- every patient should be maintained on at least 5 cm H2O of PEEP; 
- objective of optimal PEEP is to reduce the intrapulmonary Shunt; 
- since cardiac output may also be decreased, fluid administration or vasoactive drugs may also be required to restore Cardiac Output; 
- if pulmonary wedge pressure is grossly elevated, fluid infusion may be contraindicated and diuretics, vasodilators (nitroglycerin and nitroprusside), or inotropes (dobutamine & amrinone) may be needed; 
- if IMV rather than assist control is used, less depression of cardiac output may be produced by therapeutic PEEP but only if the patient has some spontaneous ventilation; 
- improvement in Cardiac Output with IMV is due to a reduction in intrathoracic presssure on inspiration and an increase in venous return; 
- in post operative patients, increasing FiO2 is usually not effective rather "The treatment of Hypoxia is PEEP" 
- major problem in post operative hypoxia is Atelectasis, and resultant Ventilation Perfusion Mismatch. 
- 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) 
- Adjusting PEEP: 
- PEEP is usually begun at 5 cm H2O & is increased by 2-3 cm increments; 
- as long as @compliance[Compliance is normal, PEEP may be increased to about 10 cm H2O with little risk of complications; 
- optimum setting: 
- Continue to increase PEEP until Pulmonary Shunt < 15-20% or the PaO2/FiO2 ratio exceeds 250; 
- Alternatively, adjust PEEP until attaining adequate oxygenation (Hb > 90) at non toxic O2 levels (<50%) 
- Problem: Over PEEPing may decrease @DXCO[CO; - Swan Ganz needed if PEEP > 12 cm H2O 

Mechanisms of impaired renal function with PEEP. 

Does positive end-expiratory pressure significantly reduce airway blood flow?
 
Effect of different levels of positive end-expiratory pressure on lung water content