The effects of ketamine–xylazine anesthesia on cerebral blood flow and oxygenation observed using nuclear magnetic resonance perfusion imaging and electron paramagnetic resonance oximetry

Abstract

Ketamine–xylazine is a commonly used anesthetic for laboratory rats. Previous results showed that rats anesthetized with ketamine–xylazine can have a much lower cerebral partial pressure of oxygen (P_tO₂), compared to unanesthetized and isoflurane anesthetized rats. The underlying mechanisms for the P_tO₂ reduction need to be elucidated. In this study, we measured regional cerebral blood flow (CBF) using nuclear magnetic resonance (NMR) perfusion imaging and cortical P_tO₂ using electron paramagnetic resonance (EPR) oximetry in the forebrain of rats under isoflurane, ketamine, ketamine–xylazine and isoflurane–xylazine anesthesia. The results show that in ventilated rats ketamine at a dose of 50 mg/kg does not induce significant changes in CBF, compared to isoflurane. Ketamine–xylazine in combination causes 25–65% reductions in forebrain CBF in a region-dependent manner. Adding xylazine to isoflurane anesthesia results in similar regional reductions in CBF. EPR oximetry measurements show ketamine increases cortical P_tO₂ while xylazine decreases cortical P_tO₂. The xylazine induced reduction in CBF could explain the reduced brain oxygenation observed in ketamine–xylazine anesthetized rats.