Head injury is a major cause of preventable death and disability in the Western world among adults younger than 45 years of age and carries a large cost in terms of manpower, resources and human suffering. The aims of those involved in the management of head injuries must be:
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to prevent or reduce the number of head injuries.
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to provide optimal care for those who suffer a head injury, and prevent secondary brain injury from further compounding primary brain injury.
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to produce an optimal environment in which rehabilitation from head injury can occur.
This chapter discusses the causes and mechanisms of head injury, the associated pathophysiology, the grading of the severity of injury, and the management of minor, moderate, and severe head injuries.
Epidemiology of Head Injury
About 200 of every 100,000 individuals in the Western world suffer a head injury each year. These range from a minor knock on the head without loss of consciousness or lasting neurological sequelae to a extremely severe head injury that leads directly to death. Collection of accurate data about the cause and seriousness of head injuries is difficult in the United Kingdom for several reasons :
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Many head injuries are minor and are unreported to medical attendants.
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Many head injuries are part of a spectrum of serious injuries sustained during polytrauma and are classified as such.
A number of different classifications of head injury exist, and are not directly comparable, leading to difficulties with aggregation or comparison of data.
Most epidemiological studies have therefore had to rely on a classification based on eventual management of the patient, which within the United Kingdom is usually split into:
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seen in the emergency department but not admitted
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admitted for observation
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transferred to a regional neurosurgical unit
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operated on in a neurosurgical unit
Clearly, this categorization does not include those patients with very severe injuries who die before reaching the hospital nor those with apparently insignificant head injuries who do not seek medical attention. Additional confounding factors include differences in the management of head injuries among different neurosurgical units: Some units transfer most or all patients with serious head injuries, whereas others elect to manage at a distance those for whom neurosurgical intervention is not indicated.
Most head injuries result from falls, vehicular accidents, pedestrian road accidents, or assaults. Cause of accident varies among different age groups. Young children and the elderly are most commonly injured by falls, whereas young men are more commonly victims of assault. Sports and other leisure activities are also an increasingly important cause of head injury.
Two peaks are observed in the incidence of death after head injury: in patients between 10 and 30 years of age and in those older than 70 years of age. Hospital admission rates follow a similar pattern. Men have a higher incidence of mortality and hospital admission after head injury than women do, and more patients with head injuries related to assault are admitted on weekends. Outcome following head injury has been demonstrated to be poorer in the elderly, deprived and in various racial/ethnic population groups.
Alcohol is undoubtedly an important factor in head injury in Western societies. In studies in which the influence of alcohol was assessed, high blood alcohol levels were associated with assault and road traffic accidents.
As a consequence of research on the causes of head injury, many Western countries have introduced legislation to enforce the wearing of seat belts and motorcycle crash helmets and to reduce vehicle speed limits, as well as controls on alcohol consumption by drivers. These preventive measures have contributed to a downward trend in the number of severe head injuries. However, in the developing world, an increasing number of head injuries are occurring as road traffic increases.
Measurement of Injury Severity and Outcome
Glasgow Coma Scale
The Glasgow Coma Scale (GCS) is the instrument most widely used to assess consciousness after a head injury. Before its development, a series of loosely defined terms such as obtunded, lethargy, stupor, and coma were used to categorize the degree of unconsciousness.
A standardized method for scoring the level of consciousness, such as the GCS, is important in the management of head injuries for several reasons. A substantial number of head-injured patients present to hospitals that do not have resident neurosurgical support. A standardized scale of consciousness, together with image linking of the computed tomographic (CT) scan, allows a rapid evaluation of the severity of injury by the neurosurgeon and a swift decision as to whether transfer to the neurosurgical unit is required. The GCS also has been shown to have prognostic value regarding the eventual outcome of the injury.
The development of the GCS permitted reliable and reproducible assessment with little interobserver variability across all classes of health care workers. The actual level of consciousness and the deterioration in that level are more clearly identifiable when regular GCS assessments are performed.
