The Alphabet Soup The Alphabet Soup of Traumatic Brain of Traumatic Brain InjuryInjury

DefinitionDefinition

Traumatic brain injury Refers to injuries that result directly from impact.

Injuries include contusions, lacerations, brainstem injuries, and diffuse axonal injury

ENA, 2010

Traumatic Brain InjuryTraumatic Brain Injury

Leading cause of death due to trauma

Outcomes are greatly affected by the severity of the initial injury and the time elapsed to definitive care.

Therefore, rapid interfacility transport is crucial.

Holleran, 2010, p. 311

Secondary Brain InjurySecondary Brain Injury

Injuries caused by pathophysiologic processes which add to the primary injury during a delay—such as transferring the patient to a higher level of care

These include expanding hematomas, increasing cerebral oedema, rising ICP and seizures

ENA, 2010

The Key Problem:The Key Problem:

The combination of primary and secondary damage leads to compromised cerebral perfusion (CPP)

HOW IS CEREBRAL HOW IS CEREBRAL PERFUSION PERFUSION SUPPOSED SUPPOSED TO TO FUNCTION?FUNCTION?

(OR, How is the (OR, How is the alphabet soup alphabet soup supposed to look?)supposed to look?)

Normal Volume Normal Volume RelationshipsRelationships

• Contents of the skull are:–Cerebrospinal fluid (150 ml)

–Blood (1400 ml) –Brain tissue (1400 ml)

Holleran, 2010, p. 387

Skull ContentsSkull Contents

Brain Tissue

Venous Blood

ArterialBlood

CSF

Cerebral Blood Flow Cerebral Blood Flow AutoregulationAutoregulation

Arterial blood flow and volume is controlled by the autoregulation process◦Cerebral arteries constrict when systemic

BP rises or when PaCO2 decreases and PaO2 increases

◦Cerebral arteries dilate when systemic BP falls or when PaO2 decreases and PaCO2 increases

The brain has the ability to maintain constant blood flow with arterial pressures between 60 and150mmHg (MAP)

Holleran, 2010, p. 389

Pressure-Volume Pressure-Volume Relationships with Acute Relationships with Acute Brain Injury Brain Injury

• Any increase in the volume of one of the components within the skull without a decrease in the volume of the other two results in increased pressure

Holleran, 2010, p. 387

Autoregulation FailureAutoregulation Failure

As ICP increases, autoregulation fails, and CBF (cerebral blood flow) decreases, resulting in decreased tissue perfusion and ischaemia.

Decreased perfusion leads to cerebral hypoxia, which disrupts cellular metabolism and the blood-brain barrier

This leads to further cerebral oedema through fluid leaking from capillaries into brain tissue

ENA, 2010

Normal Cerebral PerfusionNormal Cerebral Perfusion

Brain receives about 15 to 35% of cardiac output

Goal is to maintain a cerebral perfusion pressure (CPP) between 70 and 90 mmHg

ENA, 2010

What’s so important about What’s so important about CPP?CPP? Brain lacks metabolic reserves and depends on arterial flow (cerebral perfusion) to meet it’s needs

Factors that influence CPP include: PaO2, PaCO2, cerebral blood volume, systemic BP, cerebral oedema and ICP.

ENA, 2010

Calculating Cerebral Calculating Cerebral Perfusion PressurePerfusion Pressure

CPP = MAP – ICP Compare to cardiac preload-afterload calculations:

MAP is like blood going in (preload)

ICP is like resistance to blood flow (afterload)

A Calculation Example:A Calculation Example:MAP = (2xDP)+SP 3

Normal BP: 120/70 2x70 = 140 + 120

= 260 260/3 = 87 MAP

How Do I Measure ICP How Do I Measure ICP Directly?Directly?

ICP monitor into the cranial cavity

Measured in mmHgNormally 7-15 mmHg for a healthy, supine adult

Only available in ICU or sometimes during interfacility transfers

Assessing ICP Without an ICP Assessing ICP Without an ICP MonitorMonitor

Since it isn’t always able to be directly measured in the air transfer environment, ICP may be indirectly assessed by physical findings

How do we assess ICP physiologically?

Signs of Increasing ICPSigns of Increasing ICP Early recognition of increased ICP is vital

to preserving brain function Early warnings: Change in LOC,

irritability, mild confusion, pupillary change and decreased Glasgow Coma Score.

Late: Very difficult to arouse, coma, posturing, fixed pupils or blown pupils and ECG changes, Cushings response Cushing triad is (systolic) hypertension

with widened pulse pressure, bradycardia and respiratory depression.

ENA, 2010

Brain Injury AssessmentBrain Injury Assessment

Level of consciousnessPupil size and reactivity

Cranial nerve activityMotor activityRespiratory pattern

Holleran, 2010, p. 315

Level of ConsciousnessLevel of ConsciousnessAlert – responds readily but may be

confusedLethargic – drowsy but can be arousedObtunded – difficult to arouse, cannot

make a complete sentence, requires repeated stimulation

Stuporous – no verbal response, may moan, responds to pain by moving extremities

Comatose – no evidence of awareness

Holleran, 2010, p. 315

Berry, 1995

Pupil ResponsePupil Response

Cranial nerve IIIInjury to parasympathetic system

dilates pupilsInjury to sympathetic system

constricts pupilsBilateral fixed and dilated pupils

usually indicate global hypoxia or herniation from cerebral oedema

Holleran, 2010, p. 317

Cranial Nerve ActivityCranial Nerve ActivityII Optic nerve

◦“can you see me?”III Oculomotor nerve

◦“look up, look down”, pupil response

XI Spinal accessory nerve ◦“shrug your shoulders”

XII Hypoglossal nerve ◦“stick out your tongue”

Motor ActivityMotor ActivityConscious patient

◦Grip your hands◦Push feet against your hands

Unconscious patient◦Motor activity in response to pain Purposeful withdrawal General extremity movement

Holleran, 2010, p 317

Respiratory PatternRespiratory PatternInitial hypoventilationCheyne-stokes (crescendo-de-

crescendo)Brainstem lesions – irregular,

shallow, slowing rateMedullary lesions – respiratory

paralysisCentral neurogenic

hyperventilationHolleran, 2010, p 318

Berry, 1995

Treatment of Increased Treatment of Increased ICPICP

Keep head midline with HOB elevated to 45°

Decrease stimulation Administer Mannitol or Frusemide

per order Sedate (neuromuscular blockades/

barbiturates): decreases the metabolic rate

Temperature control

ENA, 2010

Other Possible In-flight Other Possible In-flight InterventionsInterventions

• IV fluids to maintain BP over 90 systolic to perfuse brain

• Treat seizures as needed• Continue ventilation with 100% O2

to oxygenate brain • Initial (only) hyperventilation, to

lower ICP• Prolonged hyperventilation not

recommended unless:–Dilated pupils or Extensor posturing

Holleran, 2010, p 320

Conclusion - Alphabet Conclusion - Alphabet SoupSoup

Brain trauma (CHI) happensMaintaining cerebral perfusion

(CPP) is the goalCerebral oedema (ICP)

compromises cerebral perfusionAssessment for cerebral oedema

(PERL, LOC, GCS, RR)Treatment for cerebral oedema

(BP, O2, IV)

ReferencesReferences

Berry, S. (1995). I’m still not an ambulance driver. S. Berry, Publisher.

Emergency Nurses Association. (2010). http://www.ena.org/ coursesandeducation/CATNII-ENPC-TNCC/tncc/Pages/Default.aspx

Holleran, R. (2010). ASTNA Patient transport principles and practice (4th Edition). Mosby. St. Louis, Missouri.