methemoglobinemia, cyanide, carbon monoxide blood gas differences
- related: toxicology and toxic ingestions
- tags: #literature #icu
- methemoglobinemia: methemoglobin absorbs different wavelength of light
- pulse ox is low: 80s despite 100% FiO2
- PaO2 normal or high: often 200-300 mmHg
- elevated methemoglobin (MetHb) in ABG
- in CO poisoning, CO binds hemoglobin with higher affinity than O2
- pulse ox is normal: does not distinguish between oxyhemoglobin and carboxyhemoglobin
- ABG shows elevated carboxyhemoglobin
- may have normal PaO2: CO concentration low enough to not affect PaO2 of dissolved O2
- in cyanide toxicity
- increase venous Po2: narrowing of venous-arterial PaO2 gradient (venous hyperoxia differentiates between methemoglobinemia and cyanide toxicity)