The brainstem is the lower part of the brain where it connects to the spinal cord. It consists of the midbrain, pons, and the medulla oblongata (Fig. 6-4). Most of the cranial nerves originate in the brainstem. Many neurologic functions of particular importance to the RT, such as regulation of heart rate, blood pressure, and breathing, are located in the brainstem. In addition, the brainstem contains reflex centers for certain cranial nerve functions such as the pupillary reflex, which is discussed later in this chapter. Lesions in the brainstem can cause a wide range of breathing problems from hyperventilation to apnea.

FIGURE 6-4 Left lateral view of the cerebellum showing its anatomic relationship with the brainstem.

In addition to the centers that control the function of various organs and organ systems, the brainstem also contains multiple afferent and efferent pathways that connect the brain to the spinal cord. An important feature of these pathways is that they cross over to the other side in the medulla, an area called the pyramidal tract. Therefore, if a disease affects these pathways above the pyramidal tracts, the neurologic deficit will be on the contralateral (opposite) side, but if the pathways are affected below the pyramidal tract, the neurologic deficit will be on the ipsilateral (same) side.

SIMPLY STATED

Many neurologic functions of particular importance to the RT, such as regulation of heart rate, blood pressure, and breathing, are located in the brainstem.

The cerebellum is located in the posterior part of the brain and is responsible for controlling equilibrium, muscle tone, and coordination of muscle movements. Lesions in the cerebellum cause characteristic symptoms such as loss of muscle coordination (ataxia), tremors, and disturbances in gait and balance.

The spinal cord lies within the center of the vertebral bodies and extends from the base of the brain down to the level of the first lumbar (L1) vertebra (see Fig. 6-1). The rest of the space between the vertebral bodies is taken up by the loose collection of the nerve roots that originate in the lower portion of the spinal cord and the cerebrospinal fluid (see Lumbar Puncture). This collection of nerve roots is called the cauda equina (Latin for horse’s tail). The fact that the spinal cord does not extend below L1 will become important when we discuss the anatomy of lumbar puncture. The spinal cord spans a distance of approximately 45 cm in the average adult. It serves the purpose of connecting the brain to the various parts of the body for motor and sensory function. It is an oval cylinder that has two tapering bulges: one in the cervical region and one in the lumbar region. The bulges are formed by the accumulation of extra neurons for the innervations of the upper and lower extremities, respectively.

Two sets of nerve fibers called spinal nerves project from both sides of the spinal column at 31 locations along the spine. Sensory and motor nerve roots separate as they exit the spinal cord until their fibers combine at the level of the dorsal root ganglion. The dorsal nerve root consists of posterior nerve fibers that carry sensory information into the spinal cord. The ventral nerve root consists of anterior nerve fibers that conduct motor impulses out of the spinal cord. Because all spinal nerves contain both motor and sensory fibers, they are called mixed nerves. Each has the ability to provide sensory input to the brain (e.g., feel pain) and the ability to cause muscle movement (e.g., extend the arm on command) (Fig. 6-5).

FIGURE 6-5 Caudal view of the spinal cord. The diagram shows the motor neuron (anterior) and the sensory neuron (posterior) before they come together as a spinal nerve. The sensory neuron provides sensory input to the brain to elicit a motor response.

These spinal nerves have no specific name but rather are numbered according to the level of the vertebral column at which they exit the spinal column. There are 8 cervical (C1 to C8), 12 thoracic (T1 to T12), 5 lumbar (L1 to L5), 5 sacral (S1 to S5), and 1 coccygeal pair of spinal nerves. It must be noted that the number of spinal nerves does not always equal the number of the corresponding vertebrae (8 cervical nerves vs. 7 vertebrae), which might lead to some confusion.

A herniated vertebral disk is the most common nerve root pathology that results in compression on the nerve roots. This usually results in pain with radiation into the affected area of skin (dermatome) supplied with afferent nerve fibers by a single posterior spinal root (Fig. 6-6).

FIGURE 6-6 Outcome after spinal cord or root injury.

SIMPLY STATED

A herniated vertebral disk is the most common nerve root pathology, and it causes pain with radiation into the affected area of skin (dermatome) supplied with afferent nerve fibers by a single posterior spinal root.

