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
  • increased pulmonary vascular resistance (PVR) (in West’s zone I and II where increased alveolar pressure exceeds venous pressure)
  • decreased flow in West’s zone I causing increased dead space (PA > Pa >Pv)
  • may worsen right to left intracardiac shunt by increased PVR
  • decreased hepatic artery and portal venous flow (liver congestion and LFT changes)
  • increased ICP
  • decreased peribronchial lymphatic flow (? decrease pneumonia and APO clearance)
  • decreased splanchnic blood flow (at >20cmH2O PEEP)

AN APPROACH TO SETTING PEEP IN ARDS

References and Links

LITFL

DerangedPhysiology.com

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