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What Does PEEP Do in Ventilation?

In respiratory arrest or respiratory failure a person no longer can breathe on their own, requiring mechanical ventilation for temporary support. Numerous ventilator modes have been implemented over the years, which have substantially improved the outcome of ventilated patients. Positive end-expiratory pressure (PEEP) is a form of therapy applied during mechanical ventilation.

  1. Ventilation

    • In the most basic sense, a mechanical ventilator is a closed system, similar to your lungs. It is a box supplied by electrical or pneumatic power that breathes for you by delivering a flow of air and oxygen to your lungs via a tube that has been placed into your airway. Your physician or health care provider sets certain parameters on the control panel of the ventilator, which determines the pattern of gas delivered to your lungs.

    Modes of Ventilation

    • There are numerous modes of ventilation, such as Assist/Control, Auto-Flow, Auto-PEEP, Bi-level Positive Airway Pressure and Continuous Positive Airway Pressure, or CPAP. Most ventilators used today are considered positive-pressure ventilators. This means that a pressure gradient has to exist in order for gas to flow into the lungs; this occurs naturally when you breathe. Air is then released when you passively relax your respiratory muscles.

    Positive End-Expiratory Pressure

    • The expiratory valve in the ventilator closes during inspiration, directing flow into your lungs. This valve then opens, allowing you to exhale. Besides allowing you to exhale naturally and the pressure in your lungs to return to baseline, the ventilator can apply positive pressure during the exhalation phase, which limits the lung's ability to empty completely. This process increases your functional residual capacity or FRC, which increases the mean airway pressure in your lungs. This process is called PEEP.

    Improves Oxygenation

    • PEEP improves oxygenation by a process called "alveoli recruitment"; alveoli are the air sacs in your lungs. Through positive pressure, the flow of gas into your lungs recruits the alveoli, allowing them to absorb the oxygen from the flow of gas. PEEP keeps these alveoli open longer as well as recruiting more alveoli, allowing better oxygenation. PEEP is essentially a positive baseline pressure, where ventilating without PEEP allows the expiratory pressure to return to a zero baseline.

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