Fentanyl and Cerebral Vascular Responsivity in Dogs

Abstract

The effect of high-dose fentanyl [F] on the cerebral vascular response to alterations in mean arterial blood pressure [MABP], arterial O2 tension (PaO2) and arterial CO2 tension (PaCO2) was studied in 28 mongrel dogs using the cerebral venous outflow technique. In 13 animals anesthetized with sodium pentobarbital (30 mg/kg, i.v.), bolus injection of F (25 .mu.g/kg, i.v.) decreased MABP without a change in cerebral blood flow (CBF). In these animals, the response of the cerebral circulation to changes in PaO2, PaCO2 and MABP was determined before and after F administration. F did not alter the increase in CBF caused by hypoxic hypoxia or hypercapnia. The lower and upper limit of cerebral autoregulation determined by hypovolemic hypotension and norepinephrine infusion, respectively, also were unaltered by F. The CBF response to alterations of MABP, PaO2 and PaCO2 were studied in another group of 15 dogs anesthetized with F (100 .mu.g/kg) plus small doses (3-5 mg/kg) of pentobarbital. The CBF response to PaO2 and PaCO2 in these animals was not different from that observed in animals anesthetized with barbiturates only. The lower and upper limit of cerebral autoregulation also were not different from that observed in animals anesthetized with barbiturates only. Apparently, F in doses sufficient to cause profound analgesia and anesthesia did not alter cerebral responsivity to changes in PaO2, and PaCO2 and MABP.