Transesophageal Versus Surface Electromyography of the Diaphragm in Ventilated Subjects

BACKGROUND:

Detection of diaphragmatic muscle activity during invasive ventilation may provide valuable information about patient-ventilator interactions. Transesophageal electromyography of the diaphragm ($\mathbf{\text{tE}}{\mathrm{A}}_{\mathbf{\text{di}}}$) is used in neurally adjusted ventilatory assist. This technique is invasive and can only be applied with one specific ventilator. Surface electromyography of the diaphragm ($\mathbf{\text{sE}}{\mathrm{A}}_{\mathbf{\text{di}}}$) is noninvasive and can potentially be applied with all types of ventilators. The primary objective of our study was to compare the ability of diaphragm activity detection between $\mathbf{\text{sE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ and $\mathbf{\text{tE}}{\mathrm{A}}_{\mathbf{\text{di}}}$.

METHODS:

In this single-center pilot study, $\mathbf{\text{sE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ and $\mathbf{\text{tE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ recordings were obtained simultaneously for 15 min in adult subjects in the ICU who were invasively ventilated. The number of breathing efforts detected by $\mathbf{\text{sE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ and $\mathbf{\text{tE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ were determined. The percentage of detected breathing efforts by $\mathbf{\text{sE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ compared with $\mathbf{\text{tE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ was calculated. Temporal and signal strength relations on optimum recordings of 10 breaths per subject were also compared. The Spearman correlation coefficient was used to determine the correlation between $\mathbf{\text{sE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ and $\mathbf{\text{tE}}{\mathrm{A}}_{\mathbf{\text{di}}}$. Agreement was calculated by using Bland-Altman statistics.

RESULTS:

Fifteen subjects were included. The $\mathbf{\text{tE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ detected 3,675 breathing efforts, of which 3,162 (86.0%) were also detected by $\mathbf{\text{sE}}{\mathrm{A}}_{\mathbf{\text{di}}}$. A statistically significant temporal correlation (r = 0.95, P < .001) was found between $\mathbf{\text{sE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ and $\mathbf{\text{tE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ in stable recordings. The mean difference in the time intervals between both techniques was 10.1 ms, with limits of agreement from –410 to 430 ms.

CONCLUSIONS:

Analysis of our results showed that $\mathbf{\text{sE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ was not reliable for breathing effort detection in subjects who were invasively ventilated compared with $\mathbf{\text{tE}}{\mathrm{A}}_{\mathbf{\text{di}}}$. In stable recordings, however, $\mathbf{\text{sE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ and $\mathbf{\text{tE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ had excellent temporal correlation and good agreement. With optimization of signal stability, $\mathbf{\text{sE}}{\mathrm{A}}_{\mathbf{\text{di}}}$ may become a useful monitoring tool.