Evaluation of analgesic, sympathetic and motor effects of 1% and 2% lidocaine administered epidurally in dogs undergoing ovariohysterectomy.

OBJECTIVE: To compare, versus a control, the sensory, sympathetic and motor blockade of lidocaine 1% and 2% administered epidurally in bitches undergoing ovariohysterectomy.

STUDY DESIGN: Randomized, blinded, controlled clinical trial.

ANIMALS: A total of 24 mixed-breed intact female dogs.

METHODS: All dogs were administered dexmedetomidine, tramadol and meloxicam prior to general anesthesia with midazolam-propofol and isoflurane. Animals were randomly assigned for an epidural injection of lidocaine 1% (0.4 mL kg-1 ; group L1), lidocaine 2% (0.4 mL kg-1 ; group L2) or no injection (group CONTROL). Heart rate (HR), respiratory rate (fR ), end-tidal partial pressure of carbon dioxide (Pe'CO2 ), and invasive systolic (SAP), mean (MAP) and diastolic (DAP) arterial pressures were recorded every 5 minutes. Increases in physiological variables were treated with fentanyl (3 μg kg-1 ) intravenously (IV). Phenylephrine (1 μg kg-1 ) was administered IV when MAP was <60 mmHg. Postoperative pain [Glasgow Composite Pain Score - Short Form (GCPS-SF)] and return of normal ambulation were recorded at 1, 2, 3, 4 and 6 hours after extubation.

RESULTS: There were no differences over time or among groups for HR, fR , Pe'CO2 and SAP. MAP and DAP were lower in epidural groups than in CONTROL (p = 0.0146 and 0.0047, respectively). There was no difference in the use of phenylephrine boluses. More fentanyl was administered in CONTROL than in L1 and L2 (p = 0.011). GCPS-SF was lower for L2 than for CONTROL, and lower in L1 than in both other groups (p = 0.001). Time to ambulation was 2 (1-2) hours in L1 and 3 (2-4) hours in L2 (p = 0.004).

CONCLUSIONS AND CLINICAL RELEVANCE: Epidural administration of lidocaine (0.4 mL kg-1 ) reduced fentanyl requirements and lowered MAP and DAP. Time to ambulation decreased and postoperative pain scores were improved by use of 1% lidocaine compared with 2% lidocaine.