From the Guidelines
The answer is A. High rate and prolonged I:E ratio is most likely to cause auto-positive end-expiratory pressure (auto-PEEP) in mechanical ventilation. Auto-PEEP, also known as intrinsic PEEP, develops when there is insufficient time for complete exhalation before the next breath begins 1. This occurs because a high respiratory rate shortens the available time for exhalation, while a prolonged inspiratory-to-expiratory (I:E) ratio further reduces the expiratory phase.
Key Points to Consider
- When patients cannot fully exhale before the next breath, air becomes trapped in the lungs, creating a positive pressure at the end of expiration that was not intentionally set on the ventilator 1.
- Auto-PEEP can lead to increased work of breathing, decreased cardiac output, barotrauma, and ventilator asynchrony.
- To prevent or reduce auto-PEEP, clinicians should consider decreasing respiratory rates, shortening inspiratory times, or using ventilator modes that allow for more complete exhalation.
Management Strategies
- Decreasing the respiratory rate or tidal volume can help minimize auto-PEEP 1.
- Assisting with exhalation by pressing on the chest wall after disconnection of the ventilator circuit can allow active exhalation and should lead to immediate resolution of hypotension.
- In some cases, paralytic agents may be considered if auto-PEEP persists and the patient displays ventilator dyssynchrony despite adequate sedation 1.
From the Research
Auto-Positive End-Expiratory Pressure (Auto-PEEP) Development
Auto-PEEP is a physiologic event that occurs in mechanically ventilated patients, particularly in those with acute severe asthma, chronic obstructive pulmonary disease, or patients receiving inverse ratio ventilation 2. The development of auto-PEEP is influenced by several factors, including:
- Reduction in expiratory time by increasing the respiratory rate, tidal volume, or inspiratory time 2
- High respiratory rates and decreased inspiratory-to-expiratory (I:E) ratio 3
- Ventilatory techniques during cardiopulmonary resuscitation (CPR) that generate substantial levels of auto-PEEP depending on the methods of ventilation performed 3
Factors Predisposing to Auto-PEEP
The following factors predispose to auto-PEEP:
- Increased respiratory rate
- Increased tidal volume
- Increased inspiratory time
- Decreased expiratory time
- Inverse ratio ventilation 2
Relationship Between Auto-PEEP and Ventilatory Settings
The development of auto-PEEP is more likely to occur with:
- High rates and decreased I:E ratio, as this setting can lead to a reduction in expiratory time, allowing for the development of auto-PEEP 2, 3
- Therefore, option B (High rates and decreased I:E ratio) is the most likely scenario for auto-PEEP development.
Detection and Measurement of Auto-PEEP
Auto-PEEP can be detected and measured using various methods, including: