Positive End Expiratory Pressure
PEEP is the pressure maintained within the airways at the end of expiration. In terms of the ventilator, it is also the pressure within the circuit at the end of expiration. PEEP is one of the key factors affecting oxygenation (the other being FiO2). Normal physiologic PEEP is 3-5 cmH2O and is a good starting point for the PEEP setting. PEEP and FiO2 can be titrated upwards to improve PaO2. Caution must be used with higher PEEP settings as higher PEEP can cause increased thoracic pressure, decreased venous return and barotrauma.
Patients with obstructive pulmonary diseases such as asthma or COPD may benefit from a lower PEEP setting as they are more prone to Auto-PEEP. Those with restrictive pulmonary diseases such as pneumonia, CHF or ARDS may benefit from a higher PEEP setting.
Auto-PEEP (Intrinsic PEEP)
Auto-PEEP can occur in patients without long enough of an exhalation period before the next breath occurs. Auto-PEEP can be measure using a E-Hold. These patients may benefit from a longer I:E ratio by decreasing the I-Time or breath rate.