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the Matas test (external CCA compression during angiography) used to be performed; it has been replaced by the more sensitive balloon test occlusion (BTO)

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]

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

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)

neurologic complications: 0-8.3% (average complication rate according to various studies ~ 2.2%) → more here