Hypoxic ischaemic brain injury - Cerebrovascular disease

Hypoxic ischaemic brain injury

Definition

The global brain damage resulting from a failure of tissue perfusion.

Aetiology

Generalised failure of blood flow or oxygenation may result from cardiac or respiratory arrest, severe hypoglycaemia, drowning or carbon monoxide poisoning.

Pathophysiology

The generalised loss of perfusion results in diffuse death of neurones. The blood flow through the brain is subject to autoregulation. Within the range of 80–170 mmHg systolic pressure the cerebral blood flow is independent of the perfusion pressure; however, a low oxygen concentration or a blood pressure outside the range will result in tissue damage. Shorter periods or less severe episodes lead to ‘watershed infarction’ of the junctional areas between the cerebral arteries, in particular the visual cortex and cerebellum. The hippocampus is also at risk of damage as it has a high metabolic demand.

Clinical features

Mild cases tend to have an impaired intellect with memory loss and cortical blindness. Severe cases have a prolonged comatose state with variable outcome including the persistent vegetative state.

Macroscopy

There is loss of cortical mass mainly from the white matter leading to an atrophic brain. Neurones are replaced with gliosis by astrocytes.

Management

The underlying cause requires rapid identification and management to limit the extent of necrosis. Long term care requires multidisciplinary input and may necessitate ongoing residential care.