Disclosure
Traumatic brain injury (TBI) continues to be an enormous public health problem, even with modern medicine in the 21st century. Most patients with TBI (75-80%) have mild head injuries; the remaining injuries are divided equally between the moderate and severe categories. The cost to society of TBI is staggering, from both an economic and an emotional standpoint. Almost 100% of persons with severe head injury and as many as two thirds of those with moderate head injury will be permanently disabled and will not return to their premorbid level of function. In the United States, the direct cost of care for patients with TBI, excluding inpatient care, is estimated at more than $25 billion annually. The impact is even greater when one considers that most severe head injuries occur in adolescents and young adults. Frequency: The annual incidence of TBI in the United States has been estimated to be 180-220 cases per 100,000 population. In the United States, with a population of almost 300 million, approximately 600,000 new TBIs occur per year. As many as 10% of these injuries are fatal, resulting in almost 550,000 persons hospitalized annually in the United States with head injuries. Etiology: While various mechanisms may cause TBI, the most common causes include motor vehicle accidents (eg, collisions between vehicles, pedestrians struck by motor vehicles, bicycle accidents), falls, assaults, sports-related injuries, and penetrating trauma. Motor vehicle accidents account for almost half of the TBIs in the United States, and in suburban/rural settings, they account for most TBIs. In cities with populations greater than 100,000, assaults, falls, and penetrating trauma are more common etiologies of head injury. The male-to-female ratio for TBI is nearly 2:1, and TBI is much more common in persons younger than 35 years. Pathophysiology: Appropriate management of TBI requires an understanding of the pathophysiology of head injury. In addition to the obvious functional differences, the brain has several features that distinguish it from other organ systems. The most important of these differences is that the brain is contained within the skull, a rigid and inelastic container. Because the brain is housed within this inelastic container, only small increases in volume within the intracranial compartment can be tolerated before pressure within the compartment rises dramatically. This concept is defined by the Monro-Kellie doctrine, which states that the total intracranial volume is fixed because of the inelastic nature of the skull. The intracranial volume (V i/c) is equal to the sum of its components, as follows: V i/c = V (brain) + V (cerebrospinal fluid) + V (blood) In the typical adult, the intracranial volume is approximately 1500 mL, of which the brain accounts for 85-90%, intravascular cerebral blood volume accounts for 10%, and cerebrospinal fluid (CSF) accounts for the remainder (<3%). When a significant head injury occurs, cerebral edema often develops, which increases the relative volume of the brain. Because the intracranial volume is fixed, the pressure within this compartment rises unless some compensatory action occurs, such as a decrease in the volume of one of the other intracranial components. This is intimately related to the concept of intracranial compliance, which is defined as the change in pressure due to changes in volume. Compliance = Change in volume / change in pressure Compliance is based on the pressure volume index (PVI) within the intracranial compartment. The PVI describes the change in intracranial pressure (ICP) that occurs when a small amount of fluid is added to or withdrawn from the intracranial compartment. Simply stated, the brain has very limited compliance and cannot tolerate significant increases in volume that can result from diffuse cerebral edema or from significant mass lesions such as a hematoma. The rationale for each treatment of head injury is based on the concept of the Monro-Kellie doctrine and how a particular intervention affects the intracranial compliance. When the volume of any of the components of the total intracranial volume is decreased, the ICP may be decreased. A second crucial concept in TBI pathophysiology is the concept of cerebral perfusion pressure (CPP). CPP is defined as the difference between the mean arterial pressure (MAP) and the ICP. CPP = MAP - ICP In practical terms, CPP is the net pressure of blood delivery to the brain. In the noninjured brain in individuals without long-standing hypertension, cerebral blood flow (CBF) is constant in the range of MAPs of 50-150 mm Hg. This is due to autoregulation by the arterioles, which will constrict or dilate within a specific range of blood pressure to maintain a constant amount of blood flow to the brain. 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. The CBF is no longer constant but is dependent on and proportional to the CPP. Thus, when the MAP falls below 50 mm Hg, the brain is at risk of ischemia due to insufficient blood flow, while a MAP greater than 160 mm Hg causes excess CBF that may result in increased ICP. While autoregulation works well in the noninjured brain, it is impaired in the injured brain. As a result, pressure-passive flow occurs within and around injured areas and, perhaps, globally in the injured brain. TBI may be divided into 2 categories, primary brain injury and secondary brain injury. Primary brain injury is defined as the initial injury to the brain as a direct result of the trauma. This is the initial structural injury caused by the impact on the brain, and, like other forms of neural injury, patients recover poorly. Secondary brain injury is defined as any subsequent injury to the brain after the initial insult. Secondary brain injury can result from systemic hypotension, hypoxia, elevated ICP, or as the biochemical result of a series of physiologic changes initiated by the original trauma. The treatment of head injury is directed at either preventing or minimizing secondary brain injury. Elevated ICP may result from the initial brain trauma or from secondary injury to the brain. In adults, normal ICP is considered 0-15 mm Hg. In young children, the upper limit of normal ICP is lower, and this limit may be considered 10 mm Hg. Elevations in ICP are deleterious because they can result in decreased CPP and decreased CBF, which, if severe enough, may result in cerebral ischemia. Severe elevations of ICP are dangerous because, in addition to creating a significant risk for ischemia, uncontrolled ICP may cause herniation. Herniation involves the movement of the brain across fixed dural structures, resulting in irreversible and often fatal cerebral injury. Clinical: TBI may be divided into 2 broad categories, closed head injury and penetrating head injury. This is not purely a mechanistic division because some aspects of the treatment of these 2 types of TBIs differ. The clinical presentation of the patient with TBI varies significantly, from an ambulatory patient complaining of a sports-related head injury to the moribund patient arriving via helicopter following a high-speed motor vehicle accident. The Glasgow Coma Scale (GCS) developed by Jennett and Teasdale is used to describe the general level of consciousness of patients with TBI and to define broad categories of head injury. The GCS is divided into 3 categories, eye opening (E), motor response (M), and verbal response (V). The score is determined by the sum of the score in each of the 3 categories, with a maximum score of 15 and a minimum score of 3, as follows: GCS score = E + M + V Glasgow Coma Scale
Patients who are intubated are unable to speak, and their verbal score cannot be assessed. They are evaluated only with eye opening and motor scores, and the suffix T is added to the their score to indicate that the patient is intubated. In intubated patients, the maximal GCS score is 10T and the minimum score is 2T. The GCS is often used to help define the severity of TBI. Mild head injuries are generally defined as those associated with a GCS score of 13-15, and moderate head injuries are those associated with a GCS score of 9-12. A GCS score of 8 or less defines a severe head injury. These definitions are not rigid and should be considered as a general guide to the level of injury.
