Effects of Positive End-Expiratory Pressure (PEEP) Therapy
Positive end-expiratory pressure therapy primarily results in an increase in functional residual capacity (FRC) by preventing alveolar collapse at end-expiration. 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 improves respiratory system compliance in previously de-recruited areas and enhances ventilation to dependent lung regions 1
Effects on Extravascular Lung Water
- PEEP actually increases extravascular lung water (EVLW) due to a decrease in lung lymph flow, contrary to what might be expected 2
- Studies have shown that institution of PEEP produces a reversible increase in EVLW that is linked to a decrease in pulmonary lymph flow 2
- Research has demonstrated that PEEP does not decrease lung water content in pulmonary edema caused by damage to fluid-exchanging vessels 3
Hemodynamic Effects of PEEP
- PEEP decreases cardiac preload by increasing pleural pressure, which reduces the gradient for venous return to the right ventricle 1
- PEEP reduces the pressure gradient from the upstream venous reservoir to the heart, further decreasing preload 1
- PEEP significantly reduces intravascular pulmonary fluid volumes along with cardiac output 4
- 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 Atrial Natriuretic Peptide
- The decrease in cardiac preload caused by PEEP would lead to decreased atrial stretch 1
- Since atrial natriuretic peptide (ANP) is released in response to atrial stretch, PEEP would likely decrease ANP levels due to reduced preload, though this is not explicitly stated in the evidence
Clinical Applications and Considerations
- PEEP helps prevent atelectrauma by reducing cyclic opening and closing of alveoli during mechanical ventilation 1
- PEEP improves expiratory resistance without substantially increasing peak static pressure in patients with chronic airflow obstruction 5
- Adding PEEP improves the effective triggering sensitivity of the ventilator, diminishes ventilatory drive, and reduces the mechanical work of breathing during machine-assisted ventilation 5
- Excessive PEEP levels can lead to hemodynamic compromise, barotrauma, and increased pulmonary vascular resistance 1
Answer to the Question
Based on the evidence, the correct answer is:
- (d) decrease in functional residual capacity - INCORRECT. PEEP actually increases FRC by preventing alveolar collapse 1
- (a) decrease in extravascular lung water - INCORRECT. PEEP increases EVLW due to decreased lymph flow 2
- (b) increase in cardiac preload - INCORRECT. PEEP decreases cardiac preload by increasing pleural pressure 1
- (c) decrease in atrial natriuretic peptide - CORRECT. PEEP would likely decrease ANP due to reduced preload and atrial stretch 1
Therefore, the most accurate answer among the options is (c) decrease in atrial natriuretic peptide.