HE temporary arrest of local arterial circulation by occlusion of a parent vessel has been used as an adjunct in intracranial aneurysm surgery since its introduction by Pool 20 in 1961. Increasingly, this tech- nique has been used in the management of both routine and complex aneurysms. Proponents of temporary clip- ping cite the decreased risk of intraoperative rupture, safer dissection and delineation of perforating vessels, and the ability to control hemorrhage during premature intraoper- ative rupture as advantages afforded by this procedure. 5,9, 11,14,19,21,27–29 Despite these advantages, temporary clipping can have disastrous ischemic sequelae in the territory of the temporarily occluded vessel. To lessen this risk of ischemia, temporary arterial occlusion during aneurysm surgery has been commonly performed using a protocol of multiple short periods of occlusion interspersed with periods of restoration of normal circulation. 19 Recently, Samson, et al., 21 have suggested that increasing episodes of temporary arterial occlusion may not be as well tolerat- ed as a single protracted ischemic period. Considerable experimental evidence exists establishing that repetitive episodes of global cerebral ischemia en- hance the extent of neuronal injury when compared with an equivalent single period of ischemia. 1,10,12,13,30,31 How- ever, little experimental data are available on repetitive episodes of focal ischemia. Furthermore, most studies have used protocols that do not simulate the temporal pro- files that are likely to occur during surgery. Considerable disagreement continues to exist regarding the use of brief periods of reperfusion during temporary clipping versus a single protracted period of temporary occlusion. To inves- tigate this issue, a protocol of occlusion/reperfusion that simulates the temporal profile that occurs during surgery was performed in a rat model of transient, focal cerebral ischemia. Materials and Methods Animal Preparation Sixteen adult male Sprague–Dawley rats, each weighing between 350 and 450 g, were used for the study. The rats were denied food and water the evening before the experiment. Anesthesia was induced with 3% halothane and a mixture of 70% nitrous oxide and 30% oxygen. The rats were intubated and maintained on 0.5% to J. Neurosurg. / Volume 85 / November, 1996 J Neurosurg 85:923–928, 1996 Cerebral protection by intermittent reperfusion during temporary focal ischemia in the rat CARLOS A. DAVID, M.D., RICARDO PRADO, M.D., AND W. DALTON DIETRICH, PH.D. Department of Neurological Surgery and Cerebral Vascular Disease Research Center, University of Miami School of Medicine, Miami, Florida  Temporary arterial occlusion has been routinely used as an adjunct in intracranial aneurysm surgery. This has com- monly been performed using a protocol of multiple short periods of occlusion alternating with periods of restoration of normal circulation. Recently, the logical basis of this method has come under scrutiny. There is extensive experi- mental evidence to suggest that repetitive, brief periods of global ischemia may cause more severe cerebral injury than an equivalent single period of global ischemia. Only recently has this issue begun to be addressed with regard to focal ischemia. Hence, despite the common use of temporary clipping, little experimental data are available regarding the ischemic consequences of temporary arterial occlusion with periods of reperfusion versus uninterrupted temporary occlusion. To investigate this issue, a protocol of occlusion/reperfusion that simulates the temporal profile that occurs during surgery was performed in a rat model of focal ischemia. Sixteen anesthetized Sprague–Dawley rats were divided into two groups. The animals in Group I underwent 60 minutes of uninterrupted middle cerebral artery occlusion and the animals in Group II were subjected to six separate 10-minute occlusion periods with 5 minutes of reperfusion between occlusions. Histopathological analysis was performed 72 hours postischemia. Group I had significantly increased mean infarction volumes (50.0  12.1 mm 3 ) compared to Group II (8.7  3.1 mm 3 ) (p = 0.008). Injuries in Group I occurred in both the cortex and striatum, whereas Group II showed only striatal injuries. Furthermore, the extent of the injuries in Group II was less severe, characterized by ischemic neuronal injury rather than frank infarction. The results indicate that intermittent reperfusion is neuroprotective during temporary focal ischemia and support the hypothesis that intermittent reperfusion is beneficial if temporary clipping is required during aneurysm repair. KEY WORDS • aneurysm surgery • cerebral ischemia • cerebral protection • reperfusion • temporary clipping • transient focal ischemia • rat T 923