Relevant Anatomy: Several aspects of neuroanatomy and neurophysiology require review in a discussion of TBI. Although a comprehensive review of neuroanatomy is beyond the scope of this discussion, a few key concepts are reviewed. The brain essentially floats within the CSF; as a result, the brain can undergo significant translation and deformation when the head is subjected to significant forces. In a deceleration injury, in which the head impacts a stationary object such as the windshield of a car, the skull stops moving almost instantly. However, the brain continues to move within the skull toward the direction of the impact for a very brief period after the head has stopped moving. This results in significant forces acting on the brain as it undergoes both translation and deformation. In an acceleration injury, as in a direct blow to the head, the force applied to the skull causes the skull to move away from the applied force. The brain does not move with the skull, and the skull impacts the brain, causing translation and deformation of the brain. The forces that result from either deceleration or acceleration of the brain can cause injury by direct mechanical effects on the various cellular components of the brain or by shear-type forces on axons. In addition to the translational forces, the brain can experience significant rotational forces, which can also lead to shear injuries. The intracranial compartment is divided into 3 compartments by 2 major dural structures, the falx cerebri and the tentorium cerebelli. The tentorium cerebelli divides the posterior fossa or infratentorial compartment (the cerebellum and the brainstem) from the supratentorial compartment (cerebral hemispheres). The falx cerebri divides the supratentorial compartment into 2 halves and separates the left and right hemispheres of the brain. Both the falx and the tentorium have central openings and prominent edges at the borders of each of these openings. When a significant increase in ICP occurs, caused by either a large mass lesion or significant cerebral edema, the brain can slide through these openings within the falx or the tentorium, a phenomenon known as herniation. As the brain slides over the free dural edges of the tentorium or the falx, it is frequently injured by the dural edge. Several types of herniation exist, as follows: (1) transtentorial herniation, (2) subfalcine herniation, (3) central herniation, (4) upward herniation, and (5) tonsillar herniation. Transtentorial herniation occurs when the medial aspect of the temporal lobe (uncus) migrates across the free edge of the tentorium. This causes pressure on the third cranial nerve, interrupting parasympathetic input to the eye and resulting in a dilated pupil. This unilateral dilated pupil is the classic sign of transtentorial herniation and usually (80%) occurs ipsilateral to the side of the transtentorial herniation. In addition to pressure on the third cranial nerve, transtentorial herniation compresses the brainstem. Subfalcine herniation occurs when the cingulate gyrus on the medial aspect of the frontal lobe is displaced across the midline under the free edge of the falx. This may compromise the blood flow through the anterior cerebral artery complexes, which are located on the medial side of each frontal lobe. Subfalcine herniation does not cause the same brainstem effects as those caused by transtentorial herniation. Central herniation occurs when a diffuse increase in ICP occurs and each of the cerebral hemispheres is displaced through the tentorium, resulting in significant pressure on the upper brainstem. Upward, or cerebellar, herniation occurs when either a large mass or increased pressure in the posterior fossa is present and the cerebellum is displaced in an upward direction through the tentorial opening. This also causes significant upper brainstem compression. Tonsillar herniation occurs when increased pressure develops in the posterior fossa. In this form of herniation, the cerebellar tonsils are displaced in a downward direction through the foramen magnum, causing compression on the lower brainstem and upper cervical spinal cord as they pass through the foramen magnum. Another aspect of the intracranial anatomy that has a significant role in TBI is the irregular surface of the skull underlying the frontal and temporal lobes. These surfaces contain numerous ridges that can cause injury to the inferior aspect of the frontal lobes and the temporal lobes as the brain glides over these irregular ridges following impact. Typically, these ridges cause cerebral contusions. The roof of the orbit has many ridges, and, as a result, the inferior frontal lobe is one of the most common sites of traumatic cerebral contusions.
