CNS Injuries (and Spinal Immobilization)
Injuries to the Central Nervous System (CNS) may be immediately life- and limb-threatening. Half of all trauma deaths involve head injuries. Emergency caregivers can reduce the likelihood of long term disability or death by providing an organized assessment of the victim and provide appropriate interventions. This article will address basic and expanded information of victims suffering injuries to the central nervous system and how they should be cared for.
The Central Nervous System Structures
The central nervous system actually consists of only two structures. They are the brain and spinal cord. Although they may seem relatively minor in numbers, they certainly make up for it in their importance. The brain is responsible for control of the body as well as all other characteristics which make us the most highly developed Order on the planet. The spinal cord is responsible for the transfer of information to and from the brain in the form of sensory receptors and motor function. Injury to the CNS is of major importance and requires prompt action to reduce long term disability.
Protection of the CNS
The CNS is protected by bony structures of the axial skeleton. The skull has two general regions, the face and the cranium. The brain is contained within the cranial cavity or vault. The cranial vault consists of the frontal bones, the temporal bones, the parietal bones, the occipital bone, the ethmoid bones, and the sphenoid bones. The bones of the skull are joined together at immovable joints called sutures. These bony structures allow for considerable protection of the brain, however, they do not allow for swelling as in the case of a closed head injury.
The spinal cord is protected by the spinal vertebrae, collectively called the vertebral or spinal column. There are seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae, five fused vertebrae in the sacrum, and three to five fused vertebrae in the coccyx, or "tailbone". The sacral and coccygeal vertebrae begin to fuse as a person increases in age and therefore it may be difficult to notice any separation radiographically.
Except for C1 (atlas) and C2 (axis), all of the vertebrae have the same general structure. Vertebrae are composed of spongy, or cancellous, bone. The typical vertebra consists of the body, or centrum, which is the thick, weight-bearing portion of the vertebra. The vertebral arch extends posteriorly from the body of the vertebra. It is formed by two thick processes, the pedicles, which project posteriorly from the body and unite with the laminae. The laminae form the posterior portion of the vertebral arch. The vertebral foramen is the space between the body and the vertebral arch through which the spinal cord descends. All of the vertebral foramena together form the vertebral (or spinal) canal. Three processes project from the vertebral arch: two transverse processes, which extend laterally on each side, and one spinous process that projects posteriorly and inferiorly from the junction of the laminae. These three processes serve as points of attachment for muscles.
Cervical, thoracic, and lumbar vertebrae are separated by spongy cushions of fibrocartilage called intervertebral discs. These discs permit movement of the vertebral column and act as "shock absorbers" during our daily activities. However, as a result of acute injury or excessive misuse these discs may begin to bulge, or herniate. This may cause partial or complete compression of nerves emerging from the spinal cord. This may lead to injury to the spinal cord itself or to the peripheral nervous system.
The Six Regions of the Brain
The brain may be divided into six regions. They are the cerebrum, diencephalon, mesencephalon, pons, medulla oblongata and cerebellum. Let us review what function each of the regions perform.
The cerebrum is the largest portion of the brain and contains two halves, or hemispheres, joined by the corpus callosum. The cerebrum regulates all sensory and motor function. It is considered the base of intellect controlling memory, language, learning, and analytical thinking.
The right side of the cerebrum controls the motor function for the left side of the body, and the left side of the cerebrum controls motor function for the right side of the body. This can be useful when performing patient assessment regarding motor function impairment.
The cerebrum is divided into several lobes which are named according to the cranial bone that covers them. The outer layer of the cerebrum is called the cortex.
· The cortex is responsible for voluntary skeletal movement. Injuries to this area may cause paresthesia ("pins and needles" sensation), weakness, or paralysis.
· The frontal lobe is responsible for personality. Injuries to this region may cause placid reactions and possibly seizures.
· The occipital lobe is the origin of the optic nerve (cranial nerve II). Injury to this area can cause the patient to see "stars", blurred vision, or other visual disturbances.
· The temporal lobe controls speech, long term memory, and the sensations of taste and smell.
· The parietal lobe is responsible for somatic sensory input, memory, and emotions.
