A proof of concept study of respiratory physiology in preterm neonates during high flow nasal cannula therapy

Abstract

Introduction and rationale: High flow nasal cannula therapy is being increasingly used as a form of respiratory support across the world. Its adoption and popularity have been rapid but little is known regarding its key mechanism of action even after more than a decade of its use. I conducted a proof of concept study of respiratory physiology during high flow therapy in preterm neonates. Methods: The study protocol involved measurement of nasopharyngeal airway pressures and gas concentrations as well as measurement of tidal breathing indices. A detailed descriptive review of clinical efficacy of high flow nasal cannula in preterm infants was performed. In order to identify the optimum measuring techniques, in this proof of concept study, three types of pressure measuring techniques, a gas analyser device and a non-invasive tidal breathing indices device were studied and the results are presented in this thesis. In addition, a detailed protocol for a larger randomised crossover study of respiratory physiology during continuous positive airway pressure of 6 cm H2O and high flow nasal cannula therapy ranging from 2-8 litres per minute flow was designed.. Results: In this thesis, the results of a proof of concept physiological study have been presented. The results of the measurements performed in six babies of varying gestational age (less than 37 weeks of gestation) and birth weight are presented. Valid tidal volumes were measured in all babies, nasopharyngeal gas concentrations and pressure measurements in five and two babies respectively. There were no adverse events. Conclusions: It is feasible to measure nasopharyngeal air way pressures and gas concentrations as well as non-invasive tidal breathing indices in babies on high flow nasal cannula therapy safely. This study was successfully followed up by a larger randomised cross over study involving 45 infants with the same protocol.