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Medical therapy: The treatment of head injury may be divided into the treatment of closed head injury and the treatment of penetrating head injury. While significant overlap exists between the treatments of these 2 types of injury, some important differences are discussed. Closed head injury treatment is divided further into the treatment of mild, moderate, and severe head injuries. Closed head injuryMild head injury Most head injuries are mild head injuries. Most people presenting with mild head injuries will not have any progression of their head injury; however, up to 3% of mild head injuries progress to more serious injuries. Mild head injuries may be separated into low-risk and moderate-risk groups. Patients with mild-to-moderate headaches, dizziness, and nausea are considered to have low-risk injuries. Many of these patients require only minimal observation after they are assessed carefully, and many do not require radiographic evaluation. These patients may be discharged if a reliable individual can monitor them. Patients who are discharged after mild head injury should be given an instruction sheet for head injury care. The sheet should explain that the person with the head injury should be awakened every 2 hours and assessed neurologically. Caregivers should be instructed to seek medical attention if patients develop severe headaches, persistent nausea and vomiting, seizures, confusion or unusual behavior, or watery discharge from either the nose or the ear. Patients with mild head injuries typically have concussions. A concussion is defined as physiologic injury to the brain without any evidence of structural alteration. Concussions are graded on a scale of I-V. A grade I concussion is one in which a person is confused temporarily but does not display any memory changes. In a grade II concussion, brief disorientation and anterograde amnesia of less than 5 minutes' duration are present. In a grade III concussion, retrograde amnesia and loss of consciousness for less than 5 minutes are present, in addition to the 2 criteria for a grade II concussion. Grade IV and grade V concussions are similar to a grade III, except that in a grade IV concussion, the duration of loss of consciousness is 5-10 minutes, and in a grade V concussion, the loss of consciousness is longer than 10 minutes. As many as 30% of patients who experience a concussion develop postconcussive syndrome (PCS). PCS consists of a persistence of any combination of the following after a head injury: headache, nausea, emesis, memory loss, dizziness, diplopia, blurred vision, emotional lability, or sleep disturbances. Fixed neurologic deficits are not part of PCS, and any patient with a fixed deficit requires careful evaluation. PCS usually lasts 2-4 months. Typically, the symptoms peak 4-6 weeks following the injury. On occasion, the symptoms of PCS last for a year or longer. Approximately 20% of adults with PCS will not have returned to full-time work 1 year after the initial injury, and some are disabled permanently by PCS. PCS tends to be more severe in children than in adults. When PCS is severe or persistent, a multidisciplinary approach to treatment may be necessary. This includes social services, mental health services, occupational therapy, and pharmaceutical therapy. After a mild head injury, those displaying persistent emesis, severe headache, anterograde amnesia, loss of consciousness, or signs of intoxication by drugs or alcohol are considered to have a moderate-risk head injury. These patients should be evaluated with a head CT scan. Patients with moderate-risk mild head injuries can be discharged if their CT scan findings reveal no pathology, their intoxication is cleared, and they have been observed for at least 8 hours. Moderate and severe head injury The treatment of moderate and severe head injuries begins with initial cardiopulmonary stabilization by ATLS guidelines. The initial resuscitation of a patient with a head injury is of critical importance to prevent hypoxia and hypotension. In the Traumatic Coma Data Bank study, patients with head injury who presented to the hospital with hypotension had twice the mortality rate of patients who did not present with hypotension. The combination of hypoxia and hypotension resulted in a mortality rate 2.5 times greater than if neither of these factors was present. Once a patient has been stabilized from the cardiopulmonary standpoint, evaluation of their neurologic status may begin. The initial GCS score provides a classification system for patients with head injuries but does not substitute for a neurologic examination. After assessment of the coma score, a neurologic examination should be performed. If a patient has received muscle relaxants, the only neurologic response that may be evaluated is the pupillary response. After a thorough neurologic assessment has been performed, a CT scan of the head is obtained. The results of the CT scan help determine the next step. If a surgical lesion is present, arrangements are made for immediate transport to the operating room. Fewer than 10% of patients with TBI have an initial surgical lesion. Although no strict guidelines exist for defining surgical lesions in persons with head injury, most neurosurgeons consider any of the following to represent indications for surgery in patients with head injuries: extra-axial hematoma with midline shift greater than 5 mm, intra-axial hematoma with volume greater than 30 mL, an open skull fracture, or a depressed skull fracture with more than 1 cm of inward displacement. In addition, any temporal or cerebellar hematoma that is larger than 3 cm in diameter is considered a high-risk hematoma because these regions of the brain are smaller and do not tolerate additional mass as well as the frontal, parietal, and occipital lobes. These high-risk temporal and cerebellar hematomas are usually evacuated immediately If no surgical lesion is present on the CT scan image, or following surgery if one is present, treatment of the head injury begins. The first phase of treatment is to institute general measures. Once appropriate fluid resuscitation has been completed