Elevated intracranial pressure

Overview

• Cranial vault is a fixed volume made up of 3 main components
  • brain tissue (80%) blood (10% or 150L) and CSF (10% or 150mL).
• While brain parenchyma is a relatively fixed volume, the blood and CSF are fluids with entranace and egress points into and out of the skull and are primarily affected with changes in ICP.
  • CSF is created at a rate of 20mL/hr or 500mL/day.
• Neuronal injury occurs secondary to vascular compromise to brain cells either by a reduction in cerebral blood flow or direct ischemia
  • This is an emergency and requires emergent intervention if sustained > 5-10 minutes

Clinical Signs and Symptoms

• Increased ICP generally causes headache (from increased pressure on heavily innervated meninges), Nausea/vomiting, and occasionally optic abnormalities (most notably ocular palsies (CN6 particularly long course intracranially) along with AMS and optic atrophy.
• Morning headaches are pathomnemonic (mild hypoventilation during sleeping hours causes increases in cerebreal blood flow)

Causes

• As the cranial vault is a fixed volume, Increases in ICP are either due to increased brain tissue (edema), blood (increase inflow or decreased outflow) and CSF (increased inflow/production or decreased outflow) in addition to abnormal mass lesions.

1. Mass lesions
   1. tumor, hematoma, air, abscess,foreign body
2. CSF accumulation
   1. Hydrocephalus(obstructive or communicating)
      1. Most often obstrcutive via tumor, intraventricular hemorrhage, ventriculutus/meningitis) with compression of CSF outflow
3. Vascular
   1. Either input or output failure
      1. Input failure: increased CBF or CBV due to failed autoregulatoin
      2. Outflow failure: venous congestion or sinus thrombosis
4. Cerebral edema
   1. vasogenic (vessel damage due to tumor/infection abscess
   2. Cytotoxic (ischemia)
   3. Hydrostatic: Increased transmural pressure with hydrocephalus
   4. Hypo osmolar

Management

1. Ensure data accurate
   1. observe for accurate waveforms in arterial and ICP monitors
      1. EVD zeroed at ear, changes with coughing/positioning
      2. Arterial line zeroed at ear (for accurate CPP measurement; although typically level at heart reasonably accurate
2. Assess ABC (as increased ICP often accompanies decline in mental status
   1. If need to intubate - ensure measures to avoid coughing/bucking (increases ICP).
      1. Lidocaine 1% 1ml/kg 1x IV bolus as premedication.

Goals

1. Keep CPP 60-110mmHg
   1. If <110 utilize pressors (levophed or neosynephrine; levophed preferred)
   2. Levophed: start at 4 mcg/min; maximum 20 mcg/min.
   3. Phenylepherine: start at 0.4 mcg/kg/min; maximum 9 mcg/kg/min.
2. Keep ICP < 20mmHg (nonsustained temporary elevateions ~<5 minutes ok

Take Stepwise approach to treatment

• 1st (conservative)

1. Elevate Head of Bed 30-to 45 deg; keep head midline
   1. May "sandbag" head of those in c-collar to promote venous drainage(c-collar can restrict venous outlfow)
2. Control agitation/pain
   1. narcotics, benzodiazepines, sedative hypnotics
      1. Attempt to favor short acting medications to allow neuro exam checks. Versed, Fentanyl and propofol are often appropriate.
3. Maintain Normocapnia (pCO2 35-40)
4. Maintain normothermia.
   1. Treat shivering
      1. Bear hugger (warms skin temperature)
      2. APAP 650 q6prn for temp >38.5°F
5. Maintain euvolemia (Input = output)

• 2nd (Intervention-short term)

1. hyperventilate to pCO2 ~30mmHg
   1. This is short term as patient will equilibrate; is only meant as a temporizing measure. Attempt to wean to normocapnia as soon as able. Further do not overventilate past 25mmHg as may exacerbate damage via cerbral hypoxia (CO2 is primarily involved in autoregulation of cerebral vasculature).
2. Hypertonic fluids
   1. Mannitol 20% 1-1.5g/kg rapid IV bolus (no need for central line) OR
   2. 23% Na 30mL over 15 minutes (Needs central line)
3. Consult Neurosurgery (urgent) for possible evacuation or ventricular drainage.
   1. This is especially relevant for mass lesions causing mass effect or in hydrocephalus.

• 3rd (Intervention- long term)

1. Hypertonic fluid maintenance
   1. Iatrogenic hypernatremia. Use 3% NaCl to maintain na >145 with q6hr serum Na cks.
      1. 3%NS at 1mL/kg/hr appropriate (typically start at 50mL/hr).
      2. May continue to push Na > 145, then >150 then >155 prn to manage ICP
         1. Eventually osmotic pressures will equilibrate over days. requiring higher Na values (rationale behind pushing Na slowly upward as needed rather than pushing hypernatremia to maximum).
   2. Iatrogenic hyperosmolar maintenance
      1. Mannitola 20% 0.5g/kg q4 hrsth seurm Osm checks q6hrs. (Goal Osm 300-320 mOsm/L)

• 4th (Intervention - Refractory elevation)

1. Pentobarbital coma
   1. loading dose: 5-20mg/kg bolus then 4mg;kg/hr titrated to burst supression on EEG.
2. Induced hypothermia (32-34deg)
   1. Cooling System (ie. Arctic Sunt, Stryker Medi-Therm)
      1. Must perform surveillance cultures (routine blood culture, UA, CXR) every 48 hours since artificially supressing fever.
   2. Shivering protocol
3. Paralytics
   1. Risk of ICU myopathy/neuropathy with long term use.