Tuesday, March 27, 2012

Quantifying Patient Ventilator Asynchrony

SERVO-i Ventilator screen. Using NAVA monitoring & captured screen shots to quantify patient ventilator asynchrony.

Patient ventilator asynchrony is present in the majority of ventilated patients [1].

One of the most difficult components of patient ventilator assessment is actually recognizing asynchrony. Authors of the following study “Efficacy of ventilator waveforms observation in detecting patient–ventilator asynchrony” ‘[2] demonstrate how challenging identifying asynchrony is, even for the seasoned physician.


This study aimed to evaluate intensive care unit physicians’ ability to recognize patient–ventilator asynchronies through ventilator waveforms.  In order to complete this study, forty-three 5-min reports displaying flow time and airway pressure-time tracings were assessed by ten expert and ten non-expert, intensive care unit physicians. The asynchronies recognized by experts and non-experts were matched up with those established by three independent examiners who assessed the same reports displaying, along with tracings of diaphragm electrical activity.


Specificity and negative predictive value were high with breath-by-breath analysis and slightly lower with report analysis.  On the other hand, sensitivity and positive predictive value were very low with breath-by-breath analysis and increased with report analysis. Sensitivity was significantly higher for experts than for non-experts for breath-by-breath analysis, but not for report analysis.  The frequency of asynchronies increased at higher ventilator assistance and tidal volumes, whereas it decreased at higher respiratory rates and diaphragm electrical activity.  At higher prevalence, sensitivity decreased significantly.


The capability of intensive care unit physicians to distinguish patient–ventilator asynchronies was quite low and decreased at higher prevalence.  Expertise significantly improved sensitivity for breath-by-breath analysis, whereas it only produced a trend toward improvement for report analysis.


As previously mentioned identifying asynchrony can be problematic even when utilizing ventilator graphics. One consideration is utilizing neurally adjusted ventilatory support (NAVA) to help quantify patient ventilator asynchrony.  
Many practitioners focus on “NAVA the mode” and do not even consider the benefits of using NAVA as a diagnostic tool. Evaluating the electomyographic (EMG) activity of the diaphragm, specifically the waveform is a great way to quantifying asynchrony even when using traditional modes of ventilation. The above image demonstrates EMG monitoring in PC-CMV showing how uncoupled diaphragmatic activity is in relation to the set ventilator rate.
Academics state that NAVA would be “useful in any patient with substantial asynchrony” [3]. I argue this, NAVA or at least using it diagnostically is beneficial to all mechanically ventilated patients. Recall one has to distinguish this substantial asynchrony first.

[1]. Pierson, D. (2011). Patient-Ventilator Interaction. Respiratory Care, 56 (2), 214-229.

[2]. Colombo, D., Cammarota, G., Alemani, M., Carenzo, L., Barra, F., Vaschetto, R., Slutsky, A., Corte, F. D., & Navalesi, P., (2011). Efficacy of ventilatorwaveforms observation in detecting patient–ventilator asynchrony. Critical Care Medicine, 39 (11), 2393-2592.

[3]. Kacmarek, R. (2011). Proportional Assist Ventilation and Neurally AdjustedVentilatory Assist. Respiratory Care. 56 (2), 140-152.