What is the primary effect of Positive End-Expiratory Pressure (PEEP) therapy?

Effects of Positive End-Expiratory Pressure (PEEP) Therapy

Positive end-expiratory pressure therapy will result in a decrease in functional residual capacity is FALSE. PEEP therapy increases functional residual capacity by preventing alveolar collapse at end-expiration. 1

Primary Effects of PEEP on Pulmonary Function

• PEEP increases end-expiratory lung volume (EELV) and functional residual capacity (FRC) by preventing alveolar collapse at end-expiration, which reduces atelectasis 1
• PEEP improves oxygenation by reducing intrapulmonary shunt and increasing the number of alveolar units participating in gas exchange 1
• PEEP improves respiratory system compliance in previously de-recruited areas and enhances ventilation to dependent lung regions 1
• PEEP helps prevent atelectrauma by reducing cyclic opening and closing of alveoli during mechanical ventilation 1

Hemodynamic Effects of PEEP

• PEEP decreases cardiac preload (not increases) by increasing pleural pressure, which decreases the gradient for venous return to the right ventricle 1
• PEEP reduces the pressure gradient from the upstream venous reservoir to the heart, further contributing to decreased preload 1
• PEEP may have beneficial effects on left ventricular function by decreasing LV afterload, provided there are no deleterious effects on the right ventricle 1

Effects on Extravascular Lung Water

• Contrary to option (a), PEEP actually increases extravascular lung water (EVLW) due to a decrease in lung lymph flow 2
• Research shows that institution of PEEP produces a reversible increase in EVLW that is linked to a decrease in pulmonary lymph flow 2
• Studies have demonstrated that PEEP does not decrease lung water content in pulmonary edema caused by damage to fluid-exchanging vessels 3

Effects on Atrial Natriuretic Peptide

• PEEP does not decrease atrial natriuretic peptide (ANP) as suggested in option (c) 1
• ANP is typically released in response to atrial stretch, and since PEEP decreases venous return and cardiac preload, it would be expected to decrease ANP production, not increase it 1

Clinical Applications and Considerations

• Higher PEEP levels (15.1 ± 3.6 cm H₂O) are recommended for moderate to severe acute respiratory distress syndrome (ARDS) 1
• PEEP can be beneficial in patients with chronic airflow obstruction by improving expiratory resistance without substantially increasing peak static pressure 4
• PEEP improves the effective triggering sensitivity of the ventilator, diminishes ventilatory drive, and reduces the mechanical work of breathing during machine-assisted ventilatory cycles 4
• Excessive PEEP levels can lead to hemodynamic compromise, barotrauma, and increased pulmonary vascular resistance 1

Common Pitfalls and Caveats

• Zero end-expiratory pressure (ZEEP) should be avoided as it contributes to decreased compliance and increased risk of volutrauma 1
• While PEEP improves oxygenation, it can also decrease cardiac output, which may offset some of the benefits in oxygen delivery 5
• PEEP significantly reduces intravascular pulmonary fluid volumes along with cardiac output, without necessarily changing extravascular lung water 6
• The application of PEEP must be carefully titrated to avoid overdistension of already open alveoli, which can lead to ventilator-induced lung injury 7