Outline the advantages and disadvantages of the various techniques used in the diagnosis and monitoring of vasospasm secondary to aneurysmal subarachnoid haemorrhage.
Answer and interpretation
Techniques that have proven or demonstrated potential in the diagnosis and monitoring of vasospasm include:
- In the conscious patient, may be detected clinically by new focal neurology or a drop in GCS.
- Advantages: No additional costs and readily available, can be repeated easily, non-invasive (usually), has to be performed at the bedside.
- Major disadvantage is lack of specificity often necessitating CT/angiography. Also lacks sensitivity, vasospasm can occur without a clinical correlate, early in the disease. Operator dependent.
Conventional 4 vessel DSA angiography:
- Remains the gold standard for diagnosis of vasospasm.
- May allow therapeutic intervention (angioplasty) at the time.
- Disadvantages: invasive, risks of bleeding, embolism, radiation/contrast exposure and transport. Requires skilled interventional radiology, and therefore resource heavy. Risk of stroke (quoted about 1%, but probably a little lower) just from the angio, plus the dissections etc. that occur as well. Detects vessel narrowing, not necessarily poor flow to distal tissue in all cases (either increased flow rate through narrow vessel or collateral supply. May lead to over treatment.
Transcranial Doppler (TCD):
- It is low risk, performed at the bedside, non-invasive and able to be repeated daily enabling trend analysis.
- Disadvantages: The technique is however operator dependent and there is high interobserver variability.
- Debate exists regarding correlation of flow velocity and vasospasm and although high velocities (> 200cm/sec) are predictive, lower velocity may not be as good.
- The technique may be more accurate when MCA velocity is indexed to the ipsilateral extracranial carotid artery (Lindegaard index, >3 strongly predictive).
- Colour coded TCD may offer greater accuracy than plain TCD alone.
- May be combined with perfusion allowing characterisation of both vascular anatomy and associated perfusion abnormalities.
- MR diffusion weighted imaging accurately identifies brain tissue at high risk of infarction; perfusion weighted imaging reveals asymmetries in regional perfusion.
- Both methods show correlation with delayed ischaemic neurological deficit (DIND).
- Disadvantages: Image clarity will be affected by clip/coil and contrast related issues need consideration. The overall diagnostic capability of this modality however remains unclear until further prospective studies are performed. Similar disadvantages as per angiography with respect to transport, radiation (for CT), contrast exposure, interpretation by experts.
- Can be used to obtain a picture of brain perfusion and metabolism and have shown variable correlation with vasospasm as assessed by more conventional methods.
- Disadvantages: They are resource heavy not easily available, radiation exposure, patient transport are issues.
- May provide prognostic information, focal areas of slowing correlate with angiographic
- vasospasm and a decrease in alpha to delta ratio strongly correlates with ischaemia. Sensitivity and specificity for detecting vasospasm is high.
- Disadvantage: Not readily available however and their may be issues with interpretation.
- The use of measures of tissue oxygenation using parenchymal sensors and microdialysis for monitoring biochemical indices of ischaemia are largely research tools.
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.