ICCN Articles

What Is PEEP, and How Is It Set on the Ventilator?

By Javier Castaneda ·

Positive End-Expiratory Pressure (PEEP) is one of the most important and most misunderstood knobs on the ventilator. It is the pressure that remains in the airways at the end of exhalation, preventing the lungs from fully emptying. This guide explains what PEEP does, why it matters, and how clinicians choose a setting.

What PEEP Does

Without PEEP, fragile or fluid-filled alveoli tend to collapse at the end of each breath and must be forced open again with the next one, repetitive opening and closing that injures the lung (atelectrauma). PEEP holds these air sacs open, increases the surface area available for gas exchange, and improves oxygenation. It also reduces the work of reinflating collapsed lung.

How PEEP Is Set

A typical starting point is about 5 cm H2O. From there, clinicians titrate PEEP to balance oxygenation against side effects. Common approaches include the ARDSNet PEEP/FiO2 tables (which pair a PEEP level with the oxygen requirement), minimizing driving pressure (plateau pressure minus PEEP), and individualized best-PEEP methods that watch oxygenation, compliance, and hemodynamics as PEEP is adjusted.

Too Much vs Too Little

  • Too little PEEP allows alveoli to collapse, worsening oxygenation and causing atelectrauma.
  • Too much PEEP can overdistend healthy alveoli (volutrauma or barotrauma), raise the risk of pneumothorax, and impede venous return, dropping blood pressure and cardiac output.

The right level is the one that keeps the lung open without overdistending it or compromising the circulation, which is why PEEP is always set with an eye on both the lungs and the hemodynamics.

The Bottom Line

PEEP keeps alveoli open at end-expiration, improving oxygenation and protecting the lung, but only within a window that avoids overdistension and hemodynamic harm. Setting it well is a bedside balancing act. For deeper, evidence-based guidance on PEEP, driving pressure, and lung-protective ventilation, explore more from the Interprofessional Critical Care Network.