Management of Increased Intracranial Pressure

William M. Coplin, M.D., F.C.C.M.

Departments of Neurology and Neurological Surgery

Wayne State University School of Medicine

ICP

• Intracranial pressure is a process, not an event

• There are several pathophysiological mechanisms involved in intracranial pressure

• There are basic strategies for treatment

Increased ICP

• Pathophysiology– Acute neurological condition alters equilibrium of

components within cranial vault• Causes– Primary– Secondary

• Regardless of cause, ICP decreases cerebral perfusion, stimulates further swelling, and may cause herniation

ICP - Pathophysiology

• Intracranial pressure is a process, not an event!– Secondary injury can be more damaging than

primary injury• Main mechanisms of increased intracranial pressure– Trauma• Contusion• Diffuse axonal injury

– Stroke–Mass (tumor, hematoma…)– Edema (brain swelling)

Increased ICP andCushing’s Response

ICP – Understanding Determinants of Intracranial Pressure

• Volume of intracranial vault =• Intracranial contents– 80% brain tissue– 10% blood– 10% cerebrospinal fluid

• Increase in volume of any of these contents may cause increased intracranial pressure– Brain can swell (edema)– Extravascular blood can accumulate because of hemorrhage– Cerebrospinal fluid can accumulate from blocked outflow

ICP – Key Concept #1

• The cranial vault is a fixed volume• Bone does not expand• Cranial vault also contains blood and CSF• These components usually in state of equilibrium and

produce ICP– Usually measured in lateral ventricles– Normal pressure 10 to 20 mm Hg

Monro-Kellie Hypothesis

• “…because of the limited space for expansion within the skull, an increase in any one of the components causes a change in the volume of the others.”

• What does this mean?

ICP – Understanding Physics of Intracranial Pressure

Intracranial pressure rises as brain + blood + CSF volume increases

Decreased Cerebral Blood Flow

• What happens to brain cells as blood flow decreases?• Early compensatory mechanism:– Vasomotor stimulation• Assessment findings indicate this

• Changes in concentration of CO2

– causes cerebral vasodilation– causes vasoconstriction

• Decreased cerebral outflow

Increased ICP: Clinical Manifestations

Early Indicators

• Subtle changes in LOC• Pupillary changes• Weakness of one

extremity or one side• Constant headache

increasing in intensity and aggravated by movement or straining

Late Indicators

• Continuing decrease in LOC progressing to coma

• Bradypnea, bradycardia, hypertension, and fever

• Altered respiratory pattern• Projectile vomiting• Hemiplegia, “decorticate”

(flexor), or “decerebrate” (extensor) posturing

• Loss of brainstem reflexes

Cerebral Perfusion Pressure

• What is cerebral perfusion?

• Steady cerebral perfusion can be maintained if arterial mean pressure is ~50-150 mm Hg and ICP is below 40 mm Hg

• CPP = MAP – ICP

• Normal CPP is 70-100 mm Hg

ICP – Understanding Physics of Intracranial Pressure

This patient has dangerously high intracranial pressures, which increase likelihood of morbidity and mortality

ICP

CPP

ICP – Key Concept #2

• There is only one way out of cranial vault• Opening at base of skull known as foramen magnum

ICP – Key Concept #3

• When brain is squeezed through foramen magnum (herniation), brainstem is compressed, patient stops breathing, and patient dies

Causes of ICP: Epidural Hematomas

Example of epidural hematoma on CT scan on patient's left side, obviously of traumatic origin; this patient has soft tissue damage and fractured skull

Causes of ICP: Subdural Hematomas

Example of subdural hematoma on CT scan on patient's left side. Lesion extends for considerable distance over surface of hemisphere: note shift of midline

Causes of ICP: Swelling

Observe swelling (darker tissue) on brain CT scan of 37-year-old victim of pneumococcal meningitis

Cerebral Edema

• What is it?

• What is role of autoregulation in control of cerebral edema?

Causes of ICP: Swelling

Observe diffuse swelling (yellow-green tissue) and expansion of brain tissue

Causes of ICP: Swelling

Observe widening and flattening of gyri on brain surface

Cerebral Edema

• What is it?

• What is role of autoregulation in control of cerebral edema?

1501251007550250

0

25

50

75

Cerebral Perfusion Pressure (mm Hg)

Cer

ebra

l Blo

od F

low

(m

l/10

0 g/

min

)

Autoregulation AutoregulationBreakthrough

VasodilatoryCascade

PassiveCollapse

0

25

50

ICP

(m

m H

g)

From Rose JC, Mayer SA. Neurocrit Care. 2004;1:287-299.

Hypertension Can Drive ICP Elevations

100 200

normotensive

chronic hypertensive

Mean arterial pressure (mm Hg)

Cerebral Blood Flow

Increasing risk of hypertensive

encephalopathy

Increasing risk of ischemia

Adapted with permission from Varon J, Marik PE. Chest. 2000;118:214-227.

50 150 250

Patients with chronic hypertension autoregulate cerebral blood flow

around higher set points

Chronic HTN AffectsCBF Autoregulation

100 200

normotensive

chronic hypertensive

Mean arterial pressure (mm Hg)

Cerebral Blood Flow

Increasing risk of hypertensive

encephalopathy

Increasing risk of ischemia

50 150 250

Patients with cerebral ischemia lose their ability to autoregulate

ischemia

Adapted with permission from Varon J, Marik PE. Chest. 2000;118:214-227.

Autoregulation of CBFAffected by Ischemia

Medical Management

• Increased ICP is a true medical emergency• Initiate treatment promptly– Invasive monitoring of ICP–Manipulating one or more cranial vault component• Decrease cerebral edema• Maintain cerebral perfusion• Reduce CSF and intracranial blood volume

– Controlling fever–Maintaining oxygenation– Reducing metabolic demands

ICP: Basic Principles ofClinical Management

• Monitor intracranial pressure (invasively) and intervene to lower ICP when necessary– Elevate head of bed– Medications to decrease swelling– Decrease brain activity to reduce blood delivery and swelling “medically

induced coma”– Hypothermia– Surgical decompression when risk for herniation high

• Seizure prophylaxis?– Seizures occur in ~26% of severe TBI patients, with ~50% occurring within

first 24 hours

• Other priorities– Adequate nutrition, correction of electrolyte abnormalities, strict control of

blood sugar, strict temperature regulation…

Complications

• Brain stem herniation• Diabetes insipidus• Syndrome of inappropriate ADH (SIADH)

• Cause of these complications– Hypothalamic

• Treatment– DI: volume replacement and water replacement– SIADH: adequate volume with water restriction

ICP - Prognosis

• Effect of ICP– Patients with mean ICP > 20 mmHg during

hospitalization• 47% mortality vs.

– Patients with mean ICP < 20 mmHg• 17% mortality–(p < 0.001)1

1: Balestreri M, Czosnyka M et al. Impact of intracranial pressure and cerebral perfusion pressure on severe disability and mortality after head injury. Neurocrit Care. 2006,;4(1):8-13

Looking to the Future…

• Will new imaging and/or monitoring technologies lead to advances in patient care?

• Surgical interventions?• Medications to decrease swelling?– Hypertonic saline vs. mannitol?

• Decrease brain activity– Sedation and analgesia– Anticonvulsants?– “Medically induced coma”?

• Hypothermia?

Thank You