and the volume status is determined to be normal, intravenous fluids are administered to maintain the patient in a state of euvolemia or mild hypervolemia. A previous tenet of head injury treatment was fluid restriction, which was believed to limit the development of cerebral edema and increased ICP. Fluid restriction decreases intravascular volume and, therefore, decreases cardiac output. A decrease in cardiac output often results in decreased cerebral flow, which results in decreased brain perfusion and may cause an increase in cerebral edema and ICP. Thus, fluid restriction is contraindicated in patients with TBI. Another supportive measure used to treat patients with head injuries is elevation of the head. When the head of the bed is elevated to 20-30°, the venous outflow from the brain is improved, thus helping to reduce ICP. If a patient is hypovolemic, elevation of the head may cause a drop in cardiac output and CBF; therefore, the head of the bed is not elevated in hypovolemic patients. In addition, the head should not be elevated (1) in patients in whom a spine injury is a possibility or (2) until an unstable spine has been stabilized. Sedation is often necessary in patients with traumatic injury. Some patients with moderate head injuries have significant agitation and require sedation. In addition, patients with multisystem trauma often have painful systemic injuries that require pain medication, and many intubated patients require sedation. Short-acting sedatives and analgesics should be used to accomplish proper sedation without eliminating the ability to perform periodic neurologic assessments. This requires careful titration of medication doses and periodic weaning or withholding of sedation to allow periodic neurologic assessment. The use of anticonvulsants in patients with TBI is a controversial issue. No evidence exists that the use of anticonvulsants decreases the incidence of late-onset seizures in patients with either closed head injury or TBI. Temkin et al demonstrated that the routine use of Dilantin in the first week following TBI decreases the incidence of early-onset (within 7 d of injury) seizures but does not change the incidence of late-onset seizures. In addition, the prevention of early posttraumatic seizures does not improve the outcome following TBI. Therefore, the prophylactic use of anticonvulsants is not recommended for more than 7 days following TBI and is considered optional in the first week following TBI. After instituting general supportive measures, the issue of ICP monitoring is addressed. ICP monitoring has consistently been shown to improve outcome in patients with head injuries. ICP monitoring is indicated for any patient with a GCS score less than 9, any patient with a head injury who requires prolonged deep sedation or pharmacologic relaxants for a systemic condition, or any patient with an acute head injury who is undergoing extended general anesthesia for a nonneurosurgical procedure. ICP monitoring involves placement of an invasive probe to measure the ICP. Unfortunately, noninvasive means of monitoring ICP do not exist, although they are under development. ICP may be monitored by means of an intraparenchymal monitor, an intraventricular monitor (ventriculostomy), or an epidural monitor. These devices measure ICP by fluid manometry, strain-gauge technology, or fiberoptic technology. Intraparenchymal ICP monitors are devices that are placed into the brain parenchyma to measure ICP by means of fiberoptic, strain-gauge, or other technologies. The intraparenchymal monitors are very accurate; however, they do not allow for drainage of CSF. Epidural devices measure ICP via a strain-gauge device placed through the skull into the epidural space. This is an older form of ICP measurement and is rarely used today because the other technologies available are more accurate and more reliable. A ventriculostomy is a catheter placed through a small twist drill hole into the lateral ventricle. The ICP is measured by transducing the pressure in a fluid column. Ventriculostomies allow for drainage of CSF, which can be effective in decreasing the ICP. Once an ICP monitor has been placed, ICP is monitored continuously. No absolute value of ICP exists for which treatment is implemented automatically. In adults, the reference range of ICP is 0-15 mm Hg. The normal ICP waveform is a triphasic wave, in which the first peak is the largest peak and the second and third peaks are progressively smaller. When intracranial compliance is abnormal, the second and third peaks are usually larger than the first peak. In addition, when intracranial compliance is abnormal and ICP is elevated, pathologic waves may appear. Lundberg described 3 types of abnormal ICP waves, A, B, and C waves. Lundberg A waves, known as plateau waves, have a duration of 5-20 minutes and an amplitude of 50 mm Hg over the baseline ICP. After an episode of A waves dissipates, the ICP is reset to a baseline level that is higher than when the waves began. Lundberg A waves are a sign of severely compromised intracranial compliance. The rapid increase in ICP caused by these waves can result in a significant decrease in CPP and may lead to herniation. Lundberg B waves have a duration of less than 2 minutes, and they have an amplitude of 10-20 mm Hg above the baseline ICP. B waves are also related to abnormal intracranial compliance. Because of their smaller amplitude and shorter duration, B waves are not as deleterious as A waves. C waves, known as Hering-Traube waves, are low-amplitude waves that may be superimposed on other waves. They may be related to increased ICP; however, C waves can also occur in the setting of normal ICP and compliance. When treating elevated ICP, remember that the goal of treatment is to optimize conditions within the brain to prevent secondary injury and to allow the brain to recover from the initial insult. Maintaining ICP within the reference range is part of an approach designed to optimize both CBF and the metabolic state of the brain. Treatment of elevated ICP is a complex process that should be tailored to each particular patient's situation and should not be approached in a “cookbook” manner. Many