Measurement of Diaphragmatic Electrical Activity by Surface Electromyography in Intubated Subjects and Its...

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.

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.

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).

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.