Types of Head Injury & prevention during Emergency

Head injuries cause approximately 50% of deaths resulting from trauma and are the commonest cause of subsequent life-long disability.

Primary brain damage occurs directly as a result of the trauma done to the brain at the time of the injury. This is instantaneous and irreversible.

Secondary brain damage occurs as the result of subsequent events such as hypoxia and raised intracranial pressure (ICP). Secondary brain damage is potentially preventable appropriate treatment.

Parts of Human Skull

GENERAL ANATOMY OF THE HEAD

The head contains the most important organ in the body, the brain, and receptors for the five major senses, sight, sound, smell, taste and touch. The brain is protected by several layers both outside (extracranial) and inside (intracranial) the skull.

The outermost of the protective layers is the SCALP. This word provides a useful mnemonic for remembering the extracranial layers. Proceeding from the outside inwards these are;

Layers of human Scallp

1. Skin, with hair
2. Subcutaneous tissue, which is very vascolar
3. Galea Aponeurotica; a tough, tendinous layer
4. Loose connective tissue, this is the layer of separation in 'scalping' injuries.
   Collections of blood in this layer, subgaleal hematoma, can occur as the result of blunt trauma and can be mistaken for depressed skull fractures 
5. Periosteum, the outer bone layer of the skull.

The skull is a composite of several bones. They form the facial skeleton and the vault which houses the brain. The joints between these bones are called sutures.The base of the vault is complex and has several small openings or foramina to allow passage of the cranial nerves. The largest of these is the foramen magnum.

The brain stem is continuous with the spinal cord and passes through the foramen magnum into the cervical column.

Deep to the skull are three separate layers of fibrous tissue called the meninges.which cover the brain and continue down to protect the spinal cord. Proceeding from the outside inwards the meningeal layers are:

Dura mater

Dura mater a tough fibrous layer which is firmly attached to the internal wal of the vault. Folds in the dura called falxes separate different sections of the brain.The falx cerebri runs front to back and separates the right and left hemispheres of the cerebellum. The tentorium cerebelli separates the cerebral hemispheres from The cerebellum and brain stem. The meningeal arteries are located between the dura and the skull. The dura mater splits in certain places into two separate layers to form venous sinuses, which drain blood from the brain.

Arachnoid mater

Arachnoid mater is a thin transparent membrane on the inside of the dura mater. The space between the arachnoid and pia mater is filled with cerebrospinal fluid (CSF) which bathes and cushions the brain.

Pia mater

Pia mater is a thin vascolar membrane, which firmly adheres to the brain surface.

The brain itself is divided into the cerebrum, cerebellum and brain stem. The cerebrum is the largest section and is formed by the right and left cerebral hemispheres. Each hemisphere has different lobes, which control higher motor and sensory functions. The cerebellum controls balance and coordination. The brain stem consists of the midbrain, pons and medulla. Essential functions such as cardiac output and respiration are controlled at this level.

The cranial nerves arise from the brain itself, The optic nerve is one of these and that crossover between right and left sides at the optic chiasma, exist the orbit to supply the retina in the back of the eye. The vagus nerve is other cranial nerve, which exits through the jugular foramen in the base of the skull. Peripheral nerves arise from the spinal cord.

TYPES OF HEAD INJURY

Head injuries can be blunt or penetrating and open or closed. Damage to the brain can be localised or diffuse. Most head injuries are caused by a movable object, the head, coming into contact with an immovable object, the pavement. windscreen, fist or boot. If the speed of deceleration is significant it is possible for three separate collisions to occur. Firstly the collision of a car with a wall, secondly the collision between the occupant and windscreen, thirdly the brain continues to move forward until its forward motion is stopped by the inside of the skull. The brain can rebound backward hitting the opposite inside of the skull.

This causes the contra coup injury. Damage is seen in the brain diametrically opposite to the site of initial impact.

Scalp Lacerations 

The highly vascolar layer of subcutaneous tissue beneath the scalp bleed profusely when lacerated and sufficient blood can be lost over time to cause hypovolaemic shock.

Skull Fractures 

Closed linear fracture increase the possibility of underlying damage to the brain.

Penetrating fracture or fractures of the base of the skoll which communicate with the sinuses are considered compound fractures and require antibiotic treatment to prevent meningitis. Treatment of depressed skull fractures depends on the exact site of the damage, the degree of depression and risk to underlying structures.

Intracranial Hematoma.

The presence of an expanding intracranial haematoma will cause a rise in intracranial pressure (ICP). For this reason it is important to identity the presence of these, as surgical removal may be lifesaving.

Types of Hematoma

Extradural hematoma are often caused by bleeding from the meningeal arteries. The blood collects in the space outside the dura, between it and the skull.

