From the Guidelines
Late cycling in Mechanical Ventilation (MV) refers to the phenomenon where the ventilator's inspiratory time is longer than the patient's neural inspiratory time, resulting in the patient attempting to exhale while the ventilator is still delivering a breath. This can lead to patient discomfort, increased work of breathing, and potentially longer ventilator dependence. According to the BTS/ICS guideline for the ventilatory management of acute hypercapnic respiratory failure in adults 1, the inspiratory time (Ti) should be of sufficient length to achieve an adequate volume and at a frequency that allows the patient time to fully exhale.
Key factors to consider in late cycling include:
- Inspiratory time: The duration of inspiration should be set to match the patient's natural respiratory rhythm
- Flow rate settings: Adjusting the flow rate can help synchronize the ventilator's cycling with the patient's breathing pattern
- Mode of ventilation: Switching to a mode that allows the patient more control over breath termination, such as pressure support ventilation, can help alleviate late cycling
To manage late cycling, clinicians should:
- Decrease the inspiratory time to match the patient's neural inspiratory time
- Adjust the flow rate settings to improve synchronization between the ventilator and the patient's breathing pattern
- Consider switching to a mode of ventilation that allows the patient more control over breath termination, as recommended by the BTS/ICS guideline 1.
Proper management of late cycling is crucial to improve patient comfort, reduce work of breathing, and minimize the risk of complications associated with mechanical ventilation.
From the Research
Definition of Late Cycling in Mechanical Ventilation
Late cycling in mechanical ventilation refers to the phenomenon where the ventilator delivers a breath and then waits for a prolonged period before terminating the inspiratory phase and initiating expiration.
Causes and Implications
- Expiratory flow limitation (EFL) is a key factor that can lead to late cycling, as it causes the lung volume to remain elevated, resulting in auto-positive end-expiratory pressure (PEEP) or PEEPi 2.
- In patients with chronic obstructive pulmonary disease (COPD), late cycling can occur due to the increased airway resistance and inspiratory effort, leading to dynamic hyperinflation 3.
- The management of late cycling requires careful adjustment of ventilator settings, such as external PEEP, to minimize hyperinflation and provide reasonable gas exchange, respiratory muscle rest, and proper patient-ventilator interaction 3, 2.
Detection and Management
- Late cycling can be suspected by using different means, including monitoring of respiratory mechanics and detection of EFL 2.
- Optimal ventilator strategies can be developed through continuous and thorough monitoring of respiratory mechanics during ongoing ventilator support, taking into account factors such as tidal volume and positive end-expiratory pressure (PEEP) 4.
- The use of intratracheal catheters can provide more accurate ventilator settings, particularly for optimal PEEP, compared to conventional methods 4.
Patient-Ventilator Interaction
- Patient-ventilator asynchrony can occur due to late cycling, leading to complications such as dyspnea and poor outcomes 5, 2.
- The analysis of patient-ventilator interaction is crucial in adjusting ventilator settings and minimizing the risk of late cycling and other ventilator-related complications 5.