Higher oxygen saturation levels for extremely preterm infants improve disability-free survival in the BOOST-II trials
The risk of death or disability at the age of two years among
infants born before 28 weeks' gestation was 5% higher if they had
been allocated a lower targeted oxygen saturation (range 85-89 per
cent) than a higher targeted oxygen saturation (range 91-95 per
cent), in the results of the BOOST-II study published in the
New England Journal of Medicine.
The BOOST-II Australia (conducted by CTC) and BOOST-II United
Kingdom groups combined the results of their two large multicentre
trials involving 2108 infants, 1135 in Australia and 973 in the UK.
Their work has provided neonatal specialists and hospitals with new
clinical evidence of the safer level of blood oxygen to aim for.
The results confirm similar findings from a trial in North America,
which concluded that targeting oxygen saturation below 90 per cent
in extremely preterm infants was associated with a higher risk of
death, but not of disability.
Before these findings, neonatologists had targeted oxygen
saturation across a wider range, between 85 per cent and 95 per
cent. The decision of how much oxygen to give has been a difficult
one, because too much and too little can both cause later
disability. Now the precision of the target has narrowed
In the combined analysis of the Australian and UK trial, 48.1%
of the infants in the lower-target group and 43.1% in the
higher-target group had died or had a disability diagnosed by the
age of 2 years.
During the trials, there was a correction to the algorithm that
provided data from the oxygen meters. In an extra analysis of data
from only the revised oximeters in both trials, the rates of death
were 24.5% in the lower-target group and 16.9% in the higher-target
group. This was a statistically significant difference.
Professor William Tarnow-Mordi, principal investigator of the
Australian study says: 'We now have clearer evidence that the
higher concentration of oxygen is superior, increasing survival
without an associated increase in disability. If confirmed when
combined with the results of three similar trials in the US, Canada
and New Zealand, it will help prevent a great many deaths worldwide
Professor Tarnow-Mordi is professor of neonatal medicine at the
CTC. He is a champion of trials to improve the treatment and
prospects of newborn babies. He adds: 'Randomised trials like these
are the best way to determine which treatments provide the best
outcomes. More trials of other treatments for premature
babies are urgently needed to improve their quality of survival.
With innovative investment in clinical trial networks and point of
care data capture, trials like these could finish much faster, at a
fraction of the cost'.
The principal investigator of the UK BOOST-II study is Professor
Ben Stenson. He adds 'The success of trials like these depends on
hundreds of people. Thanks to the participation and support of
parents and health professionals worldwide, the outlook for very
preterm babies has never been better - and is still improving.'
BOOST-II was funded by the National Health and Medical Research
Council in Australia and the Medical Research Council in the
10 February 2016
- When we breathe air, this oxygen enters our bloodstream through
- Most of the oxygen in our blood is carried by a molecule in the
red blood cells called haemoglobin.
- When a healthy person breathes air (21% oxygen) the haemoglobin
in their arteries carries 95-100% of its maximum possible volume of
oxygen. i.e. the arterial haemoglobin is 95-100% saturated
- If the lungs aren't working well, the oxygen saturation in
arterial blood falls below 90%.
- To compensate, patients with sick lungs are given a higher
concentration of oxygen to breathe, 22-100%.
- Doctors wrap a probe around the wrist or ankle of a baby which
shines a bright light through the artery. This probe is attached to
a machine called a pulse oximeters, which measures the saturation
of the haemoglobin in the arterial blood.
- The higher the concentration of oxygen the baby breathes, the
greater the arterial oxygen saturation.
- However, if babies are given too much oxygen to breathe for
prolonged periods, their oxygen saturation will be close to 100%
for long periods, which is associated with the risk of eye damage
- In 2005, when these studies were set up, neonatal
paediatricians aimed to give enough oxygen to babies to breathe to
keep their haemoglobin saturation at 85-95%.