From the Guidelines
The answer is A. High rate and prolonged I:E ratio is most likely to develop auto-positive end-expiratory pressure (auto-PEEP) in mechanical ventilation. Auto-PEEP, also known as intrinsic PEEP, occurs when there is insufficient time for complete exhalation before the next breath begins, leading to air trapping in the lungs. When ventilation occurs at high respiratory rates, the time available for exhalation naturally decreases. This problem is compounded when combined with a prolonged inspiratory-to-expiratory (I:E) ratio, which further reduces the expiratory time. The trapped air creates a positive pressure at the end of expiration that is not set by the ventilator but occurs physiologically, as described in the study by 1. This phenomenon is particularly problematic in patients with obstructive lung diseases like COPD or asthma, where airflow limitation during exhalation already exists. Auto-PEEP can lead to increased work of breathing, decreased cardiac output, barotrauma, and ventilator asynchrony. Some key points to consider when dealing with auto-PEEP include:
- Decreasing the respiratory rate or tidal volume to minimize auto-PEEP, as suggested by 1
- Using a slower respiratory rate with smaller tidal volumes and longer expiratory times to reduce the risk of auto-PEEP
- Being vigilant for auto-PEEP when using settings with high respiratory rates and prolonged inspiratory times
- Considering the use of sedation or paralytic agents to optimize ventilation and reduce ventilator dyssynchrony in severe cases. Overall, high rate and prolonged I:E ratio is the most likely scenario to develop auto-PEEP, and clinicians should be aware of this potential complication when managing patients on mechanical ventilation, especially those with obstructive lung diseases, as supported by the findings of 1 and 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: