The principles of brain protection

Preventing raised ICP and saving the penumbra (the area around the primary injury with potential to recover) with its compromised microcirculation is important. An uncontrolled increase in ICP and brainstem herniation is the major cause of death after TBI or primary brain haemorrhage. Because raised ICP can be caused by an increase in the volume of blood, CSF, or brain tissue, treatment is aimed at reducing the volume of these three components and is summarised in Table 9.1.

The cerebral metabolic rate for oxygen is the volume of oxygen utilised by the brain. It is around 50 ml per minute

Table 9.1 Methods to reduce intracranial pressure (ICP)

Blood

Brain tissue

Avoid high PaCO2

Nurse head up 150 if possible

Avoid coughing and straining* Keep head in midline*

Surgical drainage

Mannitol for generalised oedema Steroids for tumour-related oedema Frusemide also sometimes used

*To encourage venous drainage. CSF, cerebrospinal fluid.

and is reduced in hypothermia by 5% for each degree celsius drop. Hypothermia has been used in the past for cerebral protection during complex cardiac and neurosurgery. Interest in its potential as a treatment for brain injury has resurfaced. Animal models demonstrate its benefits but actively cooling normothermic humans with brain injury has not been shown to improve outcome. However, the converse applies. Pyrexia is associated with an adverse outcome in brain injury, including stroke, and should be treated. Active rewarming of patients who arrive with mild hypothermia in the early period after head injury is discouraged.

Hypertonic saline has been studied extensively in traumatic brain injury. The theory is that the hypertonic solution will draw intracellular water into the intravascular space, reducing cerebral oedema and expanding intravascular volume at the same time. The results of clinical trials have been mixed. In patients with other injuries, such as burns, there is an increased incidence of renal failure and death with the use of hypertonic saline, so its use is not recommended in the routine resuscitation of trauma victims.

Treatment protocols for traumatic brain injury that use the physiological principles outlined above improve outcome (Box 9.2). This is also true of non-traumatic conditions such as bacterial meningitis with raised intracranial pressure. Therefore the priority in managing all patients with brain injury, whether subarachnoid haemorrhage, TBI, meningitis with raised ICP, or stroke, is to prevent secondary brain injury.

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