-IBIS-1.5.0-
tx
nervous system
coma
diagnoses

definition and etiology

definition: Unarousable unresponsiveness, even to energetic and repeated stimulation. It is always a medical emergency.

etiology: Most comas are metabolic, traumatic or toxic in origin. Normal consciousness is maintained by the proper functioning of the reticular activating system (RAS), both cerebral hemispheres, and the connections between them. If there is a lesion in one of those areas, a coma may result. The main reasons for malfunction are:
» Bilateral hemisphere damage or suppression by toxins or drugs
» A brainstem lesion or metabolic abnormality which damages or suppresses the RAS

signs and symptoms

associated signs and symptoms suggesting cause:

• Fever: investigate systemic infection, bacterial meningitis, or brain tumor which may affect temperature regulation.

• High temperature with dry skin: investigate heatstroke.

• Hypothermia (below 31°C is needed to produce a coma): investigate exposure; hypoglycemia; drug overdose (alcohol, barbiturates, phenothiazine); myxedema; or peripheral circulatory collapse.

• Abnormal breathing patterns: investigate brainstem illness.
» Shallow and slow: Depression from drug or metabolic cause.
» Kussmaul (rapid and deep): Metabolic acidosis or pontomesencephalic lesions.
» Cheyne-Stokes (varied rate and depth): Metabolic suppression; mild bilateral hemispheral injury (in general, a mild coma).
» Gasps held in inspiration: Severe, fatal brain injury.

• Abnormal pulse, hyperventilation and hypertension: investigate increased intracranial pressure.

• Hypotension: investigate alcohol or barbiturate overdose; Addisonian crisis; heart attack; internal hemorrhaging; septicemia (gm (-) bacteria).

•Abnormal fundoscopic exam: investigate hypertensive encephalopathy; subarachnoid bleeds; and intracranial pressure.

• Marked petechiae: investigate purpura or hemorrhagic diathesis with a intracerebral bleed.

general signs may include:

• Posturing: Decorticate (upper limbs in flexion with lower limbs in extension) or decerebrate (upper limbs in extension and lower limbs in extension).

• No response to: Conversational voice, shouting, shaking, nasal tickling with a cotton swab, deep pressure on bony prominences.

• Brainstem reflexes present (indicate significant and bilateral hemispheral illness), or absent (brainstem involvement): Cranial nerves, III, IV, VI: Eye movements; caloric stimulation test of the oculovestibular apparatus (cold water irrigation of ear canal with bilateral deviation of eyes to side being irrigated); V, VII (corneal reflex).

lab findings:
• Chemical-toxicologic analysis of urine and blood
• CT scan or MRI
• EEG
• Spinal tap for cerebral spinal fluid analysis

course and prognosis

Brain death occurs when there is a total cessation of cerebral blood flow with massive infarction of the brain when respiratory and cardiovascular functions are uninjured, though respiration needs artificial assistance. It is the only coma state recognized by law as death.

No clinical signs aside that of brain death are reliable predictors of patient outcome.

differential diagnosis

bleeding areas and associated signs:
• Basal ganglia and thalamic hemorrhage: acute onset with headache, vomiting, hemiplegia.
• Subarachnoid hemorrhage: Instantaneous onset; neck stiffness; severe headache; vomiting; III or VI nerve lesions; sudden coma with extensor posturing or just transient loss of consciousness.
• Pontine hemorrhage: Acute onset; absent reflex eye movements; pinpoint pupils, posturing; hyperventilation; sweating.
• Cerebellar hemorrhage: Occipital headache; vomiting; inability to stand.
• Basal artery thrombosis: Neurologic prodrome or warning spells; dysarthria; vomiting; diplopia; asymmetric limb paresis; eye abnormalities.

causes of metabolic coma:
Hypoxia; ischemia; hypoglycemia; encephalitis; generalized epilepsy; drug ingestion; hyponatremia; hypercapnia; hyperosmolarity; renal failure; hepatic failure: so rule out metabolic coma if one of these conditions occurs in a patient.

differential diagnosis of various states of unconsciousness:
Vegetative state; akinetic mutism; abulia; locked-in syndrome; catatonic states; pseudocoma conversion states; stupor; hypersomnia; obtundation.


footnotes