Asynchrony, neural drive, ventilatory variability and COMFORT: NAVA versus pressure support in pediatric patients. A non-randomized cross-over trial

Abstract

Purpose: To determine if neurally adjusted ventilatory assist (NAVA) improves asynchrony, ventilatory drive, breath-to-breath variability and COMFORT score when compared to pressure support (PS).

Methods: This is a non-randomized short-term cross-over trial in which 12 pediatric patients with asynchrony (auto-triggering, double triggering or non-triggered breaths) were enrolled. Four sequential 10-min periods of data were recorded after 20 min of ventilatory stabilization (wash-out) at each of the following settings: baseline PS with the ventilator settings determined by the attending physician (1-PS(b)); PS after optimization (2-PS(opt)); NAVA level set so that maximum inspiratory pressure (P(max)) equaled P(max) in PS (3-NAVA); same settings as in 2-PS(opt) (4-PS(opt)).

Results: The median asynchrony index was significantly lower during NAVA (2.0%) than during 2-PS(opt) (8.5%, p = 0.017) and 4-PS(opt) (7.5%, p = 0.008). In NAVA mode, the NAVA trigger accounted on average for 66% of triggered breaths. The median trigger delay with respect to neural inspiratory time was significantly lower during NAVA (8.6%) than during 2-PS(opt) (25.2%, p = 0.003) and 4-PS(opt) (28.2%, p = 0.0005). The median electrical activity of the diaphragm (EAdi) change during trigger delay normalized to maximum inspiratory EAdi difference was significantly lower during NAVA (5.3%) than during 2-PS(opt) (21.7%, p = 0.0005) and 4-PS(opt) (24.6%, p = 0.001). The coefficient of variation of tidal volume was significantly higher during NAVA (44.2%) than during 2-PS(opt) (19.8%, p = 0.0002) and 4-PS(opt) (23.0%, p = 0.0005). The median COMFORT score during NAVA (15.0) was lower than that during 2-PS(opt) (18.0, p = 0.0125) and 4-PS(opt) (17.5, p = 0.039). No significant changes for any variable were observed between 1-PS(b) and 2-PS(opt).

Conclusions: Neurally adjusted ventilatory assist as compared to optimized PS results in improved synchrony, reduced ventilatory drive, increased breath-to-breath mechanical variability and improved patient comfort.

Trial registration: ClinicalTrials.gov NCT01159106.

Fig. 1

Definition of breath variables. Breath with trigger delay (Td): the onset of neural inspiration preceded that of inspiratory flow. EAdi Electrical activity of the diaphragm in microvolts, ΔEAdi _nTi maximum inspiratory EAdi difference, ΔEAdi _Td EAdi change during trigger delay, EAdiTP _nTi EAdi–time-product during the neural inspiratory time, EAdiTP _Td EAdi-time-product during the trigger delay, maxEAdi maximum EAdi per breath, minEAdi initial baseline inspiratory EAdi per breath, mTi mechanical inspiratory time, nTi neural inspiratory time, PEEP positive end expiratory pressure (in cmH₂O)

Fig. 2

Major asynchrony events. 1-PS _b Baseline pressure support (PS) with ventilator settings determined by the attending physician, 2-PS _opt pressure support after optimization, 3-NAVA level set so that maximum airway pressure equaled maximum airway pressure during 1-PS_b and 2-PS_opt, 4-PS _opt same pressure support settings as in 2-PS_opt. N number of asynchrony events per minute. Values in the two upper figures are presented as the median with 25–75 % interquartile range (IQR). Values in the effect size figure are given as Pearson’s correlation coefficient, r, with the 95 % confident interval (CI). Horizontal dotted lines depict the limits for small, mild and large effect size, respectively.*p < 0.0125

Fig. 3

Breath-to-breath breathing variability. CV Coefficient of variation, P _max maximum airway pressure per breath, b baseline, opt optimized, RR respiratory rate, V _t tidal volume, V _t/mTi mean inspiratory flow; for other abbreviations, see Figs. 1 and 2. Values are presented as the median with 25–75 % IQR, except for the effect size figure (bottom right corner) where values are given as Pearson’s correlation coefficient, r, with the 95 % CI; horizontal dotted lines depict the limits for small, mild and large effect size, respectively. *p < 0.0125

Fig. 4

Neural drive to triggering and COMFORT score. ΔEAdi _Td/ΔEAdi _nTi EAdi change during the triggering delay as a percentage of maximum inspiratory EAdi difference, EAdiTP _Td/EAdiTP _nTi EAdi–time-product during the triggering delay as a percentage of the EAdi–time-product during neural inspiratory time, Td/nTi triggering delay as a percentage of neural inspiratory time (see Fig. 1). Values in two left figures are given as the median with 25–75 % IQR. COMFORT score dash–dotted line delimits light (above) from deep (below) sedation level. Values in the two right figures are given as Pearson’s correlation coefficient, r, with 95 % CI; horizontal dotted lines depict the limits for small, mild and large effect size, respectively.*p < 0.0125. ^# p = 0.0125. ^## p = 0.050