Within the brain are four ventricles, which are cavities filled with cerebrospinal fluid (CSF). They function in the formation of the CSF. These cavities can fill with blood in cases of trauma or stroke (termed an intraventricular bleed), which is a life-threatening condition.
The diencephalon is the upper portion of the brainstem. Many smaller structures such as the thalamus and hypothalamus are contained within. This area is responsible for regulation of temperature, sleep, water balance, stress, and emotional control. It has a considerable job with the involuntary portion of the nervous system.
The mesencephalon is commonly referred to as the midbrain. It is located between the pons and the diencephalon. It is responsible for motor coordination and eye movement.
The pons, or "bridge", acts as a bridging device between the brain and the spinal cord allowing for nervous system impulses from incoming as well as outgoing pathways. The pons also contains the pneumotaxic and apneustic centers which, along with the medulla oblongata, help control respiration.
The medulla oblongata is found between the pons and the spinal cord. This center controls the most basic functions including respiration, cardiac activity, and vasomotor activity.
The diencephalon, the mesencephalon, the pons, and the medulla oblongata collectively make up the brainstem.
The cerebellum is the second largest portion of the brain and is located in the posterior aspect and base of the brain. It is divided into two hemispheres. It is responsible for coordinating fine motor movement, posture, equilibrium, and muscular tone.
The CNS is completely covered by three protective layers known as the meninges. The innermost layer is a thin layer that adheres directly to the brain called the pia mater ("gentle mother"). The middle layer is the arachnoid ("spider web") layer, which is a web-like layer that contains venous blood vessels that reabsorb CSF. The outermost layer is a tough, fibrous layer referred to as the dura mater ("tough mother"). Both the brain and spinal cord are bathed in cerebrospinal fluid (CSF). Cerebrospinal fluid is a clear, colorless fluid that contains glucose, proteins, urea, lactic acid, and some white blood cells. CSF has three main functions:
· Chemical protection - the CSF creates the optimum environment for neurons to fire
· Mechanical protection - it is a shock-absorbing medium
· Exchange medium for nutrients and wastes
Cranial nerves are actually part of the peripheral nervous system, but injuries to the CNS can cause swelling which can place pressure on the cranial nerve or nerves in that region. There are twelve pairs of cranial nerves. Ten pairs originate in the brainstem. The olfactory nerve (CN I) originates in the temporal lobe of the cerebral cortex and the optic nerve (CN II) originates in the occipital lobe of the cerebral cortex. Following is a table of the different cranial nerves and their function:
The Spinal Cord and Spinal Nerves
The spinal cord begins at the medulla oblongata and ends at about the second lumbar vertebra (L2). The posterior portion of the spinal cord is called the cauda equina ("horse's tail") because the nerves branch out and look like a horse's tail. The spinal cord consists of white and gray matter. The gray matter is the inner portion of the spinal cord and is shaped like an "H". The gray matter consists of unmyelinated fibers of motor and association neurons. The white matter surrounds the gray matter. It is called white matter because the axons are covered in a fatty myelin sheath which protects the axon and helps speed transmission of impulses. The myelin coating has a whitish coloring. The white matter contains both motor and sensory neurons.
The spinal nerves are part of the peripheral nervous system. 31 pairs of spinal nerves originate from the spinal cord and are named according to the region of the spine through which they emerge:
Cervical 1 - 8
Thoracic 1 - 12
Lumbar 1 - 5
Sacral 1 - 5
Each spinal nerve contains two short branches or roots. The dorsal (posterior) roots transmit sensory impulses from the body to the spinal cord and the ventral (anterior) roots transmit motor impulses from the spinal cord to the body. A dermatome is a region of the body that a specific spinal nerve controls. Dermatomes are mapped out by the level of the spinal nerve. They are useful for assessment for a specific level of spinal cord injury. The following is a table of the principle dermatomes:
Closed Head Injuries
Causes of Closed Head Injuries
The CNS may be injured by blunt or penetrating trauma. Blunt trauma to the head may cause injury in two ways. An immediate injury secondary to coup (injury directly below the point of impact) and contracoup (injury on the opposite side of the skull from the point of impact) forces may cause direct injury to the brain. A direct injury to the brain is caused by the impact, the mechanical disruption of the cells.