potential interventions are used to lower ICP, and each of these is designed to improve intracranial compliance, which results in improved CBF and decreased ICP. The Monro-Kellie doctrine provides the framework for understanding and organizing the various treatments for elevated ICP. In patients with head injuries, the total intracranial volume is composed of the total volume of the brain, the CSF, intravascular blood volume, and any intracranial mass lesions. The volume of one of these components must be reduced to improve intracranial compliance and to decrease ICP. The discussion of the different treatments for elevated ICP is organized according to which component of intracranial volume they affect. The first component of total intracranial volume to consider is the blood component. This includes all intravascular blood, both venous and arterial, and comprises approximately 10% of total intracranial volume. Elevation of the head increases venous outflow and decreases the volume of venous blood within the brain. This results in a small improvement in intracranial compliance and, therefore, has only a modest effect on ICP. The second component of intracranial vascular volume is the arterial blood volume. This may be reduced by mild-to-moderate hyperventilation, in which the PCO2 is reduced to 30-35 mm Hg. This decrease in PCO2 causes vasoconstriction at the level of the arteriole, which decreases blood volume enough to reduce ICP. The effects of hyperventilation have a duration of action of approximately 48-72 hours, at which point the brain resets to the reduced level of PCO2. This is an important point because once hyperventilation is used, the PCO2 should not be returned to normal rapidly. This may cause rebound vasodilatation, which can result in increased ICP. At one time, severe hyperventilation was an important component of the treatment of increased ICP. Reducing PCO2 to less than 25 mm Hg has been shown to cause enough vasoconstriction that CBF is reduced to the point at which a high probability exists of developing cerebral ischemia. Therefore, prolonged severe hyperventilation is not used routinely to treat elevated ICP. Brief periods of severe hyperventilation may be used to treat patients with transient ICP elevations due to pressure waves or in the initial treatment of patients in neurologic distress until other measures can be instituted. CSF represents the next component of total intracranial volume and accounts for 2-3% of total intracranial volume. In adults, total CSF production is approximately 20 mL/h or 500 mL/d. In many patients with TBI who have elevated ICP, a ventriculostomy may be placed and CSF may be drained. Removal of small amounts of CSF hourly can result in improvements in compliance that result in significant improvements in ICP. The third and largest component of total intracranial volume is the brain or tissue component, which comprises 85-90% of the total intracranial volume. When significant brain edema is present, it causes an increase in the tissue component of the total intracranial volume and results in decreased compliance and increased ICP. Treatments for elevated ICP that reduce total brain volume include diuretics, perfusion augmentation (CPP strategies), metabolic suppression, and decompressive procedures. Diuretics are powerful in their ability to decrease brain volume and, therefore, decrease ICP. Mannitol, an osmotic diuretic, is the most common diuretic used. Mannitol is a sugar alcohol that draws water out from the brain into the intravascular compartment. It has a rapid onset of action and a duration of action of 2-8 hours. Mannitol is usually administered as a bolus because it is much more effective when given in intermittent boluses than when used as a continuous infusion. The standard dose ranges from 0.25-1 g/kg, administered every 4-6 hours. Because mannitol causes significant diuresis, electrolytes and serum osmolality must be monitored carefully during its use. In addition, careful attention must be given to providing sufficient hydration to maintain euvolemia. The limit for mannitol is 4 g/kg/d. At daily doses higher than this, mannitol can cause renal toxicity. Mannitol should not be given if the patient's serum sodium level is greater than 145 or serum osmolality is greater than 315 mOsm. Other diuretics that sometimes are used in patients with TBI include furosemide, glycerol, and urea. Mannitol is preferred over furosemide because it tends to cause less severe electrolyte imbalances than a loop diuretic. Interestingly, mannitol and furosemide have a synergistic effect when combined; however, this combination tends to cause severe electrolyte disturbances. Urea and glycerol have also been used as osmotic diuretics. Both of these compounds are smaller molecules than mannitol and, as a result, tend to equilibrate within the brain sooner than mannitol; therefore, they have a shorter duration of action than mannitol. Urea has the additional problem that it can cause severe skin sloughing if it infiltrates into the skin. CPP management involves artificially elevating the blood pressure to increase the MAP and the CPP. Because autoregulation is impaired in the injured brain, pressure-passive CBF develops within these injured areas. As a result, these injured areas of the brain often have insufficient blood flow, and tissue acidosis and lactate accumulation occur. This causes vasodilation, which increases cerebral edema and ICP. When the CPP is raised to greater than 65-70 mm Hg, the ICP is often lowered because increased blood flow to injured areas of the brain decreases the tissue acidosis. This often results in a significant decrease in ICP. Metabolic therapies are designed to decrease the cerebral metabolic rate, which decreases ICP. Metabolic therapies are powerful means of reducing ICP, but they are reserved for situations in which other therapies have failed to control ICP. This is because metabolic therapies have diffuse systemic effects and often result in severe adverse effects, including hypotension, immunosuppression, coagulopathies, arrhythmias, and myocardial suppression. Metabolic suppression may be achieved through drug therapies or induced