Cerebral ischemic injury occurs secondary to carotid artery ligation in the rat hemorrhagic shock model

Background: Many rat hemorrhagic shock models use the carotid artery for access followed by ligation. We hypothesized that the combination of carotid artery ligation and hemorrhagic shock may result in cerebral injury which can influence results. Methods: Male Sprague-Dawley rats (n=44) were cannulated in the external jugular vein and either the carotid artery (n=32) or the femoral artery (n=12) under isofluorane. A five minute hemorrhage (26-28cc/kg) was performed via the arterial cannula followed by a 60 minute shock period. Resuscitation followed with three times hemorrhaged blood volume of Ringer's Lactate solution over one hour through the verious line. Fourteen animals were observed for survival data. Eighteen animals had brain harvested at 2, 24 and 72 hours after resuscitation. Brain tissue was examined fresh or after insitu perfusion with paraformaldehyde. Fixed tissues underwent H & E and TNFα immunohistochemical staining. Results: Animals with femoral artery ligation never demonstrated neurologic or brain morphologic abnormalities. In carotid artery ligation followed for survival, 7/10 of the non-survivors had abnormal neurologic activity (long-axis spinning behavior, opisthotonus, tremors and hyper-agitation). Timed harvesting in 18 animals revealed pale and edematous gross unilateral cortical injury ipsilateral to the carotid artery ligation in 8/11 fresh specimens. Although brains fixed insitu only demonstrated gross injury in 2/7 animals, histologic examination demonstrated cellular injury in the hippocampus ipsilateral to carotid artery ligation in 5/7 specimens. Immunohistochemical analysis revealed increased TNFa in ipsilateral cortical and hippocampal CA1 neurons. Conclusion: This study demonstrates cerebral injury following carotid artery cannulation in an accepted standard hemorrhagic shock model. Perfusion prior to brain harvesting may disguise the injury. Studies using carotid cannulation in the hemorrhagic shock model should be considered as a combined injury.