Traumatic Head injuries Benjamin W. Wachira - PowerPoint Presentation

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Traumatic Head injuries

Benjamin W. Wachira

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Outline

Basic Sciences –

Mechanism of injury and Physiology of ICP regulation

Independent Predictors of Poor Outcomes

Complications

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Primary Injury

Acute traumatic intracranial injuries include

Primary injury

which occurs during the initial insult, and results from displacement of the physical structures of the brain.

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Secondary Injury

Secondary injury

is defined as post-traumatic insults to the brain arising from

extracranial

sources and intracranial hypertension.

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Cerebral Blood Flow

Brain metabolism is dependent on a constant delivery of oxygen and glucose as well as the removal of "waste" products through a constant

Cerebral Blood Flow

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Cerebral Blood Flow

Cerebral blood flow is equal to the cerebral perfusion pressure (CPP) divided by the cerebrovascular resistance (CVR): CBF = CPP / CVR

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Cerebral Perfusion Pressure

Cerebral perfusion pressure (CPP) is defined as the difference between mean arterial and intracranial pressures. 

The Brain Trauma Foundation now recommends that the CPP target after severe TBI should lie between 50–70mmHg.

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Intracranial Pressure

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Clinical Correlate

A reasonable estimate of CPP can be made in head injured patients who are not sedated:

Drowsy and confused: (GCS 13-15)ICP=20 mmHg,

Severe brain swelling (GCS <8) ICP=30 mmHg

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Clinical Correlate

Thus in a confused, restless and drowsy patient It would be reasonable to estimate his ICP to be 20 mmHg.

A drop in SBP to 80 mmHg drops MAP to 65 mmHg and therefore CPP falls to less than 45 mmHg.

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Cerebral Vascular Resistance

CVR is controlled by four major mechanisms:

Pressure autoregulation

Chemical control (by arterial pCO

2

 and pO

2

)

Metabolic control (or 'metabolic autoregulation')

Neural control

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Pressure Autoregulation

In the normal brain, when the MAP is between 60 and 150 mm Hg, cerebral vessels work to maintain desirable CBF through their ability to constrict and dilate. This is termed

“autoregulation.”

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cont…

When the MAP is less than 50 mm Hg or greater than 150 mm Hg, the arterioles are unable to autoregulate and blood flow becomes entirely dependent on the blood pressure, a situation defined as

pressure-passive flow.

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Vasodilatory Cascade

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cont..

This process can only be broken by increasing the blood pressure to raise CPP, inducing the vasoconstriction cascade.

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Vasoconstriction Cascade

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Chemical Control

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Neuronal Control

Cushing Reflex - is a hypothalamic response to ischemia, usually due to poor perfusion in the brain.

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cont…

The ischemia activates the sympathetic nervous system, causing an increase in the heart's output by increasing heart rate and contractility along with peripheral constriction of the blood vessels.

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cont…

The increased blood pressure also stimulates the baroreceptors (pressure sensitive receptors) in the carotids, leading to an activation of the parasympathetic nervous system, which slows down the heart rate, causing the bradycardia

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Cerebral Vascular Resistance

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Mechanisms of Secondary Brain Injury

Mechanisms that lead to secondary brain injury are:

Hypoxia

Hypotension

Increased intracranial pressure

Hypercarbia

Acidosis

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Hypoxia

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Hypotension

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Raised Intracranial Pressure

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Brain Herniation

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Signs of Herniation

GCS of three to five.

Abnormal posturing - a characteristic positioning of the limbs indicative of severe brain damage.

One or both pupils may be dilated and fail to constrict in response to light.

Vomiting can also occur due to compression of the vomiting center in the medulla oblongata.

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Medical Therapy For Increased ICP

The indication for treatment of elevated ICP with hyperosmolar therapy is for short-term treatment while further diagnostic procedures (CT scan of the brain) and interventions (such as treatment of mass lesion found on CT scan) are performed.

