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Veterinarian Technician December 2010 (Vol 31, No 12)

Head Trauma

by Brandy Terry, CVT

    CETEST This course is approved for 1.0 CE credits

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    Head trauma is commonly seen in veterinary emergency hospitals. Animals sustain head trauma in numerous ways, including being hit by an automobile, fighting with other animals, falling from heights, and being stepped on by owners. Animals with head trauma need immediate medical attention. Other injuries may need to be addressed during initial treatment of head trauma.

    There are two types of head trauma: primary and secondary. Primary head trauma, such as skull fracture or cerebral hemorrhage, is caused by the initial insult. Secondary head trauma (e.g., ischemia, inflammation) occurs after primary trauma. An important goal of treating head trauma is to limit or prevent secondary trauma.

    Basic Anatomy

    The brain is encased within the skull, which does not allow room for inflammation or swelling. The skull cavity contains parenchymal tissue (the brain; 80% of contents), blood (10%), and cerebrospinal fluid (CSF; 10%). The main sections of the brain are the cerebrum, cerebellum, and brainstem.

    Pathophysiology

    Intracranial pressure (ICP) is the pressure exerted between the skull and the intracranial tissues. When there is inflammation or bleeding in the brain, intracranial venous blood and CSF are shunted into the body in an attempt to compensate for it. If the body has done everything it can to compensate but the ICP continues to increase, intracranial hypertension (ICH) can develop.

    Stabilizing the Patient

    Because ICH is life threatening, the ABCs (airway, breathing, circulation) of emergency management should be initiated immediately to stabilize the patient:

    • A—Is the airway patent? Ensure that the airway is patent and there is no debris or swelling in the oral cavity.
    • B—Is breathing normal? If the patient is unconscious and has apnea or dyspnea, intubate the patient and perform manual ventilation, if needed.
    • C—How is the circulation? What are the heart rate, pulse rate, and blood pressure? Ensure that the heart and pulse rates are the same. If there is a discrepancy, electrocardiography should be performed to check for arrhythmias. If the heart rate or blood pressure is not within normal limits, notify the veterinarian. Emergency intervention, which may consist of fluid resuscitation and/or pain management, may be indicated.

    Physical Examination

    Once the patient is stable, a complete physical examination should be performed to document the patient’s condition at presentation. Patients with severe head trauma can deteriorate quickly; therefore, it is extremely important to note all changes in the patient’s condition. The head and neck should be manipulated minimally during the physical examination. Manipulation can displace fractures, worsen spinal cord injuries, or occlude the jugular vein, which can decrease venous return from the brain and, in turn, increase ICP, leading to ICH. Patients with head trauma should receive supplemental oxygen until proper oxygenation is confirmed.

    A physical examination should start with assessment of the patient’s level of consciousness, changes to which can reveal the severity and progression of the injury. The levels of consciousness are as follows:

    • Alert and responsive—The patient exhibits normal behavior.
    • Obtunded—The patient is awake but responds less to stimuli (FIGURE 1).
    • Stuporous—The patient responds only to painful/noxious stimuli.
    • Comatose—The patient is unconscious and does not respond to any stimuli.

    Examination of the eyes can provide important information about the severity of brain injury. Any deviation from normal eye position is called strabismus, which is usually caused by damage to the cranial nerves or brainstem.

    It is extremely important to check for abnormal eye movement. Rhythmic eye movement that is vertical, rotary, or horizontal, fast or slow, is called nystagmus. Physiologic nystagmus can be initiated in healthy patients by moving the head horizontally or vertically, resulting in rapid eye movement (also called fast phase) toward where the head is positioned. Absence of physiologic nystagmus indicates severe brainstem damage and correlates with a poor prognosis.1 (Some of these findings are affected by state of consciousness. A dog that is comatose may not have physiologic nystagmus but does not necessarily have a brainstem injury.) Any other type of nystagmus is considered abnormal.

    In addition, the pupils’ response to light (called the pupillary light reflex [PLR]) should be assessed. Shining a bright light into the eyes should cause the pupils to constrict; they should dilate when the light is removed. A slow PLR suggests a guarded to poor prognosis. Absence of a PLR suggests a grave prognosis. Continual monitoring of the PLR can help assess the ICP.

