Understanding Patient-Ventilator Asychrony

People display normal variability in their breathing patterns even at rest. In contrast, although a necessary medical intervention, mechanical ventilation uses some sort of fixed parameter in almost all currently available modes. If the mechanical breath is delivered in a fashion that the patient doesn’t want or expect (too short, not enough flow, too long, etc.), asynchrony between the ventilator and the patient, discomfort, anxiety and fatigue can result.([FOOTNOTE=Siegel MD. Management of agitation in the intensive care unit. Clin Chest Med. 2003;24(4):713-725.],[ANCHOR=],[LINK=])

Eight out of 10 ventilated patients come off the vent within three to four days with little difficulty.([FOOTNOTE=Pohlman MC, et al. Excessive tidal volume from breath stacking during lung-protective ventilation for acute lung injury. Crit Care Med. 2008;36(11):3019-3023.],[ANCHOR=],[LINK=]),([FOOTNOTE=Puritan Bennett™ 980 Ventilator Operator's Manual],[ANCHOR=],[LINK=]) They might be uncomfortable under mechanical ventilation, but they are able to wean from the ventilator. Still, in these patients, improving patient-ventilator synchrony may potentially result in less anxiety and need for sedation.([FOOTNOTE=Wilkins RL, Stoller JK, Scanlan CL. Egan’s Fundamentals of Respiratory Care. 8th ed. Louis, MO: Mosby; 2003.],[ANCHOR=],[LINK=])

Those who stay on ventilation longer (~25%) and continue to fail to wean use 50% of our ICU resources, accounting for 40% of all ICU costs.3,([FOOTNOTE=Younes M, et al. Proportional Assist Ventilation. In: Tobin MJ. Principles And Practice of Mechanical Ventilation, Third Edition. McGraw Hill Professional; 2012.315-346.],[ANCHOR=],[LINK=]) In these patients, asynchrony may have a greater impact.2,5,([FOOTNOTE=Bosma K, Ferreyra G, Ambrogio C, et al. Patient-ventilator interaction and sleep in mechanically ventilated patients: pressure support versus proportional assist ventilation. Crit Care Med. 2007;35(4):1048-1054.],[ANCHOR=],[LINK=]),([FOOTNOTE=Younes M, Webster K, Kun J, Roberts D, Masiowski B. A method for measuring passive elastance during proportional assist ventilation. Am J Respir Crit Care Med. 2001;164(1):50-60.],[ANCHOR=],[LINK=])

What is asynchrony?

The best way to describe asynchrony is to call it poor patient-ventilator interaction. Patient-ventilator interaction is dependent upon many variables. Some of those are:

  • The patient’s pathophysiology
  • The ventilator settings
  • The patient-ventilator interface used

How often does asynchrony occur?

Asynchrony occurs at varying degrees depending on the patient population and the mechanical ventilation strategy employed. The most common types of asynchrony are ineffective efforts and double triggers. (See TABLE for definitions.)

Here is a look at the findings of different researchers. Please note that a variety of modes and approaches were used. See TABLE.

Why is asynchrony important?

Patient-ventilator asynchrony is typically uncomfortable for the patient. In addition, it may have an impact on patient outcomes. Epstein([FOOTNOTE=Sassoon C. Triggering of the ventilator in patient-ventilator interactions. Respiratory Care. 2011;56(1):39-51.],[ANCHOR=],[LINK=]) put together a list of adverse effects associated with poor patient-ventilator interaction:

  • A higher or wasted work of breathing
  • Patient discomfort
  • An increased need for sedation
  • Confusion during the weaning process
  • Prolonged mechanical ventilation
  • A longer stay
  • The possibility of higher mortality

Investigators have examined the relationship between patient-ventilator asynchrony and outcomes. Thille et al([FOOTNOTE=Thille AW et al. Patient-ventilator asynchrony during assisted mechanical ventilation. Intensive Care Med. 2006;32(10):1515-1522.],[ANCHOR=],[LINK=]) found patients with an asynchrony index >10% had a longer duration of mechanical ventilation and were more likely to need a tracheostomy. de Wit et al([FOOTNOTE=de Wit M. Monitoring of patient ventilator interaction at the bedside. Respiratory Care. 2011;56(1):61-68.],[ANCHOR=],[LINK=]) found that those patients who had an ineffective trigger index of >10% had a longer duration of mechanical ventilation, a worse 28-day ventilator-free survival, and a longer ICU time and hospital stay. Patients in the ineffective trigger group were less likely to be discharged to home. Varon et al3 found that mortality was higher in patients with an asynchrony index >30%.

What are the key takeaways?

Patients experiencing patient-ventilator asynchrony can be very uncomfortable, exhibit wasted effort and fatigue easier. Asynchrony, or poor patient-ventilator interaction, may occur as a result of the patient’s pathophysiology, the settings of the ventilator and/or the patient-ventilator interface used. Failure to address/resolve asynchrony may result in patient discomfort, longer duration of ventilator days, a worse 28-day ventilator-free survival rate, a longer ICU time and a longer hospital stay.([FOOTNOTE=de Wit M, Miller KB, Green DA, Ostman HE, Gennings C, Epstein SK. Ineffective triggering predicts increased duration of mechanical ventilation. Crit Care Med. 2009;37(10):2740-2745.],[ANCHOR=],[LINK=])