OBJECTIVES

 To determinate the pre-emptive effects of epidural administration of ketamine or S(+)-ketamine in an incisional pain model in dogs.

 To evaluate the pre-emptive analgesic effect of ketamine or S(+)-ketamine by von Frey filaments and planimetry.

MATERIALS

Twenty four healthy mongrel dogs females or males*, weighing 12(+/-3) Kg, aging 1-5 years were randomly allotted into GL (n=8), GR (n=8) and GS (n=8). After propofol anesthesia (5mg.kg-1, IV) an epidural catheter (16G) was advanced 5 cm cranially into the epidural space through an epidural Tuohy needle (16G). S(+)-ketamine (0,6mg.kg-1); ketamine (0,6mg.kg-1) or saline, were injected to GL, GR and GS dogs, respectively. The final injection volume was adjusted to 0,3ml.kg-1 with saline 0,9%. Five minutes after the epidural injection a 2 cm incision was made in the right hindlimb paw and subsequently sutured. Respiratory (RR) and heart (HR) rates, rectal temperature (T), sedation (S) and mechanical pain threshold (MPT), by von Frey filaments, were evaluated at basal, 15, 30, 45, 60, 90 minutes and then at 2, 4, 6, 8, 12 and 24 hours after the epidural injection. Planimetry was used to measure the paw bearing area at the same intervals. Comparisons were made using analysis of variance (ANOVA) following by Student-Newman-Keuls test. All data were expressed as mean +/- SD and differences were considered when p < 0.05.

RESULTS

There were no differences in RR, HR, T and S between groups. No excitement signs were observed; nevertheless motor blockade of hindlimbs was observed until 30.6 (20-45) and 20 (15-26) minutes in GL and GR animals, respectively. Bearing area of the incised paw was reduced in the entire evaluation period when compared with the basal values in the three groups, and it was higher from 30 to 90 minutes in GR when compared with GL and GS. Significant differences were observed in the MPT between GL and GS animals from 60 to 90 minutes, and between GR and GS animals from 60 minutes to 12 hours.

CONCLUSION

Ketamine and S(+)-ketamine reduced but not suppressed the post-incisional pain (secondary hyperalgesia). The von Frey filaments and planimetry methods allowed to quantify the post-incisional hyperalgesic response and the subsequent analgesic effects of the two drugs. We concluded that epidural ketamine produces more prolonged reduction of post-incisional pain (12 hours) than S(+)-ketamine (1.5 hours), and its use in clinical conditions could be more advantageous.

* This study received approval from the ethics and being animal commission of FCAV-UNESP protocol # 024696.