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Weight gain and theophylline
There was a time when a cynic on a neonatal ward round in the UK might have thought prescribing for preterm infants could be made simpler and less tedious if a drug company produced a syrup containing theophylline, vitamins and a modest amount of sodium. As time passed it might have been commercially viable to have added some phosphate, or even provided some equivalent to the sophisticated triphasic contraceptive blister packs, containing a graded dexamethasone course with or without pulsed antibiotics. A few years ago the preterm neonatal elixir would certainly have contained cisapride. We are now at a stage when prokinetic free and steroid unenhanced products would be enjoying a market advantage, but methylxanthines have to a large extent preserved a squeaky clean image.
Carnielli and colleagues (page F39) show increased carbohydrate utilisation in neonates prescribed intravenous aminophylline, and suggest a possible adverse effect on growth. In their review, Sinha and Donn (page F64) refer to other possible complications, and point out the uncertain benefits, especially in babies over 1kg birthweight. The extent of methylxanthine usage in neonatal care is exemplified by the fact that neonates as mature as 34 weeks gestation on Carnielliet al's unit are prescribed aminophylline for the prevention of apnoea of prematurity.
Knowing when (and how) to stop
Weaning preterm infants from mechanical ventilation as their hyaline membrane disease resolved used to be easy. It didn't always work, of course, but at least the theory was straightforward. The mean airway pressure was reduced by dropping the peak inspiratory pressure until it seemed safe and then the ventilatory rate was reduced. The art, and the arguments, arose from juggling these easily understood measurements. Weaning seems to be getting more scientific, or at least more complicated, and this month's Current Topic (page F64) guides the reader through some of the more complex weaning modes available on modern ventilators. Some of these methods are not available in the UK, and many will be more familiar to ventilator salesmen than to neonatologists This paper may help clinicians to hold their head high in lunchtime meetings.
It is early days in the development of some of these newer modes of ventilation and Sinha and Donn point out that there are as yet relatively few randomised evaluations of weaning practices. Empiric trials will help to define the most efficient mode or modes of weaning. We can only hope that the preferred techniques do not turn out to be those which require highly specialised machinery or highly sophisticated operators.
Lungs and brains
Chronic lung disease, defined as persisting oxygen requirement at 28 days of age, is associated with a higher risk of impaired early motor and cognitive development in surviving preterm infants. Katz-Salamon et al (page F1) report follow up data on 86 very low birthweight infants who had no significant lesions on neonatal cerebral ultrasound. Those with CLD were more likely to have impaired hand-eye coordination, perception and intelligence on testing at 10 months. The long term consequences of these early impairments remain to be seen, but the authors recommend that this group of babies requires careful neurodevelopmental follow-up, despite the normal brain scans.
Speculation as to the cause of these neurodevelopmental sequelae in infants without overt cerebral lesions is interesting. Recurrent hypoxic damage is clearly a possibility, but it may also be that the CLD and the neurological damage both arise from a common cause. Perinatal sepsis has been implicated in the aetiology of both problems, but in this small group chorioamnionitis and prolonged rupture of membranes were no more common in those babies who developed CLD.
The neurological toll of neonatal intensive care continues to be a major concern. Disappointing data in this issue from the North of England Collaborative Cerebral Palsy Survey show a 46% increase in cerebral palsy rates in the North East between the periods 1964–68 and 1989–93. The increase was even greater for the more severe cases, and the contribution of low birthweight was more marked in the latter period, when a half of the cases occurred in infants with birthweight < 2500g.
Small and irritable
Nobody knows what causes infantile colic but it seems to be more than twice as common in low birthweight babies (page F44). Is there a physiological basis for this association? Could it be due to disturbed parent–infant interactions, or social factors? Or is it an early manifestation of the short man syndrome?
For readers' information, the baby that was shown in the ultrasound scan of a fetus at twenty weeks, featured on the cover of the May 2000 issue, was born on 27th May 2000. She weighed 7lbs 9oz and is the yet-to-be-named daughter of Kathryn and Bryan Walsh.
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