Cell injury:
- If the oxygen partial pressure (in the plasma) is decreased, the oxygen saturation (on Hb) MUST also decrease.
- Thrombosis in a muscular artery is the most common cause of ischemia.
- Hypoxemia (decrease oxygen partial pressure) is a cause of hypoxia
- Respiratory acidosis ! CO2" ! pO2# ALWAYS (and vice versa).
- Hypoxemic patient that gets 100% oxygen and his pO2 didn’t increase ! shunt ! ventilation defect (ARDS, hyaline membrane disease).
- Perfusion defect (PE) ! "dead space (100% O2 will get the pO2 up)
- Diffusion defect (sarcoidosis, pulmonary edema)
- J reflex innervated by the Kent nerve, cause dyspnea (fluid in lung interstitium irritating the J receptors).
- Anemia (Hb related problem) ! pO2 normal, saturation normal, Hb decreased exertional dyspnea.
- House fire produces tissue hypoxia in 2 ways: CO poisoning (! saturation!, give 100% oxygen) and CN poisoning. Both inhibit cytochrome oxidase.
- Cyanosis is the clinical evidence of decreased saturation. Red pigment hides the cyanosis in CO poisoning (most frequent symptom is headache).
- MetHb ! saturation decreased because the Hb is Fe$ and not Fe% (chocolate color blood) ! 100% oxygen doesn’t improve cyanosis. Treatment is IV methylene blue, vitmamin C (also but not main)
- Sulfa and nitro drugs (oxidizing agent): 1. produce MetHb. 2. Hemolytic anemia, G6PD deficiency.
- MetHb common in HIV, because we use sulfa drugs to treat pneumocystis carinii.
