148 - Abdominal Muscle Activity during Nasal Ventilation in Preterm Lambs without Respiratory Distress

Non-invasive ventilation, widely used in premature infants, must be synchronized with their respiratory muscle activity to ensure optimal pulmonary ventilation. Poor patient-ventilator synchronization, and/or the presence of increased respiratory efforts, may be harmful. The presence of expiratory muscle activity during non-invasive ventilation remains largely unknown.

Objective:

The goal of this study is to describe and compare abdominal muscle activity during nasal pressure support ventilation (nPSV) and nasal neurally adjusted ventilatory assist (nNAVA) in preterm lambs without respiratory distress.

Design/Methods:

Eight preterm lambs born at 133 days (normal term = 147 days) were studied during nPSV and nNAVA 15/4 cmH₂O across the sleep stages. Electrical activity of the abdominal muscles (Eabd) was recorded during baseline ventilation, body movements, imposed hypercapnia—at levels corresponding to permissive hypercapnia, possible in nPSV only—, and during imposed epochs of autotriggering and delayed cycling. Phasic expiratory Eabd was measured as the peak Eabd during expiration and data presented as median (Q1, Q3). The non-parametric Wilcoxon signed-rank test and Friedman test were used, with the significance level set at 0.05.

Results:

Phasic expiratory Eabd was observed during baseline ventilation in 2 (1, 6) % of respiratory cycles during nNAVA and 1 (1, 5) % during nPSV, all sleep stages being taken together (p = 0.9). No effect of sleep stages was noted (p ≥ 0.6). Body movements lead to a disruption of mechanical insufflations for 11 (9, 14) s in nNAVA vs. 6 (5, 12) s in nPSV (p = 0.4). The presence of phasic expiratory Eabd significantly increased from 0 (0, 14) % in normocapnia to 41 (25, 53) % of respiratory cycles during hypercapnia (p = 0.03). Finally, phasic expiratory Eabd was observed only 8/123 times during autotriggering and 14/266 times during delayed cycling events.

Conclusion(s):

Our results illustrate Eabd during nasal ventilation for the first time. In the absence of respiratory distress, phasic expiratory Eabd is rare, apart from transient body movements. Moderate hypercapnia stimulates Eabd. Recognition of unwanted expiratory efforts during non-invasive ventilation is important to guide respiratory management of neonates in the intensive care unit.