In mechanical ventilation, the transition from inspiration to exhalation is known as cycling. Normal (synchronous) cycling occurs when inspiration ends at a clinically appropriate time that closely aligns with the patient’s own inspiratory effort. Late cycling can present as anything from minor waveform abnormalities to significant asynchrony that may require clinical intervention.

In late cycle dyssynchrony, the ventilator continues to deliver flow after the patient’s neural inspiratory effort has ended. This typically results from the ventilator’s set inspiratory time exceeding the patient’s natural inspiratory time. This becomes clinically significant when the patient initiates significant exhalation effort before the ventilator cycles to expiration.

Clinical implications of late cycle dyssynchrony include:

• Increased work of breathing
• Patient discomfort
• Potential for ventilator-induced lung injury
• Prolonged duration of mechanical ventilation

VC: volume control, PC: pressure control, CMV: continuous mandatory ventilator, CSV: continuous spontaneous ventilator, Set Point: all targets set by the operator

• Time cycling: Indicates that the mechanical ventilator breath switches from inspiration to expiration after a set time threshold is reached

• Volume-targeted breaths: Inspiration stops once the target volume is delivered

• Flow cycle: When the patient's inspiratory flow decreases to a predetermined level of certain percentage of peak inspiratory flow, the breath would cycle into exhalation

How can optimal synchrony be achieved by adjusting the cycling settings?

VC-CMV: It depends on the type of ventilator—some allow you to directly shorten the inspiratory time, while others require increasing the flow instead

PC-CMV: Decrease the inspiratory time to match the neural inspiratory time

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