The GCS consists of three parts: a motor response, a verbal response, and an eye response. The motor component responses are given in Table 4-1 . The motor response is scored as the best limb response. Failure of the patient to obey commands requires the observer to determine the patient’s response to a painful stimulus—pressure on the supraorbital nerve or on the nailbed (see Table 4-1 ). Usually, the best response is elicited in the upper limbs. An asymmetrical response indicates a focal lesion of the central nervous system.
| Action | Description | Score |
|---|---|---|
| Obeys command | Obeys spoken command | 6 |
| Localizes pain applied in area of sensation supplied by cranial nerves | Brings arm (or arms) up to stimulus | 5 |
| Withdrawal | Purposeful withdrawal from nailbed painful stimulus | 4 |
| Flexion | Flexion of the elbow on nailbed painful stimulus | 3 |
| Extension | Extension of the elbow on nailbed painful stimulus | 2 |
| None | No motor response to adequate painful stimulus | 1 |
The verbal response is assessed as indicated in Table 4-2 . Lack of a verbal response in an otherwise awake patient usually indicates damage to the speech center. The eye response ( Table 4-3 ) assesses the integrity of the brain’s arousal mechanisms. The eye response to pain should be elicited by limb stimulus, because reflex eye opening may occur with facial stimulation. Also vital are the pupillary response to light and pupillary size; these should be assessed along with the GCS score in head-injured patients.
| Speech | Description | Score |
|---|---|---|
| Oriented | Knows place, time, location | 5 |
| Confused | Talks in sentences but does not know place, time, location | 4 |
| Words | Answers in words | 3 |
| Sounds | Utters incomprehensible sounds | 2 |
| None | No speech | 1 |
| Eye Opening | Stimulus | Score |
|---|---|---|
| Spontaneously | Eyes open normally | 4 |
| To speech | Eyes open only to speech | 3 |
| To pain | Eyes open only to pain | 2 |
| None | No eye opening | 1 |
The severity of a head injury is usually classified according to the best post-resuscitation GCS. A minor head injury has a GCS score of 15; a mild injury, 13 or 14; a moderate injury, between 9 and 12; and a severe head injury, between 3 and 8. Coma is defined as inability to obey commands, no intelligible speech, and no eye opening (M5 V2 E1). This classification is used to guide management and is prognostic of the eventual outcome.
Glasgow Outcome Scale
To compare outcomes after a head injury and the beneficial effects (or otherwise) of interventions during the management of head injury, a standardized outcome measure must be used. The Glasgow Outcome Scale (GOS) was developed to measure global brain functioning rather than to specifically assess a particular mental or physical outcome.
Improvement often occurs up to 6 months after head injury and may continue to occur for 1 to 2 years, so assessment of outcome should not be performed before 6 months after the injury.
The GOS assesses outcome based on the level of dependence or independence of the patient. There are five possible outcomes ( Table 4-4 ).
| Category | Description | Score |
|---|---|---|
| Good outcome | Resumption of normal life despite minor neurological/psychological deficits | 5 |
| Moderate disability (disabled but independent) | Independent in daily life, but often significant disability remains (e.g., dysphasia, hemiparesis, cognitive dysfunction) | 4 |
| Severe disability (conscious but disabled) | Such patients are dependent on support for physical or mental activities | 3 |
| Persistent vegetative state | This is a difficult diagnosis; such patients often remain unresponsive after brain injury and may develop sleep-wake cycles | 2 |
| Death | 1 |
Good recovery implies that the patient is able to resume his or her previous employment; neurological sequelae may exist, but the patient is able to maintain an independent existence. Moderate disability indicates that the patient is independent at home and can travel by public transport, but often there are significant persisting physical or mental neurological deficits. A patient with a severe disability is conscious but is dependent on the assistance of another person each day. Persistent vegetative state (PVS) allows normal respiration and sleep-wake states. A patient with PVS may occasionally follow a moving object or look toward a bright light or loud sound and also withdraws from a painful limb stimulus. The final category is death. The scale is often abbreviated by dividing outcomes into favorable (good recovery and moderate disability) and unfavorable (severe disability, PVS, and death).
