EFFECTS OF ALFENTANIL ON CEREBRAL VASCULAR REACTIVITY IN DOGS

The effects of high dose alfentanil on the cerebral vascularresponses to alterations in mean arterial pressure (MAP), arterialoxygen tension (Pa^O2) and arterial carbon dioxide tension (Pa^CO2)were studied in 17 dogs, using the cerebral venous outflow technique.In six animals anaesthetized with sodium pentobarbitone 30 mgkg^–1 i.v., bolus injection of alfentanil 0.32 mg kg^–li.v. decreased MAP without a change in cerebral blood flow (CBF).In another group of animals(n = 5) anaesthetized with pentobarbitone30mg kg^–1 i.v. the CBF responses to changes in MAP. Pa^O2,and Pa^CO2 were studied. In a third group of animals (n = 6)anaesthetized with alfentanil 0.32 mg kg^–1 i.v. plus pentobarbitone1–2 mg kg^–1 i.v. and an infusion of alfentanil 0.32mg kg^–1h^–1 the CBF responses to alterations inMAP, Pa^O2, and Pa^CO2 were studied and compared with the barbiturate-anaesthetizedanimals. The CBF responses to hypercapnia and hypoxia in thealfentanil-anaesthetized animals were not different from thoseobserved in animals anaesthetized with barbiturate only. Thelower and upper limits of cerebral autoregulation in alfentanil-anaesthetizedanimals were not different from those observed in animals anaesthetizedwith barbiturate only. The data suggest that alfentanil, indoses sufficient to cause profound analgesia and anaesthesia,does not alter cerebral reactivity to changes in Pa^O2, Pa^CO2and MAP.