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How to diagnose and avoid ineffective efforts

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作者: David Grooms

日期: 08.07.2019

An ineffective effort is defined as a patient effort that is unable to trigger the delivery of a mechanical breath.
How to diagnose and avoid ineffective efforts

What are the causes?

The most common causes are:

  • Trigger threshold set too high
  • Pressure support too high
  • Set frequency and/or inspiratory time too high (in controlled/assisted modes)
  • Tidal volume set too high
  • Presence of AutoPEEP
  • Low respiratory drive
  • Weak inspiratory effort
  • Sedation

What is visible on the waveform?

Several waveform characteristics can assist in the diagnosis (see Figure 1):

  • The pressure/time scalar waveform will show a decrease in baseline airway pressure not followed by ventilator support
  • The flow/time scalar waveform will reveal an abrupt change in the steepness of the waveform (decrease in expiratory flow or increase in inspiratory flow not followed by ventilator support)
  • The esophageal pressure/time scalar waveform will display a decrease in pleural pressure not followed by ventilator support
Screenshot of waveforms for airway pressure, flow, and esophageal pressure
Figure 1: Waveform characteristics indicating an ineffective effort
Screenshot of waveforms for airway pressure, flow, and esophageal pressure
Figure 1: Waveform characteristics indicating an ineffective effort

How can I resolve the issue?

The most practical adjustments that can be made on the ventilator to reduce ineffective efforts are as follows:

  • Minimize AutoPEEP by reducing minute ventilation
  • Reduce pressure support and/or tidal volume
  • Adjust the expiratory trigger sensitivity (ETS) to make it more sensitive to the patient's activity (see Figures 2 and 3)
Screenshot of waveform showing change in flow
Figure 2: Ineffective effort with ETS set at 25%
Screenshot of waveform showing change in flow
Figure 2: Ineffective effort with ETS set at 25%
Screenshot of flow waveform when ETS increased
Figure 3: ETS increased to 50% at the red line, resulting in elimination of ineffective efforts
Screenshot of flow waveform when ETS increased
Figure 3: ETS increased to 50% at the red line, resulting in elimination of ineffective efforts