As with the GCS, criticisms can be made that the GOS is too global an assessment; that a significant disability, either mental or physical, can exist despite an apparently favorable outcome; and that different levels of recovery are required to return to professional or managerial employment versus manual work, which may alter the outcome category.
Measurement of Injury Severity and Outcome
Glasgow Coma Scale
The Glasgow Coma Scale (GCS) is the instrument most widely used to assess consciousness after a head injury. Before its development, a series of loosely defined terms such as obtunded, lethargy, stupor, and coma were used to categorize the degree of unconsciousness.
A standardized method for scoring the level of consciousness, such as the GCS, is important in the management of head injuries for several reasons. A substantial number of head-injured patients present to hospitals that do not have resident neurosurgical support. A standardized scale of consciousness, together with image linking of the computed tomographic (CT) scan, allows a rapid evaluation of the severity of injury by the neurosurgeon and a swift decision as to whether transfer to the neurosurgical unit is required. The GCS also has been shown to have prognostic value regarding the eventual outcome of the injury.
The development of the GCS permitted reliable and reproducible assessment with little interobserver variability across all classes of health care workers. The actual level of consciousness and the deterioration in that level are more clearly identifiable when regular GCS assessments are performed.
The GCS consists of three parts: a motor response, a verbal response, and an eye response. The motor component responses are given in Table 4-1 . The motor response is scored as the best limb response. Failure of the patient to obey commands requires the observer to determine the patient’s response to a painful stimulus—pressure on the supraorbital nerve or on the nailbed (see Table 4-1 ). Usually, the best response is elicited in the upper limbs. An asymmetrical response indicates a focal lesion of the central nervous system.
| Action | Description | Score |
|---|---|---|
| Obeys command | Obeys spoken command | 6 |
| Localizes pain applied in area of sensation supplied by cranial nerves | Brings arm (or arms) up to stimulus | 5 |
| Withdrawal | Purposeful withdrawal from nailbed painful stimulus | 4 |
| Flexion | Flexion of the elbow on nailbed painful stimulus | 3 |
| Extension | Extension of the elbow on nailbed painful stimulus | 2 |
| None | No motor response to adequate painful stimulus | 1 |
The verbal response is assessed as indicated in Table 4-2 . Lack of a verbal response in an otherwise awake patient usually indicates damage to the speech center. The eye response ( Table 4-3 ) assesses the integrity of the brain’s arousal mechanisms. The eye response to pain should be elicited by limb stimulus, because reflex eye opening may occur with facial stimulation. Also vital are the pupillary response to light and pupillary size; these should be assessed along with the GCS score in head-injured patients.
| Speech | Description | Score |
|---|---|---|
| Oriented | Knows place, time, location | 5 |
| Confused | Talks in sentences but does not know place, time, location | 4 |
| Words | Answers in words | 3 |
| Sounds | Utters incomprehensible sounds | 2 |
| None | No speech | 1 |
| Eye Opening | Stimulus | Score |
|---|---|---|
| Spontaneously | Eyes open normally | 4 |
| To speech | Eyes open only to speech | 3 |
| To pain | Eyes open only to pain | 2 |
| None | No eye opening | 1 |
The severity of a head injury is usually classified according to the best post-resuscitation GCS. A minor head injury has a GCS score of 15; a mild injury, 13 or 14; a moderate injury, between 9 and 12; and a severe head injury, between 3 and 8. Coma is defined as inability to obey commands, no intelligible speech, and no eye opening (M5 V2 E1). This classification is used to guide management and is prognostic of the eventual outcome.
Glasgow Outcome Scale
To compare outcomes after a head injury and the beneficial effects (or otherwise) of interventions during the management of head injury, a standardized outcome measure must be used. The Glasgow Outcome Scale (GOS) was developed to measure global brain functioning rather than to specifically assess a particular mental or physical outcome.
Improvement often occurs up to 6 months after head injury and may continue to occur for 1 to 2 years, so assessment of outcome should not be performed before 6 months after the injury.
