Effects of high-dose fentanyl on renal haemodynamics in conscious dogs.

Abstract

The renal haemodyrumic effects of high doses of fentanyl were examined in 17 unanaesthethed, chronically implanted dogs, in order to avoid the confusing effects of superimposed anaesthesia and acute surgical procedures. Ten to fourteen days prior to the study, a Doppler flow probe was positioned around the left renal artery and u Tygon catheter was placed into the lower abdominal aorta through a lumbar arterial side branch. During the experiments, the trained animals were lying quietly on their right side. Following steady-state awake baseline measurements, an intravenous fentanyl infusion, 25µg-kg (lower dose), or50µg.kg (higher dose) was administered over a ten-minute period. Arterial pressure, renal blood flow, calculated renal vascular resistance and arterial blood gases were measured for 20 minutes following the infusion. Observations were made during spontaneous and controlled ventilation, with FIO2 = 0.21 or 1.0. Fentanyl increased arterial pressure 10–40 per cent in all groups and did not, as a rule, significantly affect renal blood flow. Thus renal vascular resistance was increased. There were no significant differences between effects of the 25 µg.kg and the 50 µg- kg doses of fentanyl. It is concluded that these doses of fentanyl, given to the conscious, normovolaemic dog, result in renal vasoconstriction. Renal blood flow does not decrease, however, implying that autoregulation remains intact. These changes are a result of fentanyl, per se, rather than secondary to changes in oxygenation and carbon dioxide levels in the blood and do not appear to have a dose response relationship in the dosage range studied.