Subdural haematomas collect between the dura and the arachnoid mater.These can be acute, eg. when they form rapidly after a head injury, or chronic.Chronic subdural hemorrhage is more common in the elderly. The patient may not develop symptoms until several days or weeks after an accident by which time the head injury has been forgotten. Both extradural and subdural haematomas may be improved by surgery.

The significance of extradural haematoma and chronic subdural collections is that they exert their deleterious effects by raising intracranial pressure without underlying intrinsic brain damage and removal is more likely to be beneficial and may be lifesaving.

Subarachnoid hemorrhage can be caused by trauma or spontaneous rupture of an aneurysm of an artery at the base of the brain. Surgery for subarachnoid hemorrhage does not remove the previous bleeding but helps to prevent recurrence.

Bleeding into the substance of the brain itself causes intracerebral hematoma. The earlier surgical evacuation of a hematoma is done the better the outcome is likely to be.

Cerebral Contusions 

This term is used to describe bruising of the brain.

Diffuse Axonal Injury 

This causes primary brain damage and is the result of mechanical forces and energy transfer at the time of impact. The microscopic blood vessels supplying the brain cells are damaged. There is an immediate change of conscious level.

The length and depth of this depends on the severity of damage.

The cervical spine supports the head and the spinal cord is the continuation of the central nervous system for this reason any patient with a significant head injury must be considered to have a neck injury until proved otherwise.

PATHOPHYSIOLOGY OF HEAD INJURIES

Damage to the brain substance increases its oxygen requirements and initiates a response in the surrounding tissue. This causes swelling or oedema of the brain itself. As the skull is a rigid box there is a limit to the volume it can contain. In addition to oedema increasing the volume of the brain the presence of an expanding intracranial haematoma can also compromise the space and the result is a rise in intracranial pressure (ICP). As the arterial blood pressure must be higher than the ICP to allow blood to pursue the brain any tall in BP or rise in ICP reduces the oxygen delivery and so cause greater hypoxia. Hypoxia and adequate blood flow cause a rise in carbon dioxide levels which in turn results in further oedema and increase in ICP. Adequate oxygen therapy is essential to prevent secondary brain damage and deterioration of the patient's condition.

Cerebral perfusion pressure is the mean arterial pressure minus intracranial pressure

PP = MAP - ICP

As one side of the brain begins to swell increasing pressure forces the temporal lobe of the cerebral hemisphere down into the small space between the brain stem and the tentorium cerebelli (tentorial hiatus). The third cranial nerve, the ocolomotor nerve runs in this space, Pressure on the nerve causes the pupil of the eye on that side to become fixed and dilated. If the swelling continues the pressure on the other side will have the same effect. Herniation of the cerebrum through the tentorial hiatus compresses the midbrain which can be fatal.

Increasing pressure then causes the medulla of the brain stem to be forced down through the foramen magnum. A clot forming in the posterior fossa of the skull (containing the cerebellum and medulla) has the same effect.

This is known as 'coning and is a preterminal event.

PRESENTATION OF HEAD INJURIES

Alteration in conscious level is a sign of damage to the brain. Injuries to the scalp and extracranial layers can cause significant bleeding or bruising but it the patient is folly conscious there is less chance of a significant intracranial problem. Head injuries are often associated with alcohol or drugs, which will change the clinical signs, but alteration in conscious level must never be assumed to be solely the resolt of intoxication.

In an unconscious patient a history may be obtained from relatives or bystanders.

The ambulance staff may have the only opportunity to obtain information from the patient before his conscious level deteriorates. The points of an AMPLE history should be covered (Allergies, Medications, Past medical history, Last meal, Event). The mechanism of injury and duration of unconsciousness are part of the event.

Human brain

Assessment of a patient with a head injury begins with the usual ABCD priority.

D for disability is particularly relevant in these patients.

An initial assessment of conscious level can be done using the AVPU system;

1. A = alert and fully orientated
2. V = responding to voice
3. P = responding to pain
4. U = unresponsive

A more detailed assessment Involves an examination to confirm the patient's Glasgow Coma Score. This is not a static state and will change as the patient improves or deteriorates.

GCS as an Indicator of Head Injury Severity

1. GCS 14-15 = mild
2. GCS 9-13 = moderate
3. GCS 3-8 = severe
4. GCS of 8 or less is considered to be coma.

An examination of the head and neck may reveal some additional signs but should not delay the transfer of a seriously injured patient.

Pupils should be checked for their reaction to light. A fixed dilated pupil can indicate rising intracranial pressure. Alcohol and some drugs will alter pupil responses.

Presence of a watery, bloodstained fluid from the nose or ears is the sign of leaking CSF and indicates a fracture of the base of the skull. Bilateral periorbital hematoma, known as racoon or panda eyes and bruising over the mastoid process behind the ear are other signs of base of skull fractures, though they may take time to develop.

