Introduction. The clipping of large basilar artery aneurysms presents several unique and challenging considerations for the anesthesiologist. We report a successful case employing cardiopulmonary bypass (CPB) with hypothermic circulatory arrest (HCA) outlining the anesthetic concerns and neuroprotective strategies. Clinical course. A 35 year old female presented for clipping of an asymptomatic large basilar artery aneurysm. Due to the location, size, and possible need for temporary clipping of vital feeding arteries, a surgical approach necessitating HCA was planned. On the evening prior to surgery, a lumbar CSF drain was placed. The day of surgery, after placement of invasive monitors (arterial and pulmonary artery catheters), anesthesia was induced with thiopental, fentanyl, midazolam and rocuronium and maintained with isoflurane, fentanyl/midazolam infusions and pancuronium. Transesophageal echocardiography (TEE), 16 channel EEG, and cerebral near-infrared spectroscopy (NIRS) monitors were placed. The patient was positioned supine with the head turned leftward allowing a right frontotemporal craniotomy. During neurosurgical dissection, the right femoral vessels were exposed for CPB cannulation. After isolation of the aneurysm, the patient was heparinized (400 IU/kg; ACT > 450 sec) and cannulated for CPB. Venous cannulation consisted of a multiorificed right atrial cannula advanced from the femoral vein and positioned under TEE guidance. Just prior to institution of CPB, thiopental (18 mg/kg, i.v. bolus and infusion) was administered to EEG burst suppression. An insulin infusion was used to treat hyperglycemia. CPB commenced and the patient was cooled to a nasopharyngeal (NP) temp of 13.9 [degree sign]C. As the core (bladder) temperature continued to drop below 25 [degree sign]C, ventricular fibrillation ensued; TEE was used to monitor any ventricular distention. After cooling for 45 min, the circulation was arrested and blood drained into the venous reservoir to collapse the aneurysm and permit successful clipping (total circ arrest time = 12 min). Rewarming commenced and continued with the arterial inflow temp <or=to 36 [degree sign]C. Spontaneous sinus rhythm occurred at 28 [degree sign]C. Once NP and bladder temps were 36 [degree sign]C (106 min of rewarming), the patient was easily separated from CPB without inotropic support, cannulae removed, and protamine was administered. A subdural ICP probe was placed prior to closure of the dura and cranium. Platelets (3 units) and fresh frozen plasma (3 units) were administered for hemostasis. The patient awakened approximately 18 hours later and was extubated on the second postop day. She had transient right III and VII cranial nerve palsies which were thought to be related to retractor ischemia. In addition, transient right arm weakness and dysarthria, occurred, both of which quickly improved. A post-op angiogram showed complete exclusion of the aneurysm, however, a small infarct in the posterior cerebral artery territory was present on CT. She was discharged from hospital 2 weeks following surgery, to continue rehabilitation, with near-complete recovery of neurologic function. Discussion. The anesthetic considerations for this complex, multidisciplinary case are numerous [1,2]. They include, but are not limited to: lumbar CSF drain placement (with ensuing heparinization); TEE assessment for possible aortic insufficiency (which would have required an intrathoracic CPB approach for placement of an LV vent), venous cannulation guidance, monitoring of cardiac ventricular size during fibrillation and function post-CPB; antifibrinolytic and anticoagulation approaches; temperature and neurologic monitoring, possible external defibrillation during rewarming, and coagulopathy treatment. Our neuroprotective strategy included hypothermia, avoidance of hyperglycemia, and thiopental-induced EEG burst suppression effecting protection both from metabolic suppression as well as other mechanisms (such as attenuation of excitatory amino acid transmission).