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.
Primary Effects of PEEP on Pulmonary Physiology
- 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
Hemodynamic Effects of PEEP
- PEEP decreases cardiac preload by increasing pleural pressure, which reduces the gradient for venous return to the right ventricle 1
- This contradicts option B (increase in cardiac preload), as PEEP actually reduces preload by decreasing the pressure gradient from the venous reservoir to the heart 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 can actually increase extravascular lung water (EVLW) due to decreased lung lymph flow 2
- Research shows that institution of PEEP produces a reversible increase in EVLW that is linked to a decrease in lung lymphatic drainage 2
- While PEEP may redistribute pulmonary edema from alveolar to extra-alveolar spaces 3, it does not decrease the overall lung water content 4
Effects on Functional Residual Capacity
- Multiple studies confirm that PEEP increases functional residual capacity (FRC), directly contradicting option D 1, 5
- This increase in FRC is one of the primary mechanisms by which PEEP improves gas exchange and pulmonary function 5
- In patients with acute respiratory distress, PEEP maintains recruitment of previously collapsed alveoli, distributing tidal volume to more alveoli and increasing FRC 5
Clinical Applications and Considerations
- Higher PEEP levels 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 intrinsic PEEP (auto-PEEP), application of external PEEP can improve patient-ventilator interaction and reduce inspiratory effort during assisted ventilation 1
- Excessive PEEP can lead to hemodynamic compromise, barotrauma, and increased pulmonary vascular resistance 1
Effect on Atrial Natriuretic Peptide
- The evidence provided does not directly address the effect of PEEP on atrial natriuretic peptide (ANP) levels (option C)
- However, since PEEP decreases cardiac preload and right atrial filling 1, it would be expected to decrease atrial stretch, which is a stimulus for ANP release
- Therefore, option C (decrease in atrial natriuretic peptide) is likely correct based on the known physiological mechanisms, although not directly stated in the evidence