Hypotension is not caused by isolated closed head injuries though large scalp lacerations can do so. Hypertension and bradycardia if accompanied by irregolar respiration form "Cushing's triad " which indicates coning and is the result of the brain stem herniating through the foramen magnum.

The combination of the picture of shock and a head injury (even a deteriorating head injury) must imply that other associated injuries producing blood loss are present. Shock, with resulting hypoperfusion can be itself a cause of a deteriorating head injury or the cause of deterioration of any other medical condition (which may have caused the accident in the first place) which can produce rising intracranial pressure.

Fits or Convolsions

Fits Convolsions occurring immediately after a head injury usually last for only a few minutes and provided the airway is maintained, no specific treatment is required.if they are repeated or prolonged, diazepam is indicated.Patients can have a Subsequent life-long tendency to suffer epileptic fits as the result of head injuries, Particolarly those serious enough to involve a tear of the dura mater.

Vomiting

Children very often vomit after a head injury, adults do so less often. The relationship between the severity of vomiting and the severity of the head injury is not clear.

TREATMENT PRINCIPLES

Airway and Breathing

High concentrations of oxygen should be administered to all patients with more than the most minor of head injuries. It is important to check and clear the airway in patients with a reduced conscious level. In patients who are in a coma (GCS equals or less than 8), tracheal intubation will be required to maintain the airway if the patient has no gag reflex. Once intubated, ventilatory support is indicated.

Major airway and chest injuries may require treatment to prevent hypoxia.

Hyperventilation is no longer considered important in pre-hospital management.

Circulation

In order to maintain cerebral perfusion pressure it is essential to maintain blood pressure. Systolic BP shoold be maintained above 90 mmHg by using IV fluids if necessary. Obvious bleeding from the scalp or elsewhere shoold be minimised with pressure dressings. Do not plug the nose or ears even if they are the source of haemorrhage.

Monitoring of Vital Signs

This should be done regolarly. Alterations in respiratory rate may indicate hypoxia. Signs of hypovolemia suggest additional injury in the chest or abdomen if there is no obvious source of bleeding.

Neurological Examination

This should also be repeated and record regularly.

Sedation

Patients with head injuries are often restless and uncooperative. This behaviour can indicate hypoxia and it must not be assumed to be due to intoxication. If the patient develops fits the use of diazepam can be considered. Strong analgesics, particularly opiates, can depress the patient's respiration, conscious level and cause constriction of the pupils and so should be avoided.

Deteriorating Head Injuries

Any head injury where the conscious level is more depressed than that in the aftermath of impact or less than the best level observed since the impact is a deteriorating head injury, and is to be regarded as due to rising intracranial pressure.

It may be due to an intracranial clot developing but, far more commonly, and amenable to out of hospital improvement is a rise in intracranial pressure due to airways obstruction, coughing, gagging and choking, shock and hypoperfusion producing anoxia or hypercarbia due to airways obstruction, impeded or inadequate ventilation.

Cervical Spine Care

Ten percent of patients with significant head injuries have an associated spinal injury. Any patient who is unconscious after a head injury must be assumed to have a spinal Injury and should be immobilised appropriately using a semi-rigid cervical collar and spinal boards with head Immobilisation. The mechanism of injury will indicate the risk involved but it there is any doubt, full spinal immobilisation shoold be applied. Pointers to assist confirming the presumption of associated cord injury are bradycardia with low or normal blood pressure,diaphragmatic breathing or a patient where the responses to pain on assessment/observation are less than might be expected from the degree of alertness (eye opening) or speech.

REMEMBER

1. Establish and secure airway
2. Ensure adequate ventilation with an oxygen concentration as close to 100% as possible 
3. Repeat vital signs and neurological examination regularly
4. Maintain systolic BP above 90 mmHg
5. Assume an associated spinal Injury the patient is unconscious or the mechanism of injury is suggestive
6. Avoid sedation or strong analgesics
7. Do not delay transfer to hospital

EQUIPMENT

Airway and ventilation equipment to allow maximum oxygenation is essential.

The exact spinal immobilisation equipment will vary but it is important to be familiar with the use of what is available.

KEY LEARNING POINTS

1. The anatomy of the head is related to the types of head injuries which occur
2. Appropriate management can reduce secondary brain damage
3. Hypoxia must be prevented
4. An adequate BP must exist to maintain cerebral perfusion pressure
5. Only the minority of head injuries are serious but these are often fatal
6. Alcohol or drugs shoold not be assumed to be the cause of a depressed conscious level on the presence of head injury
7. Spinal Injury shoold be assumed and managed in an unconscious patient