It’s hard to gauge what’s going on inside someone’s head when they are in intensive care (Image: Ryan McVay/Corbis)
A dipstick inserted into the brain can check its energy levels, just like checking oil levels in a car. The dipstick is already available and can save lives, according to some neuroscientists.
“The goal is to save brain tissue,” says Elham Rostami of the Karolinska Institute in Stockholm, Sweden.
Last month, Rostami and 47 others published guidelines about how and when to use the technique, known as brain microdialysis, in the hope of encouraging more hospitals to adopt it.
The approach involves inserting a slim, 1-centimetre-long probe directly into the brain. It measures levels of chemicals in the fluid that bathes brain cells, including glucose, the brain’s main energy source.
When used to monitor the brains of people in intensive care after a stroke or head injury, it warns doctors if glucose starts to dip – which can cause brain damage.
The probe can theoretically monitor almost any molecule, but Rostami says the most useful parameters are glucose, which shows if there is a good blood supply, and lactate and pyruvate, two metabolites that indicate if brain cells are using the glucose to release energy. Although widely available, the device has so far mainly been used as a research tool rather than to guide treatment.
Rostami believes her use of the probe helped save a woman’s life last year. The woman was in intensive care after a stroke involving bleeding on the surface of her brain. The probe revealed that although the bleeding had stopped, the woman’s brain glucose levels had fallen, probably caused by other blood vessels constricting.
In response, Rostami’s team administered a drug to boost her heart rate and send more blood to the brain. The probe then showed glucose levels beginning to rise, and within hours the patient’s condition had improved.
“She started responding to commands to squeeze my hand,” says Rostami. “It shows [the probe’s] potential to be used as a warning system.”
The approach involves drilling a hole in the skull, then pressing the 0.6mm-diameter probe into the brain tissue. It may seem drastic, but for seriously ill people it might provide vital clues for spotting that their brain is about to suffer damage.
People in intensive care are already hooked up to a host of monitors, which together keep track of numerous parameters including heart rate and levels of glucose and oxygen in the blood. But finding out what’s going on inside a person’s head is much harder.
An electroencephalogram (EEG) can give a read-out of the brain’s electrical activity, while various kinds of scan can give a snapshot of its health, but a person in critical condition can’t remain inside a scanner all day. The probe provides a means of obtaining frequent readings relatively easily.
“Anything that gives us a better understanding of what’s going on in the brain after injury is a good thing,” says Karim Brohi – a trauma specialist at the Royal London Hospital. But he cautions that there are no figures as yet on whether such monitoring improves survival rates.
Because the technique is fairly new, its risks are not yet fully known. There have been no cases of the probe causing bleeding or damage to brain tissue, to Rostami’s knowledge, but to minimise potential problems it is generally placed on the right side of the brain. That’s because the left hemisphere is usually more important for language. The left brain also controls the right side of the body, and most people are right-handed.
Sometimes a second probe is placed near the original site of injury, to provide more information.
Journal reference: Intensive Care Medicine, DOI: 10.1007/s00134-015-3930-y