Electromyographic respiratory muscle analysis in the spontaneous breathing trial: a randomized crossover trial comparing T-piece and pressure support.

OBJECTIVE: To compare the electromyographic activity of respiratory muscles during T-piece and pressure support ventilation trials. METHODS: This was a randomized crossover trial involving 16 patients weaning from mechanical ventilation. Each patient underwent two 30-minute spontaneous breathing trials (T-piece and pressure-support ventilation with 7cmH2O), separated by a 30-minute washout period, or until vital signs returned to baseline. Surface electromyography was used to assess muscle activation (percentage root mean square) and median frequency of the pectoralis major, rectus abdominis, and external intercostal muscles (nomenclature updated from diaphragm based on SENIAM and Phinyomark/De Troyer literature to account for crosstalk). Data were collected at baseline (T0), 15 (T15), and 30 minutes (T30). Intragroup comparisons were performed using two-way repeated-measures ANOVA, and intergroup differences in deltas (Δ) were analyzed using ANCOVA, adjusting for baseline values. RESULTS: Median frequency remained stable for all muscles (p > 0.05), indicating no electromyographic fatigue. In contrast, percentage root mean square activation differed significantly between methods. During the T-piece spontaneous breathing trial, a progressive increase in percentage root mean square was observed in the pectoralis major, rectus abdominis, and external intercostals (p < 0.05). Under pressure support ventilation, only the pectoralis major showed a modest increase (p < 0.05), while other muscles remained stable. Intergroup comparisons of pre-to-post variation confirmed greater activation during the T-piece spontaneous breathing trial for the pectoralis major (p = 0.048) and rectus abdominis (p = 0.009). No significant differences were observed between methods for the external intercostal muscles. CONCLUSIONS: T-piece ventilation induces greater recruitment of thoracic and abdominal accessory respiratory muscles than pressure-support ventilation, reflecting a higher ventilatory demand. Stable median frequency values indicate preserved neuromuscular function and absence of clinically relevant respiratory muscle fatigue over 30 minutes. These findings suggest that pressure support ventilation partially unloads the respiratory system and may mask true ventilatory effort, whereas the T-piece more closely reproduces post-extubation conditions. Surface electromyography proved to be a feasible tool for physiological assessment during ventilatory weaning.