Under Pressure: Positive End Expiratory Pressure (PEEP)

Physiology of PEEP

  1. Alveolar Recruitment and Stabilization:
    • Recruitment: PEEP opens collapsed alveoli, increasing the surface area for gas exchange.
    • Stabilization: By maintaining alveoli open, PEEP prevents the cyclic opening and closing of alveoli, reducing shear stress and the risk of ventilator-induced lung injury (VILI).
  2. Improvement in Oxygenation:
    • V/Q Matching: PEEP improves ventilation-perfusion matching by redirecting blood flow to well-ventilated alveoli, reducing intrapulmonary shunting.
    • Redistribution of Edema: In conditions like ARDS, PEEP can redistribute alveolar edema, improving compliance and gas exchange.
  3. Effects on Compliance:
    • Static Compliance: PEEP can increase static compliance by recruiting alveoli, but excessive PEEP may overdistend alveoli, decreasing compliance.
    • Dynamic Compliance: PEEP may also affect dynamic compliance by altering airway resistance.
  4. Hemodynamic Implications:
    • Venous Return: Increased intrathoracic pressure reduces venous return, potentially decreasing cardiac output.
    • Afterload: PEEP may increase left ventricular afterload by increasing transpulmonary pressure.
    • Right Ventricular Function: High PEEP may cause right ventricular dilation and dysfunction, especially in the presence of pulmonary hypertension.
  5. Effects on Intracranial Pressure (ICP): PEEP may increase ICP by reducing venous outflow from the brain, a critical consideration in neurocritical care.

Clinical Application and Monitoring

  1. ARDS:
    • PEEP/FiO2 Tables: Utilizing evidence-based tables to titrate PEEP based on FiO2 requirements.
    • Recruitment Maneuvers: Often used in conjunction with PEEP to assess recruitability.
    • Monitoring with Esophageal Manometry: To assess transpulmonary pressure and individualize PEEP settings.
  2. Obstructive Lung Disease: Careful application of PEEP to prevent air trapping and intrinsic PEEP (auto-PEEP).
  3. Heart Failure and Fluid Status:
    • Echocardiographic Monitoring: To assess the impact of PEEP on cardiac function and filling pressures.
    • Pulmonary Artery Catheterization: May be used to monitor the effects of PEEP on pulmonary artery pressures and cardiac output.
  4. Protective Lung Ventilation in Surgery: Utilizing PEEP to prevent atelectasis and postoperative pulmonary complications.
  5. Weaning Process:
    • Gradual Reduction: Monitoring respiratory mechanics, work of breathing, and gas exchange.
    • Spontaneous Breathing Trials (SBT): Assessing the ability to tolerate lower PEEP levels.


PEEP is a complex and vital component of mechanical ventilation, with multifaceted effects on respiratory mechanics, gas exchange, hemodynamics, and even neurodynamics. Its application requires a nuanced understanding of underlying pathophysiology, continuous monitoring with advanced tools, and individualized titration to optimize patient outcomes. The integration of PEEP into a comprehensive respiratory care strategy exemplifies the complexity and precision required in critical care medicine.