Conference Proceedings
March 2002 / Volume 47 / Number 3 / Page 279
How to Set Positive End-Expiratory Pressure
IntroductionApplication of positive end-expiratory pressure (PEEP) in acute lung injury patients under mechanical ventilation improves oxygenation and increases lung volume. The effect of PEEP is to recruit lung tissue in patients with diffuse lung edema. This effect is particularly important in patients ventilated with low tidal volumes. Measurement of respiratory system mechanics in patients with acute respiratory distress syndrome is important to assess the status of the disease and to choose appropriate ventilator settings that provide maximum alveolar recruitment while avoiding overdistention. In patients with acute respiratory distress syndrome in whom the lungs have been near-optimally recruited by PEEP and tidal volume, the use of recruitment maneuvers as adjuncts to mechanical ventilation remains controversial. The application of PEEP in patients with unilateral lung disease may be detrimental if PEEP hyperinflates normal lung regions, thus directing blood flow to diseased lung regions. In patients with air flow limitation and lung hyperinflation, the application of additional external PEEP to compensate for intrinsic PEEP and flow limitation frequently decreases the inspiratory effort to initiate an assisted breath, thus decreasing breathing work load.
Acute Lung Injury and ARDS
PEEP and Tidal Ventilation
Static Pressure-Volume Curves of the Respiratory System
Recruitment Maneuvers During Ventilation with High PEEP
Effect of PEEP in Patients with Unilateral Lung Injury
Fraction of Inspired Oxygen
Asthma and Acute-On-Chronic Obstructive Pulmonary Disease
Overview of the Problem
Dynamic Pulmonary Hyperinflation
Intrinsic Positive End-Expiratory Pressure
Clinical Scenarios
Application of PEEP
Application of PEEP During Continuous Mandatory Ventilation
Application of PEEP During Assisted Ventilation
Application of PEEP During Noninvasive Ventilation
Application of Continuous Positive Airway Pressure
Best PEEP/CPAP in Severe Airflow Obstruction: Controversy
Summary
Introduction
Positive end-expiratory pressure (PEEP) has became an established therapy for patients with acute respiratory distress syndrome (ARDS) or with flow limitation. Pioneering studies have shown that the application of PEEP in acute lung injury patients undergoing mechanical ventilation improves oxygenation, increases functional residual capacity, and increases respiratory system compliance at moderate levels, although at high levels compliance may decrease. When patients with air flow limitation and lung hyperinflation develop intrinsic PEEP and have difficulties triggering the ventilator, the addition of applied PEEP can be of considerable help.
In addition to the lung injury induced by high inflation pressures, animal research has revealed a form of lung injury associated with an inflammatory response that is caused when mechanical ventilation results in alveolar overdistention and cyclic collapse and re-inflation of alveolar units. Consequently, current recommendations for mechanical ventilatory strategies are based on the use of a small tidal volume (VT) in order to avoid high end-inspiratory alveolar pressures and alveolar overdistention. Additionally, the use of high PEEP levels to keep alveoli open at end-expiration, thereby maintaining alveolar recruitment. Three randomized clinical trials have recently shown that treatment with a lung-protective ventilation approach (ie, low VT and moderate-to-high PEEP to protect against excessive alveolar stretching) led to improvements in several clinical outcomes in patients with acute lung injury or ARDS.
The objectives are:
- To review the effects of PEEP and VT on lung recruitment, lung overdistention, and patient-ventilator interaction.
- To describe physiologic factors influencing the response to PEEP.
- To identify strategies that would help to determine appropriate PEEP selection.
