EFFECTS OF FENTANYL, DROPERIDOL, AND INNOVAR ON CANINE CEREBRAL METABOLISM AND BLOOD FLOW

The effects of droperidol and fentanyl given individually andin combination (Innovar) on the rate of cerebral oxygen consumption(CMRo,) and cerebral blood flow (c.b.f.) were studied in dogsanaesthetized with nitrous oxide (70 percent) and oxygen. Fentanyl(0.006 mg/kg) decreased both the CMRo, and the c.b.f. (meandecreases at 15 minutes were 18 per cent and 47 percent, respectively).The duration of effect was approximately 30 minutes. Droperidol(0.3 mg/kg) produced a decrease of 40 per cent in c.b.f. dueprimarily to a 30-40 per cent increase in cerebrovascular resistance,and this effect persisted for the period of observation (60minutes). No significant change in CMRo, occurred after droperidolwas administered. With the combination drug (Innovar), the effectswere partially additive. After 15 minutes, CMRo, had decreased23 per cent; c.b.f. had decreased 50 per cent; and cerebralvascular resistance had increased 85 per cent. After 30 minutes,the effects of Innovar were indistinguishable from those ofdroperidol alone. No significant changes occurred in the rateof cerebral glucose consumption or the oxygen-glucose index.The effect of increased and decreased Paooj on c.bi. after Innovarwas compared widi that observed during halothane anaesthesia.With halothane, hypercapnia (Pacoi=60 tnm Hg) increased c.b.f.40 per cent and hypocapnia (Pace = 20 mm Hg) decreased c.b.f.40 per cent. Innovar at normocapnia reduced the c.b.f. 65 percent. With hypercapnia, the c.bi. doubled, but with hypocapnia,little further reduction in c.b.f. occurred. It is concludedthat droperidol is a potent cerebral vasoconstrictor, that thiseffect dominates when it is given in combination with fentanyl,that hypocapnia causes little further reduction in c.b.f., andthat the reduction in c.bi. produced by Innovar is not accompaniedby alterations in normal cerebral metabolic pathways