Understanding Asynchrony

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=])

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%.

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=])