Evolution of inspiratory muscle function in children during mechanical ventilation

There is no universally accepted method to assess the pressure-generating capacity of inspiratory muscles in children on mechanical ventilation (MV), and no study describing its evolution over time in this population.

In this prospective observational study, we have assessed the function of the inspiratory muscles in children on various modes of MV. During brief airway occlusion maneuvers, we simultaneously recorded airway pressure depression at the endotracheal tube (ΔPaw, force generation) and electrical activity of the diaphragm (EAdi, central respiratory drive) over five consecutive inspiratory efforts. The neuro-mechanical efficiency ratio (NME, ΔPaw/EAdi_max) was also computed. The evolution over time of these indices in a group of children in the pediatric intensive care unit (PICU) was primarily described. As a secondary objective, we compared these values to those measured in a group of children in the operating room (OR).

In the PICU group, although median NME_occl decreased over time during MV (regression coefficient - 0.016, p = 0.03), maximum ΔPaw_max remained unchanged (regression coefficient 0.109, p = 0.50). Median NME_occl at the first measurement in the PICU group (after 21 h of MV) was significantly lower than at the only measurement in the OR group (1.8 cmH₂O/µV, Q₁-Q₃ 1.3-2.4 vs. 3.7 cmH₂O/µV, Q₁-Q₃ 3.5-4.2; p = 0.015). Maximum ΔPaw_max in the PICU group was, however, not significantly different from the OR group (35.1 cmH₂O, Q₁-Q₃ 21-58 vs. 31.3 cmH₂O, Q₁-Q₃ 28.5-35.5; p = 0.982).

The function of inspiratory muscles can be monitored at the bedside of children on MV using brief airway occlusions. Inspiratory muscle efficiency was significantly lower in critically ill children than in children undergoing elective surgery, and it decreased over time during MV in critically ill children. This suggests that both critical illness and MV may have an impact on inspiratory muscle efficiency.