- 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;
