Effects of morphine and fentanyl constant rate infusion on urine output in healthy and traumatized dogs.

OBJECTIVE To determine whether healthy and traumatized dogs receiving a constant rate infusion (CRI) of either morphine or fentanyl have decreased urine production. STUDY DESIGN Prospective randomized controlled study. ANIMAL POPULATION Eighteen privately owned previously healthy dogs that had undergone trauma were included. Twenty-three privately owned healthy dogs were used as the controls. METHODS Traumatized dogs were randomized into one of two groups. Group Tmorphine received a CRI of morphine (0.12 mg kg(-1) hour(-1)) and group Tfentanyl received a CRI of fentanyl (3 microg kg(-1) hour(-1)) both administered in lactated Ringer's solution (LRS) at a rate of 60 mL kg(-1) day(-1). Control healthy dogs were randomized into one of three groups. The LRS control group (CLRS) (n = 8) received LRS at a rate of 60 mL kg(-1) day(-1). Group Cmorphine (n = 8) and group Cfentanyl (n = 7) received the same infusions as Tmorphine and Tfentanyl, respectively. Collected data were identical for all groups and consisted of measuring total fluid administered, urine output, and urine specific gravity (USG) for a 24-hour period. An analysis of variance (ANOVA) was used for statistical analysis and a p < 0.05 was considered statistically significant. RESULTS Urine output was significantly decreased (p < 0.05) in all groups compared with the LRS control group. The end mean USG was significantly lower (p = 0.003) in the LRS control group compared with all other groups. CONCLUSIONS There was a decrease in urine output with a CRI of morphine or fentanyl in both healthy and traumatized dogs. CLINICAL RELEVANCE Decreased urine output caused by an opioid effect might lead to improper assessments of renal function and urine production.