The Monro-Kellie doctrine states that the total volume of the intracranial contents (brain, blood, CSF) is fixed. In raised intracranial pressure (ICP), the first compensatory mechanism that is exhausted before ICP rises exponentially is:

• A Reduction in cerebral blood volume by venous compression
• B Cerebral autoregulation maintaining CPP at reduced MAP
• C Skull expansion via sutural diastasis (only in children)
• D Displacement of CSF from the cranial vault into the spinal subarachnoid space ✓

Explanation

According to the Monro-Kellie doctrine, initial increases in intracranial volume are compensated predominantly by translocation of CSF from the cerebral to spinal subarachnoid space, followed by reduction in cerebral venous blood volume. Once these buffering mechanisms are exhausted, further volume increases cause exponential ICP rise (poor compliance). The pressure-volume (compliance) curve is initially flat, then becomes steep — this is the basis for urgent decompression before irreversible herniation occurs.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.