When a patient is intubated, what does PEEP (positive end‑expiratory pressure) mean?

What PEEP Means in Intubated Patients

PEEP (Positive End-Expiratory Pressure) is the pressure maintained in the airways at the end of expiration that exceeds atmospheric pressure, measured in cmH₂O, and is applied during mechanical ventilation to prevent alveolar collapse and improve oxygenation. 1, 2

Core Definition and Mechanism

PEEP refers specifically to airway pressure above atmospheric at end-expiration during mechanical ventilation 1. This pressure prevents complete lung deflation between breaths, maintaining lung recruitment throughout the respiratory cycle 2.

Key Physiological Effects

Primary beneficial effects include:

• Improved oxygenation by increasing functional residual capacity (FRC) 1, 2
• Recruitment and stabilization of collapsed lung units (alveoli) 1
• Prevention of "atelectrauma" - injury from repetitive opening and closing of alveoli 3
• Improved lung compliance and decreased work of breathing 1
• Reduced need for high inspired oxygen concentrations (FiO₂) 3

Clinical Application

Standard Initial Settings

The ventilator should initially be set to deliver PEEP of 5 cmH₂O 4. Zero PEEP (ZEEP) is not recommended 4.

Disease-Specific Considerations

In ARDS (moderate to severe):

• Higher PEEP levels (typically 10-15 cmH₂O or more) reduce mortality when PaO₂/FiO₂ ≤ 200 mmHg 3
• PEEP selection should consider lung recruitability and driving pressure 3
• When applied with constant plateau pressure, PEEP reduces driving pressure and maintains lung recruitment 3

In COPD/obstructive disease:

• External PEEP can counterbalance intrinsic PEEP (PEEPi or "auto-PEEP") 5, 6
• Application of PEEP up to approximately 70% of measured PEEPi reduces work of breathing without promoting further hyperinflation 7, 6
• This improves patient-ventilator interaction and reduces inspiratory effort during assisted ventilation 5, 6

Important Distinction: External vs Intrinsic PEEP

Intrinsic PEEP (PEEPi) is end-expiratory alveolar pressure that remains positive even without external PEEP application 5. This occurs when expiratory time is insufficient for complete lung deflation, common in:

• COPD exacerbations 5
• Asthma 5
• Inappropriate ventilator settings 5

PEEPi creates an inspiratory threshold load that patients must overcome before triggering the ventilator, increasing work of breathing 5.

Potential Adverse Effects

Critical complications to monitor:

• Decreased cardiac output by reducing venous return (increased right atrial back pressure) 8, 1, 2
• Increased pulmonary vascular resistance and right ventricular afterload 8
• Barotrauma risk with excessive pressures 1, 2
• Overdistension of already-open lung units when applied with constant tidal volume 3

Hemodynamic Monitoring

Approximately 50% of alveolar pressure transmits to pleural pressure in normal lungs; less transmits in diseased, stiffer lungs 8. The normal venous return gradient is only 4-8 mmHg, so small PEEP changes can significantly affect cardiac output 8.

Monitoring and Optimization

Essential parameters to track:

• Driving pressure (plateau pressure minus PEEP) - values exceeding 15 cmH₂O are concerning 3
• Oxygenation (PaO₂/FiO₂ ratio)
• Dynamic compliance 4
• Hemodynamic stability (blood pressure, cardiac output) 3, 4

For PEEP titration: The overdistension-collapse method using electrical impedance tomography can individualize PEEP by identifying the level that minimizes both alveolar collapse and overdistension 9. A standardized PEEP range (e.g., 24 to 6 cmH₂O) improves reliability 9.

Clinical Context

PEEP is a fundamental ventilator setting that must be actively managed rather than left at default values. The optimal level depends on underlying pathophysiology: atelectatic surgical lungs respond differently than inflammatory ARDS lungs, which differ from hyperinflated COPD lungs 4. Always ensure continuous hemodynamic and oxygen saturation monitoring before and during PEEP adjustments 4.