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subarachnoid haemorrhage (SAH)


  • SAH usually refers to the sudden onset, nontraumatic presence of blood within the subarachnoid space from some pathologic process, usually from rupture of a berry aneurysm (85%) or arteriovenous malformation (AVM)
    • Cocaine abuse, sickle cell anemia (usually in children), and, rarely, anticoagulant therapy, problems with blood clotting and pituitary apoplexy can also result in SAH
  • failure to diagnose the sentinel bleed of a SAH exposes the patient to risk of death from a second more major bleed
    • 15% re-bleed early
    • 40% re-bleed within next 4 weeks
  • vasospasm is a serious complication of SAH and thus patients diagnosed with SAH are usually Rx with nimodipine to help prevent it.
  • if a cerebral aneurysm is identified on angiography, two measures are available to reduce the risk of further bleeding from the same aneurysm: clipping and coiling (better outcomes if aneurysm is accessible but risk of long term recurrence).

incidence and risk factors

  • 1% of all people have one or more cerebral aneurysms. Most of these, however, are small and unlikely to rupture
  • the average incidence of subarachnoid hemorrhage is 9.1 per 100,000 annually
    • by age (incidence per 100,000 person years)1):
      • < 25yrs = 2.0
      • 25-35yrs = 7.7
      • 35-45yrs = 10.5
      • 45-55yrs = 19.5
      • 55-65yrs = 25.4
      • 75-85yrs = 26.2
      • >85yrs = 31.3
  • risk of SAH continues to rise with age and is 60% higher in the very elderly (over 85) than in those between 45 and 55
  • risk of SAH is about 25% higher in women over 55 compared to men the same age
  • risk is increased 3-5x in first-degree relatives of people with SAH.
  • lifestyle risk factors are important - risk factors include smoking (doubles risk), hypertension and excessive alcohol intake
  • 4% of aneurysmal bleeds occur after sexual intercourse
  • 10% of people with SAH are bending over or lifting heavy objects at the onset of their symptoms

clinical presentations

  • 10-15% collapse and die before reaching hospital
  • sudden collapse and decreased mental state, confusion, restlessness or coma (>30%)
  • new sudden onset, severe headache peaking in the 1st hour:
    • often described like being kicked in back of the head
    • usually occipital becoming generalised and unrelenting
    • +/- vomiting, neck pain, meningism, altered mental state, syncope
    • +/- localising neurological signs including third nerve features with PCA aneurysm
  • seizure (7%)
  • low grade fever
  • neck or back pain
  • focal stroke

grading of SAH severity

  • Grade I: Mild headache +/- meningeal irritation, GCS 15 - mortality 30%
  • Grade II: Severe headache and a nonfocal examination, +/- mydriasis - mortality 40%
  • Grade III: Mild alteration in neurologic examination, including mental status - mortality 50%
  • Grade IV: depressed level of consciousness or focal deficit - mortality 80%
  • Grade V: posturing or comatose - mortality 90%

admission poor prognostic factors

  • high grade
  • systolic hypertension
  • PH AMI or SAH
  • liver disease
  • more blood and larger aneurysm on initial CT
  • posterior circulation aneurysm
  • older age
  • hyperglycaemia
  • genetic factors (two copies of ApoE4)

