Positive End Expiratory Pressure (PEEP)

OVERVIEW

• PEEP is the maintenance of positive pressure within the lungs at the end of expiration (positive end expiratory pressure)
• in spontaneous ventilation using non-invasive ventilation (NIV) the equivalent is CPAP (continuous positive airway pressure)
• high PEEP is used as part of an Open Lung Approach To Ventilation

ADVANTAGES

• increased airway pressure
• increased FRC (prevention of airway collapse)
• increase PaO2: increased capillary-alveoli interface for gas exchange, extra-vascular lung water displaced from alveolar interstitium to peribronchial interstitium)
• maximises recruitment of alveoli by preventing cyclic de-recruitment on expiration
• decreased airway resistance
• reduced V/Q mismatch
• improved distribution of inspired gas
• reduced work of breathing
• prevention of surfactant aggregation reducing alveolar collapse
• reduction in LV afterload (due to increased LV transmural pressure) — decreased preload and WOB also help in APO

DISADVANTAGES

• impaired CO2 elimination
• decreased RV preload, increased RV afterload, decreased LV compliance (due to intra-ventricular septum displacement)
• reduced urine output through increased ANP, decreased GFR and increased ADH