PhD ThesisIntroduction 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.Special Trustees at Newcastle Hospital
