Thoracic epidural analgesia via the lumbosacral approach using multiport catheters with a low concentration of bupivacaine and morphine in sheep.

Objective: To determine the analgesic and systemic effects of thoracic epidural administration of bupivacaine (BP) and morphine (MP) in conscious sheep.

Study Design: Randomized, crossover, experimental study.

Animals: Six healthy castrated sheep weighing between 40 and 50 kg.

Methods: Each sheep received, via the lumbosacral approach, BP (0.5 mg kg(-1)), MP (0.1 mg kg(-1)), and BP plus MP (BPMP; 0.25 mg kg(-1) + 0.05 mg kg(-1)) in a randomized order. Heart rate, blood pressure, respiratory rate, blood gas analysis, skin temperature, rectal temperature, analgesia, sedation, and motor blockade were determined before treatment and at predetermined intervals until analgesia had disappeared.

Results: The main areas of complete analgesia for the BP and BPMP treatments were the thorax and forelimb bilaterally. The median duration of analgesia was shorter with MP treatment (45 minutes; score 2) than with BP treatment (70 minutes) and BPMP treatment (140 minutes; p < 0.05). The BP and BPMP treatments caused motor block, and MP and BPMP treatments showed mild sedation. Significant decreases in systolic and diastolic arterial blood pressures were observed only with the BP treatment (p < 0.05). Epidural MP combined with the BP local anesthetic depressed ventilation but within acceptable limits in these clinically healthy sheep.

Conclusions: Thoracic epidural administration of BPMP to sheep resulted in longer duration of analgesia of the thorax and forelimbs bilaterally in conscious sheep than the administration of MP or BP alone. The incidence of complications was low, but side-effects such as depressed ventilation and muscle paralysis occurred and require appropriate management.

Clinical Relevance: This technique should be considered as another method for the relief of postoperative pain after thoracic surgery in sheep.