Continuous monitoring of regional cerebral blood flow during temporary arterial occlusion in aneurysm surgery

Object. Temporary arterial occlusion (TAO) during aneurysm surgery carries the risk of ischemic sequelae. Because monitoring of regional cerebral bloo d flow (rCBF) may limit neurological damage, the authors evaluated a novel thermal diffusion (TD) microprobe for use in the continuous and quantitativ e assessment of rCBF during TAO. Methods. Following subcortical implantation of the device at a depth of 20 mm in the middle cerebral artery or anterior cerebral artery territory, rCB F was continuously monitored by TD microprobe (TD-rCBF) throughout surgery in 20 patients harboring anterior circulation aneurysms; 46 occlusive episo des were recorded. Postoperative radiographic evidence of new infarction wa s used as the threshold for failure of occlusion tolerance. The mean subcortical TD-rCBF decreased from 27.8 +/- 8.4 ml/100 g/min at ba seline to 13.7 +/- 11.1 ml/100 g/min p < 0.0001) during TAO. The TD micropr obe showed an immediate exponential decline of TD-rCBF on clip placement. O n average, 50% of the total decrease was reached after 12 seconds, thus rap idly indicating the severity of hypoperfusion. Following clip removal, TD-r CBF returned to baseline levels after an average interval of 32 seconds, an d subsequently demonstrated a transient hyperperfusion to 41.4 +/- 18.3 ml/ 100 g/min (p < 0.001). The occurrence of postoperative infarction (15%) and the extent of postischemic hyperperfusion correlated with the depth of occ lusion-induced ischemia. Conclusions. The new TD microprobe provides a sensitive, continuous, and re al-time assessment of intraoperative rCBF during TAO. Occlusion-induced isc hemia is reliably detected within the 1st minute after clip application. In the future, this may enable the surgeon to alter the surgical strategy ear ly after TAO to prevent ischemic brain injury.