Coma

  • Definition
    • A state of prolonged unconsciousness characterized by loss of reaction to external stimuli or, a state of unrousable unresponsiveness.
  • Differentiate from:
    • Stupor
      • Unconscious but can be aroused with repeated stimuli.
    • Delirium
      • Confused state often with restlessness and hallucinations.
    • ‘Locked-in’ syndrome
      • actually conscious but unable to speak or move
      • may move eyes (massive brainstem damage)
    • Vegetative state
      • apparently awake but unresponsive (brainstem intact but widespread cortical damage)
      • may breath spontaneously.

The Reticular Activating System

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  • Consciousness is determined by the reticular activating system
    • which is located in the brainstem
    • and its ascending connections

Coma is considered a medical emergency:

  • Keep the patient alive
    • resuscitate if necessary
  • Exclude obvious factors
    • head injuries
    • hypogylcaemia, etc.
  • Obtain history
    • eyewitnesses
    • medical information cards
      • eg. MedicAlert
  • Do general and neurological examination
  • Do appropriate investigations

Causes of Coma

  • Neurological
    • Lesions within the brainstem
      • affecting the reticular activating system
    • Lesions in other parts of the brain
      • compressing the brainstem
    • Traumatic Brain Injury
      • Diffuse brain injury
      • Extradural (epidural) haemorrhage
        • Haematoma – blood collection between the skull and the dura
        • This is due to trauma resulting in rupture of arteries or veins
          • commonly the middle meningeal artery
        • Treatment is to evacuate the haematoma by drilling a burr hole.
      • Subdural haemorrhage
        • The haematoma is between the arachnoid and the dura
        • They are due to rupture of the bridging veins between the cerebral cortex and the venous sinuses
        • Mid-line shift
          • Ipsilateral ventricle effaced
        • Acute or chronic
          • chronic subdural haematomas become isodense (darker appearance) 
    • Vascular (eg. stroke)
      • majority do not result in coma
        • large strokes can act as mass lesions
    • Infections (eg. encephalitis)
    • Intracranial tumours
    • Epilepsy/Post-Ictal states
    • Hypertensive encephalopathy
  • Toxic, metabolic, inflammatory or vascular conditions diffusely affecting the brain
    • Hypoxia, CO2 Narcosis
    • Drugs / Poisons
    • Hypoglycaemia, Hyperglycaemia
    • Hepatic Encephalopathy
    • Electrolyte Abnormalities /Uraemia
    • Endocrine: Myxoedema, Addisonian
    • Liver Failure (portosystemic encephalopathy)

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Types of coma

Coma due to mass lesions

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  • Hematoma, large strokes ( a type of mass lesion)
    • compress brain tissue causing:
      • herniation of brain tissue from one compartment to another

Hypoglycaemic coma

  • Signs & Symptoms
    • blood glucose < 3.0 mmol/L
    • Sympathetic:
      • sweating
      • tremors
      • palpitations
      • anxiety
    • Neuroglycopenia
      • confusion
      • abnormal behaviour
      • coma
      • death
  • Causes
    • oral hypoglycaemic agent/insulin in treatment of diabetes
      • Give glucose immediately
      • IV if patient drowsy or unconscious
  • Whipple’s Triad
      1. Symptoms known or likely to be caused by hypoglycemia
      2. A low plasma glucose measured at the time of the symptoms
      3. Relief of symptoms when the glucose is raised to normal

Hyperglycaemic comas

  • There are two types of hyperglycaemic comas in diabetes:
    • Diabetic Ketoacidosis (DKA)
      • Type 1 diabetes
    • Hyperosmolar Hypergylcaemic Non-Ketotic Coma (HHNC)
      • Type 2 diabetes
      • The new term is: HHS or Hyperosmolar Hyperglycaemic State. However only about 20% of HHS have coma

Drugs & Coma

  • Drug overdose may be accidental or intentional
  • Diagnosis
    • History important
    • Suspect if
      • IV needle marks
      • pin-point pupils

Liver Failure (Portosystemic Encephalopathy)

