Patient-ventilator interaction during neurally adjusted ventilatory assist in low birth weight infants

Abstract

Neurally adjusted ventilatory assist (NAVA), a mode of mechanical ventilation controlled by diaphragmatic electrical activity (EAdi), may improve patient-ventilator interaction. We examined patient-ventilator interaction by comparing EAdi to ventilator pressure during conventional ventilation (CV) and NAVA delivered invasively and non-invasively. Seven intubated infants [birth weight 936 g (range, 676-1266 g); gestational age 26 wk (range, 25-29)] were studied before and after extubation, initially during CV and then NAVA. NAVA-intubated and NAVA-extubated demonstrated similar delays between onset of EAdi and onset of ventilator pressure of 74 +/- 17 and 72 +/- 23 ms (p = 0.698), respectively. During CV, the mean trigger delays were not different from NAVA, however 13 +/- 8.5% of ventilator breaths were triggered on average 59 +/- 27 ms before onset of EAdi. There was no difference in off-cycling delays between NAVA-intubated and extubated (32 +/- 34 versus 28 +/- 11 ms). CV cycled-off before NAVA (120 +/- 66 ms prior, p < 0.001). During NAVA, EAdi and ventilator pressure were correlated [mean determination coefficient (NAVA-intubated 0.8 +/- 0.06 and NAVA-extubated 0.73 +/- 0.22)]. Pressure delivery during conventional ventilation was not correlated to EAdi. Neural expiratory time was longer (p = 0.044), and respiratory rate was lower (p = 0.004) during NAVA. We conclude that in low birth weight infants, NAVA can improve patient-ventilator interaction, even in the presence of large leaks.

Figure 1. EAdi-neural timing profile for the group of infants, plotted for conventional ventilation and NAVA-intubated and NAVA-extubated

Figure depicts neural timing (x axis) in relation to EAdi (y axis). For each condition, four points of the breathing cycle are plotted (in solid symbols, as they appear from left to right): onset of inspiration, peak of inspiratory EAdi, 60% of peak EAdi, and end of neural expiration. Half-filled symbols indicate where triggering occurred and open symbols describe where off-cycling occurred for the different ventilation modes. Note that the tonic EAdi (baseline) is not zero (see Table 2), but for simplicity, the y-axis begins at zero.

Figure 2. Relationship between peak diaphragm activity and peak ventilator pressure

Panels A and B: Peak diaphragm electrical activity (x-axis) and peak ventilator delivered pressure (y-axis) are plotted breath-by-breath in one infant breathing on NAVA while intubated (Panel A), and while extubated (Panel B). Note the strong correlation between EAdi and Pvent. Panels C and D: Peak diaphragm electrical activity (x-axis) and peak ventilator delivered pressure (y axis) are plotted breath-by-breath in one infant breathing on pressure support, (Panel C), and in another infant during pressure support + volume guarantee. Note the poor correlation between EAdi and Pvent.

Figure 3. Tracings EAdi and PVent obtained in one subject while breathing on pressure support + volume guarantee, NAVA-intubated and NAVA-extubated

Waveforms of EAdi (top tracings) and ventilator-delivered pressure (bottom tracings) are depicted for one infant breathing on PSV+VG (left), NAVA while intubated (middle), and during non-invasive NAVA (right). Note the synchrony in terms of timing and proportionality, even in the presence of the leak for the NAVA periods.