new_n_lost
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A 25-year-old white woman presents to the emergency room with the complaint of extreme shortness of breath of acute onset. She was actually seen in the same emergency room 24 hours previously where she was diagnosed with a urinary tract infection and given prescriptions for phenazopyridine (Pyridium) and sulfamethoxazole. She is overweight and sedentary and smokes two packs of cigarettes a day. On physical exam she is markedly dyspneic and extremely cyanotic. Arterial blood gases fail to reveal any hypoxia, but a ventilation-perfusion scan is obtained anyway, which is read as low probability. What should be the next course of action?
A) Repeat the arterial blood gas to look for progression and development of hypoxia.
B) Proceed to pulmonary arteriography.
C) Begin anticoagulation.
D) Administer methylene blue.
E) Transfuse two units of packed RBCs.
Explain UR Answers PLZ
Edited by new_n_lost on 03/22/07 - 05:46 PM
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| usmle4me
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?D
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| girl^interrupted
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D?
Oxidizing agents like nitro and sulpha drugs cause conversion of Fe3+ into ferrous Fe2+ Hence forming metHb.
Oxidized Hb cannot bind O2 ...Hence decreased oxygen content and SaO2, with normal Po2 so revealing no hypoxia in bld...
I hope it isnt wrong
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| girl^interrupted
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I ddint understand this part:
but a ventilation-perfusion scan is obtained anyway, which is read as low probability.
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| mytime
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B. PE.
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| new_n_lost
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Low probability On a V/Q scan means: A single large- or moderate-sized matched segmental defect. More than 3 small segmental perfusion defects (!25% of a segment) with a normal chest X-ray. Probable PE mimic (absent perfusion in entire lung, solitary lobar mismatch, mass, or other chest X-ray lesions causing mismatches). Moderate-sized pleural effusion (larger than the costophrenic angle but less than one third of pleural cavity) with no other perfusion defect in either lung. Markedly heterogeneous perfusion.
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| new_n_lost
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Excellent Job Again Girl^Interrupted Correct Explanation too!!!!
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| new_n_lost
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Answer: D
Explanation: Recognize an individual with methemoglobinemia who has been exposed to an offending agent. Rapid development of extreme dyspnea and cyanosis, in the setting of no hypoxia, should be the clue to consider methemoglobinemia.
In this case, the patient was exposed to two different known medications (pyridium and sulfamethoxazole) associated with increased levels of Methemoglobin in susceptible individuals.
Methemoglobin is the derivative of hemoglobin, in which the iron of the heme group is oxidized from the ferrous to the ferric state. It is the oxidation status that determines the oxygen-carrying capacity of hemoglobin. When iron is in the ferrous form (deoxyhemoglobin), oxygen can easily bind, in contrast to the inability to bind to the ferric hemes of Methemoglobin. Steady-state methemoglobin levels in the blood are usually <1% but can increase markedly when susceptible individuals (heterozygotes for methemoglobin reductase deficiency) are exposed to certain medications or chemicals.
Correct therapy is prompt institution of methylene blue, to which individuals will respond rapidly with resolution of cyanosis
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| mytime
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| unique1
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Thank you so much NnL for a very good q and its excellent explanation. It gave me a clear concept about methemoglobinemia. I would be grateful if you could kindly explain how methylene blue corrects it.
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| new_n_lost
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Owing to its reducing agent properties, methylene blue is employed as a medication for the treatment of methemoglobinemia, which can arise from ingestion of certain pharmaceuticals or broad beans. Basically, methylene blue acts to reduce the heme group from methemoglobin to hemoglobin,
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| unique1
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Do broad beans cause methemoglobinemia? How ?
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| new_n_lost
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Dunno U will have to Search it
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| keepgoing
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its very well given in 1st or 2nd lect of day 1 dr goljan..
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| nandrolone
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it acts as a proton acceptor in the NADPH associated Meth HB reductase system
Ascorbic acid helps it in the action
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| nandrolone
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The question can also be asked likre
a mountaineer after drinking surface water from muntais developes cyanosis cause?
ANS surface water contain nitrates which act as oxidising agents of Hb.
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