Critical illnesses have detrimental effects on the diaphragm, but their impact on other major muscles of the respiratory system have mainly been neglected over time. This longitudinal  study aimed to evaluate the impact of critical illness on the respiratory muscle pump’s most important muscles; specifically on expiratory muscles of children under mechanical ventilation. Also, the correlation between changes in the thickness of the expiratory muscles and the diaphragm was assessed.

This observational cohort study included thirty-four mechanical ventilated children at a tertiary pediatric ICU. Daily assessments of the thickness of the diaphragm and expiratory muscles were conducted using ultrasound. The contractile activity of the expiratory muscles was estimated by the muscle thickening fraction in each respiratory cycle. In the first four days, the  expiratory muscle and diaphragm thickness decreased in 44.0% of all the children. However, it must be noted that no correlation was found between the development of atrophy and the contractile activity of the muscles.

The changes in thickness of the abdominal expiratory muscles are observed at a rapid rate after mechanical ventilation in critically ill children. The data gathered demonstrate that the respiratory system’s distinct components respond differently to critical illness and mechanical ventilation. The observations provide unique insights into the effects of critical illness on the respiratory muscle pump that may have implications for monitoring and treating ventilated children.