the diagnostic dilemma for the ED physician

  • misdiagnosis is common (12-50% of sentinel bleeds are misdiagnosed as migraine or tension headache) and exposes substantial risk of mortality
  • accounts for <1% of ED presentations for headache but perhaps closer to 10% of ED presentations with severe, sudden onset headache
  • obviously obtunded patients usually require intubation and resuscitation prior to embarking on diagnostic Ix, the following applies to potential grade I/II bleeds.
  • diagnosis may require a series of time consuming, resource intense investigations which expose patient to some risks:
    • non-contrast CT brain (preferably within 6 hours of onset):
      • overall sensitivity with modern scanners read by experienced radiologists is nearly 100% if performed within 6 hours of onset2) 3)
      • sensitivity falls to 95-98% if done 6-12 hours after onset, and 93% by 24 hours, and down to only 50% by 1 week after onset.
    • lumbar puncture (LP) performed at least 12 hours after onset (some use 6hrs as cutoff):
      • if CT scan is negative for SAH in areas where CT scan reporting is less reliable, or performed after 6 hours from onset, then LP is required to further reduce probability of a misdiagnosis
      • NB. LP may be contraindicated (eg. coagulopathy, evidence of raised intracranial pressure, refusal of patient informed consent, etc)
      • diagnostic cerebrospinal fluid (CSF) features are either:
        • an elevated number of red blood cells present equally in all tubes
          • ie. not just a traumatic tap where RBC count decreases with each tube
        • the presence of xanthochromia
          • but xanthochromia takes ~12 hours to develop, hence many delay LP for at least 12 hours from onset to increase its sensitivity
    • angiography:
      • patients with a negative non-contrast CT scan who decline or are not suitable for LP can be considered for CT angiography:
        • sensitivity for aneurysms > 3mm is 98% on a 64slice CT scanner with 100% specificity4)
        • thus if no aneurysm found and pre-test probability low to moderate for SAH then a neg. CT angio may suffice to rule out SAH
          • unfortunately, even a small aneurysm less than 3mm may bleed so if high pre-test probability of SAH then further investigation may be warranted
      • patients with negative CT scan and LP but a high probability clinical picture may end up have CT or MR angiography pending consultation with neurosurgical team.
        • to further complicate matters at least 2% may have an incidental aneurysm which is not the cause of the current presentation, hence an LP may still need to be done if not already done to help decide if there is a SAH with aneurysm or whether this is just an incidental aneurysm
      • patients with a positive LP or CT scan for SAH but no aneurysm on CT angio:
        • 10% of non-traumatic SAH cases are of non-aneurismal perimesencephalic hemorrhage (PMH) pattern and may relate to venous bleeds and these are at much lower risk of re-bleeds or vasospasm although 4% of these are vertibro-basilar aneurysms not visible on CT angio.5)
  • thus the ED doctor must make a careful clinical risk assessment of each patient with headache or syncope to decide on whether or not they proceed down the SAH rule out pathway.

high risk clinical features indicating SAH rule out pathway

  • sudden collapse and persistent altered mental state which is not otherwise explainable by known epilepsy, etc.
  • collapse with headache
  • sudden onset, severe headache different to past headaches
  • clinical gestault suspicion of SAH
  • Canadian rule for SAH:
    • adults with a chief complaint of non-traumatic headache peaking within an hour or of syncope associated with a headache.6)
    • essentially, there appears to be 100% sensitivity for SAH if patient also has ANY ONE of the following features:
      • age > 40 years
      • neck pain or stiffness
      • witnessed LOC
      • onset with exertion
      • at least one vomit
      • arrival by ambulance
      • systolic BP > 160mmHg
      • diastolic BP > 100mmHg
    • they have used 3 variations on these to make a rule and each has 100% sensitivity but only 28-38% specificity

Ix of patient with thunderclap headache

  • urgent CT brain
    • no further testing for SAH needed if:
      • no SAH seen by experienced radiologist, AND,
      • scan done within 6 hours of onset of headache, AND,
      • patient has no focal neurology or reduced mental state
    • if no SAH found on CT but the above do not apply:
  • if SAH confirmed, manage as below

Mx of SAH in the ED

  • urgent consult with neurosurg team and transfer to a neurosurgical centre
  • nil orally
  • nurse with head up 30deg
  • hourly neuro obs
  • antiemetics to minimise vomiting
  • avoid sedatives (cease iv chlorpromazine if this was started for Mx of possible migraine)
  • if headache severe, consider judicious doses of parenteral opiates and opioids
  • aim to control systolic BP < 140mmHg with either:
    • oral nimodipine 60mg qid, or,
    • iv hydralazine 5mg by slow iv, repeat if needed
  • if decreased GCS, consider intubation prior to transfer
sah.txt · Last modified: 2021/07/03 14:21 by gary1