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Medical Therapy For Increased ICP

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Hypercarbia

Hypercarbia

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Hyperventilation to Reduce ICP

Thus hyperventilation can lead to a mean reduction in intracranial pressure of about 50% within 2-30 minutes.

When PaCO

2

 is less than 25 mmHg (3.3kPa) there is no further reduction in CBF.

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Hyperventilation to Reduce ICP

Acute hypocapnic vasoconstriction will only last for a relatively short time (5 hours) due to a gradual increase in CBF towards control values leading to cerebral hyperaemia (over-perfusion) if the PaCO

2

 is returned rapidly to normal levels

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Contributing Events In The Pathophysiology Of Secondary Brain Injury

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Independent Predictors of Poor Outcome

Age

Head CT intracranial diagnosis

Pupillary reactivity

Post-resuscitation GCS

Presence or absence of hypotension.

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1. Age

There is an increasing probability of poor outcome with increasing age, in a stepwise manner with a significant increase above 60 years of age.

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2. Head CT Intracranial Diagnosis

Initial CT examination demonstrates abnormalities in approximately 90% of patients with severe head injury.

Prognosis in patients with severe head injury with demonstrable pathology on initial CT examination is less favorable than when CT is normal.

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2. Head CT Intracranial Diagnosis

Individual CT characteristics found to be particularly relevant in terms of prognosis were:

Compressed or absent basal cisterns measured at the midbrain level.

tSAH

Blood in the basal cisterns

Extensive tSAH

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2. Head CT Intracranial Diagnosis

Individual CT characteristics found to be particularly relevant in terms of prognosis were:

Presence and degree of midline shift at the level of the septum pellucidum

Presence and type of intracranial lesions

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3. Head CT Intracranial Diagnosis

Marshall Classification of Diffuse Brain Injury

Grade 1 = normal CT scan (9.6% mortality)

Grade 2 = Basal cisterns present, shift < 5mm (13.5% mortality)

Grade 3 = Basal cistern compressed/ absent, shift <5mm (34% mortality)

Grade 4 = Shift > 5mm (56.2% mortality)

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4. Pupillary Reactivity

The parasympathetic, pupilloconstrictor, light reflex pathway mediated by the third cranial nerve is anatomically adjacent to brainstem areas controlling consciousness.

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4. Pupillary Reactivity

Pupillary size (<4mm) and light reflex (>1 mm) are indirect measures of dysfunction to pathways subserving consciousness and, thus, an important clinical parameter in assessing outcome from traumatic coma.

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5. Post-Resuscitation GCS

If the initial GCS score is reliably obtained and not tainted by

prehospital

medications or intubation, approximately 20% of the patients with the worst initial GCS score will survive and 8%-10% will have a functional survival.

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6. Presence or Absence of Hypotension

A systolic blood pressure less than 90 mm Hg was found to have a 67% PPV for poor outcome and, when combined with hypoxia, a 79% PPV.

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6. Presence or Absence of Hypotension

A single episode of hypotension (SBP <90 mm Hg) is associated with doubling of mortality and increased morbidity when compared to similar patients without hypotension.

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Complications

Skull base fracture – CSF leak

Depressed skull fractures – infection risk

Pneumocephalus

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Complications

Traumatic subarachnoid haemorrhage

Chronic subdural haematoma

Epilepsy

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Complications

Hydrocephalus

Cranial nerve trauma

Concussion

Post-traumatic encephalopathy after repeated injury

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Summary

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References

An Evidence-Based Approach To Severe Traumatic Brain Injury – Emergency Medicine Practice; December 2008 Volume 10, Number 12

Head Injury - A Multidisciplinary Approach;

Edited by Peter C. Whitfield Consultant Neurosurgeon and Honorary Clinical Senior Lecturer South West Neurosurgery Centre Derriford Hospital Plymouth Hospitals NHS Trust Plymouth, UK