Novel relationship of oxygen levels in the brain in premature babies
12 June 2003
Premature babies are at risk of brain injury. One important cause is lack of oxygen to the brain.
This is because their brains are immature and they are unable to maintain normal blood pressure. Low blood pressure means that not enough oxygen is getting to the brain and this can result in organ failure, brain haemorrhage and brain damage. Lack of oxygen to the brain is a major cause of mortality in preterm infants.
Leading medical charity Action Research has found two novel relationships related to oxygen levels in the brain and brain injury.
The research at the University of Liverpool looked at the relationship between levels of oxygen in the brain and the rest of the body, brain injury, blood pressure and cardiac function in the first four days. All the babies in the study were all less than 32 weeks (eight weeks premature) and some weighed as little as 1500 grammes.
The team investigated the correlation between blood flow and the oxygen supply to the brain in two types of brain injury, which affect premature babies. Brain injury can be either a brain haemorrhage which is bleeding into the brain tissue or breakdown of the brain tissue resulting in cysts.
The research discovered that oxygen extraction by the premature baby’s brain is related to how well a baby’s heart is functioning. Low cardiac output means low blood pressure. This means that less blood and oxygen are delivered to the brain when the blood pressure is low. They found that even where there is low blood pressure, and hence reduced amounts of blood going to the brain, organs such as the brain are able to compensate for this by extracting more oxygen from the blood that is available. This has not been described before in such very small babies.
It had been previously thought that a possible cause of both conditions was variation in the brain’s blood supply – too much causing haemorrhage and too little causing death of brain tissue and consequent cyst formation.
The group have shown that brain haemorrhage is associated with fluctuating brain oxygenation, implying wide variations in the blood supply to the brain. By contrast, where there was breakdown of the brain tissue there was a constant non-fluctuating supply of oxygen to the brain.
The implication of this finding is that the causes of these two important conditions are different. It supports a view that, while brain haemorrhage is likely to be due to fluctuations in the blood and oxygen supply to the brain, the formation of cysts in the brain is due to an entirely different mechanism – one alternative proposition is that infection may play a part. Simon Moore, Chief Executive of Action Research said: "It is always wonderful to be able to help the most vulnerable people in the world and premature babies must come at the top of the list. Understanding more about the blood supply and the supply of oxygen that babies need during the first days of their lives will mean that evidence-based clinical guidelines can be formed which will benefit many thousands of babies and their families each year."
Professor Michael Weindling of the University of Liverpool said: "The first four days of life are very important in terms of the special care that premature babies need. More research is needed, but this work will form the basis of guidelines on what is the best way to help these vulnerable babies and ensure that they get the best treatment available."
Babies’ brains need more oxygen as they get older so it is important that babies who are receiving oxygen have the levels adapted to their individual needs.
Currently, the amount of oxygen to the brain is not measured directly but is determined by other factors which are all monitored as part of the intensive care regime that premature babies receive in hospital.
Measuring the flow of blood to the brain as well as to other parts of the body is done using near infra-red spectroscopy (NIRS).
In any one year the Liverpool Women's Hospital has 800 admissions to the neonatal unit and half of these are ventilated. Of these 400, around half again are of very low birth weight. The percentage of premature babies who survive depends on how many weeks early they are born. If a baby is 12 weeks premature then it is expected that 80 per cent of them will survive. This drops to only about 40 per cent if the baby is born 16 weeks premature.
There are around 600,000 babies born each year in the UK and of this number 7,000 will be significantly premature. Further research has to be done which will then be developed into guidelines for other specialists to use.
Your donation could help fund vital research for children