hypothermia. Barbiturates are the most common class of drugs used to suppress cerebral metabolism. Barbiturate coma is typically induced with pentobarbital. A loading dose of 10 mg/kg is administered over 30 minutes, and then 5 mg/kg/h is administered for 3 hours. A maintenance infusion of 1-2 mg/kg/h is begun after loading is completed. The infusion is titrated to provide burst suppression on continuous electroencephalogram monitoring and a serum level of 3-4 mg/dL. Typically, the barbiturate infusion is continued for 48 hours, and then the patient is weaned off the barbiturates. If the ICP again escapes control, the patient may be reloaded with pentobarbital and weaned again in several days. Hypothermia may also be used to suppress cerebral metabolism. The use of mild hypothermia involves decreasing the core temperature to 34-35°C for 24-48 hours and then slowly rewarming the patient over 2-3 days. Patients with hypothermia are also at risk for hypotension and systemic infections. Another treatment that may be used in patients with TBI with refractory ICP elevation is decompressive craniectomy. In this surgical procedure, a large section of the skull is removed and the dura is expanded. This increases the total intracranial volume and, therefore, decreases ICP. Which patients benefit from decompressive craniectomy has not been established. Some believe that patients with refractory ICP elevation who have diffuse injury but do not have significant contusions or infarctions will benefit from decompressive craniectomy. Management of elevated ICP involves using a combination of treatments. Each patient represents a slightly different set of circumstances, and treatment must be tailored to each patient. Although no rigid protocols have been established for the treatment of head injury, many published algorithms provide treatment schemas. The American Association of Neurologic Surgeons published a comprehensive evidence-based review of the treatment of TBI, called the "Guidelines for the Management of Severe Head Injury." In these guidelines, 3 different categories of treatments, standards, guidelines, and options are outlined. Standards are the accepted principles of management that reflect a high degree of clinical certainty. Guidelines are a particular strategy or a range of management options that reflect a high degree of clinical certainty. Options are strategies for patient management for which clinical certainty is unclear. Penetrating trauma The treatment of penetrating brain injuries involves 2 main aspects. The first is the treatment of the TBI caused by a penetrating object. Penetrating brain injuries, especially from high-velocity missiles, frequently result in severe ICP elevations. This aspect of penetrating brain injury treatment is identical to the treatment of closed head injuries. The second aspect of penetrating head injury treatment involves debridement and removal of the penetrating objects. Penetrating injuries require careful debridement because these wounds are frequently dirty. When objects penetrate the brain, they introduce pathogens into the brain from the scalp surface and from the surface of the penetrating object. Penetrating injuries may be caused by high-velocity missiles (eg, bullets), penetrating objects (eg, knives, tools), or fragments of bone driven into the brain. Bullet wounds are treated with debridement of as much of the bullet tract as possible, dural closure, and reconstruction of the skull as needed. If the bullet can be removed without significant risk of neurologic injury, it should be removed to decrease the risk of subsequent infection. Penetrating objects such as knives require removal to prevent further injury and infection. If the penetrating object either is near or traverses a major vascular structure, an angiogram is necessary to assess for potential vascular injury. When the risk of vascular injury is present, penetrating objects should be removed only after appropriate access has been obtained to ensure that vascular control is easily achieved. Penetrating brain injuries are associated with a high rate of infection, both early infections and delayed abscesses. Appropriate debridement and irrigation of wounds helps to decrease the infection rate. Some of the risk factors for infection following penetrating brain injury include extensive bony destruction, persistent CSF leak, and an injury pathway that violates an air sinus. Late-onset epilepsy is a common consequence of penetrating brain injuries and can occur in up to 50% of patients with penetrating brain injuries. No evidence exists that prophylactic anticonvulsants decrease the development of late-onset epilepsy. During the Vietnam War, prophylactic anticonvulsants were used, and the rate of late-onset epilepsy was not different from that of previous wars, when prophylactic anticonvulsants were not used. Head injury in childrenHead injuries in children differ from head injuries in adults in several ways. Children tend to have more diffuse injuries than adults, and traumatic intracerebral hematomas are less common in children than in adults. In addition, early posttraumatic seizures are more common in children than in adults. Overall, children have much lower morbidity and mortality rates from traumatic head injury compared to adults. When a child with a head injury is being evaluated, nonaccidental trauma must be excluded. In the United States, as many as 1 million cases of nonaccidental trauma in children may occur annually. TBI is the most common cause of morbidity and mortality in nonaccidental trauma in children. Radiographic signs of nonaccidental trauma include unexplained multiple or bilateral skull fractures, subdural hematomas of different ages, cortical contusions and shearing injures, cerebral ischemia, and retinal hemorrhages. If any of these are present, the case should be referred to the proper child welfare agency. Follow-up care: For excellent patient education resources, visit eMedicine's Back, Ribs, Neck, and Head Center, Back, Neck, and Head Injury Center, and Eye and Vision Center. Also, see eMedicine's patient education articles Concussion, Bicycle and Motorcycle Helmets, and Black Eye.
