Positive end-expiratory pressure (PEEP) is a fundamental parameter in mechanical ventilation, and PEEP in mechanical ventilation plays a critical role in maintaining lung stability during the respiratory cycle. By influencing alveolar mechanics, oxygenation, and lung-protective ventilation strategies, PEEP directly affects both respiratory physiology and clinical outcomes, particularly in critically ill patients. Understanding the basic concept of PEEP is essential before evaluating its physiological effects and clinical applications.
What Is PEEP (Positive End-Expiratory Pressure)?
PEEP (Positive End-Expiratory Pressure) refers to the positive pressure maintained in the airways and alveoli at the end of expiration during mechanical ventilation. This pressure prevents complete alveolar collapse. It helps keep the lungs open. It increases functional residual capacity.
PEEP prevents repetitive opening and closing of alveoli during each respiratory cycle. In this way, it reduces the risk of ventilator-induced lung injury.
The importance of PEEP is even greater in patients with ARDS. In these patients, alveoli are prone to collapse. In intensive care practice, PEEP is carefully adjusted to optimize oxygenation and to limit lung injury.
Physiological Effects of PEEP on the Lungs
The physiological effect of PEEP is based on maintaining positive pressure in the alveoli at the end of expiration, thereby keeping the lungs open. This pressure prevents alveolar collapse. It reduces the development of atelectasis. It increases functional residual capacity.
PEEP prevents alveoli from repeatedly opening and closing during each breathing cycle. As a result, shear stress is reduced. The risk of ventilator-induced lung injury decreases. The alveolar surface area is preserved.
With the recruitment of collapsed alveoli, alveolar ventilation increases. Ventilation–perfusion matching improves. Alveolar–capillary gas exchange becomes more effective. Consequently, arterial oxygenation increases.
Role of PEEP in Oxygenation and Gas Exchange
The relationship between PEEP and oxygenation is based on keeping alveoli open at the end of expiration. PEEP prevents alveolar collapse and reduces atelectasis. It increases functional residual capacity. The number of alveoli participating in gas exchange increases.
Maintaining alveolar patency improves ventilation–perfusion matching. The intrapulmonary shunt fraction decreases. Alveolar–capillary oxygen diffusion becomes more effective. As a result, arterial oxygen tension (PaO₂) increases.
Low vs High PEEP: Benefits, Risks, and Complications
Low PEEP leads to alveolar closure at the end of expiration. The risk of atelectasis increases. Functional residual capacity decreases. Ventilation–perfusion matching deteriorates. Intrapulmonary shunt increases. Oxygenation worsens. Repetitive opening and closing of alveoli may cause ventilator-induced lung injury.
High PEEP may cause alveolar overdistension. The risk of barotrauma and volutrauma increases. Pulmonary capillary perfusion may decrease. Ventilation–perfusion matching may be impaired. Intrathoracic pressure increases. Venous return decreases. Cardiac output may fall. Hypotension may develop.
Clinical Importance of PEEP in ARDS and ICU Patients
In ARDS and intensive care settings, PEEP maintains alveolar patency. It reduces atelectasis. It improves oxygenation. It decreases intrapulmonary shunt. It is a fundamental component of lung-protective ventilation.
PEEP is critical for stabilizing collapse-prone alveoli in ARDS. It enhances the effectiveness of mechanical ventilation in the ICU. Inappropriate levels may cause lung injury and hemodynamic impairment. Therefore, individualized titration is required.
Frequently Asked Questions
1. Why is PEEP in mechanical ventilation essential in ARDS?
Because it prevents alveolar collapse. It reduces atelectasis. It improves oxygenation.
2. Does high PEEP provide better oxygenation in all patients?
No. Inappropriate high PEEP may cause alveolar overdistension and hemodynamic instability.
3. Is oxygenation alone sufficient when setting PEEP?
No. Lung mechanics and hemodynamic status should be evaluated together.
References
Tobin MJ. Principles and Practice of Mechanical Ventilation. 3rd ed. McGraw-Hill; 2013.
ARDS Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and ARDS. N Engl J Med. 2000;342:1301–1308.
Marini JJ, Gattinoni L. Management of COVID-19 respiratory distress. JAMA. 2020;323(22):2329–2330.
West JB. Respiratory Physiology: The Essentials. 10th ed. Lippincott Williams & Wilkins; 2016.
Gattinoni L, Caironi P, Cressoni M, et al. Lung recruitment in patients with ARDS. N Engl J Med. 2006;354:1775–1786.