Neurosurgery notes/Trauma/Management of trauma/Neuromonitoring/ICP monitoring

ICP monitoring

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Neuromonitoring
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Non‑invasive pressure estimation
Invasive ICP monitoring techniques

Conversion factors between mm Hg and cm H2O

  • The density of mercury is 13.6 times that of water, and CSF is fairly close to water
  • 1 mm Hg [torr] = 1.36 cm H₂O
  • 1 cm H₂O = 0.735 mmHg [torr]

Indications

Brain trauma foundation

  • For salvageable patients with severe traumatic brain injury (GCS≤8 after cardiopulmonary resuscitation)
    • With an abnormal admitting brain CT OR
      • Abnormal CT:
        • Hematomas (EDH, SDH or ICH)
        • Contusions
        • Compression of basal cisterns
        • Herniation
        • Swelling
    • With a normal CT scan if two or more of the following features are noted at admission:
      • Age over 40 years,
      • Unilateral or bilateral motor posturing,
      • Systolic blood pressure (BP) <90 mm Hg

For moderate head injury (Godoy et al 2022)

  • Postoperative period after removal of acute subdural hematoma or multiple cerebral contusions:
    • Sudden changes in ICP could indicate hemorrhages due to decompression or reperfusion, new extra-axial collections, or worsening brain swelling.
  • GCS of 9-11 and cerebral contusion (temporal or bifrontal) without surgical intervention:
    • ICP monitoring aids in recognizing progression of contusions.
  • General anesthesia for emergency non-cranial surgery, especially with conservatively treated intracranial lesions:
    • Loss of clinical evaluation and potential effects of anesthetics on cerebrovascular autoregulation require ICP monitoring.
  • Concomitant severe chest trauma requiring deep sedation, high PEEP levels, recruitment maneuvers, or prone ventilation:
    • May cause hypercapnia or impair cerebral venous return, leading to cerebral vasodilation and increased ICP.
  • Concomitant intra-abdominal compartment syndrome associated with intracranial hypertension.
  • Prolonged traumatic shock increases the risk of cerebral edema.

Neurologic criteria

  • Some centres monitor patients who don’t follow commands.
    • Rationale:
      • Patients who follow commands (GCS ≥ 9) are at low risk for IC-HTN
      • One can follow sequential neurologic exams in these patients and institute further evaluation or treatment based on neurologic deterioration
  • Some centres monitor patients who don’t localize, and follow neuro exam on others

Multiple systems injured with altered level of consciousness

  • Especially where therapies for other injuries may have deleterious effects on ICP, e.g.
    • High levels of PEEP
    • Need for large volumes of IV fluids
    • Need for heavy sedation)

With traumatic intracranial mass (EDH, SDH, depressed skull fracture…)

  • A physician may choose to monitor ICP in some of these patients
  • Post-op, subsequent to removal of the mass

Non-traumatic indications for ICP monitoring

  • Some centres monitor ICP in patients with acute fulminant liver failure with an INR> 1.5 and Grade III of IV coma.
    • A subarachnoid bolt may be inserted after administration of factor VII 40 mcg/kg IV over 1–2minutes
      • The bolt is inserted as soon as possible (usually within 15 minutes and no more than 2 hours after administration) without significant risk of hemorrhage.
  • All patients were treated with hypothermia;
  • Other ICP treatment measures were used for refractory IC-HTN

Alali et al. prediction tool for intracranial hypertension

  • This tool may help to identify patients who require
    • ICP monitoring in high resource settings OR
    • ICP-lowering treatment in resource-limited environments.
  • Sensitivity of 94%
  • Specificity of 42%.
  • High ICP would be suspected in the presence of 1 major or ≥ 2 minor criteria.
    • Major criteria are:
      • Compressed cisterns (CT classification of Marshall diffuse injury III),
      • Midline shift > 5 mm (Marshall diffuse injury IV), or
      • Nonevacuated mass lesion.
    • Minor criteria are
      • GCS motor score ≤ 4
      • Pupillary asymmetry
      • Abnormal pupillary reactivity
      • Marshall diffuse injury II.

