Neurologic assessment is a method of obtaining specific data in relation to the function of a patient’s nervous system. It is a comprehensive evaluation that covers several areas: mental status, cranial nerve function, motor system, coordination, sensory system, and various reflexes. Although different aspects of neurologic examination are often done by the respiratory therapist (RT), nurse (RN), or other member of the health care team, a detailed and in-depth assessment is usually the ultimate responsibility of the attending physician or the neurologist. Injuries that involve the nervous system often affect the patient’s respiratory system and the ability of the patient to cooperate with respiratory care procedures; therefore, the RT should become familiar with the key components of the neurologic assessment. The challenges of examining an intubated, restrained, and often sedated patient in the intensive care unit (ICU) make neurologic assessment difficult in many patients. This chapter covers in detail the clinical neurologic assessment and the terminology usually used to describe it. Ancillary tests, neurologic control of vital organ function, and determination of brain death are discussed briefly at the end of the chapter. The reader is reminded that the terminology used in the description of neurologic assessment is often misused and misinterpreted in clinical practice, even by highly qualified professionals. For documentation and communication purposes, it is generally preferred to give a descriptive assessment of the neurologic status, such as stimuli applied to the patient and the responses they elicited.
Proper clinical assessment of the nervous system emphasizes the neurologic history and examination. Obtaining a thorough history from the patient or family members can help the clinician characterize the dysfunction, whereas the neurologic examination will assist in localizing and quantifying its severity. The neurologic examination is often brief if initial interactions with the patient are normal (e.g., the patient responds appropriately to verbal stimuli) and the patient has no symptoms suggesting neurologic disease. This initial interaction with the patient could provide insights about the patient that might affect the patient’s adherence to respiratory care and performance of complex tasks that require coordination of multiple sensorimotor systems (e.g., the use of a pressurized metered-dose inhaler). A more extensive examination is performed when abnormalities are suspected and may involve the expertise of a neurologist. The initial examination establishes baseline data with which to compare subsequent assessment findings. Neurologic observation allows monitoring and evaluation of changes in the nervous system that aid in the diagnosis and treatment that later affect patient prognosis and rehabilitation. It also gauges the patient’s response to the clinician’s interventions. After a thorough evaluation is done on admission or at the beginning of each shift, subsequent assessments should be tailored to the patient’s condition. The frequency of these assessments will depend on the patient’s diagnosis, acuity of the condition, and how rapidly changes are occurring or expected to occur.
To perform or understand a neurologic assessment, the examiner needs a basic understanding of anatomy and function of the nervous system. The neurologic system is made up of two major parts: the central and peripheral nervous systems. The central nervous system (CNS) contains the brain and spinal cord (Fig. 6-1), whereas the peripheral nervous system is composed of the 12 cranial nerves and the 31 spinal nerves. The brain consists of three parts: the cerebrum, which contains two hemispheres; the brainstem (midbrain, pons, and medulla); and the cerebellum.
The peripheral nervous system is organized according to its function into sensory (afferent, from the Latin word afferens, to bring to) and motor (efferent, from Latinefferens, to bring out) divisions. This functional organization allows the clinician to understand how signals are transmitted to and from the CNS (Fig. 6-2).
The cerebrum is the largest part of the brain and is made up of two hemispheres and areas that control specific intellectual or motor functions (Fig. 6-3). Lesions in the cerebrum can lead to abnormalities in functions such as movement, level of consciousness, ability to speak and write, emotions, and memory.
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.
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.
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).
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).
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.
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.
|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|
|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|
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.
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.
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).
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).
|Best verbal response||Oriented||5|
|Best motor response||Obeys commands||6|
Patients with GCS scores of 12 to 15 often do not require ICU admission. Scores of 9 to 12 on the GCS indicate a significant insult with a moderate coma. Patients with GCS scores lower than 9 have a severe coma and typically require endotracheal intubation for airway protection and ventilatory assistance (other textbooks may use the mnemonic “less than eight, intubate” to easily remember this concept). Such absolute dependence on the neurologic status and the GCS score in decision making for endotracheal intubation may be warranted only in certain situations. For example, patients with head trauma and low GCS score may need to be intubated because they will have a prolonged recovery period, but patients with more transient neurologic deficit (such as drug or alcohol overdose) may not benefit from intubation based solely on their GCS score.