Two spinal nerves important for respiratory function are the right and left phrenic nerves that innervate the diaphragm to control breathing. The phrenic nerves arise from the cervical spine roots of C3 to C5. Damage to this portion of the spinal cord (or above) can result in complete paralysis of the diaphragm as well as the intercostal muscles and make the patient dependent on a ventilator for life. The additional muscles of respiration, such as intercostal muscles, are innervated by the spinal nerves that originate in the thoracic portion of the spinal cord. These nerves, although normal, will be cut off from the efferent impulses originating above the injury (C3 to C5 level, or above) and will be rendered ineffective. Figures 6-6 and 6-7 illustrate the typical outcome after spinal cord or root injury.

FIGURE 6-7 Schematic representation of dermatomes.

SIMPLY STATED

The phrenic nerves arise from the cervical spine roots of C3 to C5. Damage to this portion of the spinal cord can result in complete paralysis of the respiratory muscles and ventilator dependency.

Assessment of Consciousness

The cerebral hemispheres (or lobes) represent the highest and most complex level of neurologic function. Although a great deal of the mental status reflects integration of cortical function, it can still be divided into functional areas that correspond to anatomic regions of the cerebral hemispheres (Fig. 6-8). Table 6-1 gives a brief overview of areas of cortical function that can be assessed by components of the mental status examination.

TABLE 6-1

Assessment of Cerebral Cortical Function

Cerebral Lobe	Cortical Function	Assessment
Frontal	Attention: working memory	Digit span, spelling backward, and naming months of the year backward
	Judgment: abstract reasoning	Problem solving, verbal similarities, and proverbs
	Set generation	Verbal fluency and the ability to generate a set of items
Temporal	Orientation, memory	Questions about month, date, day of week, and place
		Three-word recall (recent memory)
		Naming U.S. presidents (remote memory)
Frontal-temporal	Receptive language	Following commands (spoken and written language)
	Expressive language	Fluency and correctness of content and grammar
	Expressive language	Reading comprehension
Parietal (dominant)	Gnosis	Identifying objects placed in the hand and numbers written on the hand with eyes closed
	Constructional	Attending to the contralateral side of the body
		Drawing a face, clock, or geometric figures
		Right-left orientation, naming fingers, and calculations
Parietal (nondominant)	Praxis	Performing skilled motor tasks without any nonverbal prompting
Occipitotemporal	Visual recognition	Recognition of colors and faces

FIGURE 6-8 Graphical representation of the cerebral lobes or hemispheres and their corresponding cortical function.

Assessing Consciousness

Whenever evaluating consciousness, it is important to assess the level of consciousness (wakefulness and alertness) as well as the content of consciousness (awareness and thinking). A change in either is usually the first clue to CNS dysfunction. The initial goals of the examination of a patient with altered mental status are to determine whether the patient is conscious and then to determine awareness.

Assessment of consciousness begins when you first encounter the patient. A neurologically healthy patient will be awake and interacting with those around. If asleep, the patient can be easily aroused to an awake, alert state. Different levels of consciousness from full alertness to coma have been defined (Box 6-1). These and other terms used to categorize consciousness are frequently used imprecisely, so it is often recommended to avoid using them. Instead, a brief description of the applied stimulus and arousal pattern is preferred.

Box 6-1 Levels of Consciousness

Full consciousness: The patient is alert and attentive, follows commands, responds promptly to external stimulation if asleep, and once awake, remains attentive.

Lethargy: The patient is drowsy but partially awakens to stimulation; the patient will answer questions and follow commands but will do so slowly and inattentively.

Obtundation: The patient is difficult to arouse and needs constant stimulation to follow a simple command. Although there may be verbal response with one or two words, the patient will drift back to sleep between stimuli.

Stupor: The patient arouses to vigorous and continuous stimulation; typically, a painful stimulus is required. The only response may be an attempt to withdraw from or remove the painful stimulus.

Coma: The patient does not respond to continuous or painful stimulation. There are no verbal sounds and no movement, except possibly by reflex.

