Definition of Coma

A state of impaired arousability and impaired responsiveness to external stimuli (verbal, tactile, noxious).

Etiologies

• Disturbance of bilateral cerebral hemispheres or bilateral thalami:
  • Compression (supratentorial structural lesion that is bilateral or causing herniation): intracranial hemorrhage (epidural hematoma, subdural hematoma, intracerebral hemorrhage), abscess, ischemic infarct with edema, tumor, or inflammatory lesion
  • Metabolic disturbance (electrolyte abnormalities, hyperammonemia, hypothyroidism, uremia, hypercarbia, etc.)
  • Meningoencephalitis
  • Global cerebral ischemia (e.g. post-cardiac arrest)
  • Intoxication (opioids, alcohol, medicati0on overdose, etc.)
  • Ictal or post-ictal state
• Disturbance of reticular activating system (RAS) in the brainstem:
  • Compression (structural lesion), infarct (basilar artery thrombosis), hemorrhage, osmotic demyelination  

Evaluation

• ABCs, vital signs, neurologic exam (pupils, brainstem reflexes, motor response)
• Check and treat for reversible causes
  • Finger stick glucose and if low, give 25g dextrose with 100mg thiamine
  • Give 0.4-1.2mg IV naloxone if opioid ingestion is possible
• Draw basic labs: renal panel/electrolytes, CBC, coags, LFTs, TSH, ammonia, urine tox screen, blood gas
• Non-contrast head CT. If concerned for brainstem pathology, consider CT angiogram head and neck (to rule out basilar thrombosis)

Physical Exam

Aimed at elucidating underlying cause(s) and assessing depth of coma.

• General:
  • Vital signs
  • Breathing pattern: hyperventilation, Cheyne-Stokes respirations (alternating tachypnea and apneic pauses, indicative of bihemispheric lesions but also seen in heart failure), apneic pauses
  • Signs of trauma: raccoon eyes, boggy areas of scalp, otorrhea, rhinorrhea
  • Nuchal rigidity (can be seen in meningitis, SAH); be careful if history of trauma
  • Skin inspection: color, temperature, rashes/discolorations
• Fundoscopic exam: examine for signs of increased ICP (papilledema)
• Cranial nerves:
  • Visual fields: check blink to threat (bilateral absence in coma; unilateral absence in unilateral lesion)
  • Pupils: check size, reactivity, symmetry (up to 0.5mm difference = normal population variant)
    • Pinpoint: toxic effect (e.g. opioids) vs. pontine or medullary lesion
    • Dilated: toxic effect (e.g. stimulants) vs. midbrain lesion (unilateral dilation concerning for uncal herniation, unilateral medication effect, or traumatic injury)
  • Extraocular muscle movements:
    • Eyes at rest: dysconjugacy and roving movements are normal in coma; persistent deviation may indicate stroke (gaze toward lesion) or seizure activity (away from seizure focus if seizing and toward lesion if post-ictal)
    • Oculocephalic reflex: hold eyelids open, turn head quickly to one side. Eyes should cross the midline symmetrically in the direction opposite the head movement. Repeat in the other direction. If eyes move with the head, this is indicative of brainstem lesion. Do not perform on patients in cervical collar/suspicion for head/neck trauma with cervical spine instability
  • Corneal reflex: hold both eyelids open. Apply sterile normal saline to cornea (over iris) and evaluate for blink response; if absent, touch cornea lightly with sterile gauze; asymmetry indicates CN V or VII pathology
  • Facial strength: facial asymmetry indicates CN VII or contralateral motor tract pathology
  • Gag reflex: use suction to stimulate posterior oropharynx and assess for gag
  • Cough reflex: use endotracheal suction to stimulate carina and assess for cough in intubated patient

• Motor response:
  • Apply painful stimulus centrally (trapezius pinch, sternal rub) or peripherally (nailbed pressure) and evaluate motor response (see section Glasgow Coma Scale):
    • Purposeful/semi-purposeful movements (i.e. localizing/withdrawing from pain)
    • Decorticate posturing (flexion at elbow, wrist, fingers) indicates cerebral hemisphere or thalamic injury but intact brainstem (lesion above red nucleus in midbrain)
    • Decerebrate posturing (extension at elbow, forearm pronation, wrist flexion) indicates severe injury to the brainstem (lesion below red nucleus)
  • Important: asymmetric posturing indicates a brain lesion until proven otherwise!

Further Workup

If etiology unexplained after workup above, consider more detailed neurologic testing:

• LP (CT first to rule out impending herniation) with opening pressure (legs straight) to evaluate for infectious and inflammatory etiologies
• EEG to evaluate for subtle or non-convulsive seizures
• MRI brain (can be with or without contrast depending on patient) to evaluate for structural lesion

Key Points

• Patients in a coma are suffering from either a bilateral hemispheric lesion or a brainstem lesion
• Assess and treat for common reversible causes
• Cranial nerve exam and motor responses are key for localizing
• Further evaluation with LP, EEG, and MRI may be helpful

Plum F, Posner JB. The Diagnosis of Stupor and Coma Edition 3. FA Davis Company: Philadelphia. 1982.