximeter
What effect does methemoglobin have on pulse oximetry readings?
What effect does methemoglobin have on pulse oximetry readings?
What causes the saturation gap in methemoglobinemia diagnosis?
What causes the saturation gap in methemoglobinemia diagnosis?
Which condition is associated with methemoglobinemia?
Which condition is associated with methemoglobinemia?
What is the primary reason for inaccuracies in pulse oximetry in methemoglobinemia?
What is the primary reason for inaccuracies in pulse oximetry in methemoglobinemia?
What happens to oxygen saturation readings on pulse oximetry in the presence of high-level methemoglobinemia?
What happens to oxygen saturation readings on pulse oximetry in the presence of high-level methemoglobinemia?
Which form of iron is present in methemoglobin?
Which form of iron is present in methemoglobin?
What characterizes methemoglobinemia?
What characterizes methemoglobinemia?
What is the primary cause of methemoglobinemia?
What is the primary cause of methemoglobinemia?
Which condition may cause cyanosis that responds to oxygen administration?
Which condition may cause cyanosis that responds to oxygen administration?
How does acute methemoglobinemia often occur?
How does acute methemoglobinemia often occur?
What fraction of methemoglobin is considered normal?
What fraction of methemoglobin is considered normal?
Cyanosis that is unresponsive to high oxygen concentrations indicates what condition?
Cyanosis that is unresponsive to high oxygen concentrations indicates what condition?
Patients with what level of methemoglobin might experience mild cyanosis?
Patients with what level of methemoglobin might experience mild cyanosis?
Which of the following substances is known to induce methemoglobinemia?
Which of the following substances is known to induce methemoglobinemia?
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Study Notes
Methemoglobinemia Overview
- Condition characterized by methemoglobin levels exceeding 1% in red blood cells.
- Methemoglobin is formed when iron is in the ferric (Fe 3+) form, impairing oxygen delivery.
Causes and Risk Factors
- Associated with exposure to nitrate-contaminated water, aniline dyes, and amide medications.
- Ortho-toluidine, a metabolite of prilocaine, can also induce the condition.
Symptoms and Diagnosis
- Initial symptoms can be vague, making early diagnosis challenging.
- Cyanosis: Presence of more than 5 g/dL deoxygenated hemoglobin; specific to methemoglobinemia as it remains unresponsive to high oxygen concentrations.
- Cyanosis may be confused with other conditions like cardiac or pulmonary diseases, which typically respond to oxygen.
- Symptoms correlate with methemoglobin levels:
- 3%–15%: Slight skin discoloration.
- 15%–20%: Mild cyanosis, often asymptomatic.
- 25%–50%: Headache, dyspnea, lightheadedness, syncope, weakness, confusion, palpitations, chest pain.
- 50%–70%: Dysrhythmias, altered mental status, seizures, profound acidosis.
- Exceeding 70%: High risk of death.
Diagnostic Challenges
- Presence of methemoglobin can falsely elevate oxygen saturation readings on arterial blood gases (ABGs).
- "Saturation gap" can indicate methemoglobinemia: discrepancy between pulse oximetry readings and calculated ABG oxygen saturation.
- Pulse oximetry can give misleading values; low levels may show falsely low saturation, while high levels often plateau around 85%.
- Severity of cyanosis does not correspond with pulse oximetry readings.
Diagnostic Tools
- Co-oximetry is essential for accurate diagnosis, measuring methemoglobin levels effectively.
- Newer co-oximeters can also identify sulfhemoglobin, which may be confused with methemoglobin in older devices.
Importance of History Taking
- Detailed history of exposure to potential methemoglobinemia-inducing substances is crucial for accurate diagnosis and management.
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