Nasal CPAP support of newborn infants : measurements of interface leakage and performance of selected systems

Abstract

Objective: The most common treatment for newborns in respiratory distress is nasal continuous positive airway pressure (nCPAP). Comparing clinical studies have shown a better outcome and a lower risk of chronic lung disease compared to invasive mechanical ventilation (MV) when used as primary treatment. Still, when CPAP fails, mechanical ventilation is the available rescue treatment. Since the clinical use of non-invasive CPAP caught on in the 1970’s, a range of devices and interfaces have been developed, of which some are no longer used. Still today, there is a lack of knowledge to guide clinicians around the world as to what device, interface and settings will maximize the clinical CPAP benefit. The overall aim of my dissertation is to evaluate CPAP equipment´s mechanical properties and factors that can affect CPAP performance in patients to identify possible improvements that can reduce the need for harmful mechanical ventilation.

Methods: 1. Selected flow meters were tested with mechanical lung simulations to determine their performance in the in-line and flow-through position. 2. Resistance, CPAP performance and mechanism of action were determined for the MediJet pressure generators using mechanical lung simulations. 3. The unconventionally designed Pumani bubble-CPAP system, aimed for developing countries, was tested with regard to resistance and CPAP performance using mechanical lung simulations. A traditional bubble-CPAP system was added for comparison. 4. A scoping review was performed to determine common alterations to the original bubbleCPAP design in clinical use. The effects of these modifications on CPAP performance were tested in-vitro using mechanical lung simulations. 5. A randomized, clinical cross-over study was performed, comparing absolute interface leakage with prongs and nasal mask. The effects of common leakage-reducing care maneuvers were evaluated.

Results: 1. In the in-line position, the flow meter volume added dead space. An increased flow meter resistance increased the work of breathing, both in the in-line and flow-through position and added to the CPAP pressure in the flow-through position. 2. The encapsulated versions of MediJet created pressure by resistance, were pressure unstable and had high imposed work of breathing. 3. The Pumani system was pressure unstable and induced a high work of breathing. Pressure was mainly created by resistance and the achieved pressure correlated poorly with submersion level. 4. An increased interface resistance caused pressure instability and an increased imposed work of breathing. An increased expiratory tubing resistance resulted in an increased imposed work of breathing compared to traditional bubble-CPAP systems and a higher CPAP pressure than indicated by submersion depth. 5. Interface leakages were significantly lower with prongs than nasal mask. Simple reducing maneuvers, such as adjusting the interface fit, were successful in most cases.

Conclusions: 1. To measure flows without affecting the child is best achieved with a low resistance flow meter in the flow-through position. 2. The MediJet pressure generators, based on the Benveniste valve, have changed their mechanism of action and CPAP properties due to their encapsulation. 3. The Pumani adds more to the work of breathing than a traditional bubble-CPAP system. The achieved pressure cannot be determined by submersion depth. 4. The patient interface should be placed close to the breathing circuit. Low-resistance interfaces and expiratory tubing should be used to minimize the imposed work of breathing and to achieve the desired pressure indicated by submersion depth. 5. During neonatal CPAP treatment, prongs leak less than nasal mask. In most cases, leakage can be reduced with simple reducing care maneuvers.