Intravenous lidocaine may contribute to postoperative analgesia without detectable adverse effects in cats undergoing ovariohysterectomy: a randomized trial.

Abstract

OBJECTIVE: To evaluate clinical and analgesic effects of IV lidocaine bolus followed by continuous infusion in cats undergoing ovariohysterectomy. METHODS: 24 healthy female domestic shorthair cats were premedicated with IM acepromazine (0.05 mg/kg) and methadone (0.2 mg/kg). Anesthesia was induced with propofol and maintained with isoflurane in oxygen. Cats were randomly assigned to receive a lidocaine bolus (2 mg/kg) followed by infusion (3 mg/kg/h; GL), a lidocaine bolus followed by saline infusion (GB), or saline bolus and infusion (GC; n = 8/group). Intraoperative variables were monitored, and lidocaine-related adverse effects were clinically assessed. Pain was evaluated for 24 hours postoperatively with a validated feline pain scale. Analgesic rescue was provided with fentanyl (intraoperatively) or morphine (postoperatively) when indicated. RESULTS: End-tidal isoflurane concentration was significantly lower in GL compared to GC at 10 minutes after bolus administration, at musculature incision, and at 30 minutes after bolus administration (mean reduction of approx 18%). Despite this difference, all animals remained within stage 3 of anesthesia according to the Guedel classification. No differences were detected among groups in fentanyl rescue frequency, although GL had fewer events (17.86% and 32.35% reduction vs GC and GB, respectively). Total morphine rescues were significantly lower in GL (P = .038). No signs of lidocaine toxicity were observed in any cat. CONCLUSIONS: At the administered dose, lidocaine was tolerated and may have reduced postoperative analgesic requirements in cats undergoing ovariohysterectomy. CLINICAL RELEVANCE: Continuous lidocaine infusion did not result in obvious signs of toxicity in healthy cats and it's use was likely to contribute to the reduction of postoperative analgesic rescue in this study.