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 as suggested in option D.
Physiological Effects of PEEP
Effects on Lung Volumes and Capacity
- PEEP increases end-expiratory lung volume (EELV) and functional residual capacity (FRC) by preventing alveolar collapse at end-expiration, which reduces atelectasis 1
- PEEP helps maintain open alveoli throughout the respiratory cycle, which is one of its primary therapeutic mechanisms 1
- The application of PEEP significantly improves FRC in patients with respiratory failure, contrary to option D which incorrectly suggests a decrease 2
Effects on Extravascular Lung Water
- PEEP actually increases extravascular lung water (EVLW) due to a decrease in lung lymph flow, rather than decreasing it as suggested in option A 3
- Studies show that institution of PEEP produces a reversible increase in EVLW that is linked to a decrease in pulmonary lymph flow 3
- While PEEP may redistribute extravascular water to the extra-alveolar interstitial space, it does not decrease the total amount of lung water 4
Hemodynamic Effects
- PEEP decreases cardiac preload by increasing pleural pressure, which decreases the gradient for venous return to the right ventricle 1
- This reduces the pressure gradient from the upstream venous reservoir to the heart, contrary to option B which incorrectly suggests an increase in cardiac preload 1
- The hemodynamic effects of PEEP must be carefully monitored as excessive PEEP can lead to compromised cardiac output 1
Clinical Applications and Considerations
Benefits in Respiratory Failure
- PEEP improves oxygenation by reducing intrapulmonary shunt and increasing the number of alveolar units participating in gas exchange 1
- In patients with acute respiratory distress syndrome (ARDS), PEEP helps prevent atelectrauma by reducing cyclic opening and closing of alveoli during mechanical ventilation 1
- PEEP improves respiratory system compliance in de-recruited areas and enhances ventilation to dependent lung regions 1
Potential Pitfalls and Caveats
- 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
- In patients with chronic airflow obstruction, PEEP should be applied cautiously but can improve lung mechanics and reduce work of breathing when auto-PEEP is present 5
Effect on Hormonal Regulation
- While not directly addressed in the provided evidence, option C suggests a decrease in atrial natriuretic peptide (ANP) with PEEP
- This is physiologically inconsistent, as increased intrathoracic pressure from PEEP would typically increase atrial wall tension, which would stimulate ANP release rather than decrease it
Conclusion on Multiple Choice Options
- Option A is incorrect: PEEP increases, not decreases, extravascular lung water 3
- Option B is incorrect: PEEP decreases, not increases, cardiac preload 1
- Option C is incorrect: PEEP would likely increase, not decrease, atrial natriuretic peptide due to increased atrial wall tension
- Option D is incorrect: PEEP increases, not decreases, functional residual capacity 1, 2