In pressure control mode, airway pressure remains constant throughout the inspiratory phase. However, if the patient attempts to exhale before the set inspiratory time ends, the pressure transiently rises above the set inspiratory pressure. This occurs when the patient’s neural inspiratory time is shorter than the ventilator’s set inspiratory time—a phenomenon known as late cycling . Late cycling can be recognized on ventilator waveforms by a pressure spike  on the pressure–t

In pressure control mode, airway pressure remains constant throughout the inspiratory phase. However, if the patient attempts to exhale before the set inspiratory time ends, the pressure transiently rises above the set inspiratory pressure. This occurs when the patient's neural inspiratory is shorter than the ventilator's set inspiratory time- a phenomenon known as late cycling. Late cycling can be recognized on ventilator waveforms by a pressure spike on the pressure-time sc

The following waveforms show a pressure spike that begins in mid-inspiration, with the pressure during latter half of the inspiratory phase rising above the initial set pressure. This occurs when the patient attempts to exhale before the set inspiratory time ends, causing an increase in intrathoracic pressure that is reflected as a pressure rise on the airway pressure waveform. This phenomenon, known as late cycling, occurs when the set inspiratory time exceeds the patient's

Suspect late cycling in pressure control mode when a brief negative flow appears during the latter part of the inspiratory phase accompanied by a pressure spike. Although subtle on the pressure-time scalar, careful inspection reveals a pressure rise in mid-inspiration, corresponding to the onset of expiratory muscle activity. Late cycling occurs when the set inspiratory time exceeds the patient's neural inspiratory time. To correct this dyssynchrony, the inspiratory time shou

These ventilator waveforms are from a patient on volume control mode. During the initial phase of inspiration, the airway pressure remains close to the baseline, indicating strong patient inspiratory effort. This is followed by a steep rise in pressure, likely due to relaxation of the inspiratory muscles and/or expiratory muscle contraction. The flow–time scalar shows a small bump early in inspiration, suggesting that the ventilator briefly switched to a pressure support–like

In pressure control mode, expiratory muscle contraction during the inspiratory phase produces a pressure spike and a rapid return of inspiratory flow to baseline. In some cases, the flow may even cross the baseline into negative values. This pattern indicates late cycling dyssynchrony, occurring when the set inspiratory time exceeds the patient’s neural inspiratory time.

The following example shows a flow–time scalar with two distinct peaks. The initial peak corresponds to the patient’s inspiratory effort, followed by a rapid return of flow to baseline as the inspiratory effort ends and/or expiratory muscle contraction occurs. Subsequently, a stepwise increase in flow appears as the ventilator delivers additional flow to compensate for a leak. A second flow peak is then observed, representing a new patient inspiratory effort. The presence of

The expiratory flow–time scalar shows a small upward deflection early in expiration, which could be mistaken for early cycling dyssynchrony. However, a closer look at the inspiratory flow–time scalar reveals two distinct flow peaks. The first peak corresponds to the initial inspiratory effort, while the second peak represents a new inspiratory effort that begins just before the ventilator cycles to expiration and continues into the expiratory phase, creating waveform changes

In pressure support mode, cycling to expiration occurs when the inspiratory flow decreases to a preset percentage of the peak inspiratory flow. However, in the presence of an air leak, the flow may fail to drop to the preset threshold, as the ventilator continues to deliver additional flow to maintain the target pressure and compensate for the leak. This results in a prolonged inspiratory phase and delayed cycling. In this example, the pressure–time scalar shows a notch durin

These waveforms illustrate multiple patient–ventilator dyssynchronies, highlighting the consequences of inappropriate ventilator settings. In the pressure–time scalar, immediately after the breath is triggered, the airway pressure drops to the level of PEEP, indicating a strong inspiratory effort and significant work shifting from the ventilator to the patient. This is followed by a steep rise in pressure, which reflects inspiratory muscle relaxation and expiratory muscle con

A step-up in airway pressure near the end of the inspiratory phase, along with a return of inspiratory flow to baseline or even a brief negative flow, indicates that the patient is activating expiratory muscles while the ventilator is still delivering inspiration. This occurs when the mechanical inspiratory time exceeds the patient’s neural inspiratory time, resulting in late (delayed) cycling dyssynchrony. This dyssynchrony can be corrected by reducing the set inspiratory ti

A pressure spike at the end of inspiration is sometimes misinterpreted as delayed (late) cycling. However, it is important to recognize that a similar spike can occur simply due to relaxation of the inspiratory muscles, even without active expiratory effort. When a strong inspiratory effort suddenly stops, the ventilator may not immediately compensate, leading to a brief overshoot in airway pressure. Thus, not all end-inspiratory pressure spikes indicate late cycling; some ma

The following volume control waveforms demonstrate severe work shifting, late cycling dyssynchrony, and active expiratory effort. In the pressure–time scalar, a pronounced drop below the baseline during the early inspiratory phase indicates significant work shifting (previously referred to as flow starvation ), where the ventilator’s delivered flow does not meet the patient’s inspiratory demand. As the inspiratory muscles relax and the expiratory muscles contract, the airway

Work shifting: During the initial phase of inspiration, the pressure is lower than the set Positive End-Expiratory Pressure (PEEP) because of the large inspiratory efforts (strong Pmus). Late cycling (delayed cycling): As the inspiratory muscles relax and expiratory muscles contract, the pressure waveform rises above the baseline. The patient completes a breath (inspiration and expiration) and begins another breath within the set inspiratory time. This can be identified by

Work shifting: During early inspiratory phase, the pressure-time scalar is deviated towards the baseline indicating strong inspiratory effort  Late Cycling: with relaxation of inspiratory muscles and contraction of expiratory muscles the pressure rises above the baseline. Patient completes one breath and starts another breath during the same inspiratory phase (identified by the pressure drop during late inspiratory phase). This pressure drop is sensed by the ventilator and

These breaths are patient triggered breaths. Due to significant air leak from the mask, the % flow cycling threshold is not reached, and the ventilator fails to terminate inspiration. Meanwhile, the patient completes one full breath cycle (inspiration and expiration) and initiates another, leading to a second peak in the inspiratory flow-time scalar. In pressure control or pressure support modes, an air leak causes the ventilator to increase flow in an attempt to maintain the

In late cycling, neural inspiration concludes, but the ventilator remains in the inspiratory phase because the set inspiratory time exceeds the patient's neural inspiratory time. The patient's use of expiratory muscles to counteract mechanical inflation causes a pressure spike in the late inspiratory phase and an early return of the flow waveform to the baseline.