NEUROIMAGING / DSA
Balloon Test Occlusion (BTO)
Created 29/04/2021, last revision 06/11/2023
- acute internal carotid artery (ICA) occlusion is associated with a high risk of ischemic neurological deficits (20-49%) (Seet, 2012)
- in a meta-analysis of 20 studies of patients with ICA occlusion, the annual risk of stroke was 5.5% (2.1% ipsilateral). Those with hemodynamic compromise on functional imaging had a stroke risk of 12.5% (9.5% ipsilateral)
- the clinical course of ICA occlusion is variable, ranging from asymptomatic lesions to devastating strokes (Klijn, 1997)
- the balloon test occlusion (BTO) is performed to determine whether an artery can be temporarily or permanently occluded without significantly affecting brain perfusion
- if the BTO is well tolerated, the risk of subsequent ischemia is significantly reduced
- pharmacologically induced hypotension during BTO further increases the sensitivity of the test
Indications
- functional testing in patients scheduled for ICA occlusion (inoperable aneurysms, glomus tumors, intracranial tumors, tumors in the ENT region)
- the Matas test (external CCA compression during angiography) used to be performed; it has been replaced by the more sensitive balloon test occlusion (BTO)
Procedure
Patient preparation
- allergy premedication (if necessary)
- premedicate with NIMOTOP 60 mg PO (2 tablets) every 4h
- insert a urinary catheter and intravenous cannula
- start normal saline solution at 150 mL/h at least 4h before the procedure
- ensure anesthesiologist supervision
- IV heparinization at the beginning of the procedure
- undiluted HEPARIN – bolus of 5000-7000 IU (1 – 1.4 mL)
- diluted heparin – 4ml (1ml = 5000jj) + 16mL of NS (20mL solution = 20 000jj)
- followed by diluted HEPARIN 1-3 mL/h IV (1000-3000 IU/h) with the target APTT 2-3x
- flush the distal catheter section above the balloon with normal saline + a low dose of heparin
- HEPARIN 0.5 ml (500IU) + 500 ml of NS (1ml=1IU) – a continuous infusion of 60mL/h (1 IU/min) [Standard, 1995]
Clinical and TCCD monitoring during the procedure
- check the neurological status every 5 minutes after balloon inflation
- stop the test:
- if neurological deficits develop
- if the patient tolerates occlusion for 20 minutes without neurologic deficits [Kikuchi, 2014
- in addition to a neurological examination, TCCD/TCD monitoring of the MCA may be used [Sorteberg,2008]
- if PSV drops to the max. 65% of baseline, ICA occlusion is safe
- if it drops to < 54%, there is an increased risk of hypoperfusion
- a 20-minute test with medically induced hypotension may be added
- labetalol (TRANDATE) IV injection (bolus 5-20 mg) or sodium nitroprusside (2.5 to 7.5mg/kg body weight per minute)
- lower the mean blood pressure to 2/3 of the baseline
- hypotension is maintained for approx. 20 minutes
- the negative test identifies patients who can safely undergo ICA occlusion with 95% accuracy [Standard, 1995]
- extract the balloon after the test is completed
- neutralize heparin with PROTAMIN → Neutralization of the anticoagulant drugs
- remove the sheath, apply external groin compression, or seal the puncture
- observe the patient in the ICU for the next 24h
Assessment of collateral circulation
- assess the contrast filling of ACA (A1-A4 segments) and the MCA (segments M1-M4) on the occluded side (Kikuchi, 2014]
- assess the anatomy of the circle of Willis (especially the presence and quality of ACoA and PCoA, A1 and P1 segments bilaterally)
Complications
- neurologic complications: 0-8.3% (average complication rate according to various studies ~ 2.2%) → more here