A secondary, or indirect, injury to the brain may occur as swelling, or edema, develops within the cranial vault causing structures to be compressed. This causes an increase in intracranial pressure (ICP). This will eventually lead to a decrease in cerebral perfusion pressure. As the brain begins to have a reduction in oxygenation and an increase in waste production, herniation of the brain through the foramen magnum (the exit way for the spinal cord through the skull) may occur. This will interrupt normal function of the respiratory, cardiovascular, and vasomotor activity eventually leading to death. Changes in respiratory function may be caused by indirect compression or direct injury to the medulla oblongata. Therefore, strict attention must be paid to airway assessment and early intervention.
Cushing's Response is a syndrome manifested by changes in blood pressure and pulse rate caused by increased intracranial pressure. During the early period of increased ICP, the patient's systolic blood pressure and pulse rate may remain unchanged. Frequently, changes in the level of consciousness may be noted as the patient becomes anxious, combative, or even "lethargic."
As Cushing's Response continues in relation to further increasing ICP, the systolic blood pressure begins to elevate as the pulse rate decreases. Aggressive interventions are necessary to prevent continued deterioration of the patient's condition. Eventually, Cushing's Response will demonstrate a drastic fall in systolic blood pressure accompanied by a dramatic increase in heart rate. It is during this period, described as a critical point, that the patient's cerebral perfusion pressure drops preventing adequate delivery of oxygenated blood to the brain tissues. No treatment to date has proven to be of long-term benefit during this stage.
The time duration of Cushing's response is varied based upon the type of insult suffered by the patient. Depending on the rate of swelling of brain tissue or the severity of intracranial bleeding it may take minutes to hours for Cushing's Response to occur in an acute injury. All pre-hospital care must be geared to adequate delivery of oxygenated blood to the brain and prevention of intracranial pressure increases.
Advanced EMS personnel may alter the likelihood of increased intracranial pressure by pharmacological therapy as well as alteration in CO2 retention. Mannitol, an osmotic diuretic, may be administered by physician order. This drug causes a decrease in osmotic pressure within the vasculature resulting in a diuresing of the system.
Endotracheal intubation with mild hyperventilation of PaCO2 down to approximately 30 has been demonstrated to be of some benefit as well. This may be measured in the pre-hospital environment with a portable ETCO2 monitor. It is imperative to note however, that overzealous hyperventilation may actually cause an increase in injury to the brain by shunting the blood. Your physician medical director should establish a target value for ETCO2 as a result of your mild hyperventilation treatment regimen. Check your local protocols.
A detailed patient assessment must always be performed. Changes in level of consciousness (LOC) must be recognized early. The suggested format is the AVPU method. This mnemonic stands for A - Alert, V- Verbal stimulus arouses patient, P -Painful stimulus arouses patient, U - Unresponsive to any stimulus.
The Glasgow Coma Score (GCS) is another method of evaluating a victim. It depends on the assessment of three areas. These areas are eye opening, verbal capabilities and motor function. A score of 3 to 15 is calculated with 3 representing deep coma and 15 finding no abnormalities. Here is the adult version of the Glasgow Coma Score:
The Glasgow Coma Score (GCS) is a tool which should be utilized in pre-hospital care. It is easy to commit to memory and is a very definable value of patient condition. A GCS of 13 - 15 is considered a mild head injury, a GCS of 8 - 12 is considered a moderate head injury, and a GCS of less than 8 indicates a severe head injury. Several researchers have retrospectively reviewed patient outcomes in comparison to initial GCS scores. Obviously, those who present with a lower GCS have a higher morbidity or mortality rate.
One thing which is virtually unanimous among physicians providing acute care is that patients who present with a GCS of 8 or less should have their airway protected with an endotracheal tube. Utilization of the GCS scoring system will dramatically ease your explanation of need for advanced airway procedures. One note however, insertion of an endotracheal tube dramatically effects the GCS score by taking away the victim's ability to verbalize. In such cases you may indicate this by adding a "T" (tubed) at the end of the score. Patients who have been endotracheally intubated should not be able to score higher than an 11"T" as they cannot verbalize. Administration of chemical paralytics changes each category as well. You should indicate this, as well, as part of your GCS score.