Evidence

  • Alali 2013: Management of severe TBI patients using information from ICP monitoring is recommended to reduce in-hospital and 2-week post-injury mortality
  • BEST:TRIP: Chesnut 2012: ICP monitor vs clinical exam + CT
    • ICP monitoring is not superior over clinical assessment in
      • 6 month mortality
      • 6 month GOS-E
      • Composite of 21 measures

Contraindications (relative)

  • "Awake” patient:
    • Monitor usually not necessary, can follow neuro exam
  • Coagulopathy (including DIC):
    • Frequently seen in severe head injury.
    • If an ICP monitor is essential, take steps to correct coagulopathy (FFP, platelets…) and consider subarachnoid bolt or epidural monitor (an IVC or intraparenchymal monitor is contraindicated).

Duration of monitoring

  • Remove monitor when ICP is normal × 48–72 hrs after withdrawal of ICP therapy.
  • Caution:
    • IC-HTN may have delayed onset
      • Often starts on day 2–3
      • Day 9–11 is a common second peak, especially in paeds
        • Also see delayed deterioration.
      • Avoid a false sense of security imparted by a normal early ICP.

Complications of ICP monitors

Monitor type
Bacterial colonizationᵃ
Hemorrhage
Malfunction or obstruction
IVC
ave: 10–17%
range: 0–40%
1.1%
6.3%
Subarachnoid bolt
ave: 5%
range: 0–10%
0
16%
Subdural
ave: 4%
range: 1–10%
0
10.5%
Parenchymal
ave: 14%
(two reports, 12% & 17%)
2.8%
9–40%
  • ᵃsome studies report this as infection, but do not distinguish between clinically significant infection and colonization of ICP monitor
  • Infection: see below
  • Haemorrhage:
    • Overall incidence is 1.4% for all devices
    • Defined as
      • Acute or subacute symptoms (any of: headache, seizure, impaired consciousness, or new/worsened focal neurological deficit) accompanied by radiological, pathological, surgical, or (rarely) only cerebrospinal fluid evidence of recent extra- or intralesional haemorrhage
    • Risk of significant hematoma requiring surgical evacuation is ≈ 0.5–2.5%15,23,24
  • Malfunction or obstruction:
    • With fluid coupled devices
    • Higher rates of obstruction occur at ICPs > 50mm Hg
  • Malposition:
    • 3% of IVCs require operative repositioning
  • Infection with ICP monitors
    • Colonization of the monitoring device is much more common than clinically significant infection (ventriculitis or meningitis).
    • Fever, leukocytosis and CSF pleocytosis have low predictive value
    • CSF cultures are more helpful
    • Range of reported infection rates: 1–27%
    • Identified risk factors for infection include:
      • Intracerebral, subarachnoid or intraventricular haemorrhage
      • ICP > 20mm Hg
      • Duration of monitoring:
        • Contradictory results in literature.
          • One prospective study in 1984 found an increased risk with monitor duration >5 days
            • Infection risk reaches 42% by day #11
          • Another found no correlation with monitoring duration. A retrospective analysis found a non-linear increase of risk during the first 10–12 days, after which the rate diminished rapidly
      • Neurosurgical operation: including operations for depressed skull fracture
      • Irrigation of system
      • Leakage around IVCs
      • Open skull fractures (including basilar skull fractures with CSF leak)
      • Other infections: septicemia, pneumonia
    • Factors not associated with increased incidence of infection:
      • Insertion of IVC in neuro intensive care unit (instead of O.R.)
      • Previous IVC
      • Drainage of CSF
      • Use of steroids
    • Treatment of infection
      • Removal of device if at all possible
        • If continued ICP monitoring is required consideration may be given to inserting a monitor at another site
      • Appropriate antibiotics.