Coma – Metabolic Causes
Neurology Course –
4th Year
Definition Of Conciousness
“Consciousness is wakefulness plus awareness”
 Brainstem mechanisms control the state of consciousness;
 Cortical activity provides the contents of consciousness
 The ARAS is inhibited by sleep centres in the hypothalamus, depressed by
alcohol, sleep-inducing drugs, anaesthetics and tranquilizers. This de-activates
the thalamocortical neurons leading to the changed firing mode. This results in a
low degree of consciousness.
Definition Of Levels Of Arousal (Conciousness)
 Consciousness requires:
Intact pontine reticular activating system
Iintact cerebral hemisphere, or at least part of a hemisphere
 Coma requires dysfunction of either :
Pontine reticular activating system or
Bihemispheric cerebral dysfunction
Classification:
 Supratentorial lesions cause coma by either widespread bilateral disease,
increased intracranial pressure or herniation.
 Infratentorial lesions involve the ARAS, usually with associated brainstem signs
 Metabolic coma causes diffuse hemispheric involvement and depression of
ARAS, usually without focal findings
Glasgow Coma Scale (GCS)
Best eye
response (E)
4 Eyes opening
Best verbal
response (V)
Best motor
response (M)
5 Oriented
6 Obeys commands
4 Confused
5 Localizes to pain
3 Inappropriate words
4 Withdraws from pain
2 Incomprehensible
3 Flexion in response to
sounds
pain
1 None
2 Extension to pain
spontaneously
3 Eye opening to
speech
2 Eye opening in
response to pain
1 No eye opening
1 No motor response
Metabolic Coma - Etiologies
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Respiratory: Hypoxia, Hypercarbia
Hypoglycemia, Hyperglycemia
Hepatic encephalopathy
Severe renal failure
Hormonal: Hypothyreosis, Hyperthyreosis, Addisonian Crisis, Pituitary Failure
Electrolyte: Hyponatremia, Hypercalcemia
Infectious: Meningitis, Encephalitis
Toxins, drugs
Metabolic Causes – Temperature Changes
Hypothermia
Hyperthermia (febrile coma)
Metabolic causes of coma -Hepatic coma
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The disturbance of consciousness due to raised ammonia
Evidence of altered blood brain barrier
Impaired cellular Na+K+ -ATP pump resulting in glial cell edema
Inappropriate cerebral vasodilatation
Renal coma
May occur in acute or chronic renal failure
 Raised blood urea alone cannot be responsible for the loss of consciousness but
 Metabolic acidosis, electrolyte disturbances and water intoxication due to fluid
retention may be responsible
Disturbances of Glucose Metabolism
Diabetic Ketoacidosis
Hyperglycaemic non-ketotic diabetic coma
Diabetic hyperosmolar coma
Hypoglycaemic coma
Rare Causes of Metabolic Coma
Hypothyroidism
Hyperthyroidism
Pituitary failure
Adrenocortical failure
Metabolic Coma – Drugs and Alcohol
The most commonly drugs in suicide attempts are :
Benzodiazepines
Paracetamol
Antidepressants
Narcotic overdoses (heroin)
Alcohol intoxication
At low plasma concentrations of alcohol - mental changes
At higher levels coma ensues
Prognosis of Coma
In general, coma carries a serious prognosis.
This is dependent to a large extent on the underlying cause.