(b) Adaptation of current explanation of Monro-Kellie doctrine within advanced trauma life support (ATLS) and most critical care teaching demonstrating that additional mass results in a large volume of CSF then venous blood displacement. This article reviews the Monro-Kellie doctrine, categorises venous outflow limitation conditions, relates physiological mechanisms to clinical conditions and suggests specific management options. Multiple clinical conditions and the cerebral effects of altitude and microgravity relate to imbalances in this dynamic rather than ICP per se. Interpreting ICP without interrogating its core drivers may be misleading.
Failure of venous efferent flow to precisely match arterial afferent flow will yield immediate and dramatic changes in intracranial blood volume and pressure. Neuro-critical care practice focusing on arterial and ICP regulation has been questioned. The slow production of CSF (0.35 ml/min) is dwarfed by the dynamic blood in and outflow (∼700 ml/min). However, each volume component may not deserve the equal weighting this static concept implies. On this doctrine’s “truth or relative untruth” depends many of the critical procedures in the surgery of the central nervous system.
When not possible, attempts to increase a volume further increase ICP. Cushing conceptualised the Monro-Kellie doctrine stating that a change in blood, brain or CSF volume resulted in reciprocal changes in one or both of the other two. For 200 years, the ‘closed box’ analogy of intracranial pressure (ICP) has underpinned neurosurgery and neuro-critical care.
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