    Checking the size of the pupils is also important. With head trauma, the pupils can be normal, constricted (miosis), dilated (mydriasis), or asymmetric (anisocoria). Miotic (pinpoint) pupils are usually due to cerebral injury or edema, indicating a guarded to fair prognosis.1 Mydriasis is usually associated with stress, medications, ophthalmic disease, and impending cardiopulmonary arrest. Mydriasis is not directly associated with brain injury but is important to recognize in debilitated patients because it can be associated with cardiopulmonary arrest. Anisocoria has several causes, including oculomotor nerve damage or compression, direct eye injury, and uveitis (inflammation of the uvea). Mid-size pupils that are unresponsive to light usually indicate a brainstem injury and a grave prognosis.1 Changes in the pupils’ size should be closely monitored and recorded in the medical record. Pupils that change from miotic to mydriatic and become fixed (unresponsive to light) may indicate brain herniation and a grave prognosis.

    The menace response is the involuntary blink of the eyelids in response to movement toward the eyes. If the menace response is intact, the patient will blink when something approaches the face, indicating sight. The staff member who evaluates this response should be careful not to move air toward the face, which can cause the eyes to blink, possibly leading to a false-positive test result. Neonates can be difficult to assess because they may not yet have developed a menace response.

    Blindness may indicate that either the nerves to the eyes and brain are too inflamed to work or there is a problem with the eye(s). Vision problems usually indicate major nerve problems within the head. Treatment decisions are not made based only on blindness. In many cases of blindness due to head trauma, vision can be restored.

    The patient’s body position can be used to help the veterinarian determine the severity of the brain injury and the prognosis. In a position called opisthotonus or decerebrate rigidity, the patient is recumbent and comatose with all limbs rigidly extended, the neck extended, and the head back. Opisthotonus indicates severe brainstem injury and usually carries a grave prognosis.2 Decerebellate posture, which has a more favorable prognosis than decerebrate rigidity, may indicate an acute cerebellar lesion or herniation.3 In decerebellate posture, the patient’s forelimbs are extended and hindlimbs flexed. Patients with this posture are usually conscious and have responsive pupils. Close monitoring of the patient is important because subtle changes in posture can indicate progression of the injury. Schiff-Sherrington syndrome, which may appear similar to decerebrate posture, is characterized by extended, rigid forelimbs and paralyzed, flaccid hindlimbs. This syndrome indicates a thoracolumbar spinal lesion. It is extremely important for the veterinarian to carefully assess the patient to avoid confusion and misdiagnosis.

    Patient Monitoring

    Because patients with head trauma can deteriorate quickly, they must be closely monitored. After the initial assessment, an intravenous (IV) catheter should be placed and blood drawn for an extended database (venous and arterial blood gas values, complete blood count, and chemistry panel). Drawing blood from the jugular vein is contraindicated because occlusion of the vein decreases venous outflow from the brain, thereby increasing ICP. The packed cell volume and total solids value are used to check for hemorrhage. The blood glucose level is monitored to ensure that the patient is not hypoglycemic and is supplemented only until the level is normal. Hyperglycemia (iatrogenic or related to brain trauma) is associated with high mortality and poor outcome in humans and with more severe head injuries in animals.4 To avoid hyperglycemia, the blood glucose level should be maintained at 62 to 108 mg/dL in dogs and 61 to 124 mg/dL in cats.5 Blood gas analysis is used to check ventilation, oxygenation, perfusion, and acid–base status. The carbon dioxide (CO2) level should be monitored because an increase in it can induce cerebral vasodilation and increase blood flow to the brain, thereby increasing ICP and possibly causing ICH. The CO2 level should be maintained in the low normal range: 40 to 45 mm Hg (venous); 35 to 40 mm Hg (arterial).4 Hypercapnia can increase ICP, which may necessitate mechanical ventilation of the patient. Hypocapnia should also be avoided because it can cause cerebral vasoconstriction, which can lead to cerebral ischemia.

    Serial monitoring of the following is recommended: mucous membranes, capillary refill time, heart rate, respiratory rate and effort, pulse rate and quality, lung sounds, temperature, the heart’s electrical action (by electrocardiography), oxygenation (by pulse oximetry or arterial blood gas measurement), and blood pressure (by oscillometry, Doppler ultrasound, or direct arterial blood pressure measurement). By closely monitoring these parameters, technicians can detect changes in a patient’s status and notify the doctor before they become life threatening.

