Measurement of Diaphragmatic Electrical Activity by Surface Electromyography in Intubated Subjects and Its Relationship With Inspiratory Effort

BACKGROUND: Quantification of patient effort during spontaneous breathing is important to tailor ventilatory assistance. Because a correlation between inspiratory muscle pressure (P mus ) and electrical activity of the diaphragm (EA di ) has been described, we aimed to assess the reliability of surface electromyography (EMG) of the respiratory muscles for monitoring diaphragm electrical activity and subject effort during assisted ventilation. METHODS: At a general ICU of a single university-affiliated hospital, we enrolled subjects who were intubated and on pressure support ventilation (PSV) and were on mechanical ventilation for > 48 h. The subjects were studied at 3 levels of pressure support. Airway flow and pressure; esophageal pressure; EA di ; and surface EMG of the diaphragm (surface EA di ), intercostal, and sternocleidomastoid muscles were recorded. Respiratory cycles were sampled for off-line analysis. The P mus /EA di index (PEI) was calculated by relying on EA di and surface EA di (surface PEI) from an airway pressure drop during end-expiratory occlusions performed every minute. RESULTS: surface EA di well correlated with EA di and P mus , in particular, after averaging breaths into deciles (R = 0.92 and R = 0.84). When surface PEI was used with surface EA di , it provided a reliable estimation of P mus (R = 0.94 in comparison with measured P mus ). CONCLUSIONS: During assisted mechanical ventilation, EA di can be reliably monitored by both EA di and surface EMG. The measurement of P mus based on the calibration of EA di was also feasible by the use of surface EMG.