Sunday, April 10, 2011

Premature Cycling

Image 1: Patient coughing, notice the peak pressure spikes (yellow pressure waveform) this may lead to premature cycling. 

Premature Cycling
Premature cycling  also known as premature termination or short cycling occurs when the ventilator breath cycle ceases abruptly, while the patient requires a longer inspiratory phase. It is defined by the delivered inspiratory time is less than 50% of the mean inspiratory time [1,2].
Premature cycling may be attributed to pressure over-shots, causing the breath to cycle-off when the generated pressure meets the safety threshold setting. A good example of this is when a patient coughs during volume controlled ventilation (VC-CMV, VC-SIMV), in which the exhalation valve is closed throughout the set inspiratory time. 

Premature cycling can be very uncomfortable to the patient and may lead to inadequate tidal volume delivery (as pictured above), too aggressive suctioning, over sedating the patient, and prolonged time on mechanical ventilation.

[1] Epstein, S. (2011). How Often Does Patient-Ventilator Asynchrony Occur & What are the Consequences? Respiratory Care. 56 (1). 
[2] Gentile, M. (2011). Cycling of the Mechanical Ventilator Breath. Respiratory Care. 56 (1).