    Based on extensive research on head trauma and hypotension, blood pressure (as measured by Doppler ultrasound) should be maintained at 100 to 150 mm Hg and mean arterial pressure at 80 to 110 mm Hg.4 Hypotensive patients have decreased cerebral perfusion, which may lead to brain ischemia.

    In the past, it was thought that administration of IV fluids would increase ICP, causing more brain trauma. Research has found that early and rapid establishment of euvolemia and avoidance of overhydration are essential.6 There has been much discussion about whether crystalloid or colloid fluid therapy is better for rehydrating head trauma patients. Either therapy can be used as long as hypovolemia is treated and blood pressure is maintained in the normal range.

    During the physical examination, if nonhemorrhagic fluid is present on or around the head, specifically the nares and ears, the glucose level of the fluid should be checked using a glucometer. A glucose level of =80 mg/dL indicates that the fluid is CSF, and the presence of spinal fluid in the nose or ears means that the patient might develop septic meningitis.6 To prevent nosocomial infections, gloves should be worn while handling these patients.

    When the ICP is dangerously high, it can trigger the Cushing reflex, in which the patient’s blood pressure increases and heart rate decreases (bradycardia). The Cushing reflex is life threatening, so immediate identification and treatment are important. Affected patients should be monitored by continuous electrocardiography and regular blood pressure monitoring (FIGURE 2).

    Certain breathing patterns are associated with head trauma. Therefore, patients should be monitored closely to detect changes in breathing. One breathing pattern is called Cheyne-Stokes breathing, which occurs in hyperpneic patients with apnea phases. Cheyne-Stokes breathing is associated with a severe cerebral or rostral brainstem lesion.2 Affected patients must be monitored very closely using pulse oximetry and arterial blood gas readings to ensure proper oxygenation and a normal CO2 level. Agonal (apneustic) breathing involves rapid inspiratory breaths with short, incomplete expiratory breaths. This terminal breathing pattern is usually related to severe brainstem injury.2 When agonal breathing is observed, immediate intervention, including intubation and continuous ventilation, is necessary to prevent respiratory and cardiac arrest.

    Treatment

    There are two main treatments for an increase in ICP: mannitol or hypertonic saline therapy. Mannitol is a diuretic, hyperosmotic agent that quickly decreases ICP by drawing fluid away from the brain. Mannitol is given as an IV bolus as needed for signs of increased ICP. Mannitol has a very profound diuretic effect; therefore, patients should receive fluids before and after mannitol therapy. Mannitol crystallizes easily at room temperature, so it should be warmed before administration and administered through a 0.22-µm filter.

    Hypertonic saline is also a hyperosmotic agent that is given as an IV bolus. Hypertonic saline is usually diluted with a colloid solution in a 60-mL syringe. A 23% hypertonic saline solution must be diluted to a 7.5% solution before administration. To do this, add 17 mL of 23% hypertonic saline solution to 43 mL of a colloid solution. Over a 20-minute period, dogs should receive 4 to 7 mL/kg of the solution and cats should receive 2 to 4 mL/kg. Hypertonic saline therapy is contraindicated in patients with hyponatremia because increasing the sodium level too quickly can be detrimental to the brain. When the sodium level is increased at a rate of >1 mEq/L/h, the brain can become dehydrated. Dehydration of the brain can lead to intracranial hemorrhage and, in turn, neurologic signs. In hyponatremic patients, mannitol should be used instead of hypertonic saline.

    Furosemide, a diuretic, has been used to help manage cerebral edema. However, furosemide can deplete intravascular fluid volume, resulting in systemic hypotension and a decrease in cerebral perfusion pressure, leading to cerebral ischemia. Because furosemide can adversely affect patient outcome, it is one of the least used diuretics for treating an increase in ICP. Furosemide can be used alone or with mannitol, but it is normally given once, whereas mannitol can be given several times.

    The use of corticosteroids is not recommended for treating head trauma patients. Research in humans has found that the use of corticosteroids is detrimental to patient recovery.7 In a clinical study involving more than 10,000 people who sustained head injuries, corticosteroid therapy was associated with worse outcomes.7 The Human Brain Trauma Foundation recommends that corticosteroids not be given to patients with traumatic brain injuries.7 Veterinary medicine has followed this recommendation.

