Saturday, May 12, 2012

The Importance of Identifying Patient Ventilator Asynchrony

There are many factors that increase the risks for prolonged mechanical ventilation (PMV). So It is imperative that the practitioner is able to identify factors that they can proactively emend.

One factor associated with PMV is inappropriate ventilator settings. The below abstract reinforces how ventilator asynchrony increases the likelihood of  PMV. 


The study aimed to determine whether high rates of ineffective triggering within the first 24 hours of mechanical ventilation (MV) are associated with longer MV duration and shorter ventilator-free survival (VFS). The study was a prospective cohort and took place in a medical intensive care unit (ICU) at an academic medical center, including 60 patients requiring invasive MV.  Patients had pressure-time and flow-time waveforms recorded for 10 minutes within the first 24 hours of MV initiation. Ineffective triggering index (ITI) was calculated by dividing the number of ineffectively triggered breaths by the total number of breaths (triggered and ineffectively triggered). A priori, patients were classified into ITI ≥10% or ITI <10%. Patient demographics, MV reason, codiagnosis of chronic obstructive pulmonary disease (COPD), sedation levels, and ventilator parameters were recorded.


Multivariable analyses adjusting for pressure triggering also demonstrated that ITI ≥10% was an independent predictor of longer MV duration and shorter VFS.  Patients with ITI ≥10% had a longer ICU length of stay and hospital length of stay. Mortality was the same in the two groups, but patients with ITI ≥10% were less likely to be discharged home.


Ineffective triggering is a common problem early in the course of MV and is associated with increased morbidity, including longer MV duration, shorter VFS, longer length of stay, and lower likelihood of home discharge.


Ineffective efforts also known as ineffective triggering, wasted efforts or missed trigger attempts is defined as “an abrupt airway-pressure decrease of at least 0.5 cmH2O with a simultaneous decrease in expiratory flow that did not result in a patient-triggered breath”. Ineffective efforts are the most common trigger asynchrony and may occur during both inspiration and expiration [2]. 

During the triggering phase strategies for preventing asynchronies include measures that decrease PEEPi, increase respiratory drive, and/or reducing the use of sedation.
If available the operator may consider using Neurally Adjusted Ventilatory Assist (NAVA), which triggers the breath based on diaphragmatic EMG signal versus the traditional flow or pressure trigger.


The intrinsic diaphragmatic frequency.

Waveform of the week: Ineffective efforts.


[1]. de Wit, M., Miller, K. B., Green, D. A., Ostman, H. E., Gennings, C., & Epstein S. K., (2009). Ineffective triggering predicts increased duration of mechanical ventilationCritical Care Medicine, 37(10), 2740-2745.

[2]. Richey, S. (2011). Ventilator Graphics: Identifying Patient Ventilator Asynchrony and Optimizing Settings