- Ferrous (Fe++) irons of heme oxidized to the ferric (Fe+++) state --> unable to bind O2.
- O2 affinity of remaining ferrous hemes in Hgb tetramer is increased --> O2 dissociation curve shifted to left
- Note: Autooxidationof Hgb --> met-Hgb occurs spontaneously at a slow rate (0.5-3%)
- Reduction: NADH-dependent reaction (cytochrome b5 reductase)
Posted 03/08/17 09:09:27 AM by Matthew Cummings
When to suspect met-hemoglobinemia?
- Sudden onset of cyanosis with symptoms of hypoxia after administration or ingestion of an agent with oxidative potential.
- Hypoxia that does not improve with an increased fraction of inspired oxygen.
- Abnormal coloration of the blood observed during phlebotomy “chocolate”-colored.
- Clinical cyanosis in the presence of a calculated normal PaO2
Posted 03/08/17 09:10:03 AM by Matthew Cummings
- When to treat? Symptomatic or met-Hgblevel >20%?
- Methylene blue (MB) and/or ascorbic acid
- Single dose of MB reduces toxic levels of met-Hgbto non-toxic levels (<10%) within 10-60 minutes
- Ascorbic acid requires multiple doses, may take 24+ hours to reach similarly low levels
- Exchange transfusion and hyperbaric oxygen treatment second-line options
Posted 03/08/17 09:11:23 AM by Matthew Cummings
Posted 03/08/17 09:13:56 AM by Matthew Cummings
Created by Christopher Kelly
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