Head injury

Severe head injury is accompanied by both direct and indirect effects on CBF and metabolism, which show both temporal and spatial variations. CBF may be high, normal, or low soon after the ictus, but is typically reduced.112 Of patients undergoing CBF studies within 6-8 hours of a head injury, 30% have significant cerebral ischaemia.118 Global hypoperfusion in these studies was associated with a 100% mortality rate at 48 hours, and regional ischaemia with significant deficits. CBF patterns also vary with relation to the time after injury116 (Fig. 7.16). Initial reductions are replaced, especially in patients who achieve good outcomes, by a period of relative increase in CBF, which towards the end of the first week post ictus may be replaced by reductions in CBF that are the consequence of vasospasm associated with subarachnoid haemorrhage.120 CBF changes are non-uniform in the injured brain. Blood flow tends to be reduced in the immediate vicinity of intracranial contusions,121 122 and cerebral ischaemia associated with hyperventilation may be extremely regional and not reflected in global monitors of cerebrovascular adequacy123 (Fig. 7.17).

Elevations in ICP result in reductions in CPP and cerebral ischaemia, which lead to secondary neuronal injury. There is strong evidence that maintenance of a CPP above 60 mm Hg improves outcome in patients with head injury and raised ICP.124 Traditionally, patients with intracranial hypertension have been nursed head-up in an effort to reduce ICP. It is important to realise, however, that such manoeuvres will also reduce the effective MAP at the level of the head and run the risk of reducing CPP. Feldmann et al125 suggest that a 30° head-up elevation may provide the optimal balance by reducing ICP without decreasing CPP.

Fig 7.16 Spectrum of cerebral blood flow (CBF) patterns after severe head injury. Following an initial period of ischaemia lasting less than 24 hours, CBF begins to rise and may exceed normal values on days 2 to 4. CBF may fall to subnormal levels at later time points, chiefly as a result of the presence of vasospasm secondary to traumatic subarachnoid haemorrhage. CBF levels may never rise in some patients, especially those who have a poor outcome.

Fig 7.16 Spectrum of cerebral blood flow (CBF) patterns after severe head injury. Following an initial period of ischaemia lasting less than 24 hours, CBF begins to rise and may exceed normal values on days 2 to 4. CBF may fall to subnormal levels at later time points, chiefly as a result of the presence of vasospasm secondary to traumatic subarachnoid haemorrhage. CBF levels may never rise in some patients, especially those who have a poor outcome.

Fig 7.17 PET image of cerebral blood flow (CBF) showing the effect of hyperventilation within the first 24 hours after head injury. Despite the maintenance of X1O2 values at acceptable levels, hyperventilation results in increases in the volume of brain tissue where CBF falls below recognised thresholds of ischaemia.

Fig 7.17 PET image of cerebral blood flow (CBF) showing the effect of hyperventilation within the first 24 hours after head injury. Despite the maintenance of X1O2 values at acceptable levels, hyperventilation results in increases in the volume of brain tissue where CBF falls below recognised thresholds of ischaemia.

Do Not Panic

Do Not Panic

This guide Don't Panic has tips and additional information on what you should do when you are experiencing an anxiety or panic attack. With so much going on in the world today with taking care of your family, working full time, dealing with office politics and other things, you could experience a serious meltdown. All of these things could at one point cause you to stress out and snap.

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