Complications resulting from TBI are common and can be divided into 2 categories, systemic and neurologic complications. The systemic complications of TBI are typical of any severe injury and depend on the types of intensive treatments used. Be aware of the complications of intensive care treatment when considering systemic complications of head injury. The neurologic complications of TBI include focal neurologic deficits, global neurologic deficits, seizures, CSF fistulae, hydrocephalus, vascular injuries, infections, and brain death. Focal neurologic deficits Focal neurologic deficits are quite common following TBI. Cranial nerves are affected often because of their anatomic location at the base of the brain. When the brain shifts within the skull as it undergoes either acceleration or deceleration forces, significant force is often placed on the entire brain and the cranial nerves. The cranial nerves are tethered at their exit sites from the skull, and, as a result, they may be stretched when the brain shifts as a result of acceleration or deceleration forces. In addition, the cranial nerves are very susceptible to injury as they course through narrow bony canals and grooves. The cranial nerves that are injured most commonly in patients with TBI are cranial nerves I, IV, VII, and VIII. Anosmia caused by traumatic injury to the first cranial nerve occurs in 2-38% of patients with TBI. It is more common in those with frontal fractures and in those with posttraumatic rhinorrhea. Posttraumatic anosmia improves slowly, and as many as one third of patients do not show any improvement in olfaction. Injuries to the fourth cranial nerve, the trochlear nerve, are also quite common. This nerve is often injured in patients with head trauma because it has the longest intracranial course of the cranial nerves. Injury to the trochlear nerve causes a positional diplopia, in which those affected experience diplopia when they look down and toward the eye in which the trochlear nerve is injured. As a result, to compensate, the head is tilted up and away from the side of the injury. Trochlear nerve injuries resolve fully in approximately two thirds of those with unilateral injury and in one fourth of those with bilateral injuries. Facial nerve injuries often occur with head injuries in which the temporal bone is fractured. From 10-30% of persons with longitudinal fractures of the temporal bone and 30-50% of those with transverse fractures of the temporal bone have either acute or delayed facial nerve injury. Immediate facial nerve injury suggests direct injury to the nerve, while delayed injury suggests progressive edema within the nerve. In severely injured patients, a delay in the diagnosis of facial nerve injuries occurs frequently because facial nerve function is difficult to assess in obtunded patients. Cochlear nerve injury (cranial nerve VIII) is also a common occurrence in patients with head injury, especially in patients with temporal bone fractures. In addition, vestibular disorders, including vertigo, dizziness, and tinnitus, are extremely common in patients with head injuries. Hydrocephalus Hydrocephalus is a common late complication of TBI. Posttraumatic hydrocephalus may present as either ventriculomegaly with increased ICP or as normal pressure hydrocephalus. In patients with increased ICP secondary to posttraumatic hydrocephalus, the typical signs of hydrocephalus are often observed and include headaches, visual disturbances, nausea/vomiting, and alterations in the level of consciousness. Normal pressure hydrocephalus usually manifests as memory problems, gait ataxia, and urinary incontinence. The diagnosis of normal pressure hydrocephalus may be difficult to make in patients with TBI because they often have memory difficulties and gait abnormalities secondary to their head injury. In addition, as many as 86% of patients with TBI demonstrate some degree of ventriculomegaly on follow-up CT scan images. This ventriculomegaly is often secondary to diffuse brain atrophy, and radiographic features rarely help make the distinction between atrophy and normal pressure hydrocephalus. Any patient who develops neurologic deterioration weeks to months following TBI should be evaluated for the possibility of normal pressure hydrocephalus. When CT scan findings cannot help distinguish between normal pressure hydrocephalus and ventriculomegaly secondary to brain atrophy, a high-volume lumbar puncture tap test is performed to ascertain if CSF drainage would improve the patient's neurologic condition. Seizures Posttraumatic seizures are a frequent complication of TBI and are divided into 3 categories. Early seizures occur within 24 hours of the initial injury, intermediate seizures occur 1-7 days following injury, and late seizures occur more than 7 days after the initial injury. Posttraumatic seizures are very common in those with a penetrating cerebral injury, and late seizures occur in as many as half of these patients. Cerebrospinal fluid fistulae Cerebrospinal fistulae, either in the form of rhinorrhea or otorrhea, may occur in as many as 5-10% of patients with TBI. They may present either immediately or in a delayed fashion and are more frequent in patients with basilar skull fractures. Approximately 80% of acute cases of CSF rhinorrhea resolve spontaneously within 1 week. A 17% risk of meningitis exists when CSF rhinorrhea is present. Prophylactic antibiotics have not been demonstrated to decrease this meningitis risk, although very few studies have examined this issue. More than 95% of acute episodes of CSF otorrhea resolve spontaneously within 1 week, and CSF otorrhea is complicated by meningitis in fewer than 4% of cases. When acute CSF fistulae do not resolve spontaneously, a lumbar subarachnoid drain may be placed for several days in an attempt to divert CSF and allow the fistula to close. If this fails, radiographic dye is introduced into the subarachnoid space via lumbar puncture (metrizamide cisternogram), and a high-resolution CT scan is performed in an attempt to identify the origin of the CSF fistula. A craniotomy is performed, and the fistula site is repaired. Delayed CSF fistulae may occur from 1 week after the initial injury to years later. These delayed fistulae are more difficult to treat and frequently require surgical intervention. Vascular injuries Vascular injuries are uncommon sequelae of TBIs. Arterial injuries that may occur following head trauma include arterial transactions, thromboembolic phenomena, posttraumatic aneurysms, dissections, and carotid-cavernous fistulae (CCF). Arterial occlusions secondary to transactions or thromboembolism following closed head injuries are uncommon occurrences. Posttraumatic intracranial aneurysms, which are also rare, differ from congenital aneurysms because the posttraumatic aneurysms tend to be located distally, as opposed to the congenital aneurysms, which are typically proximal in location. Arterial dissections are more common than the aforementioned arterial injuries and should