- Is defined as ml of blood per 100g cerebral tissue,
- Calculated based on measures of CBF using stable xenon and mean transit time after injection of contrast material.
- Is reflective of CBV under normal conditions,
- High CBV (hyperaemia)
- Aka:
- Vascular engorgement
- Luxury perfusion
- Definition
- Disruption of flow-metabolism coupling when CBF exceeds CMRO2 requirements.
- Does not always cause cerebral swelling in severe TBI;
- There are other factors which can lead to cerebral swelling and refractory hypertensive ICP.
- Increased CBV often indicates posttraumatic hyperaemia which in conjunction with elevated ICP portends poor recovery.
- While acute hyperaemia is frequently associated with hypertensive ICP (>20 mmHg), subnormal flow indicates intact flow- metabolism coupling rather than ischaemia.
- Hyperaemic ICP patients are often in
- Younger,
- Present with low mean GCS (≤6),
- Risk effacement of basal cisterns and refractory hypertension,
- Demonstrate gross loss of autoregulation.
- CBF is functionally coupled to CMRG (cerebral metabolic rate of glucose) and not CMRO2, thereby luxury perfusion may be an appropriate metabolic response to hyperglycolysis after injury.
- Historically, hyperventilation was initiated to decrease CBF and subsequently ICP, however this approach has been tempered by the risk of inducing ischaemia.
- After brain injury, CBF may no longer accurately reflect CBV due to disruption in normal physiology, and in patients with acute SDH, elevated ICP, and ischaemia, CBV is half of normal value.
- Therefore, multiple aetiologies may contribute to intracranial hypertension and cerebral swelling after severe head trauma.
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