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Oxygenation of Ventilated Patients

 


 

- See: ABG 
- oxygenation is Independent of minute volume until ventilation is low; 
- hence: increasing minute volume does not improve oxygenation; 
- note: at pO2 of 75 mm Hg, the saturation = 95% at pO2 of 60 mm Hg, the saturation = 90% hence: pO2 of 75 is adequate for all patients, and it is reasonalbe to decrease FiO2. (O2 > 0.50 or 0.60 is toxic); 
- w/ pO2 < 75, esp if < 60 mm Hg, serious hypoxia exists: 
- in postop period patients, increasing FiO2 is usually not effective rather "treatment of Hypoxia is PEEP
- major problem in post operative hypoxia is atelectasis, & resultant ventilation perfusion mismatch; (see Shunt
- even w/ high levels of inspired O2 are ineffective in raising pO2 when major shunting (Atelectasis) occurs; 
- to improve oxygenation: nonvented lungs must be expanded; (ie. ventilation perfusion relationship must be corrected); 
- PEEP 
- begin at 5 cm H2O; then incr by: 2.5 increments up to 12 cm; (at times PEEP levels of 20-25 will be required)
- FiO2 needs to be increased w/: 
- diffusion blocks (See A-a grad
- as in CHF, Intersitial Edema from ARDS; 
- oxygen toxicity Does Not occur unless FiO2 is maintained above 50% or 60% for more than 24 hrs; 
- thus maintaining patient on 100% O2 initially after returning from operating room until set of ABG is drawn is OK