Contribution and evolution of respiratory muscles function in weaning outcome of ventilator-dependent patients

Abstract

Background: The present study was designed to investigate the evolution and the impact of respiratory muscles function and limb muscles strength on weaning success in prolonged weaning of tracheotomized patients. The primary objective was to determine whether the change in respiratory muscles function and limb muscles strength over the time is or is not associated with weaning success.

Methods: Tracheotomized patients who were ventilator dependent upon admission at a weaning center were eligible. Diaphragm function was assessed with the phrenic nerve stimulation technique and with ultrasound to measure the diaphragm thickening fraction (TFdi) and diaphragm excursion (EXdi). Global respiratory muscle function was assessed with the maximal inspiratory pressure (MIP) and the forced vital capacity (FVC). Limb muscle strength was measured with the Medical Research Council Score (MRC). Measurements were made on a weekly basis. Patients were compared according to their outcome at discharge: complete weaning, partial weaning or death.

Results: Among the 60 patients who were enrolled, 30 patients finally achieved complete weaning, 20 had partial weaning and 10 died. At 6 months, 6 patients were lost of follow-up, 33 achieved complete weaning, 10 had partial weaning and 11 died. In median, 2 (1-9) assessments were performed per patient. Diaphragm dysfunction was present in all patients with a median Ptr,stim of 5.5 cmH₂O (3.0-7.5). Ptr,stim, MIP, TFdi and EXdi at admission were not different between patients who achieved complete weaning and their counterparts. At discharge of the weaning center, MIP, Ptr,stim and EXdi significantly increased in patients who achieved complete weaning. The MRC score significantly increased only in patients with complete weaning. At discharge, diaphragm dysfunction was highly prevalent even in patients with complete weaning (Ptr,stim < 11 cmH₂O in n = 11 (37%)).

Conclusion: Respiratory muscle function and limb muscles strength are severely impaired in patients with prolonged weaning from mechanical ventilation. Significant improvement of diaphragm ultrasound indices was associated with successful weaning from mechanical ventilation and ICU-acquired weakness upon admission was significantly associated with good outcome suggesting that it was an amendable determinant of weaning failure in this population.

Keywords: Diaphragm dysfunction; Diaphragm ultrasound; ICU-acquired weakness; Mechanical ventilation; Prolonged weaning.

Fig. 1

Typical preparation for performing bilateral anterior magnetic phrenic nerve stimulation in a tracheostomized patient

Fig. 2

Flow chart of the study

Fig. 3

Patient’s outcomes at weaning center discharge and at 6 months

Fig. 4

Evolution over time of A the tracheal pressure in response to magnetic stimulation (Ptr,stim), B the maximum inspiratory pressure (MIP), C diaphragm thickening fraction, D diaphragm excursion, and E vital capacity in complete weaning patients (blue line) and partial weaning patients and non survivors (red line). Each point represents one assessment, a line connects repeated assessment of the same patient. The thick smoothed curve represents the non-linear regression (using Non-Linear Least Squares) according to the weaning status