Nasal high flow in preterm infants: A dose‐finding study

Abstract

Objective To investigate the relationship between applied flows of nasal high flow (NHF) and physiological outcomes and work of breathing (WOB), to identify an optimal delivery flow which results in reduced WOB in preterm infants. Design A prospective observational clinical study with randomly applied NHF rates. Patients and Setting Preterm infants within 72 hours of commencement of NHF respiratory support. Interventions Infants were initially placed on 8 L/min of NHF and flows of 2, 4, and 6 L/min were then applied in random order. Measurements and Results WOB was measured using transcutaneous electromyography and respiratory inductance plethysmography. Physiological variables were also recorded. Measurements taken 10 minutes after each flow change were compared with 8 L/min. Sixteen infants with a median gestational age of 28 (range 24‐31) weeks and postnatal age of 14 (2‐55) days were included in the study. The median flow rate before the study was 6 (4‐8) L/min and a fraction of inspired oxygen (FiO2) was 0.21 (0.21‐0.26). Changes in flow resulted in changes in activity in the front diaphragm (P = .027) and intercostals (P = .034). The electrical activity of the front diaphragm at 8 L/min was significantly lower than that at 2 L/min (P = .016). Respiratory rate was lowest at 6 L/min (P = .002) and SpO2/FiO2 was highest at 8 L/min (P < .04). Conclusion In preterm infants, changes in WOB resulting from randomly applied levels of NHF can be demonstrated by measuring the electrical activity of the diaphragm and intercostal muscles with transcutaneous electromyography. In combination with physiological measurements, the similarities in electrical activity between 4, 6, and 8 L/min suggest that these three flows may be equally as effective.

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

“…However, in clinical practice, changes in respiratory support are not based on single breaths but more on a trend over time. Recent studies already showed that dEMG is able to monitor breathing in preterm infants and detect changes in diaphragm activity over time following changes in the mode or level of respiratory support 6,29 . The aggregated analysis in this study showed that combining individual breath data results in a modest‐to‐good correlation between dEMG and WOB.…”

“…Recent studies already showed that dEMG is able to monitor breathing in preterm infants and detect changes in diaphragm activity over time following changes in the mode or level of respiratory support. 6,29 The aggregated analysis in this study showed that combining individual breath data results in a modest-to-good correlation between dEMG and WOB. The current analysis is done offline but further development of this technique could result in a bedside tool, which provides a useful WOB assessment from time to time.…”

“…4,5 Furthermore, titration of respiratory support should ideally be based on the actual WOB, instead of indirect measures (e.g., gas exchange) or nonspecific clinical signs like chest retractions and tachypnea. 6 WOB is defined as the integral of the inspiratory pressure generated by the respiratory muscles, with respect to inspiratory volume. When determining the inspiratory pressure, the contribution of the chest wall is usually neglected and WOB is approximated by calculating the product of the change in intrapleural pressure and the resulting change in tidal volume.…”

“…Ideally, the optimal mode and level of respiratory support should be individually titrated in each patient, as both too little and too much support may have serious adverse effects 4,5 . Furthermore, titration of respiratory support should ideally be based on the actual WOB, instead of indirect measures (e.g., gas exchange) or nonspecific clinical signs like chest retractions and tachypnea 6 …”

Diaphragm electrical activity during weaning of nasal high-flow therapy in preterm infants

“…Intercostal muscle activity precedes diaphragm activation during inspiration, and contributes to maintenance of FRC therefore it is possible that changes in intercostal muscle activity compensate for the reduction in flow [24,25]. However, Hough et al reported no difference in intercostal muscle activity, measured using transcutaneous electromyography, at different HF rates suggesting this is not the case [22].…”