Intracranial Pressure

Aka: Intracranial Pressure, CSF Pressure, CSF Opening Pressure, Cerebral Perfusion Pressure

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II. Background

  1. Intracranial Pressure is not affected by systemic Blood Pressure
  2. Sensitive to blood pCO2
    1. Hyperventilation lowers Intracranial Pressure

III. Technique: Measurement of ICP

  1. Counsel patient to try to relax
    1. Avoid Hyperventilation (lowers pressure)
    2. Avoid straining (raises pressure)
  2. Patient lies in lateral decubitus position
    1. Legs and neck should be in neutral position
    2. Opening pressure not accurate in sitting position

IV. Interpretation:

  1. Unit Conversions
    1. cmH2O = 1.3 x mmHg
    2. cmH2O = mmH2O / 10
  2. Normal
    1. Adults and older children: 7 to 15 mmHg (9 to 20 cm H2O)
    2. Younger children: 3 to 7 mmHg (4 to 9 cm H2O)
    3. Term Infants: 1 to 6 mmHg (2 to 8 cm H2O)
    4. Rangel-Castillo (2008) Neurol Clin 26(2): 521-41 [PubMed]
  3. Modifying Factors that increase Intracranial Pressure
    1. With pulse: 1 to 4 mmHg (2 to 5 cm H2O)
    2. With respirations: 3 to 8 mmHg (4 to 10 cm H2O)
    3. With sitting upright (compared with lateral decubitus): 11.4 mmHg (14.8 cm H2O)
      1. Abualenain (2011) Acad Emerg Med 18(1): 244 [PubMed]
  4. Decreased: Intracranial Hypotension (uncommon)
    1. Opening Pressure: <6 mmHg
    2. Trauma with secondary Cerebrospinal Fluid Leak
    3. Recent Lumbar Puncture (Spinal Headache)
    4. Spontaneous, Idiopathic Intracranial Hypotension (associated with positional Headache)
  5. Increased: Intracranial Hypertension
    1. Opening Pressure >20 mmHg
    2. Mild if 20 to 30 mmHg (26 to 39 cmH2O)
    3. See Increased Intracranial Pressure Causes

V. Calculation: Cerebral Perfusion Pressure (CPP)

  1. Cerebral Perfusion Pressure (CPP) = Mean Arterial Pressure (MAP) - Intracranial Pressure (ICP)
    1. Critical to maintain in Increased Intracranial Pressure in Trauma
    2. If continuous ICP monitoring, Arterial Line transducer should zeroed at the ear (kept at same height of head)
    3. Decreased Cerebral Perfusion Pressure risks brain ischemia
  2. Monroe-Kellie Hypothesis
    1. CSF volume (blood, brain, csf) remains constant
      1. When one volume increases (e.g. blood in Intracranial Hemorrhage), then another decreases (e.g. csf, brain)
    2. Typical volumes (total 1450-1700 ml)
      1. Brain: 1300-1400 ml
      2. CSF: 65-150 ml
      3. Blood: 110-150 ml

VI. References

  1. Kooiker in Roberts (1998) Procedures in ER, p. 1067-75
  2. Ravel (1995) Lab Medicine, Mosby, p. 294-9
  3. Tunkel in Mandell (2000) Infectious Disease, p. 974-8
  4. Seehusen (2003) Am Fam Physician 68:1103-8 [PubMed]

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