Ultrasound evaluations revealing compensatory patterns of respiratory muscles following post-operative unilateral diaphragmatic dysfunction

Background Unilateral phrenic nerve injury is common in mediastinal tumor resections, which leads to diaphgram dysfunction and acute respiratory failure. However, it remains unclear how the other unaffected respiratory muscles compensate for the respiratory weakness caused by unilateral diaphragmatic dysfunction. This study aims to (1)observe the morbidity of respiratory failure following unilateral phrenic nerve injury after mediastinal tumor resections; and (2) to evaluate relationship between ultrasonic performance of respiratory muscles (parasternal intercostal muscles and contralateral diaphragm) and the necessity of respiratory support. Methods The prospective observational study enrolled 40 ICU patients with post-operative unilateral diaphragmatic dysfunction due to mediastinal tumor surgery. The corhort was divided into Conventional Oxygen Therapy (COT) group and Respiratory Support (RS) group according to whether patients received upgraded respiratory support therapies such as: high-flow nasal cannulation, non-invasive ventilation and invasive mechanical ventilation. Bed-side ultrasound was used to evaluate parasternal intercostal muscles and diaphragm activities at several time points during ICU stay. Results The Respiratory Support group demonstrated a significantly higher proportion of male patients (76.2% versus 36.8%, p=0.012) and elevated Sequential Organ Failure Assessment scores (2.15±1.23 versus 1.11±0.81, p=0.003). Upon intensive care unit admission, the RS group exhibited significantly elevated intercostal muscle thickening fraction, respiratory rate, and intercostal muscle thickening fraction to diaphragmatic thickening fraction ratio when compared with the COT group. These parameters subsequently normalized by the time of intensive care unit discharge. Both cohorts demonstrated increased bilateral diaphragmatic thickening fraction at discharge relative to admission values, with the RS group maintaining higher overall measurements. During the respiratory support intervention period, intercostal muscle thickening fraction demonstrated transient amelioration. Notably, the contralateral diaphragm exhibited significant compensatory augmentation in thickening fraction, whereas alterations in intercostal muscle thickening fraction remained independent of the laterality of diaphragmatic dysfunction. The RS group experienced prolonged intensive care unit length of stay (6.09±6.55 versus 2.84±1.34 days, p=0.037), extended total hospitalization duration (20.43±12.87 versus 13.11±6.58 days, p=0.029), and increased incidence of bloodstream infections (28.6% versus 5.3%, p=0.036). Conclusion Respiratory failure represents a frequent complication following post-operative unilateral phrenic nerve injury, affecting 52.5% of the studied population. Initial compensatory mechanisms predominantly involve augmented intercostal muscle activity, as evidenced by elevated intercostal muscle thickening fraction measurements. However, sustained respiratory compensation ultimately requires enhanced contralateral diaphragmatic function. These findings indicate that systematic ultrasonographic monitoring of respiratory muscle morphology provides valuable prognostic information and may facilitate optimized clinical management strategies for patients presenting with unilateral diaphragmatic dysfunction.