1. Coma – Metabolic Causes
Neurology Course – 4th Year

2. 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.

3. 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

4. Glasgow Coma Scale (GCS)
Best eye response (E)
Best verbal response (V)
Best motor response (M)
4 Eyes opening spontaneously
5 Oriented
6 Obeys commands
3 Eye opening to speech
4 Confused
5 Localizes to pain
2 Eye opening in response to pain
3 Inappropriate words
4 Withdraws from pain
1 No eye opening
2 Incomprehensible sounds
3 Flexion in response to pain
1 None
2 Extension to pain
1 No motor response

5. Metabolic Coma - Etiologies
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

6. Metabolic Causes – Temperature Changes
Hypothermia
Hyperthermia (febrile coma)

7. Metabolic causes of coma -Hepatic coma
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

8. 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

9. Disturbances of Glucose Metabolism
Diabetic Ketoacidosis Hyperglycaemic non-ketotic diabetic coma Diabetic hyperosmolar coma Hypoglycaemic coma

10. Rare Causes of Metabolic Coma
Hypothyroidism Hyperthyroidism Pituitary failure Adrenocortical failure

11. 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

12. Prognosis of Coma
In general, coma carries a serious prognosis. This is dependent to a large extent on the underlying cause.