Is this a) a flow asynchrony, b) an ineffective effort, c) early cycling, or c) auto-triggering?
Answer: Ineffective effort
The patient’s effort fails to trigger the ventilator. This is indicated on the flow waveform by an abrupt change in the steepness of the waveform (1) (a decrease in expiratory flow or an increase in inspiratory flow) that is not followed by ventilatory support (2).
How to recognize it:
Expiratory flow does not decelerate straight down to 0 l/min, but shows a positive deflection instead.
Depending on when the effort starts, it is also possible that the patient does not achieve positive flow values and stays in the negative range. 72% of health care professionals that we surveyed use waveform analysis to monitor and recognize asynchronies1. See the list of possible causes and solutions below.
Common possible causes:
- Trigger threshold set too high
- Pressure support too high
- Set frequency and/or inspiratory time too high (in controlled modes)
- Tidal volume set too high
- Presence of Auto-PEEP
- Low respiratory drive
- Weak inspiratory efforts (maybe due to a low respiratory drive and/or sedation)
Evaluate the patient’s respiratory drive and correct as needed. Assess the patient for over-sedation and reduce the rate of sedative infusion. Determine whether the patient is receiving too much assistance; adjust pressure-support ventilation to reduce tidal volume if necessary.
Reference: Result of internal survey conducted online from May 27 - June 23, 2019 with 155 voluntary participants worldwide (respiratory therapists, physicians, nurses, biomed/technician/engineer, paramedics, other).
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