2 CREDITS 5 MARKS Flashcards
(5 cards)
Q1
A 32-year-old man presents to the emergency department with complaints of shortness of breath, fatigue, and a bluish tint to his lips and fingers that has been gradually worsening over the last 24 hours. He reports a recent history of using a topical numbing agent containing benzocaine to treat a sore throat. He denies any significant medical history and is not on any chronic medications. On examination, he appears cyanotic, and his oxygen saturation on pulse oximetry reads 85%, despite being given supplemental oxygen. His arterial blood gas (ABG) shows a normal PaO2 but a decreased oxygen saturation. A co-oximeter reveals a methemoglobin level of 18%.
Question 1: What is the most likely diagnosis in this patient? and why do you think so?
Question 2: What is the pathophysiology behind methemoglobinemia?
Question 3: How would you manage this patient’s condition?
Q1: methemoglobinemia, which is suggested by the patient’s cyanosis, hypoxia despite normal PaO2, and abnormal pulse oximeter readings. benzocaine is a known cause of methemoglobinemia,
Q2: hemoglobin is oxidized to methemoglobin (MetHb), which cannot carry oxygen effectively. Normally, hemoglobin is in the ferrous (Fe2+) state, but in methemoglobinemia, it is in the ferric (Fe3+) state, which impairs oxygen binding and release.
Q3: Discontinuing the offending agent
Administering 100% oxygen
Methylene blue
if methylene blue is not effective or contraindicated (e.g., in patients with G6PD deficiency), exchange transfusion or other supportive measures may be necessary
2
A 45-year-old woman presents to the emergency department with complaints of dizziness, confusion, and fatigue. Her husband mentions that she has been feeling unwell for the last two days, with progressively worsening symptoms. She has a history of using an over-the-counter teething gel containing benzocaine for her sore gums. Upon examination, the patient appears mildly cyanotic, and her oxygen saturation is 87% on room air. The initial ABG shows a normal PaO2, and a co-oximeter reveals a methemoglobin level of 22%.
Questions:
Q1: What clinical findings would raise suspicion for methemoglobinemia in this patient?
Q2: What is the role of co-oximetry in the diagnosis of methemoglobinemia?
Q3: What is the initial treatment for this patient, given her methemoglobin level?
ANS:
Q1
Cyanosis that is not relieved by oxygen therapy.
Normal PaO2 with low oxygen saturation on pulse oximetry.
Use of a benzocaine-containing product
hypoxic symptoms
Q2
measures the levels of methemoglobin (MetHb) in the blood, which pulse oximetry cannot differentiate from oxygenated hemoglobin. Co-oximetry provides a more accurate measurement of oxygen saturation and helps confirm the diagnosis.
Q3
Discontinuing the offending agent
Administering 100% oxygen
Methylene blue
if methylene blue is not effective or contraindicated (e.g., in patients with G6PD deficiency), exchange transfusion or other supportive measures may be necessary.
3
A 10-month-old child is brought to the emergency department with cyanosis and lethargy. The parents report that the child ingested an entire tube of nitrate-containing ointment that was mistakenly left within reach. The child is tachypneic, and their oxygen saturation is 75% on pulse oximetry. ABG shows a normal PaO2 but low oxygen saturation, and co-oximetry reveals a methemoglobin level of 30%.
Questions:
* Why is this child at higher risk for methemoglobinemia compared to adults?
* What immediate treatment should be provided to this child?
* What are the potential complications of severe methemoglobinemia in this case?
Q1
immature enzyme systems (e.g., cytochrome b5 reductase) that are less efficient at reducing methemoglobin back to normal hemoglobin
Q2
Discontinue the nitrate-containing ointment immediately.
Administer 100% oxygen to help reduce methemoglobin levels.
Methylene blue may be used, but the dose must be carefully adjusted for the child’s weight. In severe cases, exchange transfusion might be considered
Q3
Severe hypoxia due to impaired oxygen delivery.
Organ dysfunction (especially to the brain and heart) from lack of oxygen.
Seizures, coma, or death if the methemoglobin levels are not corrected quickly.
A 60-year-old man with a history of chronic obstructive pulmonary disease (COPD) presents to the emergency department with increased shortness of breath, confusion, and a bluish discoloration of the lips and fingers. The patient has been using a topical anesthetic for a painful ulcer in his mouth. Pulse oximetry shows a saturation of 88%, and his PaO2 is 60 mmHg on ABG. Co-oximetry reveals methemoglobin levels of 16%. His condition does not improve with supplemental oxygen.
Questions:
Q1: What factors could predispose this patient to methemoglobinemia?
Q2: Why might this patient have a low oxygen saturation despite receiving oxygen therapy?
Q3: What is the role of methylene blue in treating this patient, and what are the potential contraindications?
Q1
Chronic obstructive pulmonary disease (COPD): Patients with chronic lung disease may have underlying oxygenation problems, making it more difficult to detect the effects of methemoglobinemia.
Use of a topical anesthetic (e.g., benzocaine) in the oral cavity, which can oxidize hemoglobin.
Older age: As people age, their ability to metabolize drugs and chemicals may decrease, potentially making them more susceptible to methemoglobinemia.
Q2
Pulse oximetry cannot distinguish between oxygenated hemoglobin and methemoglobin. Therefore, even with supplemental oxygen, the methemoglobin may falsely elevate the oxygen saturation reading, giving the impression that the patient is adequately oxygenated when they are not.
Q3
acts as a reducing agent, converting methemoglobin back to normal hemoglobin. However, methylene blue should be avoided in patients with G6PD deficiency, as it can cause hemolysis
5
A 25-year-old male who works as a chemical engineer presents to the emergency department with cyanosis, dizziness, and confusion after accidentally inhaling nitrogen dioxide gas while working in a confined space. His oxygen saturation is 80% on room air, and his ABG shows a PaO2 of 70 mmHg. The pulse oximeter gives an erroneous reading of 95%. Co-oximetry reveals a methemoglobin level of 35%.
Questions:
Q1: What is the most likely cause of methemoglobinemia in this patient?
Q2: How can inhalation of nitrogen dioxide lead to methemoglobinemia?
Q3: What are the treatment options for this patient with methemoglobinemia induced by inhalation of toxic gases?
ANS:
Q1
Inhalation of nitrogen dioxide (NO2), a known industrial toxin, can cause methemoglobinemia. NO2 oxidizes hemoglobin to methemoglobin, impairing oxygen transport and leading to symptoms of hypoxia
Q2
Nitrogen dioxide is an oxidizing agent that can directly oxidize hemoglobin to methemoglobin, leading to impaired oxygen binding and delivery. This process can occur even in small exposures, especially in a confined space where the gas may accumulate.
Q3
Discontinue the nitrate-containing ointment immediately.
Administer 100% oxygen to help reduce methemoglobin levels.
Methylene blue may be used, but the dose must be carefully adjusted for the child’s weight. In severe cases, exchange transfusion might be considered
