Abstract Introduction Accurate respiratory monitoring is critical in preterm infants, who commonly experience apneas and irregular breathing. The current bedside standard, transthoracic impedance (TTI), estimates breathing effort but is often affected by cardiac interference and movement artefact. Respiratory inductance plethysmography (RIP) provides a more direct measure of breathing effort, while nasal thermistors capture airflow. To better understand the limitations of TTI for respiratory monitoring in the neonatal intensive care unit (NICU), this study aimed to evaluate the reliability of TTI-derived respiratory rate compared to (1) abdominal RIP as a reference for breathing effort, and (2) nasal thermistor as a reference for airflow. Methods Twenty spontaneously-breathing preterm infants (gestational age 32weeks; postmenstrual age 37weeks) were recruited from the Montreal Children’s Hospital NICU. RIP and a nasal thermistor provided reference measures of breathing effort and respiratory airflow, respectively, while TTI was collected from the bedside monitor for 3h. Noninterpretable data were excluded before analysis. Respiratory rates (RRs) were estimated using peak-detection methods over 60-second windows and compared using Bland-Altman analyses. Using Fast Fourier Transform, the ratio of the power in the respiratory frequency band (0.2-1.4Hz) to the power outside the respiratory band was computed for each window. The log of this value was taken to obtain the signal-to-noise-ratio (SNR). The median SNR value was computed for each subject and compared between signals using the Mann-Whitney U-test. Results Participants had a median IQR gestational age of 28.4 27.1, 29.7 weeks, corrected age of 35.3 33.6, 35.6 weeks, and weight of 2165 1883, 2533 grams. The total interpretable data-time in minutes (% of recorded signal) for TTI, RIP and thermistor was 2792 (79.9%), 2746 (78.1%), and 2878 (81.9%) respectively. The mean difference between RIP- and TTI-derived RRs was −0.5 bpm (Limits of agreement, LOA: −12.2, 11.2; n = 2598), and between thermistor and TTI was -1.3 bpm (LOA: -13.7, 11; n = 2653; Figure 1A,B). TTI exhibited statistically lower SNRs relative to the reference signals for all patients (p 0.0005; Figure 1C-E). Conclusion TTI exhibited broad limits of agreement and lower signal quality relative to both RIP and thermistor, reflecting limited reliability in respiratory rate assessment compared to reference standards. These findings support re-evaluating clinical reliance on TTI and highlight the importance of integrating airflow-based measurements and multimodal approaches to more accurately estimate respiratory rates and characterize breathing patterns and apneas in preterm infants. This abstract is funded by: the Pediatric Research Foundation and the Montreal Children’s Hospital Foundation
Jeanne et al. (Fri,) studied this question.