Types of Closed Head Injuries
Many injuries may be caused by blunt head trauma. There are three general types of brain injuries: concussion, contusion, and laceration.
A concussion is an abrupt, but temporary loss of consciousness following a blow to the head or sudden deceleration. No obvious bruising to the brain is evident. The patient may experience amnesia (memory loss).
A contusion is visible bruising to the brain caused by trauma. Small blood vessels are damaged. The pia mater may be torn.
A laceration is actual tearing of the brain tissue caused by skull fractures or penetrating trauma to the head. Large blood vessels are damaged resulting in bleeding in the subarachnoid space and within the brain itself. The resulting hematoma and edema will lead to increased intracranial pressure (ICP).
Specific Types of Brain Injuries
An epidural hematoma may occur secondary to laceration of the middle meningeal artery. This injury allows for blood to accumulate between the dura mater and the skull. This injury may be immediately life-threatening depending on how fast blood accumulates.
A subdural hematoma is more common and is caused by bleeding from small arteries and veins between the dura mater and the arachnoid space. These bleeds are often slow in their presentations taking from hours to weeks to develop.
Subarachnoid bleeds may be caused by lacerations to the brain itself. These bleed more slowly then those mentioned above but may prove to cause substantial problems. The patient may have bloody CSF and meningeal irritation.
Intracerebral bleeds occur when there is accumulation of blood within the brain tissue itself. This hemorrhagic stroke will manifest itself by affecting the functions of the particular area of the brain involved.
Strokes may also be caused by occlusion of a cerebral vessel with an embolus or thrombus (blood clot).
Hemorrhagic and occlusive strokes have one great similarity. They both prevent adequate delivery of oxygenated blood to regions of the brain. Pre-hospital treatment of victims with strokes require a detailed patient assessment, appropriate positioning of the victim with the head slightly elevated to promote venous drainage, and early attention to airway management including suctioning and possibly endotracheal intubation.
Signs and symptoms of a closed head injury may include the following:
· mechanism of injury
· alteration in LOC
· decreasing GCS
· unequal pupils
· unexplained unresponsiveness
Treatment of Closed Head Injuries
Pre-hospital treatment of a victim with blunt head trauma is geared towards management of airway compromise and shock. For the EMT-I and EMT-P this would include:
· Assessment with cervical spine precautions
· Administration of high-flow oxygen with a non-rebreathing device and be prepared to assist ventilations with a BVM
· Endotracheal intubation for patients with a GCS of 8 or less and mild hyperventilation
· Application of spinal motion restriction devices
· Treat for shock
· Rapid, safe transport to the hospital (Trauma Center is preferred; consider EMS helicopter transport)
· Initiation of ECG monitoring and IV access with large bore catheter at KVO. Do not use dextrose containing products. The IV solution of choice is normal saline or Lactated Ringer's
· Early notification of medical control and/or receiving hospital
· Physician may order Mannitol 1 gm/kg IV. Be sure to use blood Y tubing with an in-line filter with this medication to avoid infusion of crystallized particles.
· Consider administration of paralytics and sedation as per protocol.
Treatment of abnormal blood pressures is controversial. You should discuss with your medical director his or her wishes in regard to medication administration versus close monitoring. Hospital treatment of strokes may include medical treatment only, surgical treatment for hemorrhagic strokes or thrombolytic treatment of occlusive strokes caused by a thrombus.
Penetrating Head Injuries
Penetration of the cranial vault may occur secondary to a severe blow to the head or a projectile such as a bullet wound. These types of wounds lead to immediate damage of the brain as well as secondary injury caused by swelling. These wounds are often devastating. In many cases, the patient may never regain consciousness.
Any of the above problems noted with closed head injuries may occur with penetrating head injuries. Patients may also bleed significantly due to the immense vasculature of the brain. Open wounds should be covered with sterile dressing but no attempt should be made to "pack the wound" as this will only lead to an increase in intracranial pressure (ICP). Management similar to that of a closed head injury should be performed.
