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

    terri

    Terri is obsessed with making medical school as painless as possible. She studies and compiles medical school notes in a concise, easy-to-understand format. She also enjoys reading contributions by others. She is an investor in sustainability projects. Her ideal weekend is wine tasting and experimenting on bread-making. She has yet to master the art of Sourdough baking.

    1 Comment

    Nataliya Piletska · June 10, 2014 at 10:10 am

    Thank you for this, I found it really useful!

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