Traumatic brain injury: a case of too much oxygen?

The term itself is scary enough-“traumatic brain injury” (TBI). What exactly does it mean? Well, it is possibly the commonest cause of death and disability worldwide. It refers to neurological symptoms that occur as a consequence of sudden trauma to the brain. It is most commonly due to a direct blow to the head, but some authorities also include other accidents in this definition, such as episodes of acute acceleration/deceleration which lead to brain injury, such as being thrown from a moving object. The symptoms vary significantly from one individual to another. A lot of sufferers who survive the acute injury develop chronic symptoms that may last a lifetime and for which there is no definite cure. These symptoms include changes in cognition, impaired mobility, problems with concentration and changes in personality and mood. These impairments affect not only the patient, but may have significant impact on friends and family. What is even more distressing for patients, is that these deficits cannot be directly measured and there is no simple test that tells the patient how severe the damage is or what the prognosis is likely to be. While some cases of TBI are mild and resolve, other patients have very serious brain injury which may affect long-term function and, in acute cases, possibly even survival.

In these severe cases, there has been considerable research on how these patients should be managed in the setting of an intensive care unit. In this issue of JNNP, there is a very important paper by Rincon and colleagues that looks at the role of oxygenation in determining the outcome of TBI http://jnnp.bmj.com/content/85/7/799.full . As noted in the accompanying Editorial http://jnnp.bmj.com/content/85/7/711.full , one of the principles of intensive care management is the provision of adequate oxygenation for the patient. The study by Rincon et al however explores an alternative possibility in TBI: what if we are doing damage by giving too much oxygen? Their results provide evidence that high levels of oxygen were associated with a worse outcome in patients with severe TBI. Why is this case? They suggest that providing high levels of oxygen may actually result in a reduction in oxygen delivery to the brain due to changes in cardiac output and that these reductions may impair the metabolic activities of neurons.

This is a large multi-centre study with interesting conclusions. Importantly from a clinical perspective, the study has implications for how we manage patients with severe TBI.

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