Patient-ventilator dyssynchronies

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Dyssynchronies between inspiratory attempts of the patient and the inspiration by the ventilator could cause ventilator-induced lung injury (VILI). It is therefore important to recognize these dyssynchronies and act accordingly. On this page, you’ll find a quick overview of common dyssynchronies and how to treat them.

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Normal patient ventilator interaction
  1. Patient wants to inhale: neural signal travels to inspiratory muscles, inhalation begins
  2. Ventilator is immediately triggered as a result of the patient’s respiratory effort (triggering) and the ventilator immediately provides the inspiration
  3. Patient wants to exhale → ventilator opens the expiratory valve immediately (cycling)
  4. Exhalation is finished for both the patient and the ventilator; a new inhalation is possible

Patient ventilator dyssynchronies

There are 6 patient-ventilator dyssynchronies you should be able to recognize and treat. These are Delayed triggering, Ineffective triggering, Auto-triggering, Reverse triggering, Premature cycling and Delayed cycling. Read on below!

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Patient wants to inhale, but the ventilator is late on delivery. This leads to increased work of breathing. Causes include muscle weakness, insensitive trigger and dynamic hyperinflation (intrinsic PEEP).

How to resolve Delayed triggering: increase trigger sensitivity.
In case of intrinsic PEEP, apply extrinsic PEEP (80% of intrinsic PEEP)

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Patient wants to inhale, but the ventilator is does not deliver the inspiration. Causes include muscle weakness, insensitive trigger and dynamic hyperinflation (intrinsic PEEP).

How to resolve Ineffective triggering: see Delayed triggering.
Increase trigger sensitivity. In case of intrinsic PEEP, apply extrinsic PEEP (80% of intrinsic PEEP)

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No patient effort whatsoever; the machine is triggered by something else. Check for turbulence caused by eg. excessive secretions by looking at the expiratory flow curve.

How to resolve Auto-triggering:
Suction, correct leaks, optimize trigger sensitivity. Unsure if it's auto-triggering or patient effort? Perform an
expiratory hold to see if there is patient effort!

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Ventilator delivers a passive breath and triggers the diaphragm of the patient, resulting in double triggering.

See the section on “Reverse triggering” below!

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Patient wants to inhale longer than the ventilator allows. This usually results in double triggering: two inspirations by the ventilator. This results in high tidal volumes and could induce VILI by volutrauma.

How to resolve Premature cycling:
In support mode, reduce the cycle off criteria; in controlled mode, increase the inspiratory time or I:E ratio. Consider increasing sedation.

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Patient wants to exhale earlier than the ventilator allows. This could lead to high transpulmonary pressures and could induce VILI by barotrauma.

How to resolve Delayed cycling:
In support mode, increase the cycle off criteria and decrease rise time; in controlled mode, reduce the inspiratory time or I:E ratio.

Reverse triggering

  • Ventilator delivers a passive breath and triggers the diaphragm of the patient, resulting in double triggering: two inspirations by the ventilator. This results in high tidal volumes and could induce VILI by volutrauma.
  • Only occurs in deeply sedated patients, who are not paralyzed with neuromuscular blockers
  • Is considered the most damaging form of patient-ventilator dyssynchronies
  • Occurs in patterns, like 1:1, 1:2, 1:3, etc.
  • Can be recognized by looking at the flow curve. Flow curve indicates double triggering, which looks like an inspiratory effort by the patient. This could either be an actual double trigger performed by the patient, or reverse triggering. You can make this distinction by performing an expiratory hold. When you see no patient effort whatsoever, it’s reverse triggering.
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Red = diaphragmatic contractions || Green = double cycle

How to resolve Reverse triggering:
- Either reduce sedation
- Or give neuromuscular blocking agents
This means that your choice depends on whether or not you would allow this patient to trigger the ventilator, i.e. how sick their lungs are.

Written by

I'm an intensivist and clinical pharmacologist, spreading the love for and knowledge of acute and critical care medicine on YouTube https://crit-ic.com/

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