be considered if significant injury has occurred to the petrous portion of the temporal bone, through which the carotid artery passes, or when an unexplained neurologic deficit is present. A cerebral angiogram is often necessary to help exclude arterial injury in these cases. Posttraumatic CCF occur when the internal carotid artery is injured within the cavernous sinus, resulting in a direct connection between the carotid artery and the veins of the cavernous sinus. This overloads the venous system and results in chemosis and proptosis on the affected side. Other signs of CCF include diplopia, ophthalmoplegia, visual disturbances, and headaches. Some high-risk fistulae may cause intracerebral hemorrhage. CCF are treated with endovascular balloon occlusion of the fistula origin. Specific intracranial venous injuries are uncommon following TBI if one excludes the injury to the bridging veins, which are the most common source of subdural hematomas. Depressed skull fractures overlying any of the major intracranial venous sinuses may cause injury to the sinus. When these venous sinus injuries require treatment, substantial, and sometimes life-threatening, blood loss can occur. A second type of venous injury following TBI involves venous sinus thrombosis. Although very rare following head injury, this is a potentially life-threatening injury because the impaired venous drainage often causes severe ICP elevations and venous infarction. The treatment for venous sinus thrombosis is anticoagulation, which presents significant risk in those with acute head injuries. If the thrombosis progresses despite systemic anticoagulation, direct intracranial intravenous thrombolysis is necessary. Infections Intracranial infections are another potential complication of TBI. In uncomplicated closed head injury, infection is uncommon. When basilar skull fractures and/or CSF fistulae are present, the risk of infection is increased. In addition, if a patient has had a ventriculostomy for ICP monitoring, the risk of infection is also increased, for either a ventriculitis or meningitis. Other intracranial infections such as subdural or epidural empyema and intraparenchymal abscesses are rare following closed head injury. As one would expect, the incidence of infection in penetrating cerebral injuries and open depressed skull fractures increases. Brain death Brain death can result from either massive initial injury or as the result of prolonged severe elevations of ICP. Brain death is defined as the absence of brain function. A rigid protocol is necessary to prove that brain death has occurred. It must be established that no sedating medications or neuromuscular blocking agents are present. The patient's electrolyte levels, blood count, body temperature, and arterial blood gas values must be within the reference ranges. The neurologic examination should demonstrate fixed nonreactive pupils, lack of corneal and gag reflexes, fixed position of the eyes during rotation of the head (ie, negative doll's eyes), no response to supraorbital pain, and no movement of the eyes to cold-water calorics. A lack of any neurologic response is not sufficient to establish brain death, and confirmatory testing must be performed. One of these tests is an apnea test, which involves removing a patient from the ventilator for a brief period to assess any sign of spontaneous respiration. This is performed after a 30-minute preoxygenation period with 100% oxygen. At the conclusion of the testing period, if the patient has not had any spontaneous respirations and the arterial blood gas measurements demonstrate a PCO2 of greater than 65 mm Hg, the test results are consistent with brain death. Two neurologic examinations and 2 apnea tests 12 hours apart are sufficient for determining brain death. A nuclear blood flow study or a cerebral angiogram may be performed instead of one of the apnea tests for brain death determination. The results of these studies demonstrate the absence of CBF when brain death has occurred. In most states, brain death is considered to be death.
The outcome of TBI is related to the initial level of injury. While the initial GCS score provides a description of the initial neurologic condition, it does not correlate tightly with outcome. Various methods have been used in an attempt to predict the outcome of TBI, and these are beyond the scope of this discussion. However, one simplified model uses 3 factors, ie, age, motor score of the GCS, and pupillary response (ie, normal, unilateral unresponsive pupil, bilateral unresponsive pupils), to provide a probability of outcome. The Traumatic Coma Data Bank analyzed 780 patients with head injuries and identified 5 factors that correlated with a poor outcome, as follows: (1) age older than 60 years, (2) initial GCS score of less than 5, (3) presence of a fixed dilated pupil, (4) prolonged hypotension or hypoxia early after injury, and (5) presence of a surgical intracranial mass lesion. Many methods exist for evaluating the outcome of TBI. A simple and commonly used method is the Glasgow outcome scale. This divides outcome into 5 categories, as follows: (1) good, (2) moderate disability, (3) severe disability, (4) vegetative, and (5) dead. The scale can be divided further into good outcomes (eg, good plus moderate disability) and poor outcomes (eg, severe disability, vegetative, dead).
The treatment of TBI has undergone significant change in the last 20 years. A tremendous national effort has been undertaken to promote head injury prevention. Mandatory air bags in automobiles and the helmet laws have significantly reduced the incidence of serious head injuries. The future of head injury treatment has several major goals. One of these goals is to develop a noninvasive ICP monitor. Transcranial low-frequency ultrasound has shown promise as a potential noninvasive ICP monitor; however, it has not undergone clinical testing. Significant efforts have been directed toward the development of a noninvasive CBF monitor. Cerebral oxygen monitoring as an adjunct to ICP monitoring is under active investigation. The need also exists for a more effective treatment to control ICP that is refractory to standard therapies. The most significant controversy today in the treatment of TBI is the minimum desirable CPP to achieve in the patient with a head injury. Previously, a CPP of 79 mm Hg was considered the minimum; however, many now believe that a CPP of 60 mm Hg is sufficient. Further controversy also exists as to whether elevated ICP or decreased CPP is a more important prognostic factor. This is an important distinction because it directs the main goals of therapy in severely injured patients. If ICP elevations are considered a more important factor, then efforts may be directed at lowering ICP as a primary goal and improving CPP as a secondary goal. If one considers CPP to be the more important factor, then the primary goal of treatment should be to maintain an appropriate CPP.
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