Intrinsic PEEP

Abstract

In mechanically ventilated patients, alveolar pressure can remain positive if the time available to breathe out is shorter than the time required for lung volume to return to V_r [1]. This can be the consequence of: a) reduced lung elastic recoil; b) increased flow resistance; c) expiratory flow limaation; d) excessive tidal volume (VT); and e) short duration of expiration (TE) (due, for instance, to high breathing frequency or shorter duty cycle). Under these circumstances, expiration is not completed before the onset of the next mechanical lung inflation and the end-expiratory lung volume (EELV) will stabilize above relaxed functional residual capacity (FRC) or V_r [1–4]. The end-expiratory elastic recoil (Pel,rs), due to incomplete expiration has been termed auto PEEP, occult PEEP [5], inadverted PEEP, endogenous PEEP, internal PEEP, and intrinsic PEEP [6]. Basically, in mechanically ventilated patients, factors causing the elevation of EELV and intrinsic PEEP (PEEPi) and determining its magnitude are:

• abnormal Patient res Diratory mechanics, i.e. high resistance and compliance, and expiratory flow limaation;

• added flow resistance, i.e. endotracheal tube and ventilator circuas and valves;

• ventilatory pattern, with large Vt, high frequency, short Te (due to the ventilator setting, a patient’s own ventilatory pattern and demand, or both), and the end-inspiratory pause.