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); 
- 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

Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Thursday, September 8, 2011 3:04 pm