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19 Cards in this Set
- Front
- Back
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Methemoglobinemia
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Hemoglobin oxidized to methemoglobin (ferrous iron -> ferric iron); ferric hemes are UNABLE to bind oxygen
Oxidation of one of the hemes in the Hb tetramer INCREASES the affinity for the remaining hemes in the tetramer |
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Effects of methemoglobinemia on the oxygen dissociation curve
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Cytochrome B5 Redutcase Deficiency (NADH-Methemoglobin Reductase Deficiency)
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Functional deficiency of RBCs only
MetHb concentrations 10-35%; cyanotic but asymptomatic Heterozygotes at increased risk for acquired methemoglobinemia |
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When do levels of MetHb become life threatening?
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>50%
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Main drugs that can cause acquired methemoglobinemia
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Dapsone
Benzocaine and related topical anesthetics |
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How to tx acquired methemoglobinemia?
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Bright red molecule
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Carboxhemoglobin; shifts ODC left
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Brown molecule
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Methemoglobin; shifts ODC left
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Blue molecule
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Deoxyhemoglobin; shifts ODC right
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Methylene Blue
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Used to tx increased MetHb levels; decreases the levels and shifts ODC to the right
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Sulfhemoglobinemia
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Sulfur binds to the B-prrole ring of the moiety; can't bind oxygen and has a green color; does not respond to methylene blue tx
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Summary Slide
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How does MetHb vs SulfHb affect the oxygen dissociation curve?
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Sulfhemoglobinemia considered w a cyanotic/gray pt who has normal oxygen tension, and has failed to respond to methylene blue therapy; usually asymptomatic unless other globinemias presnt
pts have a GRAY appearance |
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How does MetHb vs SulfHb affect the oxygen dissociation curve?
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Sulfhemoglobinemia considered w a cyanotic/gray pt who has normal oxygen tension, and has failed to respond to methylene blue therapy; usually asymptomatic unless other globinemias presnt
pts have a GRAY appearance |
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How does methylene blue work as a tx for methemoglobinemia?
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Methylene blue functions as an artificial electron acceptor for NADPH methemoglobin reductase; NADPH generated via hexose monophosphate shunt
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What is the problem in HbM disease?
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the HbM is not amenable to reduction to ferrous states despite intact enzyme systems; acquired congenital methemoglobinemia
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How can G6PD deficiency cause methemoglobinemia?
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There is impaired production of the cofactor NADPH, required for the reduction of methemoglobinemia
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Why might pyruvate kinase deficiency cause methoglobinemia?
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Impaired production of NADH, essential cofactor for diaphorase I
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cytochrome-b5 reductase
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Same as NADH methemoglobin reductase; reduces via electron donation the spontaneous formation of methemoglobin; disruption of this enzyme may lead to methemoglobineima
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