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Title: Studies and observations on different kinds of oxygen monitoring, oxygen therapy, and associated morbidities in preterm infants
Author: Quine, David
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2010
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Introduction: Oxygen is ubiquitous, can be life saving, and is one of the most commonly used therapies in neonatal intensive care for the past 60 years. Despite this there is no consensus among neonatologists as to what is the most appropriate way to monitor oxygen, what target level to aim for, and how to change inspired oxygen levels. There may be two or more distinct time periods that can be defined, in the early life of extreme preterm infants who go onto suffer from bronchopulmonary dysplasia (BPD) for which the best oxygen target levels need to be clearly identified. Infants with BPD have difficult early years, often failing to thrive, requiring frequent readmission to hospital for respiratory exacerbations, and having significant chance of other morbidities of prematurity. Yet current definitions of BPD based on the use of oxygen therapy alone give wide variations in the incidence of disease that reflect little more than clinician variation and have little relevance to the severity of any underlying pathology. Objectives: To compare methods of oxygen monitoring, look at how infants oxygen dissociation curves affected oxygen tensions achieved, and see how our reaction to monitors affect oxygen stability. Finally, to measure V/Q and shunt non-invasively in infants with BPD at 36 weeks corrected gestational age and examine whether this would be a useful physiological definition of BPD. Four studies were carried out. Study 1: Aimed to determine whether care based on transcutaneous oxygen tension (TcPO2) or saturation (SpO2) monitoring is associated with less time spent with high oxygen tension and less variability of oxygenation. Care based on Sp02 monitoring was associated with more time spent with high oxygen tension, more time with low oxygen tension, more variability in oxygen tension and more variability in oxygen saturation than care based on TcPO2 monitoring. Within the target ranges studied SpO2 monitoring was associated with significantly more variable oxygenation than TcPO2 monitoring. Study 2: Aimed to describe the range of oxygen tensions likely to be achieved in the first three weeks of life in a population of high risk preterm infants at currently targeted oxygen saturation levels, and to determine whether infants who develop adverse outcome have different haemoglobin oxygen dissociation characteristics than infants who remain well. Study 3: Aimed to see which nurse oxygen adjustment practices influence oxygen stability and degree of adherence to oxygen saturation targets in preterm ventilated infants by separating out the variation in oxygen stability attributable to the condition and behaviour of the baby from that attributable to the nurse oxygen adjustment practices. Variations in oxygen adjustment practices were also related to nursing seniority. After controlling for the intrinsic instability of the infant we found that larger and more frequent changes in FiO2 may contribute to instability of oxygenation. More senior nurses achieved less hyperoxic time and, made smaller oxygen changes. Stability of oxygenation in ventilated preterm infants is influenced by the oxygen adjustment practices of the staff who care for the baby. These are potentially modifiable practices. Study 4: Aimed to quantify the severity of gas exchange impairment in preterm infants with BPD in a graded fashion and to partition this between the contribution made by reduced ventilation/perfusion ratio (VA/Q) and that due to right to left shunt, using non-invasive measurements of PIO2 and SpO2. The predominant gas exchange impairment in BPD is a reduced VA/Q described by the right shift of the SpO2 vs PIO2 relationship. This provides a simpler method for defining BPD that grades disease severity. Summary: In summary this series of studies found that the method by which oxygenation is monitored and the ways that staff adjust oxygen levels have an important influence on the oxygen levels achieved. The overall oxygen affinity of the neonatal blood did not appear to be an important determinant of the risk of adverse outcome. Individual infants vary widely in their stability in terms of oxygenation. The optimal oxygen levels for developing preterm infants remain uncertain and this is the subject of a major prospective international research collaboration (NeOPRoM). Interpretation of the results of the clinical trials of different saturation targets that are currently recruiting will be difficult unless good data on compliance with protocol are gathered. A simple non-invasive measure of gas exchange impairment that might better grade disease severity of BPD has been defined. These studies will help to focus future research, and should assist clinicians in achieving improved compliance to oxygen targets.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available