Snapshot A 20-year-old woman with a history of celiac disease presents to the dermatologist with pruritic papules on her bilateral extensor elbows. She is started on dapsone for dermatitis herpetiformis, an itchy rash commonly seen in patients with celiac disease. A few weeks later, she reports feeling very tired, with frequent episodes of lightheadedness. At an urgent care clinic, she is noted to have pulse oximetry readings of 90% with no improvement on supplemental oxygen. A methemoglobin level is found to be > 3%. She is sent to the emergency room for treatment. Introduction Overview methemoglobinemia causes tissue hypoxia due to accumulation of methemoglobin in the blood methemoglobin hemoglobin (Hb) that contains ferric form of iron (Fe3+) Epidemiology demographics infants are at increased risk risk factors drugs nitrates anesthetics dapsone lidocaine, benzocaine, and bupivacaine nitroglycerin infants are more susceptible to hemoglobin oxidation food well water Pathogenesis methemoglobin is the oxidized form of Hb, which has an affinity for cyanide oxygen does not bind as easily to the heme subunit with the ferric form of iron remaining heme sites has increased affinity for oxygen results in decreased ability to release oxygen to tissues causes left-shift of the oxygen-hemoglobin dissociation curve tissue hypoxia functional anemia Presentation Symptoms may be asymptomatic if levels are low headache lightheadedness fatigue shortness of breath seizures or coma at very high levels of methemoglobinemia Physical exam pulse oximetry shows decreased oxygen saturation level (< 90%) supplemental oxygen will not improve pulse oximetry reading tachycardia cyanosis altered mental status “chocolate brown” or blue blood Studies Arterial blood gas normal pO2 this indicates dissolved oxygen in the blood Pulse oximetry oxygen saturation 85-90% Methemoglobin level > 3% (normal values < 1%) measured with CO-oximetry device Differential Cyanide poisoning distinguishing factor arterial blood gas shows metabolic acidosis from the accumulation of lactic acid CO-oximetry is normal does not respond to methylene blue Treatment Medical 100% oxygen + methylene blue mechanism reduces hemoglobin to non-oxidized form contraindications pregnancy methylene blue is a teratogen G6PD deficiency may cause hemolytic anemia patients taking an SSRI may precipitate serotonin syndrome as methylene blue has some monoamine oxidase inhibitor activity, which increases levels of neurotransmitters such as serotonin vitamin C indication in patients with contraindications to methylene blue failure of methylene blue treatment Complications End-organ failure Acute respiratory distress syndrome
QUESTIONS 1 of 2 1 2 Previous Next Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (M1.HE.14.59) A 26-year-old woman is brought to the ED by her fiance with cyanosis and shortness of breath. Gradually over the last few days she has also experienced headaches, fatigue, and dizziness. Her past medical history is significant only for mild anemia attributed to menorrhagia, for which she takes an iron supplement. Per her fiance, she was recently laid-off, but is very excited about her new entrepreneurial endeavor of selling silk scarfs that she dyes in their basement. She is afebrile, tachypneic, and tachycardic, and her oxygen saturation is 85% on room air, which seems high for her perceived degree of cyanosis. An arterial blood gas is drawn and the patient's blood is chocolate-colored. After a few minutes on 6 liters nasal canula, her oxygen saturation is still 85%. In addition to maintaining her airway, breathing, and circulation, what treatment should this patient also receive? QID: 100124 Type & Select Correct Answer 1 Sodium bicarbonate 4% (9/203) 2 Pralidoxime 3% (6/203) 3 Deferoxamine 16% (32/203) 4 Dimercaprol 6% (13/203) 5 Methylene blue 67% (137/203) M 3 Question Complexity D Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 5 Review Tested Concept Review Full Topic