Performance of NCPAP systems for neonatal use and development of a new system for infant resuscitation

Abstract: Objective Nasal continuous positive airway pressure (NCPAP) is the most commonly used respiratory support for newborn infants. It is a technique for non-invasive respiratory support of both term and preterm infants with respiratory distress. NCPAP is preferred to mechanical ventilation in preterm infants after several clinical trials showed equal or improved outcome when it is used as primary support. Finding treatment strategies that reduce the need for intubation and mechanical ventilation to improve outcome and survival, have been a core theme in neonatal research. There is a wide range of NCPAP systems and little information to facilitate the choice. This leaves the clinician with multiple options and uncertainties. Research on performance as well as optimising and combining NCPAP with resuscitation systems, has the potential to further reduce the need for mechanical ventilation and improve outcome. The aim of this thesis is to describe the performance of continuous positive airway pressure (CPAP) systems (1), to evaluate techniques for measuring flows during CPAP treatment (2) and to develop a new system for neonatal resuscitation (3). Methods 1) A mechanical lung model was used to measure pressure stability and the imposed work of breathing (WOB) during simulated breathing. The tests of CPAP systems included different levels of CPAP, breathing profiles and leakage. 2) Flow meters were evaluated in the mechanical lung model using the in-line and the flowthrough placement technique. 3) Infant resuscitation system prototypes were designed, manufactured in 3D printers and tested for pressure stability in the mechanical lung model. The final design was tested in a clinical feasibility trial. Results 1) The tested CPAP systems showed large differences in pressure stability and imposed WOB. 2) The flow meters intended for neonatal use had a higher resistance and lower dead space than the other tested flow meters. In-vitro tests in the flow-through position showed that resistance generated CPAP. Two flow meters with low resistance had acceptable flow recording quality in the flow-through position. 3) In simulated spontaneous breathing, the new resuscitation system (prongs or facemask interface) had a marked reduction in imposed WOB compared to standard T-piece resuscitators. The clinical feasibility trial of 36 preterm infants did not reveal any problems with safety or usage of the new system. Conclusions 1) The clinical importance of pressure stability for CPAP systems and imposed WOB is unclear but has been suggested as an important factor for some premature infants. This should be considered when choosing CPAP systems, designing trials and interpreting results. 2) Measuring breathing during nasal CPAP seems possible with the flow-through technique. This should result in measurements with no added WOB or dead space. 3) The new infant resuscitation system has low imposed WOB and will allow future investigations of the importance of imposed WOB, patient interfaces and CPAP levels.

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