Key Learning Points

1. 1. The physiological changes governing the Monro–Kellie doctrine become quickly exhausted when the intracranial volume reaches a critical value, thus expediting intracranial hypertension.

2. 2. The main factors influencing the balance between cerebral oxygen delivery and consumption are cerebral blood flow (CBF), arterial oxygen saturation (SaO2), haemoglobin concentration and cerebral metabolic rate of oxygen (CMRO2).

3. 3. In the critical care unit, the most common advanced neuromonitoring technique involves measurement of intracranial pressure (ICP) and estimation of cerebral perfusion pressure (CPP). However, brain tissue oxygen tension (PtiO2), jugular venous oxygen saturation (SjvO2), cerebral microdialysis, transcranial Doppler ultrasound and continuous electroencephalography are also helpful to detect early complications.

4. 4. Jugular venous oxygen saturation (SjvO2) values <55 per cent may indicate elevated CMRO2, low CBF, systemic oxygen desaturation or cerebral ischaemia. Conversely, readings >75 per cent may represent high CBF, metabolic suppression or massive cerebral infarction.

5. 5. Cerebral microdialysis is an evolving technique that can help to diagnose cerebral ischaemia, traumatic axonal injury and inflammatory insults at early stages. However, more research is needed to validate its clinical use.