How to perform a temporary balloon test occlusion

Honorary senior lecturer. University of Natal, and consultant radiologist in private practice, Durban A temporary balloon test occlusion is performed prior to endovascular occlusion of carotid or vertebral arteries. It may also be performed preoperatively when vascular sacrifice is intended or possibly during surgical therapy for tumours of the cervical region or skull base. I The indications for parent artery vessel occlusion include certain giant aneurysms, pseudoaneurysms and carotid cavernous fistulae which cannot be treated with preservation of the parent vessel.'


Honorary senior lecturer. University of Natal, and consultant radiologist in private practice, Durban
A temporary balloon test occlusion is performed prior to endovascular occlusion of carotid or vertebral arteries. It may also be performed preoperatively when vascular sacrifice is intended or possibly during surgical therapy for tumours of the cervical region or skull base. I The indications for parent artery vessel occlusion include certain giant aneurysms, pseudoaneurysms and carotid cavernous fistulae which cannot be treated with preservation of the parent vessel.'

Tests used to predict tolerance to permanent occlusion
A temporary balloon test occlusion is performed to predict the ability of the patient to tolerate permanent occlusion. The risks of ipsilateral hemispheric ischaemia or infarction largely depend on the adequacy of collateral circulation. Various tests have been used to assess tolerance during temporary occlusion.

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SA JOURNAL OF RADIOLOGY. January 2000 Assessment of neurological status (motor, sensory, speech and level of alertness) during trial occlusion is used in all patients unless it is not possible, or desirable to perform the procedure under local anaesthesia. It does not however, identify all patients at risk for post occlusion infarction. This is probably because there is a group of patients with marginal cerebral blood flow reserves who are able to tolerate temporary occlusion, but who are at risk for developing flow related infarction during episodes of hypo tension, anaemia, hypoxaemia or hypoglycaemia.
Various other tests have been used in combination with clinical testing during trial occlusion. Stump pressure is not an accurate predictor of stroke risk." Anglograpbic evidence of cross filling via cellaterals is a poor indicator of whether the patient will tolerate permanent occlusion. The venous phases of an angiogram are a better predictor of tolerance to permanent occlusion.' If there is less than a 1.5 second delay in the appearance of the venous phase, following an injection into the opposite carotid or vertebral artery, permanent occlusion isprobably safe.' Transcranial Doppler has not been used extensively. The disadvantage of using transcranial Doppler is that only flow in major vessels is assessed. Permanent occlusion is considered to be relatively safe if the peak systolic velocity in the middle cerebral artery decreases by no more than 65%.4 Several tests have been used in an attempt to identify patients with marginal eBF reserves -SPEeT, PE1: Xenon Cl' eBF and tolerance to induced hypotension during trial occlusion. S Single-photon emission Cl' (SPEeT) and stable Xenon Cf eBF take direct intracranial measurements of parameters linked to eBF to assess eBF reserves. Although PET scanning has been used to assesscerebral blood flow quantitatively during balloon occlusion, the technology is not widely available.f Xenon Cl' eBF is performed by placing and inflating the balloon in the angiography suite and performing a trial occlusion with neurological monitoring. If the patient experiences no deficit, the balloon is deflated and the patient transferred to the CI' scanner where the balloon is reinflated (without fluoroscopic guidance) and the Xenon eBF study performed. Quantitative information can be obtained using regions of interest. It is considered safe to proceed with permanent occlusion if the cerebral blood flow is greater than 30 ml/WO g/min. Ten to fifteen per cent of patients will pass the clinical occlusion test, but will have a eBF of less than 30 ml/WO g/min and this group of patients is thought to be at moderate risk for infarction after permanent occlusion. Patients with a eBF ofless than 23 mlIIOOg/min are at high risk for ischaemia during balloon oeelusion.' To perform a SPEeT scan, 99mTcHMPAO (hexamethyl propylene amine oxime) is injected intravenously during temporary occlusion. The balloon is then deflated and the SPEeT scan performed. A baseline study can be performed prior to the test occlusion, or in patients showing hypoperfusion, 24 hrs later. Areas of asymmetric hypoperfusion not present on the baseline study are considered to be abnormal and place the patient in a high risk category for cerebral infarction following permanent occlusion." Induced hypotension, where the systolic blood pressure is decreased by 30% for a period during trial occlusion has also been used to assess tolerance to parent vessel occlusion.'

