Role of Dyspnea in the Progression of Pediatric Acute Respiratory Distress Syndrome

Pediatric acute respiratory distress syndrome (ARDS) is a life-threatening clinical syndrome, and dyspnea is its key symptom. Strenuous respiratory effort is a "second hit" for ARDS lungs, inducing changes in regional lung aeration and amplifying lung damage in preclinical studies, a phenomenon known as "patient self-inflicted lung injury". In a clinical setting, clinicians are concerned about the possible connection between dyspnea and ARDS progression based on indirect evidence, such as the worse outcomes associated with delayed intubation or failed weaning from mechanical ventilation. Dyspnea is hard to quantify due to its subjective nature. Still, it can be assessed through its interrelated and independent components: respiratory drive (neural stimuli), respiratory effort (muscle contraction), and work of breathing (energy expenditure).

This project aims to identify mechanical thresholds of dyspnea components to predict early ARDS progression and outcome. The role of respiratory effort is particularly relevant in three phases of ARDS where a transition between spontaneous and controlled ventilation occurs: 1) acute phase, when clinicians try to prevent mechanical ventilation (MV) through non-invasive support; 2) intermediate phase, transitioning from controlled to assisted MV; and 3) late phase, during weaning from MV. These transitions are challenging because it is difficult for clinicians to titrate adequate support and avoid both under- and over-assistance.

In critically ill children, there are no established thresholds for dyspnea components that predict ARDS progression, and it remains unknown whether regional changes in lung aeration can anticipate this clinical deterioration. This is particularly relevant because the oxygenation decline signals that ARDS progression has already occurred, leading to a less reversible condition.

The investigators will use and integrate advanced respiratory monitoring tools to quantify these components, including surface electromyography, occlusion maneuvers, and esophageal manometry. Additionally, electrical impedance tomography, recently adapted for pediatric use, will be employed to detect early changes in regional aeration. All of these tools are gold standards for each parameter and allow real-time, bedside measurements without adding invasiveness to usual care.

To test the hypothesis, the investigators will quantify respiratory drive, effort, work of breathing, and regional lung aeration throughout all transitional phases of pediatric ARDS. In the acute phase, drive will be assessed via spectral analysis of surface electromyography, and in intermediate and late phases, via airway occlusion pressure at 100 ms. Esophageal manometry will be used to measure effort (swings of esophageal pressure) and work of breathing (pressure-time product). Changes in regional aeration (overstretching, collapse, and heterogeneity) will be assessed using electrical impedance tomography.

The investigators will define mechanical thresholds and cut-off points for each dyspnea component that predict early ARDS progression and outcomes at each transitional phase. Based on the study results, the investigators envision the future development of algorithms to help guide safer transitions between spontaneous and controlled ventilation, to improve outcomes, and prevent residual morbidity. The interdisciplinary team of clinicians and biomedical engineers will work to customize respiratory care in critically ill children, optimizing ventilatory assistance across disease stages.