2 Structures in the brain which induce coma if abnormal

3 Conditions which can induce coma

4 Items in the neurologic exam which are important

There is no great mystery regarding the region of nervous system disorder that is affected in stuporous or comatose patients; it is in the brainstem or above. The neurologic examination is directed mainly at determining whether this pathology is due to a structural lesion or due to metabolic dysfunction (including drug effects). The most pertinent examination findings are abnormal reflexes that indicate dysfunction in specific regions of the brainstem, or a consistent asymmetry between right- and left-sided responses.

1. There is 1 thing to check immediately in all coma patients – the capillary blood sugar. Be prepared to give 50% glucose IV if low. Narcan can be considered as well if narcotic overdose is even a remote possibility.

2. There are 2 structures in the brain which, if abnormal, can induce coma:

1. The brainstem reticular activating system – either a lesion or damage from herniation

2. Both hemispheres. A typical stroke will not be a cause of coma unless brain swelling is sufficient to cause herniation. This is unlikely to be an early event.

3. There are 3 conditions affecting the brain which can account for coma:

1. Systemic toxic or metabolic encephalopathy

2. Structural lesion affecting both hemispheres or causing herniation

3. Postictal state or ongoing siezure.

4. There are 4 items which are important in the neurological examination:

1. Respiratory rate and arterial blood gases including evaluation for acidosis, hypoxemia and hypercarbia

2. Pupil size, symmetry and reactivity. Preserved pupillary reflexes in coma are characteristic of metabolic encephalopathy.

3. Extra ocular eye muscle movement evaluation by calorics or doll’s eyes reflex. Loss of eye motion is characteristic of sedative drug overdose.

4. Motor response to a painful stimulus. Any motion away from the painful stimulus, even if unilateral, must be considered to be an early indicator of a significant structural lesion. The supraorbital ridge is an ideal site. Noxious stimulation of the lower extremity (produced by squeezing a nailbed or pinching the skin of the foot) may produce triple flexion (dorsiflexion of the ankle, with flexion of the knee and hip) purely as a local withdrawal reflex. To look for purposeful withdrawal, the stimulus should be applied in a location where triple flexion would be an inappropriate response, such as the anterior thigh: hip flexion would indicate purely reflex withdrawal, whereas hip extension would indicate a purposeful movement.

Sources:

1. Simon, Audio Digest Emergency Medicine, 1985.

2. Gelb D, The Neurologic Examination in Special Circumstances, UpToDate Desktop Application 13.3, 2006