Balloons used for trial occlusion test
Several methods have been described for performing trial occlusions. One uses a detachable balloon which is detached in the same position, without deflation, if the patient passes the occlusion test. This has the advantage of simulating the effect of permanent occlusion most closely as the balloon

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SA JOURNAL OF RADIOLOGY-January 2000 is inflated in its detachment position. There is however a risk of premature detachment. The second method uses a non-detachable balloon. This is more time consuming and necessitates deflating the balloon and reinflating the detachable balloon if the patient passes the trial occlusion test. A double lumen balloon catheter, which allows perfusion of the distal stump with heparinised saline has also been used. Although the double lumen balloon catheter has the theoretical advantage of preventing thrombus formation in the distal stump, it seems unnecessary in practice." There are proponents of each of these methods.

Complications
Trial occlusion has a complication rate of about 3%. Some of the complications are asymptomatic (dissections, pseudo aneurysm and embolus) and the remainder ischaemie (although usually transient). I The incidence of stroke following permanent occlusion in patients who have passed the temporary balloon occlusion test is reported to be topage23 between 10 and 20%.10 About 4% of ischaemie events are permanent and 10% are transient.' They may be due to thromboembolism or secondary to decreased flow. Hypoperfusion is a particular problem in the elderly, whose blood pressure and cardiac output may be less stable than in younger patients.

Procedure
Many different techniques are utilised in performing a trial occlusion test. The following is the technique used by the author.
The patient is fully conscious for the trial occlusion test. Bilateral femoral artery punctures are performed. A SFr sheath is placed in the left femoral artery. A sheath to match the chosen guiding catheter is placed in the right femoral artery. A diagnostic angiogram is then performed.
The patient is heparinised. A loading dose of 5000 iu is given. The ACT (activated clotting time) is maintained above 300 seconds for the duration of the procedure by giving additional boluses of heparin during the procedure. The diagnostic catheter is positioned in the artery on which the trial occlusion test is to be performed. This is exchanged over a 260 cm exchange wire for the chosen guiding catheter. The guiding catheter selected will depend on the balloon size. It is important to keep the tip of the wire below the skull base, and stationary during the exchange to prevent spasm. The guiding catheter is connected to a rotating haemostat valve (RHV) and continuously flushed with heparinised saline (3000 iu in IL NIS). The diagnostic catheter is then placed in the contralateral internal carotid artery.
If a permanent occlusion is going to be performed after a successful trial occlusion test, a detachable balloon is used to perform the trial occlusion test. Only if it seems unlikely that the patient will pass the trial occlusion test, or if a permanent occlusion is not planned, is a non-detachable balloon used. The detachable balloon is filled with isoosmolar solution of contrast and sterile water. It is inflated and checked for a leak. The RHV is disconnected from the guiding catheter and the delivery catheter advanced through the RHV The balloon is then mounted on the tip of the delivery catheter. It is inflated and air purged from the system. It is then deflated. It is important to perform this step to be certain that it is properly mounted and that the balloon will in fact deflate (if the tip of the delivery catheter does not extend beyond the valve it will not deflate).
The RHV is reconnected to the guiding catheter and the balloon is advanced beyond the tip of the guiding catheter under fluoroscopic contro1. Ideally this should be done using a roadmap image (subtracted fluoroscopy). The balloon is positioned at the site of the anticipated permanent occlusion. The author uses transcraniaJ Doppler as part of the assessment and a baseline velocity in the middle cerebral artery is obtained. The ACT is checked immediately prior to inflation of the balloon.
The balloon is progressively inflated until it completely occludes the artery.A check angiogram through the guiding catheter is done to confirm occlusion.The velocity in the middle cerebral artery is checked. A check angiogram isperformed from the opposite side and the timing of the venous phase of the angiogram in the two cerebral hemispheres compared. A neurological assessment is performed. If no deficit has developed, the middle cerebral artery velocity has decreased by no more then 50% and the venous phases are separated by less than 2 seconds, the test is continued for 30 minutes. The above parameters are checked intermittently during this period. If a neurological deficit develops, the test is immediately terminated. If the patient passes the test, the balloon is detached and a second 'safety' balloon placed proximally.Patients often experience headache and retro-orbitalpainduringthe procedurewhich can be treated with opioid analgesia.