Neurology - Coma and brainstem death Flashcards
What is the definition of coma?
GCS <8 is a generally accepted definition of coma. Patients are therefore unable to open there eyes or obey commands.
What causes coma?
Causes of coma can be divided into diffuse and focal causes
Name some diffuse causes of coma?
1) Toxic - alcohol abuse and OD
2) Metabolic/ endocrine - hypoglycaemia, HONK, DKA, renal failure, uraemia, electrolyte disturbances (esp. hypo/hypernatraemia and hypercalcaemia), myxoedema coma, hepatic failure
3) Vascular - SAH, vasculitis
4) Ischaemia - anoxic encephalopathy (post CPR), carbon monoxide poisoning
5) Infection - meningitis, encephalitis, sepsis
6) Posttraumatic
7) Epilepsy - Postictal state and status
Focal causes of coma
These causes can be supra or infratentorial
- Infarction
- Neoplasm (primary or secondary)
- Infection - intraparenchymal abscess, subdural empyema
- Haematoma
What brain system is important in maintaining consciousness?
A conscious state depends on a functioning reticular activating system (RAS):
- Fibres for RAS start in the pons and ascend in the midbrain to terminate in the thalamus and hypothalamus
- Infratentorial lesions may directly affect the RAS while a supratentorial lesion may cause cortical dysfunction and transtentorial herniation leading to brainstem distortion
- Diffuse or metabolic causes cause coma by impairing cerebral metabolism
How should a comatose patient be examined?
“ABCD” approach:
- Airways (risk of compromised airway)
- Breathing (respiratory rate, rhythm and character - e.g. Cheyene-Stokes, hyperventilation, apneustic or ataxic pattern due to progressive herniation)
- Circulation (pulse rate, rhythm, BP - check for Cushing’s triad = increased BP, decreased HR and irregular respiratory pattern)
- Disability - GCS
- Temperature and glucose
- Exposure (purpuric rash, alcoholic fetor, jaundice, blood from ear)
- Eyes (AFRO for pupils, extra ocular movements, caloric testing and oculocephalic reflex)
- Brainstem function (gag reflex, corneal reflex)
- Motor (tone, power, reflex)
Why is a pupil examination useful in identifying the cause of coma in a patient?
Presence of equal and reactive pupils usually indicates a diffuse or toxic cause
Unilateral, fixed and dilated pupil usually suggests oculomotor nerve palsy due to progressive herniation from a focal supratentorial mass lesion
(NB - atropine and glutethimide can cause fixed/ dilated pupils, while opiates lead to small pupils with sluggish response to light)
Key investigations in a comatose patient?
1) Imaging - CT head if focal lesion is suspected
2) Blood tests - FBC, U+E, serum osmolarity, LFT, glucose, calcium, blood alcohol, ABG, drug levels
3) LP - useful for excluding meningitis or encephalitis when suspected in the presence of meningeal signs or fever
4) EEG - non convulsive status, or generalised changes suggesting encephalitis
5) Urine - MC&S, osmolarity
What is key in managing a comatose patient?
When approaching the comatose patient remember to start with BOTH assessment and management of ABC
Further management is tailored to the underlying cause - below are just a few examples:
- IV glucose (unless definitely normal) and thiamine
- Naloxone or flumazenil
- Initial measures to lower ICP
- Insertion of ICP monitor
- If meningitis or encephalitis suspected commence empirical antibiotics and antiviral drugs
- Phenytoin IV if status or non-convulsive status (on EEG)
Complications of coma
Depend on the underlying cause:
- Airway compromise due to reduced GCS
- Progressive herniation and death due to raised ICP
- Rapid correction of hyponatraemia can lead to central pontine myelinolysis
- Prolonged hypoglycaemia leading to irreversible brain damage
What is the prognosis in coma?
Depends on the underlying cause
- Coma related to drug or alcohol abuse or hypoglycaemia (if corrected quickly) has a better outcome
- If no improvement patients will need testing for brainstem death to decide regarding withdrawal of ventilator support
Criteria for brainstem death
- Irreversible brainstem damage
- Known irreversible cause (therefore no hypothermia, endocrine or metabolic disturbance or presence of drugs including CNS depressants or neuromuscular blockers)
- No brainstem function with an unresponsive patient on a ventilator (no spontaneous respiratory
- Adequate SBP > 90mmHg
What tests are carried out to confirm brainstem death and how many doctors need to perform them?
Tests are performed by 2 different senior doctors on 2 separate occasions:
- Fixed dilated pupils bilaterally
- Absent corneal reflex
- Absent occulocephalic and vestibule-occular reflex
- Absent gag reflex
- No purposeful response to painful stimuli
- After pre oxygenation (15 mins of ventilator on 100% oxygen) patient is disconnected from ventilator and pCO2 is allowed to rise to >6.65kPa. Absence of spontaneous respiration indicates failure of respiratory centre in medulla
Difference between decorticate and decerebrate posture?
Decorticate posturing - knees inwardly rotated and arms flexed like a “C” shape
- Usually caused by a lesion at the cortical or subcortical level, or the spinal cord
Decerebrate posturing - knees outwardly rotated, arms extended
- Usually caused by brainstem pathology
What is a persistent vegetative state?
= No awareness of self or environment with no purposeful response or movement following traumatic head injury or another cause of brain damage
Spontaneous respiration and stable circulation are present
