Transcutaneous monitoring of diaphragm activity as a measure of work of breathing in preterm infants

Objective: Monitoring work of breathing (WOB) is important to assess the pulmonary condition and adjust respiratory support in preterm infants. Conventional WOB measurement (esophageal pressure, tidal volume) is invasive and we hypothesized that monitoring diaphragm activity could be a noninvasive alternative to estimate WOB. The objective was to determine the correlation between conventional WOB measures and diaphragm activity, in preterm infants. Methods: WOB and diaphragm activity, measured with transcutaneous electromyography (dEMG), were simultaneously recorded at different nasal continuous positive airway pressure (nCPAP) levels. During a 30-s recording at each nCPAP level, dEMG parameters, inspiratory WOB (WOBi), and pressure time product (PTPin) were calculated per breath. The correlation coefficient between WOB- and dEMG-measures was calculated using single breaths and after aggregating all breaths into deciles of incremental WOBi. Results: Fifteen preterm infants were included (median gestational age, 28 weeks). Single-breath analysis showed a poor median correlation of 0.27 (interquartile range [IQR], 0.03 to 0.33) and 0.08 (IQR, −0.03 to 0.28), respectively, for WOBi and PTPin with peak diaphragmatic activity (dEMGpeak). A modest median correlation coefficient of 0.65 (IQR, 0.13 to 0.79) and 0.43 (IQR, −0.33 to 0.69) was found for, respectively, WOBi and PTPin with dEMGpeak in the aggregated analysis. Conclusion: Diaphragm activity showed a modest correlation with WOBi and PTPin in an aggregated analysis. This finding warrants further studies in infants with more significant lung disease.