The assessment of the content of consciousness starts with orientation. The patient will often be asked to state his or her name, the current date, and the present location. A fully conscious patient will be expected to answer those questions in detail—for example, first and last name, month, day and year, and the ward and name of the hospital. Such patients can be described as alert and oriented times three (one score for each name, date, and location). However, a patient who just woke up from coma or heavy sedation may not be able to answer these questions in such detail. A partial response (e.g., first name only, month and year, but not the exact date) may substitute for a correct answer in such situations. The content of consciousness has multiple additional components, many of which are outside of the scope of this chapter.

The two common conditions often present in hospitalized patients are coma and delirium. Although coma is characterized by the absence of arousal and awareness, a patient with delirium has a fluctuating course with alternating levels of consciousness as well as marked deficits in attention and organized thinking (confusion). Several studies have shown that delirium occurs in 60% to 80% of mechanically ventilated patients and that it is independently associated with longer stay in the hospital, higher mortality, and poor long-term cognitive function. Once again, when referring to a patient with delirium, it is better to give a descriptive evaluation of the patient’s behavior and thinking, rather than a simple statement of “confusion” or “delirium,” which can often be misleading. The causes of delirium are frequently multifactorial, including some combination of hypoxia, electrolyte or acid-base imbalance, concomitant medical illness, sleep deprivation, use (previous or current) of sedation, unfamiliarity with surroundings, and side effects of medications. A patient with preexisting dementia may present similarly to a patient with delirium, and it may be difficult to tell them apart without knowledge of the patient’s medical history.

SIMPLY STATED

Coma and delirium are two common dysfunctions of the level and content of consciousness, respectively, that are often present in hospitalized patients, especially in the ICU. Delirium occurs in 60% to 80% of mechanically ventilated patients and is associated with longer stay in the hospital, higher mortality, and poor long-term cognitive function.

Some patients who recover from their initial severe neurologic injury will remain in a persistent vegetative state. The patient’s eyes may be open, but the patient cannot be engaged. Patients with this condition may appear to be, but actually are not, aware of their surroundings, do not respond to verbal stimuli or commands in a meaningful way, do not track object or individuals, and do not respond to environmental changes. Overall prognosis is usually poor, even though breathing may not be impaired if the brainstem is unaffected by the injury. The term persistent vegetative state is frequently misused by medical and nonmedical professionals and should be avoided in favor of more descriptive statements.

Another commonly misused term is encephalopathy. When translated from Latin, it simply means suffering of the brain. Naturally, any condition affecting the brain can be classified as encephalopathy, but the term is usually reserved for patients with a combination of alteration in both level and content of consciousness (e.g., lethargy and confusion in patients with advanced liver disease, a condition often called hepatic encephalopathy).

Glasgow Coma Scale

The Glasgow Coma Scale (GCS) was published in 1974 by Graham Teasdale and Bryan J. Jennett at the University of Glasgow as the neurologic assessment tool in patients with head injury. It has multiple limitations outside of its initial scope in acute traumatic brain injury patients, especially in ICU patients, but the simplicity of the scale makes it widely useful for nearly every member of the health care team from emergency medical services personnel for initial evaluation to ICU staff in daily neurologic assessment. The GCS is commonly incorporated in other, more complex and comprehensive acute illness scoring systems in the ICU. It is the most widely used instrument for quantifying neurologic impairment. The GCS is used to test best motor response, best verbal response, and eye opening. Although it is easy to perform and readily reproducible, it is poorly suited to patients who have impaired verbal responses caused by aphasia, hearing loss, or tracheal intubation or more subtle alterations of consciousness, such as delirium. A scale that goes from 3 (deep coma or death) to 15 (fully awake) is useful for rapid triage (Table 6-2). Endotracheal intubation makes it impossible to test the patient’s verbal response, so the letter “T” is often attached to the GCS score to indicate the presence of the tube (e.g., GCS 5T).

TABLE 6-2

Glasgow Coma Scale

Action	Response	Score
Eyes open	Spontaneously	4
	To speech	3
	To pain	2
	None	1
Best verbal response	Oriented	5
	Confused	4
	Inappropriate words	3
	Incomprehensive sounds	2
Best motor response	Obeys commands	6
	Localized pain	5
	Flexion withdrawal	4
	Abnormal flexion	3
	Abnormal extension	2
	Flaccid	1
	Total	15