Perioperative analgesic effects of a modified supratemporal retrobulbar block in dogs undergoing corneal and endocular surgery

Objectives: To evaluate the perioperative efficacy of a modified supratemporal retrobulbar block in dogs undergoing ocular surgery.

Materials and methods: In this prospective randomized clinical trial, dogs were premedicated with dexmedetomidine (1 mcg/kg im) and methadone (0.1 mg/kg im), induced with propofol to effect and maintained with isoflurane (FE'Iso 1.1%). In the retrobulbar group a mixture of lidocaine 2% (5.5 mL) and ropivacaine 0.75% (2 mL) was administered at 0.1 mL/kg, via a modified supratemporal technique using a Tuohy needle. No block was performed in the controls. When heart rate or mean arterial pressure increased above 30% of the pre-incisional values, fentanyl (1 mcg/kg iv) was administered. Propofol (1 mg/kg iv) was injected when anaesthesia was deemed too light. After a total of three administrations regardless of the type of drugs (fentanyl/propofol), a constant rate infusion of fentanyl (5 mcg/kg/h iv) was started. Quality of recovery (blindly assessed using a descriptive score scale), postoperative eye rubbing and complications were studied.

Results: Eighteen dogs were included. The retrobulbar group (nine) dogs had significantly less risk of receiving fentanyl than controls (nine) (Relative risk: 0.142, 95% CI: 0.021 to 0.936) and a recovery score > 2 (RR: 0.058, 95% CI: 0.003 to 0.887). The median amount of fentanyl (mcg/kg) was statistically lower in the retrobulbar group than in the controls: 0 mcg/kg (range, 0 to 1) versus 2 mcg/kg (range, 0 to 8.49), respectively. Only controls showed eye rubbing.

Clinical significance: The modified supratemporal retrobulbar block reduced the intraoperative rescue analgesia and improved the quality of recovery.