Subarachnoid Haemorrhage Dr Mark Putland MBBS FACEM CoDEMT
Subarachnoid Haemorrhage Dr Mark Putland MBBS FACEM Co-DEMT
Basics • What is the subarachnoid space?
Basics • Epidemiology – 3% of strokes – 5% of stroke deaths – 25% of life years lost to stroke – Peak age 40 -60 years – Smokers, hypertensives, family history, connective tissue problems (PCKD, NF, Sickle Cell, α-1 antitrypsin deficiency)
Basics • Aetiology – Most are traumatic – Of the non-traumatic • • Aneurysm account for most AVM is the most common in kids and young adults Mycotic aneurysm Dissection Hypertensive crisis Sickle cell Tumour Bleeding tendency
Pathology • Site – Majority in anterior circulation at arterial branch points • Circle of Willis • Trifurcation of MCA • Basilar tip (posterior circulation)
History • Thunderclap headache • Exercise or sex induced • Nausea, vomiting and syncope are common • Meningeal irritation develops over time • Seizures in 15% • Prodrome from expanding aneurysm may cause CN palsy, seizure, TIA, mass effect rarely
History • Drugs • Premorbid state • Social context
Examination • Red flags for SAH – Meningism – HT – Depressed or CLOUDED conscious state – Focal neurology
Examination • Once SAH diagnosed – GCS – Focal neurology – BP – Complications • APO • Arrhythmia
Grading Grade Survival WFNS Hunt and Hess GCS Motor 1 Asymptomatic, slight headache, slight nuchal rigidity 15 No 70% 2 Mod-sev h/a, CN palsy or no defect 13 -14 No 60% 3 Drowsy, confused, mild focal deficit 13 -14 Yes 50% 4 Stupor, mod-sev hemi, vegetative posturing 7 -12 Y/N 40% 5 Deep coma, decerebrate, moribund 3 -6 Y/N 10%
Diagnosis • CT – 90 -95% sensitive in first 24 hours – 80% sensitive at 3 days – 50% sensitive at 1 week • Can we just get a better scanner? • CT grading system
Diagnosis • Why is the sensitivity still 93%
Diagnosis • What does a sensitivity of 93% mean for my patient? • What does a sensitivity of 93% mean for my practice?
Stats • Sensitivity – A/(A+C) – How good is the test at finding the disease • Specificity – D/(B+D) – How good the test is at ruling out the disease Disease Test Result Yes No + A B - C D
Stats • Positive Predictive Value – A/(A+B) – How meaningful a positive test is in this population • Negative predictive value – D/(C+D) – How meaningful a negative test is for this population Disease Test Result Yes No + A B - C D
HELP!!!!!! • How many people with a thunderclap headache have SAH? – 8% – This is the background prevalence rate Disease Test Result Yes No + A B - C D
HELP!!!!!! • The patient starts out with an 8% chance of SAH • NPV – You have a negative scan – This means you have x chance of not having a bleed – 920/(920+5)= 99. 5% Disease Test Result Yes No + 75 0 - 5 920
HELP!!!!!! • So when the patient doesn’t want an LP what is the chance they have a bleed? • 1/200 Disease Test Result Yes No + 75 0 - 5 920
HELP!!!!!! • What does this mean in your practice? – I probably see about 2 of these headaches a week – 10 years in EM means 1000 such headaches – This gives me 80 cases of SAH in 10 years Disease Test Result Yes No + A B - C D
HELP!!!!!! • Sensitivity of 93% means out of 1000 thunderclap headaches we capture 75 SAH cases and miss 5. • That’s 5 big lawsuits in 10 years Disease Test Result Yes No + 75 0 - 5 920
HELP!!!!!! • So the individual patient cares about negative predictive value • The doctor cares about sensitivity Disease Test Result Yes No + 75 0 - 5 920
So what next with a negative CT? • LP – RBC • Traumatic tap rate ~20% • Decreasing cell counts are unreliable so have a wide margin of error – Xanthochromia • Usually appears within 6 hours, definitely within 12 • Longer delay means more rebleeds • Generally aim for 6 -12 hours
So what next with a negative CT? • MRI – Good for delayed presentations (up to 2 weeks) – Must specify the indication to get the right protocol • CT angiogram – Finds all but the smallest aneurysms – What’s the catch?
CT angio- what’s the catch? • It’s a big one! • 2% of the normal population have an aneurysm • A tiny fraction of these will ever bleed. • CT angiogram creates a disease in people who don’t have one.
CT within 6 hours? • http: //www. bmj. com/content/343/bmj. d 4277. abstract • • • 3000 patients 11 ED’s Canada (similar to here) 7 -8% rate of bleed overall 93% sensitivity overall 121 out of 953 bleeds in patients scanned within 6 hours
Management • Protect the injured brain – CO 2 , Temp, BSL, head up, seizure prevention • Get to a neurosurgeon before – Rebleed – Vasospasm – Hydrocephalus – Cerebral salt wasting disease, SIADH
Management • Neurosurgical hospitals – St V, Monash, RMH, Alfred, Austin • ARV – Defined transfer process. – 1300 36 86 61
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