Double cycling with breath-stacking during partial support ventilation in ARDS: Just a feature of natural variability?

Abstract

Background: Double cycling with breath-stacking (DC/BS) during controlled mechanical ventilation is considered potentially injurious, reflecting a high respiratory drive. During partial ventilatory support, its occurrence might be attributable to physiological variability of breathing patterns, reflecting the response of the mode without carrying specific risks.

Methods: This secondary analysis of a crossover study evaluated DC/BS events in hypoxemic patients resuming spontaneous breathing in cross-over under neurally adjusted ventilatory assist (NAVA), proportional assist ventilation (PAV +), and pressure support ventilation (PSV). DC/BS was defined as two inspiratory cycles with incomplete exhalation. Measurements included electrical impedance signal, airway pressure, esophageal and gastric pressures, and flow. Breathing variability, dynamic compliance (C_Ldyn), and end-expiratory lung impedance (EELI) were analyzed.

Results: Twenty patients under assisted breathing, with a median of 9 [5-14] days on mechanical ventilation, were included. DC/BS was attributed to either a single (42%) or two apparent consecutive inspiratory efforts (58%). The median [IQR] incidence of DC/BS was low: 0.6 [0.1-2.6] % in NAVA, 0.0 [0.0-0.4] % in PAV + , and 0.1 [0.0-0.4] % in PSV (p = 0.06). DC/BS events were associated with patient's coefficient of variability for tidal volume (p = 0.014) and respiratory rate (p = 0.011). DC/BS breaths exhibited higher tidal volume, muscular pressure and regional stretch compared to regular breaths. Post-DC/BS cycles frequently exhibited improved EELI and C_Ldyn, with no evidence of expiratory muscle activation in 63% of cases.

Conclusions: DC/BS events during partial ventilatory support were infrequent and linked to breathing variability. Their frequency and physiological effects on lung compliance and EELI resemble spontaneous sighs and may not be considered a priori as harmful.

Keywords: Breath stacking; Breathing variability; Double cycling; Partial support ventilation.

Fig. 1

Representative tracings with breath-stacking cycles in NAVA, PAV + and PSV Fig. 1 illustrates three representative cases with respiratory variables and EIT-derived signals over time showing regular and breath-stacking cycles during NAVA (patient #5), PAV + (patient #18) and PSV (patient #14). On each panel, from top to bottom: tidal volume, airway pressure (Paw), flow, esophageal pressure (Pes) and global impedance change (∆Z), in arbitrary units, A.U. Breath-stacking events are indicated under gray boxes. Please notice that breath-stacking cycles have two consecutive efforts

Fig. 2

Comparisons between breath-stacking and regular cycles, and changes of end-expiratory lung impedance and dynamic lung compliance before-and-after breath-stacking cycles. Individual values and mean (solid line) of [A] tidal volume (VT) and [B] muscular pressure (P_MUS), in regular cycles (blue empty circles), double cycling with breath-stacking cycles (DC/BS) with one inspiratory effort (1-Eff, black empty circles), and DC/BS with two inspiratory efforts (2-Eff, dark gray empty circles). The p-values correspond to linear mixed models adjusted by modes, comparing regular breaths with DC/BS with one and two efforts. Similar findings were observed in regional stretch at dependent and non-dependent regions. Panels C and D show individual values of delta end-expiratory lung impedance (ΔEELI_ml) and delta dynamic lung compliance (ΔC_Ldyn) between the regular cycles before-and-after breath-stacking cycle, depending on the behavior of expiratory muscle activity after DC/BS. The horizontal lines represent the means of ΔEELI_ml and ΔC_Ldyn (blue without expiratory activity and black with expiratory activity). The p-values correspond to linear mixed models adjusted by modes. The associations between expiratory muscle activation and ΔEELI or ΔC_Ldyn are independent of the number of inspiratory efforts