The GOS assesses outcome based on the level of dependence or independence of the patient. There are five possible outcomes ( Table 4-4 ).
| Category | Description | Score |
|---|---|---|
| Good outcome | Resumption of normal life despite minor neurological/psychological deficits | 5 |
| Moderate disability (disabled but independent) | Independent in daily life, but often significant disability remains (e.g., dysphasia, hemiparesis, cognitive dysfunction) | 4 |
| Severe disability (conscious but disabled) | Such patients are dependent on support for physical or mental activities | 3 |
| Persistent vegetative state | This is a difficult diagnosis; such patients often remain unresponsive after brain injury and may develop sleep-wake cycles | 2 |
| Death | 1 |
Good recovery implies that the patient is able to resume his or her previous employment; neurological sequelae may exist, but the patient is able to maintain an independent existence. Moderate disability indicates that the patient is independent at home and can travel by public transport, but often there are significant persisting physical or mental neurological deficits. A patient with a severe disability is conscious but is dependent on the assistance of another person each day. Persistent vegetative state (PVS) allows normal respiration and sleep-wake states. A patient with PVS may occasionally follow a moving object or look toward a bright light or loud sound and also withdraws from a painful limb stimulus. The final category is death. The scale is often abbreviated by dividing outcomes into favorable (good recovery and moderate disability) and unfavorable (severe disability, PVS, and death).
As with the GCS, criticisms can be made that the GOS is too global an assessment; that a significant disability, either mental or physical, can exist despite an apparently favorable outcome; and that different levels of recovery are required to return to professional or managerial employment versus manual work, which may alter the outcome category.
Physiology of Head Injury
An understanding of the concepts of cerebral blood flow, cerebral perfusion pressure, and intracranial pressure is essential to comprehend the pathophysiology and management of head injury.
Cerebral Blood Flow, Intracranial Pressure, and Cerebral Perfusion Pressure
The brain receives approximately one fifth of the total cardiac output—about 1 L/min at rest. This is equivalent to a mean cerebral blood flow (CBF) in gray matter of 49 mL per 100 g of brain per minute. The brain has little capacity to store either glucose or oxygen and is therefore dependent on continuous blood flow. Reduction in CBF to between 25 and 39 mL/100 g/min causes confusion and sometimes loss of consciousness. Reduction to 15 mL/100 g/min causes loss of measurable neuronal electrical activity, and flow of less than 8 mL/100 g/min causes neuronal death.
Cerebral Blood Flow
The flow (Q) of a Newtonian fluid through a rigid vessel is described by Poiseuille’s equation:
where r is the radius, µ is the viscosity of the fluid, and L is the length of the pipe. Clearly in the physiological situation, the pressure gradient and the blood vessel diameter have important effects on CBF. The pressure gradient is known as the cerebral perfusion pressure (CPP) and is usually calculated as follows:
Intracranial Pressure
The Monro-Kellie principle states that because the skull is a rigid structure and the skull contents of brain, cerebrospinal fluid (CSF), and blood are incompressible, an increase in any one or several of these, or development of a mass lesion such as a hematoma, will cause an increase in ICP.
Measurement of Intracranial Pressure
ICP can be measured by inserting a pressure transducer into the ventricular system, into the subarachnoid space, subdurally, or intraparenchymally. The “gold standard” measurement is that of ventricular pressure. The pressure is normally measured in centimeters of water relative to the foramen of Munro. Normal adult ICP ranges from 0 to 15 cm H 2 O.
Autoregulation
Autoregulation is defined as maintenance of a constant CBF over a range of CPPs. Constant CBF is maintained through variation in arterial diameter: The arterial diameter increases when the CPP falls and decreases when the CPP increases.
When the autoregulatory mechanism is exhausted or deficient, as may be the case after head injury, the CBF is dependent on the CPP and, consequently, on the blood pressure. Low blood pressure therefore decreases the CBF, and cerebral ischemia occurs as the CPP falls below 50 mm Hg. After brain injury, loss of autoregulation is usually patchy within the brain, and some areas retain normal autoregulation. Flow “steal” may then occur when blood vessels in normally functioning areas of brain dilate and therefore have a lower cerebrovascular resistance than the blood vessels in the abnormal area of brain.
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