What is the cause of a late ventilator cycle (ventilator-assisted breathing)?

From the Guidelines

A late ventilator cycle is primarily caused by patient-ventilator asynchrony, which can be addressed by adjusting the ventilator's trigger sensitivity and evaluating for auto-PEEP. To address this issue, consider the following adjustments:

• Decrease the flow trigger threshold (typically to 1-2 L/min) or pressure trigger threshold (to 0.5-1.5 cmH2O) depending on your ventilator type, as suggested by various studies 1.
• Reduce the inspiratory time or increase the flow rate to better match the patient's respiratory demands.
• Evaluate for auto-PEEP by performing an expiratory hold maneuver, as air trapping can delay trigger recognition, and consider applying a low level of PEEP and/or continuous positive airway pressure (CPAP) to counterbalance PEEPi 1.
• In cases of persistent asynchrony, sedation adjustments may be necessary, but aim to optimize ventilator settings first. Late cycling causes patient discomfort, increased work of breathing, and potentially prolonged mechanical ventilation, which can negatively impact morbidity, mortality, and quality of life. This asynchrony happens because the ventilator's response time lags behind the patient's neural respiratory drive, often due to inadequate trigger sensitivity settings or underlying conditions like COPD that affect respiratory mechanics, as highlighted in a study from 2016 1. Some key points to consider when addressing late ventilator cycles include:
• Patient-ventilator asynchrony is associated with a prolonged duration of mechanical ventilation, and increased morbidity and mortality 1.
• New modes of ventilation, such as proportional assist ventilation (PAV) and neurally adjusted ventilatory assist (NAVA), can improve patient-ventilator interaction and minimize asynchrony 1.
• The effect of these modes on sleep quality has shown mixed results, but improving patient-ventilator synchrony is crucial for optimizing patient outcomes.

From the Research

Causes of Late Ventilator Cycle

The causes of a late ventilator cycle can be attributed to several factors, including:

• Patient-ventilator asynchrony, which can lead to ineffective triggering and delayed cycling 2
• Inappropriate mechanical ventilation strategies, such as high tidal volumes and plateau pressures, which can cause lung injury and lead to delayed ventilation cycles 3
• Deranged respiratory drive, which can result in abnormal breathing patterns and delayed ventilation cycles 4
• Inadequate sedation and analgesia, which can cause patient discomfort and lead to asynchronous breathing patterns 5
• Ventilator settings that are not optimized for the patient's respiratory needs, such as inadequate positive end-expiratory pressure (PEEP) or peak inspiratory flow 6

Factors Contributing to Late Ventilator Cycle

Several factors can contribute to a late ventilator cycle, including:

• Patient characteristics, such as lung compliance and respiratory muscle strength
• Ventilator settings, such as tidal volume, respiratory rate, and PEEP
• The presence of respiratory diseases, such as acute respiratory distress syndrome (ARDS)
• The use of sedatives and opioids, which can affect respiratory drive and breathing patterns 5, 4
• The need for precise monitoring and modulation of respiratory drive to prevent potentially injurious consequences 4