  • In liver failure
    • there is accumulation of ammonia in the systemic circulation
    • leading to coma
  • It may occur in
    • Acute liver failure
      • acute fulminant hepatitis
      • paracetamol overdose
    • Chronic liver disease
      • alcoholics
      • chronic hepatitis B, C
  • Specific signs to look for
    • Early
      • Drowsiness
      • confusion
      • altered sleep pattern
      • fetor hepaticus
      • Asterixis
        • flapping tremor
      • constructional apraxia
        • loss of the ability to execute or carry out learned purposeful movements
        • despite having the desire and the physical ability to perform the movements
        • disorder of motor planning
    • Late
      • Coma
      • +ve Babinski signs

CNS infection & Coma

  • Serious Infections
    • Encephalitis
    • Meningitis
    • Brain abscess
  • Suspect if
    • fever
    • headache
    • progressive drowsiness
    • fits prior to coma
    • Physical signs of neck stiffness
      • meningism in meningitis
    • Papilloedema
      • may be present indicating raised intracranial pressure

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Postures found in comatose status

*Refer posture and balance lecture

Decerebrate Posture

  • Brainstem Injury
    • Extension of arms with internal rotation
    • Pronation of wrists and flexion of fingers
    • Legs extended with plantar flexion of feet

Decorticate Posture

  • Lesions above brainstem
    • Arms adducted and flexed across the chest
    • Wrist and fingers flexed
    • Legs extended with plantar flexion of feet

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Glasgow Coma Scale
Measure consciousness

  • Based on 3 clinical responses: (EVM)
    • Eye Opening
    • Verbal Response
    • Motor Response

  • Record the best response
    • Minimum Score 3
    • Maximum Score 15
  • Chart initial and subsequent scores
  • The GCS record is the patient’s change in conscious level with time.

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Brain death

  • Definition
    • A condition in which there is:
      • Permanent and irreversible loss of the functions of the brain
      • together with irreversible loss of the capacity to breathe
  • This person is supported by:
    • Artificial mechanical ventilation
    • Other supportive measures
  • A person certified to be brain dead is considered to be legally dead
  • Criteria
    • Coma
    • No spontaneous respiration
    • No response to external stimulation
    • Absence of brainstem reflexes
  • Ethical issues
    • Medicolegal
      • who has the right to determine who should be kept alive by life support?
    • Beneficence
      • the duty of the doctor to do good
    • Justice
      • How is it justified?
      • How is healthcare distributed under circumstances of limited human and financial resources and who / how determines
      • ‘who gets what’?
    • Dignity
      • Everyone has a right to a dignified death
    • Autonomy
      • What would the patient have wanted?
  • Many countries now have legal and medical definitions for brain death:
    • The patient is in apnoeic coma on a ventilator
    • There is evidence of a significant medical or CNS event that would result in brain death
    • Formal tests of brainstem function confirm absent brainstem reflexes
  • Before diagnosing brainstem death exclude:
    • Hypothermia (T<35°C)
    • Drug Intoxication
    • Acid-Base Imbalance
    • Electrolyte Abnormality
    • Hypoglycaemia/Endocrine Disorder
  • Tests of brainstem death:
    • No pupillary response to light
      • pupils fixed
    • No oculocephalic reflex
      • Doll’s Eye
    • No vestibulo-ocular reflex
    • No motor response within cranial nerve distribution
      • No corneal reflex/gag reflex/grimacing to painful stimulus
    • No cough response to pharyngeal/laryngeal/tracheal stimulation
    • Apnoea with no respiratory effort when ventilator is switched off & PaCo2 rises to above 6.7kPa (50mmHg)
  • Tests of brainstem death must be done twice at least 6-24 hours apart
    • Tests must be done independently by 2 different senior doctors, one of whom must not be in the medical team managing the patient
    • EEG is not routinely required
  • Once the diagnosis is established, inform the next-of-kin and explain the diagnosis
    • Allow adequate time for the family to understand and discuss the issue amongst themselves
    • Informed consent must be obtained before withdrawing life support
    • In suitable cases discuss and obtain informed consent from next-of-kin for organ donation
      • Members of the surgical transplant team and the medical team looking after the potential recipient should not be involved in certification of brain death of the donor and in counselling / obtaining consent from the donor’s next-of-kin regarding organ transplantation

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