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

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.

Key Points

1. Incidence of DC/BS in Assisted Ventilation: DC/BS events were infrequent across all ventilation modes, occurring in only 0.6% of cycles in NAVA, 0.0% in PAV+, and 0.1% in PSV, suggesting that these events are not a common issue in partial ventilatory support.
2. Breath-Stacking and Respiratory Variability: The occurrence of DC/BS was significantly associated with the coefficient of variation for tidal volume (p = 0.014) and respiratory rate (p = 0.011), indicating that these events may be a feature of natural breath-to-breath variability rather than pathological asynchrony.
3. Physiological Effects of DC/BS: DC/BS cycles showed higher tidal volumes, increased muscular pressure, and regional lung stretch compared to regular breaths. However, these events were not necessarily followed by signs of respiratory distress or expiratory muscle activation.
4. End-Expiratory Lung Impedance and Compliance Changes: DC/BS cycles frequently resulted in improved end-expiratory lung impedance (EELI) and dynamic lung compliance (CLdyn), similar to the physiological role of spontaneous sighs.
5. Patient Effort in DC/BS Events: In 42% of cases, DC/BS resulted from a single strong inspiratory effort, while in 58%, it was due to two consecutive inspiratory efforts. These variations suggest that DC/BS may represent a natural attempt to optimize lung recruitment.
6. Comparison Across Ventilation Modes: While DC/BS was more frequent in NAVA than in PAV+ or PSV, its occurrence remained low across all modes. NAVA was associated with greater respiratory variability, which may explain the slightly higher DC/BS incidence.
7. Lack of Expiratory Muscle Activation: In 63% of cases, DC/BS cycles were not followed by expiratory muscle activation, suggesting that they were not a result of distressing ventilator asynchrony. Instead, they may serve a beneficial physiological role in maintaining lung aeration.
8. DC/BS as a Natural Phenomenon: Given their low frequency and positive effects on lung compliance, the study proposes that DC/BS during partial ventilatory support should not be automatically considered harmful. Instead, they may function as spontaneous sighs, promoting lung recruitment.
9. Implications for Clinical Practice: The findings suggest that sedation or ventilator adjustments to eliminate DC/BS in partial support ventilation may not be necessary unless they occur frequently or lead to worsening patient-ventilator interaction.
10. Future Research Needs: Additional studies should explore long-term effects of DC/BS in different ARDS phenotypes and assess whether certain patient populations might benefit from targeted ventilatory adjustments to optimize lung mechanics.

ACCESS FULL ARTICLE HERE

Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.