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The classical applications of Weibull statistical theory of size effect in quasi-brittle structures such as reinforced concrete structures, rock masses, ice plates, or tough ceramic parts are heing reexamined in light of recent results. After a brief review of the statistical weakest-link model. distinctions between structures that fail hy initiation of macroscopic crack growth (metal structures) and structures that exhibit large macroscopic crack growth prior to failure (quasi-brittle structures) are pointed out. It is shown that the classical Weibull-type approach ignores the stres~ redistrihutions and energy release due to stable large fracture growth prior to faIlure, whIch causes a strong deterministic size effect. Further, it is shown that, according to this classical theory, every structure is equivalent to a uniaxially loaded bar of variable cross section, which means that the mechanics of the failure process is ignored. Discrepancies with certain recent test data on the size effect are also pointed out. Modification of the Weibull approach that can eliminate these shortcomings is left for a subsequent paper.

BackgroundThe optimal strategy for weaning very preterm infants from nasal continuous positive airway pressure (NCPAP) is unclear. Reported strategies include weaning NCPAP to a predefined pressure then trialling stopping completely (abrupt wean); alternate periods of increased time off NCPAP whilst reducing time on until the infant is completely weaned (gradual wean); and using high flow nasal cannula (HFNC) to assist the weaning process. The aim of this study was to determine the optimal weaning from NCPAP strategy for very preterm infants.MethodsA pilot single centre, factorial design, 4-arm randomised controlled trial. Sixty infants born <30 weeks gestation meeting stability criteria on NCPAP were randomly allocated to one of four groups. Group 1: abrupt wean with HFNC; Group 2: abrupt wean without HFNC; Group 3: gradual wean with HFNC; Group 4: gradual wean without HFNC. The primary outcomes were duration of respiratory support, chronic lung disease, length of hospital stay and time to full suck feeds.ResultsThe primary outcome measures were not significantly different between groups. Group 1 had a significant reduction in duration of NCPAP (group 1: median 1 day; group 2: 24 days; group 3: 15 days; group 4: 24 days; p = 0.002) and earlier corrected gestational age off NCPAP. There was a significant difference in rate of parental withdrawal from the study, with group 2 having the highest rate. Group 3 had a significantly increased duration on HFNC compared to group 1.ConclusionsUse of high flow nasal cannula may be effective at weaning infants from NCPAP but did not reduce duration of respiratory support or time to full suck feeds. Abrupt wean without the use of HFNC was associated with an increased rate of withdrawal by parent request.Trial registrationThis study is registered at the Australian New Zealand Clinical Trials Registry (www.anzctr.org.au/). (Registration Number = ACTRN12610001003066).

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Use of occlusive polyethylene wrap improved admission temperatures for infants less than 27 weeks gestation. This intervention is easy to implement and does not interfere with resuscitation. However, removal of the wrap should be considered following admission to a closed care system in the neonatal intensive care unit because, in the intervention group, hyperthermia in the first 12 hours was a potential side effect.

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Both severity of illness scores are ascertained during the first 12 h of life and perform similarly. Both can facilitate risk-adjusted comparisons of mortality and quality of care after the first post-natal 12 h. CRIB-II scores have the advantage of being simpler to collect and calculate.

Developmental care is a safe practice model. The interdisciplinary study facilitated professional development and increased the knowledge of nurses.