Neuro Protection - Cerebral Perfusion Pressure
Cerebral Perfusion Pressure
Minor head injuries are common in children and will often need no treatment. But in this case there are some red flags. The mechanism and the fact that he then has a fit, raises the possibility that the crew is dealing with a more significant problem. So what do they need to think about when managing a case of a potentially serious head injury?
To answer this we need to talk a bit about the brain. If you imagine a jelly, tightly encased in a sealed box (the skull), that is the brain (of course, under about 1 year of age the box is not completely sealed but we’ll talk about that in a minute). When the brain suffers a significant injury, the response is that it swells. Swelling of the brain inside the sealed box leads to an increase in pressure and that can lead to further damage. When the brain swells, it sets off a complicated metabolic processes which is a bit like hitting a self destruct button,. If not interrupted these self destruct mechanisms can lead to further damage and the potential for death.
So when a child has a significant head injury, that initial injury may lead to primary damage to the brain.
This damage is done and there is nothing that you can do about it (this is where it’s all about prevention such as helmets for cycling, scootering etc). What you can do is work to prevent secondary damage of the type caused by brain swelling. As the brain swells in its tight box, the pressure inside the box rises to the point that the blood pressure is not strong enough to squeeze the blood into the brain. Clearly the lack of blood flow will further compound the insults that are affecting that poor brain.
So what can we do to stop this?
In the early stages after a head injury, before the brain has swelled significantly, we need to do all that we can to make the environment within the brain a good one. First make sure that there is a good oxygen supply. If the airway is obstructed or breathing is affected these need to be addressed then all patients with a potentially significant head injury should be given supplemental oxygen. Pivotal to this is ensuring that there is good blood flow and pivotal to that is ensuring that the blood pressure is adequate. So clinicians dealing with children with potentially significant head injures need to ensure a good blood flow (perfusion) to the brain.
A low blood pressure in the situation of a significant head injury is a real cause for concern and needs to be addressed. In addition we would use other ‘secondary injury prevention’ strategies such as tilting the bed up by 30 degrees, avoiding the use of cervical collars (inline stabilisation, blocks etc are all appropriate), minimising stimulation of the brain (good pain relief, keep the environmental noise down if possible), treating things like seizures and supporting blood pressure.
In a child who is significantly obtunded, taking control of the airway and ventilation is important if the team have the skills to do so.
For those crews that do not have advanced airway skills, maintaining an open airway and the use of airway adjusts is important. In the hospital setting, if there are signs to suggest brain swelling (raised intracranial pressure, indicated by reduced conscious level and dilated pupils in severe cases) the use of hypertonic saline or mannitol and ventilation to low normal CO2 may help reduce pressure. The patient can then be taken to CT to establish whether or not there are reversible causes for the deterioration (such as bleeds on the brain).
In infants the signs of raised intracranial pressure may be delayed. Until the bones of the skull fuse the skull itself acts as alert off valve in the setting of raised pressure. When the pressure exceeds the capacity for the skull to compensate, these infants will show the classic signs described above but this may mean that diagnosis is delayed by their in-built compensatory mechanism.