ICP AND MANAGEMENT
July 2014
OUTLINE
• Intracranial contents
• Monroe-Kellie Doctrine
• ICP monitors and waveforms
• Calculate cerebral perfusion pressure
• Types of edema and Herniation Syndromes
• Management of ICP
VAULT CONTENTS
Blood
10%
Other
1%
CSF
10%
Brain
79%
MONROE-KELLIE DOCTRINE
• An increase in the volume of any of the contents
within the intracranial vault must be met with a
decrease in the volume of another or the intracranial
pressure will increase
• V (vault)= V (CSF) + V (brain) + V (blood) + V (other)
INTRINSIC COMPENSATORY MECHANISMS
• Brain- none
• CSF- redistributed into compliant
paraspinal CSF space
• Blood- venous blood forced into
internal jugular veins
• When compensatory mechanisms are
exhausted, ICP rises more rapidly
CBF VIA AUTO-REGULATION
Maximally Dilated
Ischemia
Ischemia,
disrupted
BBB, inc
ICP
• Maintains CBF via auto-regulation over
wide range of MAP by altering
resistance of cerebral blood vessels
• This insures supply of oxygen and
metabolic substrates to neurons are
unaltered
• ICP > 20 has been shown in both adult
and pediatric studies to be associated
with increased morbidity and mortality
LOSS OF AUTO-REGULATION
• CPP = MAP – ICP
• Minimal CPP is age variant
• Infants 50 mmHg
• Children 60 mmHg
• Adults 70 mmHg
MAINTAINING ADEQUATE BRAIN
OXYGENATION
• Hypoxia results in vasodilation therefore increasing CBF and potentially worsening
ICP
• Another way of maintaining good oxygenation is to attack it from the consumptive
end
• Decrease cerebral metabolism
• Keep patient adequately sedated
• In extreme cases, use a pentobarbital induced coma
ETIOLOGIES OF ELEVATED ICP
• Increased ICP can occur with any CNS pathology that results in a space
• occupying mass lesion, edema (osmotic, vasogenic, cytotoxic), or obstruction to
• CSF flow. Some common etiologies include:
• • Trauma: epidural, subdural bleeds, contusion, hematomas, diffuse axonal
• injury, intraventricular hemorrhage
• • Infection: meningitis, encephalitis, cerebritis
• • VP shunt malfunction
• • Mass lesion: tumors, AVM
• • Metabolic: hepatic encephalopathy, DKA
• • Vascular or embolic disease, stroke with subsequent edema or mass effect
ICP MONITORS AND WAVEFORMS
•
•
Intraventricular monitoring
•
advantage of accuracy, simplicity of measurement, and the
unique characteristic of drainage of CSF.
•
disadvantage is infection, up to 20 percent of patients,
hemorrhage
Intraparenchymal (thin electronic or fiberoptic transducer)
•
Advantages include ease of placement, and a lower risk of
infection and hemorrhage (<1 percent) than with intraventricular
devices
•
Disadvantages include the inability to drain CSF for diagnostic or
therapeutic purposes and the potential to lose accuracy (or
"drift") over several days, since the transducer cannot be
recalibrated following initial placement
WAYS TO DECREASE ICP
• Size of the box
• May increase size of vault with decompressive crainectomy
• Decrease the volume of the contents
• Remove “others”- tumors, crowbars, hematomas, bullets, etc.
• Must decrease volume of one of the components of the intracranial vault
• Brain
• CSF
• Blood
TYPES OF EDEMA
Vasogenic
Interstitial
Cytotoxic
Increased permeability of brain
capillary endothelium leads to edema
and is usually seen around tumors,
abscesses, intracerebral hematomas,
encephalitis & meningitis.
Edema results from increased CSF
hydrostatic pressure and is usually
seen in hydrocephalus or decreased
CSF absorption by arachnoid villi, e.g.
intraventricular hemorrhage.
Neuronal swelling occurs secondary
to cell injury caused by failure of the
ATPase – dependent pump as occurs
in diffuse axonal injury.
Neurons are not primarily injured.
Reduction of this type of edema can
minimize secondary injury
This type of injury is often
irreversible.
5 WAYS TO DECREASE INTRACRANIAL
PRESSURE USING THE MONRO-KELLIE
DOCTRINE
• Enhance venous drainage
• Elevate head 30°
• If in a cervical collar, check fit
• Hyperosmolar therapy
• Hyperventilation
• CSF Drainage
• Decompression
DECOMPRESSIVE CRANIECTOMY
• Done infrequently
• Usually done at an OSH prior to transfer OR in conjunction with hematoma evacuation
• Remember to save the bone flap for reimplantation later
CSF DRAINAGE
• Neurosurgical Procedure
• Always push for an EVD, not just an ICP monitor
• Therapeutic AND diagnostic
• Can stay in long-term (no drift)
• Requires INR < 1.5 and PLTS > 100K
HYPEROSMOLAR THERAPY
• Increase serum osmolality to draw water out of brain parenchyma
• Mannitol
• Decreases bld viscosity
• 0.5 - 1g/kg
• Maximal effect in 10 min, duration 75 min
• 3% Saline (500 mEq/L)
• Osmotic, hemodynamic, vasoregulatory, and immunodmodulatory
• Every 1.5 cc/kg will increase Na by ≈ 1 mEq/L
• Known to have a longer lasting effect
• In general, check Na+ and osmolality q6h
• Target Na2+ 150-160
• Target osmolality > 300
HYPERVENTILATION CAUSES A
DECREASE IN CEREBRAL BLOOD FLOW
• Pic of blood flow with hypervent
• Skippen. Crit Care Med. 1997 Aug;25(8):1402-9
USE OF HYPERVENTILATION
• Worse long-term outcome
• Target normocapnea
•
Works for acute spikes in ICP
• Target pCO2 of about 35
• Avoid hypercapnea
AVOID THE BAD “H”S
• Hypotension
• Hypoxia
• Hyponatremia
• Hypervolemia
• Hyperglycemia
• Hyperthermia
• Hypermetabolism (seizures, agitation)
SUMMARY OF KEY POINTS
• Many of the goals of increased ICP management are based using the Monro-Kellie
Doctrine to our advantage
• Goal ICP < 20 mmHg
• Hyperventilation is not a long-term strategy
• CPP = MAP – ICP; Maintain CPP > 40 mmHg
• Goal Na2+ 150-160
• Avoid the bad “H’s”