Traumatic brain injury, or TBI for short, is one of the leading causes of death and disability, with TBI especially affecting the younger population although older people are not immune. Almost 1 in every 1000 Australians are affected by TBI every year, and this can range from mild concussion to serious life-threatening injuries. The total cost to the Australian community each year from head injuries is estimated to be around $8 Billion.
A severe TBI often occurs following falls, motor vehicle accidents, or assaults, and should be treated in a trauma verified hospital as a matter of urgency. A CT scan will demonstrate an injury to the brain and sometimes the skull or even the spine, and some people will have multiple injuries all over their body. After a head injury the brain may be swollen, which can elevate the pressure of the brain inside the rigid skull. For many years the mainstay of managing people with a severe TBI has been to monitor and regulate the pressure inside the skull, which we call intracranial pressure, or ICP for short. This requires the insertion of a very small catheter inside the brain via a small hole in the skull, called a burr hole. The ICP monitor provides a pressure reading in real time, and intensive care specialists can commence therapies to limit increased ICP, usually in the form of sedatives to relax the brain and keep the patient in an induced coma. Sometimes surgery is necessary to remove a blood clot from within or around the brain, to remove a large section of the skull (called a decompressive craniectomy), or to insert a drain to remove some of the normal brain fluid; all of these surgical techniques aim to help by reducing ICP to normal levels. Ultimately the brain will relax with time, and these therapies are designed to reduce ICP and help minimise any damage associated with raised pressures until brain relaxation has occurred.
We now know that head injuries are far more complicated than simply raised ICP from a swollen brain. After a TBI there is a huge cascade of inflammation, the normally highly regulated brain blood flow can be disturbed, and there is a real risk of the brain developing a low oxygen state with further brain injury because of this. A constant supply of oxygen and glucose is vital for normal brain function and to prevent brain cell death, and if the brain is deprived of oxygen after a TBI this can have a significant negative effect on a patient’s outcome after their injury with an increase in the risk of death. We call brain injury that develops after the injury due to raised ICP or low oxygen states secondary brain injury. Doctors cannot influence the damage that occurs at the time of the primary brain injury, but we can reduce further damage to the brain by limiting secondary injuries. Although we give supplementary oxygen to brain injured patients we don’t always know what the level of oxygen is within the brain tissue where it is needed most, therefore new studies are being performed to measure this and to see if keeping levels of brain tissue oxygen above a certain limit will improve the outcome after a severe TBI. Brain tissue oxygen levels can be monitored in a similar way to measuring ICP, and involves insertion of a small catheter placed right next to the ICP monitor. If we can show that ensuring brain oxygen levels are optimised in addition to our standard level of care that we already do for these patients results in better clinical outcomes then this will influence the way that severe TBI is managed around the world.
There are currently two international clinical trials looking to compare standard ICP driven care for severe TBI patients with monitoring and treating brain oxygen levels in addition to standard care. In the United States the BOOST-III trial has commenced recruiting patients addressing this question, and in Australia and New Zealand the BONANZA trial is also underway and will be looking to find an answer to the same problem. In fact, considering that these two trials are so similar, the results of both studies may be pooled to definitively show whether or not we can improve patient outcomes by monitoring brain tissue oxygen in addition to ICP. It sounds like common sense, but until it has been proven in a properly composed clinical trial it cannot be accepted by the medical community as evidence based care, which is why clinical trials are so important in furthering our understanding of brain injuries.