Monday, March 21, 2011

Intrinsic PEEP (PEEP i)

Assessment of PEEPi based on a end-expiratory occlusion. Maneuver is high-lighted.

Intrinsic PEEP (PEEPi) is the difference between total PEEP and external PEEP, and provides information on the amount of dynamic hyper-inflation working on the respiratory system as well as the intra-thoracic organs. 

PEEPi has the same adverse effects of PEEP regarding both hemodynamics, barotrauma, and volutrauma.
PEEPi affects patient triggering by creating a inspiratory threshold load to be over come by the patient during spontaneous breathing.

Increased risks for auto-PEEP include a minute volume greater than 15lpm, an airway resistance greater than 15 cmH2O, and evidence of expiratory flow obstruction.

PEEPi is easily to quantify when using newer generation mechanical ventilators, by utilizing a end-expiratory occlusion maneuver. There should be no PEEPi, a moderate amount is 2-to-6 cmH2O, and a high amount is greater than 8 cmH2O.

Another way to quantify expiratory flow obstruction is to evaluate the expiratory time constant (RCexp), this indicates the rate at which the lungs empty. In adults, an RCexp value greater than 1.2 seconds indicates airway obstruction.

Strategies to reduce PEEPi include increasing expiratory time, decreasing respiratory rate, and decreasing expiratory resistance.