Because the comatose patient cannot understand and follow commands, the examination of the comatose patient is a modified version of the neurological examination of an alert patient. If a patient is comatose, it is safe to assume that the nervous system is being affected at the brainstem level or above. The goal of a neurological examination in a comatose patient is to determine if the coma is induced by a structural lesion or from a metabolic derangement, or possibly from both.
Two findings on exam strongly point to a structural lesion: 1. consistent asymmetry between right and left sided responses, and 2. abnormal reflexes that point to specific areas within the brain stem.
Mental status is evaluated by observing the patient's response to visual, auditory and noxious (i.e., painful) stimuli. The three main maneuvers to produce a noxious stimulus in a comatose patient are: 1. press very hard with your thumb under the bony superior roof of the orbital cavity, 2. squeeze the patient's nipple very hard, and 3. press a pen hard on one of the patient's fingernails.
Comatose patients may demonstrate motor responses indicative of more generalized reflexes. Decorticate posturing consists of adduction of the upper arms, flexion of the lower arms, wrists and fingers. The lower extremities extend in decorticate posturing. Decerebrate posturing consists of adduction of the upper arms, extension and pronation of the lower arms, along with extension of the lower extremities.
In general, patients with decorticate posturing have a better prognosis than patients who exhibit decerebrate posturing. Posturing does not have any localizing utility in humans.
Visual acuity cannot be tested in a comatose patient, but pupillary responses may be tested as usual. Visual fields may be partially evaluated by noting the patient's response to sudden objects introduced into the patient's visual field. Extra-ocular muscles may be evaluated by inducing eye movements via reflexes. The doll's eyes reflex, or oculocephalic reflex, is produced by moving the patient's head left to right or up and down. When the reflex is present, the eyes of the patient remain stationary while the head is moved, thus moving in relation to the head. Thus moving the head of a comatose patient allows extra-ocular muscle movements to be evaluated.
An alert patient does not have the doll's eyes reflex because it is suppressed. If a comatose patient does not have a doll's eyes reflex, then a lesion must be present in the afferent or efferent loop of this reflex arc. The afferent arc consists of the labyrinth, vestibular nerve, and neck proprioceptors. The efferent limb consists of cranial nerves III, IV and VI and the muscles they innervate. Furthermore, the pathways that connect the afferent and efferent limbs in the pons and medulla may also be disrupted and cause a lack of the doll's eyes reflex in a comatose patient.
If the patient is being examined in the emergency department or if there is a history of potential cervical spine injury, the doll's eyes reflex should not be elicited until after a cervical spine injury is ruled out.
The oculovestibular reflex, or cold calorics, is produced by placing the patient's upper body and head at 30 degrees off horizontal, and injecting 50-100cc of cold water into an ear. The water has the same effect on the semicircular canal as if the patient's head was turned to the opposite side of the injection. Therefore, the patient's eyes will look towards the ear of injection. This eye deviation lasts for a sustained period of time. This is an excellent manuever to assess extra-ocular muscles in the comatose patient with possible cervical spine injury.
If the oculovestibular reflex is absent, a lesion of the pons, medulla, or less commonly the III, IV, IV or VIII nerves is present. Unlike the oculocephalic reflex, the oculovestibular reflex is present in awake patients. In alert patients, this reflex not only induces eye deviation, it also produces nystagmus in the direction of the non-injected ear. The slow phase is towards the injected ear and the fast phase is away.
Cranial nerve V may be tested in the comatose patient with the corneal reflex test. Cranial nerve VII may be examined by observing facial grimicing in response to a noxious stimulus. Cranial nerves IX an X may be evaluated with the gag reflex.
The motor system is assessed by testing deep tendon reflexes, feeling the resistance of the patient's limbs to passive movements, and testing the strength of posturing and local withdrawl movements. Local withdrawl movements may be elicited by pressing a pen hard on the patient's fingernail and observing if the patient withdrawls the respective limb from the noxious stimulus.
Upper motor neuron lesions are characterized by spasticity. Spasticity is increased muscle tone leading to resistance of the limbs to passive manipulation. This spasticity classically results in the clasp-knife response. The clasp-knife response is when the spastic limb is passively moved with great resistance, when suddenly the limb "gives", becoming very easy to move. The clasp knife response is most prominent in the muscle groups least affected by the upper motor lesion, e.g., flexors in the upper extremities or extensors in the lower extremities.
The sensory system can only be evaluated by observing the patient's response, or lack of response, to noxious stimuli in different parts of the body.
In addition to withdrawing from noxious stimuli, patient's may localize towards noxious stimuli. Localization indicates a shallower coma compared to the patient that withdraws.
A common prognostic assessment, called the Glascow Coma Scale, is often used to measure the depth of coma. The Glascow Coma Scale is often used serially as a means to follow a comatose patient clinically. It has 3 sections: I. best motor response, II. best verbal response, and III. eye opening.
A lower score indicates a deeper coma and a poorer prognosis.