Spinal Cord Injuries
Assessment of Spinal Cord Injuries
Injuries to the spinal cord may occur from blunt or penetrating trauma. The most common causes of spinal cord injuries are motor vehicle accidents, falls, penetrating injuries, and sports injuries. Mechanisms of injury that should create a high index of suspicion for spinal cord injury are:
· High speed MVA's
· Falls greater than three times the patient's height
· Injuries to the head or torso
· Sports injuries, such as diving injuries or football injuries
High cervical cord injuries may lead to immediate cessation of breathing. Fractures of cervical vertebra 2 (C2) or separation of C1/C2 are sometimes referred to as a hangman's fracture. This was the injury caused by a rope and noose when someone was hanged. Injuries to the cervical spinal cord and high thoracic areas may lead to paralysis from the upper extremities down. Injuries to the middle and lower thoracic spinal cord may affect areas from the chest down. Lumbar and sacral branches provide function from the stomach and lower extremities.
Injuries to the spinal cord may also occur in two fashions. There may be an immediate injury caused by shearing of the spinal cord caused by complete separation of spinal vertebrae. There may also be a slow onset of spinal cord injury caused by swelling from a whiplash or subluxation injury. The patient may have a "spinal injury", which is injury to the bony portion of the spine, without actual spinal cord injury. This injury can also cause swelling which can eventually affect the spinal cord.
A patient with a spinal injury may be in neurogenic shock. Because of the spinal injury, the patient's body loses the ability to communicate with the brain which is responsible for the control of blood vessel constriction and dilation. The result is a dilation of the blood vessels. The container becomes too large for the available blood to fill even if there is no subsequent blood loss associated with the injury. Because of the lack of communication with the brain, catecholamines are not released in response to the lowered blood pressure. Signs and symptoms of neurogenic shock will be different from other types of shock in that the patient's heart rate remain in the normal range, rather than increasing, as the blood pressure decreases and their skin will remain warm and dry.
It is imperative that patients be continuously reassessed to see if symptoms are improving or worsening. Patients should be assessed for pain, sensation and motor function. Ask the patient about weakness, numbness, paresthesia, or referred pain. Have the patient wiggle their fingers and toes to assess motor function. Assess if the patient can distinguish between pressure and light touch.
Treatment of Spinal Cord Injuries
Pre-hospital use of steroids (e.g. Solu Medrol) is currently under investigation. Some researchers believe that steroids given within six hours of an injury may help to reduce some of the swelling occurring around the site of injury. By decreasing pressure around that area of the cord it is believed that it may prevent further damage or actually reverse current abnormal signs and symptoms. Consult your protocols for use of steroids for spinal injuries.
Treatment for spinal cord injuries would include:
· Assessment and cervical spine precautions
· Administration of high flow oxygen with non-rebreathing device
· Treatment of shock
· Application of spinal motion restriction devices. Consider use of the Kendrick Extrication Device (KED) if the patient's vital signs are stable and the index of suspicion is high for spinal injury.
· Rapid, safe, and smooth transport to the hospital or Trauma Center (Consider aeromedical evacuation)
· Initiate ECG monitoring and IV access with two large bore IV's of normal saline or Lactated Ringer's
· Early notification of medical control and the receiving hospital
· Physician may order SoluMedrol at 30 mg/kg IVPB over 30 minutes.
With conscientious efforts you may save the life of patients suffering from head and spinal trauma.
Spinal Motion Restriction
Careful spinal motion restriction may prevent long term disability or paralysis for these patients. Spinal motion restriction may be performed by utilization of several devices. Historically, this would involve utilization of a rigid cervical collar, long spine board, cervical immobilization device, and a restraining device such as a spider strap, webbing, or triangular bandages.
Recently, we have seen an increase in the use of tape as a restraining device. One should be aware that some tape may not keep the patient restrained during some procedures. You may be required to tilt the board if the victim is pregnant or if they begin to vomit suddenly. Your medical director and your department should evaluate devices as to their efficiency and decide which devices are best suited for your needs. Other devices such as a short spine board or Kendrick Extrication Device (KED) may be utilized during situations not requiring rapid extrication.