Effects of alfentanil on cerebral vascular reactivity in dogs

The effects of high dose alfentanil on the cerebral vascular responses to alterations in mean arterial pressure (MAP), arterial oxygen tension (PaO2) and arterial carbon dioxide tension (PaCO2) were studied in 17 dogs, using the cerebral venous outflow technique. In six animals anaesthetized with sodium pentobarbitone 30 mg kg-1 i.v., bolus injection of alfentanil 0.32 mg kg-1 i.v. decreased MAP without a change in cerebral blood flow (CBF). In another group of animals(n = 5) anaesthetized with pentobarbitone 30 mg kg-1 i.v. the CBF responses to changes in MAP, PaO2, and PaCO2 were studied. In a third group of animals (n = 6) anaesthetized with alfentanil 0.32 mg kg-1 i.v. plus pentobarbitone 1-2 mg kg-1 i.v. and an infusion of alfentanil 0.32 mg kg-1 h-1, the CBF response to alterations in MAP, PaO2, and PaCO2 were studied and compared with the barbiturate-anaesthetized animals. The CBF responses to hypercapnia and hypoxia in the alfentanil-anaesthetized animals were not different from those observed in animals anaesthetized with barbiturate only. The lower and upper limits of cerebral autoregulation in alfentanil-anaesthetized animals were not different from those observed in animals anaesthetized with barbiturate only. The data suggest that alfentanil, in doses sufficient to cause profound analgesia and anaesthesia, does not alter cerebral reactivity to changes in PaO2, PaCO2 and MAP.