ⓘEducational use only — not medical advice. This is a teaching example and must not be used to guide care of any individual patient.Learn more →
Early cycle in Pressure Support
How early cycling can happen in pressure support producing, at times, double triggering in this mode.
PSVEarly cycleM2M5
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Fig 1.Early cycling happens when the cycle variable, the variable that controls the duration of inspiration, is set shorter than the duration of patient’s inspiratory effort. Inspiratory effort here extends past the end of inspiration into expiration. This can be noted as a positive deflection in early expiratory flows (compare expiratory flows of the 2nd, 5th and 6th breaths where you see that positive deflection in expiratory flows with those from the 1st, 3rd and 4th breaths where that positive deflection is not present). If the inspiratory effort extending to early expiration is strong enough to meet the inspiratory trigger sensitivity, then double triggering will occur, as you can see with the last few breaths. On PS, inspiration is set to end once inspiratory flows drop to a certain percentage of peak flows to give patients control over their itime (the longer the patient contracts their inspiratory muscle, the longer higher inspiratory flows are maintained). Once the patient relaxes their inspiratory muscles, flows drop and inspiration ends. This patient, however, had chronic severe restrictive lung disease and profound deconditioning so she could not maintain high enough inspiratory flows, leading to very short itimes in the order of 0.4 seconds.
