Optimisation of neonatal ventilation from birth using physiological measurements as outcomes

    Student thesis: Doctoral ThesisDoctor of Philosophy

    Abstract

    Aim: To optimize mechanical ventilation in the labour suite and on the neonatal unit using the results of physiological measurements as outcomes. A series of studies was undertaken to test the following hypotheses.
    1. During the resuscitation of prematurely born infants, inflation pressures of 25/5 cmH2O would increase the expired tidal volume and end tidal carbon dioxide levels. In addition, maintenance of the first five inflations for two to three seconds would lead to higher tidal volumes.
    2. In infants born at or near term, volume targeted ventilation (VTV) when compared to pressure limited ventilation (PLV) would be associated with shorter time to extubation, reduced work of breathing and better respiratory muscle strength.
    3. In a dynamic lung model representing bronchopulmonary dysplasia, resistive unloading during proportional assist ventilation (PAV) would reduce the inspiratory load.
    4. In infants with evolving bronchopulmonary dysplasia, PAV when compared to assist control ventilation (ACV) would be associated with reduced work of breathing, increased respiratory muscle strength and be associated with less ventilator-infant asynchrony and improved oxygenation as indicated by the oxygenation index (OI).
    5. Extubation failure would be predicted by the tension time index of diaphragm (TTdi) and the tension time index of respiratory muscles (TTmus).
    Results:
    1. The resuscitation study demonstrated that higher inflation pressures, but not longer inflation times produced significantly higher expired tidal volumes.
    2. There were no significant differences in the time to successful extubation in at or near term-born infants supported by VTV or PLV; however, VTV was associated with significantly fewer episodes of hypocarbia.
    3. The in-vitro study of PAV showed that the resistive unloading was relatively ineffective and hence as currently delivered is unlikely to be of clinical benefit to infants with a high resistance load.
    4. PAV compared with ACV in prematurely born infants ventilated beyond the first week after birth resulted in a reduced work of breathing and a lower OI.
    5. The TTdi study demonstrated that the TTdi and TTmus results significantly differed according to extubation outcome in ventilated infants. Overall TTdi ≥0.08 had 83% sensitivity and 81% specificity (90% sensitivity and 60% specificity in the preterm infants) in predicting extubation failure. Overall TTmus ≥0.19 had 50% sensitivity and 100% specificity (54% sensitivity and 100% specificity in the preterm infants) in predicting extubation failure.
    Date of Award2017
    Original languageEnglish
    Awarding Institution
    • King's College London
    SupervisorAnne Greenough (Supervisor) & Gerrard Rafferty (Supervisor)

    Cite this

    '