Impact of ventilatory modes on the breathing variability in mechanically ventilated infants

Abstract

Objectives: Reduction of breathing variability is associated with adverse outcome. During mechanical ventilation, the variability of ventilatory pressure is dependent on the ventilatory mode. During neurally adjusted ventilatory assist (NAVA), the support is proportional to electrical activity of the diaphragm (EAdi), which reflects the respiratory center output. The variability of EAdi is, therefore, translated into a similar variability in pressures. Contrastingly, conventional ventilatory modes deliver less variable pressures. The impact of the mode on the patient's own respiratory drive is less clear. This study aims to compare the impact of NAVA, pressure-controlled ventilation (PCV), and pressure support ventilation (PSV) on the respiratory drive patterns in infants. We hypothesized that on NAVA, EAdi variability resembles most of the endogenous respiratory drive pattern seen in a control group.

Methods: Electrical activity of the diaphragm was continuously recorded in 10 infants ventilated successively on NAVA (5 h), PCV (30 min), and PSV (30 min). During the last 10 min of each period, the EAdi variability pattern was assessed using non-rhythmic to rhythmic (NRR) index. These variability profiles were compared to the pattern of a control group of 11 spontaneously breathing and non-intubated infants.

Results: In control infants, NRR was higher as compared to mechanically ventilated infants (p < 0.001), and NRR pattern was relatively stable over time. While the temporal stability of NRR was similar in NAVA and controls, the NRR profile was less stable during PCV. PSV exhibited an intermediary pattern.

Perspectives: Mechanical ventilation impacts the breathing variability in infants. NAVA produces EAdi pattern resembling most that of control infants. NRR can be used to characterize respiratory variability in infants. Larger prospective studies are necessary to understand the differential impact of the ventilatory modes on the cardio-respiratory variability and to study their impact on clinical outcomes.

Keywords: children; diaphragm; mechanical ventilation; neurally adjusted ventilatory support; pediatric intensive care.

Figures

Figure 1

Non-rhythmic to rhythmic (NRR) index for electrical activity of the diaphragm [EAdi (A)] and ventilatory pressure (B) signals, calculated over 10 min (blue bars) or 2 min (red bars) periods in infants without ventilatory support (control) and during mechanical ventilation in neurally adjusted ventilatory assist (NAVA), pressure support ventilation (PSV), and pressure-controlled ventilation (PCV). Note that time scale of assessing variability using NRR index has an effect on estimating EAdi variability (p = 0.03), but not on estimating the ventilator pressure variability (p = 0.44). NRR, arbitrary units. Data are presented as median [25–75%]. *p < 0.01 in pairwise comparison.

Figure 2

Representative example of the variability of non-rhythmic to rhythmic (NRR) index for electrical activity of the diaphragm (EAdi, left panels) and pressure (right panels) over 5 min in an infant during mechanical ventilation in neurally adjusted ventilatory assist (NAVA), pressure support ventilation (PSV), and pressure-controlled ventilation (PCV), and in a spontaneously breathing infant (control, with only EAdi signal). In each panel, the original signal is displayed in the upper part of the box (the signal on the EAdi column is the log 10 of the original EAdi signal), the time-varying power spectrum (the time–frequency representation determined by synchrosqueezing transform) is continuously represented on a vertical axis (gray distribution), and the piecewise constant blue dotted lines represent the NRR shifted up by 1.3 for the corresponding 2 min intervals. Note that the more rhythmic the oscillation is, the smaller the NRR value becomes. Also note the change in power spectra of both pressure and EAdi at the end of the PCV recording, which is translated into an increase in NRR.

Figure 3

(A) Variation of non-rhythmic to rhythmic (NRR) index during the five consecutive 2-min periods for electrical activity of the diaphragm (EAdi) signal in infants without ventilatory support (control) and during mechanical ventilation in neurally adjusted ventilatory assist (NAVA), pressure support ventilation (PSV), and pressure-controlled ventilation (PCV). NRR EAdi, arbitrary units. (B) Corresponding intra-patient coefficients of variation (CV) of NRR for EAdi signal. Median [25–75%]. *p < 0.05 vs. control.