Intracranial Pressure (ICP)

Intracranial Pressure (ICP)

David Ray Velez, MD

Table of Contents

Definition
Signs of Elevation
Monitoring
Management

See Also:
*See Traumatic Brain Injury (TBI)

Definition

Intracranial Pressure (ICP): The Pressure within the Skull that the Brain, Blood, and Cerebrospinal Fluid Exert on the Skull’s Dural Envelope

Cerebral Prefusion Pressure (CPP): The Pressure that Drives Blood into the Brain to Deliver Oxygen and Nutrients

  • CPP = MAP – ICP

Monro-Kellie Doctrine

  • The Sum of the Volumes of the Brain Matter, Cerebrospinal Fluid (CSF), and Intracranial Blood is Constant
  • An Increase in One Component Will Cause a Decrease in One or Both of the Others
  • Therefore an Elevated ICP will Result in Decreased Cerebral Perfusion Pressure and Risk for Herniation

Normal Values

  • Intracranial Pressure (ICP)
    • Normal: 7-15 mmHg
    • General Goal: < 20 mmHg
    • Peaks 48-72 Hours After Trauma
  • Cerebral Perfusion Pressure (CPP)
    • General Goal: > 60 mmHg to Avoid Secondary Brain Injury
    • Range 50-70 mmHg

Signs of Elevation

Cushing’s Triad

  • A Triad of Findings Seen from Increased Intracranial Pressure
  • Due to Increased Sympathetic and Parasympathetic Activity
  • Findings are a Late Sign and Suggest Impending Herniation
  • Triad:
    • Hypertension (Widened Pulse Pressure)
    • Bradycardia
    • Irregular Breathing Pattern
  • Stages:
    • First Stage
      • Increased ICP Causes Increased Sympathetic Activity
      • Elevated Blood Pressure and Heart Rate
    • Second Stage
      • Hypertension Activates Aortic Arch Baroreceptors Causing Increased Parasympathetic Activity
      • Decreases Heart Rate
    • Third Stage
      • High ICP, Heart Rate Changes, and Endogenous Stimuli All Distort Brainstem Pressures
      • Causes Irregular Breathing

Additional Signs of Elevated ICP

  • Pain and Headache
  • Double Vision (Due to Cranial Nerve VI Palsy)
  • Signs of Uncal Herniation
    • Eye Findings are the Earliest Sign of Uncal Herniation
      • Ptosis
      • Anisocoria (Unequal Pupil Size)
      • Impaired Movement
    • A Dilated/Blown Pupil Indicates Pressure on Ipsilateral Oculomotor CN III

Monitoring

Types of ICP Monitors

  • Bolt (Codman/Camino ICP Monitor)
    • Bolt Placed into the Parenchyma with Fiberoptic Monitoring
    • Only Measures ICP
  • External Ventricular Drain (EVD/Ventriculostomy)
    • Drain Placed into the Ventricle
    • Measures ICP and Allows Therapeutic CSF Drainage

Indications for ICP Monitoring (Bolt vs EVD)

  • Severe Head Injury (GCS ≤ 8) with an Abnormal CT
  • Severe Head Injury (GCS ≤ 8) with a Normal CT but ≥ 2 of:
    • Age > 40
    • Motor Posturing
    • SBP < 90 mmHg

ICP Waveform

  • Waveform Peaks:
    • P1: “Percussion Wave” – Represents Blood Pressure Transferred to the CSF
    • P2: “Tidal Wave” – Represents the Reflection of the Pressure Wave in the Cerebral Parenchyma
    • P3: “Dicortic Wave” – Related to Aortic Valve Closure and Venous Pulsation
  • Reported Mean ICP Describes the Average of the ICP Peaks Over a Short Period of Time
  • Elevated P1 May Represent Hypertension
  • Decreased P1 May Represent Loss of CPP
  • Elevated P2 May Represent Increased ICP and Decreased Compliance

Optic Nerve Sheath Diameter (ONSD)

  • Ultrasound Measurement of the ONSD Allows a Noninvasive Evaluation of ICP
  • Elevated ICP is transmitted Through the Subarachnoid Space Increasing the Size of the Optic Nerve Sheath
  • ONSD > 5 mm Suggests Elevated ICP
  • High Sensitivity (94%) and Specificity (90%)

ONSD (Red Bar) 1

Management

Goal CPP > 60 mmHg (50-70 mmHg) to Avoid Secondary Brain Injury

  • Goal ICP < 20 in General

Initial Measures

  • IV Fluids (Normal Saline)
  • Pressor Support and Avoid Hypotension
  • Elevate Head-of-Bed to 30 Degrees – Support Adequate Venous Drainage
  • Sedation and Analgesia – Decrease Metabolic Demand
  • Maintain Normothermia – Fever Increases Metabolic Demand and Blood Flow
  • Intermittent CSF Drainage (If an EVD is Present)
  • Avoid:
    • Steroids – Increase Mortality
    • Lumbar Puncture – Can Precipitate Herniation

Secondary Options

  • Osmotic Therapy
    • Goal Na: 145-155
    • Hypertonic Saline or Mannitol Boluses (Not Continuous)
    • Avoid Mannitol (Diuretic) if Hypotensive or Hypovolemic
  • Hyperventilate
    • Goal PaCO2: 30-35
    • Induces Cerebral Vasoconstriction
  • Exchange Parenchymal Pressure Monitor (Bolt) for an External Ventricular Drain (EVD) to Allow Intermittent CSF Drainage

Refractory Treatment

  • Neuromuscular Paralysis
  • Barbiturate Coma
  • Therapeutic Hypothermia
  • Decompressive Craniectomy
    • Improves Survival but More Survivors are Dependent on Others and Higher Risk of Unfavorable Outcomes (RESCUEicp and DECRA Trials)

References

  1. Bergmann KR, Milner DM, Voulgaropoulos C, Cutler GJ, Kharbanda AB. Optic Nerve Sheath Diameter Measurement During Diabetic Ketoacidosis: A Pilot Study. West J Emerg Med. 2016 Sep;17(5):531-41. (License CC BY-4.0)