Prior to permanent balloon occlusion, a test occlusion must be performed. Many methods are advocated to assess the efficacy of the intracranial collateral circulation following test occlusion. These include transcranial Doppler ultrasound, Xenon CT, 133Xenon SPECT, 99MTechnetium hexamethyl-propylene-amine oxide (HMPAO) SPECT, PET, EEG monitoring, somatosensory evoked potential monitoring, retinal artery pressure measurement and hypotensive challenge. Many of these techniques are, however, complex and time-consuming and cannot be used without transferring the patient from the angio suite [3,4].
The method described here is practiced by the author and is similar to the technique widely practiced in the UK. The patient should be awake and only sedated by a mild intravenous neuroleptic anesthetic agent, such as 5-10 mg diazemuls. Intravenous access with a wide-bore cannula is mandatory. After insertion of bilateral femoral sheaths, the patient is anticoagu-lated by using intravenous heparin. After anticoagulation, its adequacy is assessed by estimation of the ACT, which should be 2-3 times baseline.
A 7 or 8 French guide catheter is placed in the internal carotid artery supplying the aneurysm or lesion and a non-detachable balloon (e.g. NDSB 1505 Boston Scientific) is inflated as near as possible to the site of permanent occlusion, i.e. near the aneurysm neck, and inflated under road mapping to occlude the artery. Careful clinical assessment is then carried out for up to 30 minutes (ideally by a neurologist or physician, independently from the operator). If neurological symptoms develop, the balloon is immediately deflated. If the patient is asymptomatic, an injection is made into the contralateral internal carotid artery (or vertebral) to assess angiographic collateral flow (Fig. 19.1). There should be a delay of no more than 1 s in venous phase appearance when comparing the occluded side with the opposite injected side.
Transcranial Doppler monitoring of middle cerebral artery flow may also be used. As long as decrease in flow does not exceed 30% and the patient passes the other two tests, it is safe to occlude the artery .
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