Sunday, April 17, 2011

Delayed Cycling

One form of delayed cycling  is when the operator inappropriately sets the inspiratory time too

However, delayed cycling is also very common during CSV-PS.

A pressure spike at the end of inspiration may indicate delayed cycling however this is not always associated with expiratory muscle activity . The spike may also be due to the relaxation of the inspiratory muscles, the spike is caused by the returning of pressure creating a temporary increase in pressure (usually associated with higher levels of pressure support > 10 cmH2O). 

Always evaluate the patient for distress to determine if it is delayed cycling vs. muscle relaxation. If the patient looks relaxed and the P0.1 is within limits then the spike is most likely due to muscle relaxation.

A 25% expiratory cycling threshold is a common default setting in most mechanical ventilators. This setting is appropriate in a large percent of the patient population. As previously mentioned a default setting of 25% may be too short in patients recovering from ALI, conversely , in patients with histories of airway obstruction this setting may be too long.

Prolonged expiratory cycling in the COPD patient may increase work of breathing, intrinsic PEEP, and trigger asynchronies (ineffective efforts).Waveform book  at