Comparative analgesic and cardiopulmonary effects of bupivacaine and ropivacaine in the epidural space of the conscious dog.

OBJECTIVE

To compare the cardiopulmonary effects and sensory blockade of epidural bupivacaine and ropivacaine.

STUDY DESIGN

Prospective randomized study.

ANIMALS

Six young adult medium-sized crossbred dogs weighing 25.7 ± 7.1 kg.

METHOD

Dogs were chronically implanted with a lumbosacral epidural catheter. Acepromazine sedated dogs received all treatments: 0.5% bupivacaine at 0.14 mL kg (LB5) or 0.22 mL kg (HB5); 0.5% ropivacaine at 0.14 mL kg (LR5) or 0.22 mL kg (HR5); 0.75% bupivacaine at 0.22 mL kg (HB7.5) or 0.75% ropivacaine at 0.22 mL kg (HR7.5). Loss of sensation was tested at the level of the perineum, hind toe webs, flank, and caudodorsal rib areas before injection, and post-injection (PI) up to 150 minutes PI. Systemic arterial blood pressure and heart rate were recorded before injection, and every 10 minutes PI until 150 minutes PI. Arterial blood gas analyses were performed prior to injection, and at 30, 60 and 150 minutes PI.

RESULTS

No statistical differences existed between groups for the cardiopulmonary data or time to onset of block. Group HR7.5 had lower systolic (10-70 minutes PI) and diastolic (10-70 minutes PI) blood pressures and group HR5 had lower mean (10-90 minutes PI) and diastolic (10-90 minutes PI) blood pressures compared to baseline. Heart rate was lower compared to baseline in groups LR5 and HB7.5. A significant, but mild metabolic acidosis developed in groups LR5 and HB7.5 (150 minutes PI). No differences were present for the duration of block between groups, but duration of block in the dorsocaudal rib area was shorter in group HR5 compared to HR7.5.

CONCLUSION

Epidural ropivacaine and bupivacaine at the doses used have mild effects on the cardiopulmonary system, and extent of block are similar.

CLINICAL RELEVANCE

The 0.75% concentration of bupivacaine and ropivacaine at 0.22 mL kg appeared to contribute to greater success of block (>80%) at dermatomes L-L.