Effects of Positive End-Expiratory Pressure (PEEP) Therapy
Positive end-expiratory pressure therapy will result in an increase in functional residual capacity, not a decrease. 1
Primary Physiological Effects of PEEP
- 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 enhances respiratory system compliance in previously de-recruited areas and improves ventilation to dependent lung regions 1
Effects on Hemodynamics and Fluid Dynamics
- PEEP decreases cardiac preload by increasing pleural pressure, which reduces the gradient for venous return to the right ventricle 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
- PEEP can increase extravascular lung water (EVLW) due to a decrease in pulmonary lymph flow, as demonstrated in sheep models 2
- Studies show that PEEP application resulted in a decrease in lung lymph flow (from 7±1 to 5±1 ml/h) with a corresponding increase in EVLW (from 498±40 to 630±58 ml) 2
Clinical Applications
- Higher PEEP levels (approximately 15 cm H₂O) are recommended for moderate to severe acute respiratory distress syndrome (ARDS) 1
- PEEP helps prevent atelectrauma by reducing cyclic opening and closing of alveoli during mechanical ventilation 1
- In patients with chronic airflow obstruction, low levels of PEEP may improve lung mechanics and reduce the work of breathing without substantially increasing the risks of hyperinflation 3
Important Considerations and Potential Adverse Effects
- Excessive PEEP levels can lead to hemodynamic compromise, barotrauma, and increased pulmonary vascular resistance 1
- PEEP must be carefully titrated to avoid overdistension of already open alveoli, which can lead to ventilator-induced lung injury 1
- While PEEP improves oxygenation and lung mechanics, it does not necessarily decrease extravascular lung water in models of non-cardiogenic pulmonary edema 4
Answer to the Multiple Choice Question
Based on the evidence presented, the correct answer is:
- (d) decrease in functional residual capacity - INCORRECT. PEEP actually increases functional residual capacity by preventing alveolar collapse 1
- (a) decrease in extravascular lung water - INCORRECT. PEEP may actually increase extravascular lung water due to decreased lymphatic drainage 2
- (b) increase in cardiac preload - INCORRECT. PEEP decreases cardiac preload by increasing pleural pressure 1
- (c) decrease in atrial natriuretic peptide - This is not directly addressed in the evidence provided