    Sedatives and pain relievers are indicated if a patient is anxious, may worsen its injury through self-trauma, or seems painful. The sedative or analgesic that is used should be reversible. Valium, midazolam, and butorphanol can be given to anxious animals and reversed with flumazenil (a benzodiazepine antagonist) or naloxone (an opiate antagonist). Buprenorphine is ideal for treating pain because it does not depress the respiratory system or central nervous system as much as fentanyl or hydromorphone. Seizures are a common complication of head trauma. If a patient has seizures, traditional anticonvulsants (e.g., valium, midazolam, phenobarbital) should be administered. If the seizures are not controlled with these medications, administration of propofol is recommended. Propofol, which induces anesthesia, can be given as a one-time bolus (to see if the seizures stop) or a constant-rate infusion. If propofol is needed for long periods of time, the patient should be intubated and given supplemental oxygen. The respiratory rate and effort, and heart rate, should be monitored closely while the patient is under anesthesia. An arterial blood gas reading should be obtained to ensure adequate ventilation until the patient is awake. Monitoring the end-tidal CO2 level is helpful if the clinic is not able to check the blood gas values.

    Patient Care

    Patient care is an important part of what veterinary technicians can do for head trauma patients, which are usually recumbent. It is very important to turn these patients at least every 4 hours. Patients should be maintained on a clean, dry, padded area to prevent decubital ulcers. While the patient is recumbent, it is very important to elevate the cranial end of the body to 30° to 40° to decrease the ICP and thereby help prevent ICH. Elevating the head alone may restrict the jugular veins, decreasing blood flow from the brain and thereby increasing the ICP.

    Because patients may not be able to blink, their eyes should be flushed with ocular wash and lubricated with artificial tears at least every 4 hours to prevent dry eyes and formation of ulcers.

    Obtunded or comatose patients might have difficulty swallowing, causing saliva and debris to accumulate in their mouths; therefore, the mouth should be wiped out every 4 to 6 hours, as needed, to remove secretions and keep it moist. An oral cleaning spray can be used to clean the mouth, and diluted liquid glycerin can be used to keep the mouth moist. Rarely, the mouth and oral pharynx might need to be suctioned to remove a large amount of secretions.

    If the patient cannot walk or stand or use a litterbox, the bladder should be expressed at least every 3 to 6 hours or an indwelling urinary catheter and closed collection system should be placed to help keep the patient clean and dry and to avoid development of an atonic bladder.

    Recovery time can be prolonged, and nutrition is an important part of recovery. If the patient can eat, it should be helped into a sternal position and encouraged to eat every 4 to 6 hours. If the patient is obtunded or comatose, a feeding tube should be placed or the patient should be given IV nutrition (e.g., partial or total parenteral nutrition).

    Muscle wasting can occur in nonambulatory patients; therefore, passive range of motion exercises (PROM) may be indicated for all the limbs every 6 to 8 hours. PROM should be performed with caution, or not at all, in patients that also have a spinal injury or a broken limb. Consult a doctor before starting PROM.

    While head trauma patients can be difficult to manage, it is always very rewarding to see them recover and go home to their families.

    Downloadable PDF

    1. Macintire DK, Drobatz KJ, Haskins SC, Saxon WD. Manual of Small Animal Emergency and Critical Care Medicine. Philadelphia: Lippincott Williams & Wilkins; 2005:260.

    2. Sturges B, LeCouter R. Intracranial hypertension. In: Silverstein D, Hopper K, eds. Small Animal Critical Care Medicine. Philadelphia: Saunders Elsevier; 2009:426.

    3. Macintire DK, Drobatz KJ, Haskins SC, Saxon WD. Manual of Small Animal Emergency and Critical Care Medicine. Philadelphia: Lippincott Williams & Wilkins; 2005:261.

    4. Fletcher D. Head trauma management: new and up-to-date information. IVECCS Proc 2007.

    5. Serum biochemical reference ranges. The Merck Veterinary Manual. Whitehouse Station, NJ: Merck & Co; 2008. Accessed September 2010 at www.merckvetmanual.com/mvm/htm/bc/tref7.htm.

    6. Vernau K. Management of head trauma [lecture]. Proc Annu Vet Neurol Symp 2005.

    7. Fletcher D, Syring R. Traumatic brain injury. In: Silverstein D, Hopper K, eds. Small Animal Critical Care Medicine. Philadelphia: Saunders Elsevier; 2009:661.

    References »

    NEXT: Tech Tips (December 2010)

    CETEST This course is approved for 1.0 CE credits

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