Overview
This lecture reviews intracranial pressure (ICP), its clinical significance, relevant thresholds, the Monroe-Kellie hypothesis, and types of brain herniation.
ICP Waveforms and Measurement
- ICP monitors display three waveforms, loosely relating to arterial pulsation and blood flow, but waveform analysis is rarely clinically useful.
- The primary clinical concern is the measured ICP value, not detailed waveform interpretation.
- ICP above 22 mmHg is associated with increased mortality and should prompt intervention.
Clinical Guidelines for ICP Management
- Brain Trauma Foundation recommends treating ICP above 22 mmHg.
- Decisions to treat should integrate ICP values, imaging results, and clinical examination findings.
Monroe-Kellie Hypothesis
- The cranial compartment has a fixed volume, mainly filled by brain tissue, with smaller volumes of cerebrospinal fluid (CSF) and blood.
- Increases in any intracranial component lead to raised ICP.
- At a certain point, small increases in volume cause dramatic ICP rises, escalating herniation risk.
Brain Herniation
- Herniation is the abnormal displacement of brain tissue into another intracranial compartment due to raised ICP.
- Uncal herniation: Medial temporal lobe moves past the tentorium, compressing the brainstem; often fatal.
- Subfalcine herniation: Frontal lobe shifts under the falx cerebri.
- Tonsillar herniation: Inferior cerebellar tissue herniates through the foramen magnum.
- Other types: Upward and downward herniation.
Key Terms & Definitions
- ICP (Intracranial Pressure) — The pressure within the skull, typically measured in mmHg.
- Monroe-Kellie Hypothesis — The concept that the intracranial volume is fixed, with brain, blood, and CSF as its components.
- Herniation — Pathological shift of brain tissue into another compartment due to increased ICP.
- Uncal herniation — Herniation of the medial temporal lobe past the tentorium compressing the brainstem.
- Subfalcine herniation — Displacement of brain under the falx cerebri.
Action Items / Next Steps
- Review Brain Trauma Foundation Guidelines on ICP management.
- Understand clinical signs and imaging features of herniation syndromes.