Comparison of lidocaine, lidocaine-morphine, lidocaine-tramadol or bupivacaine for neural blockade of the brachial plexus in fat-tailed lambs

To evaluate the onset time and duration of action of lidocaine, lidocaine-morphine, lidocaine-tramadol or bupivacaine for a neural blockade of the brachial plexus in fat-tailed lambs. Prospective, randomized, crossover, experimental study. Seven healthy female fat-tailed Ghezel lambs weighing 27.0 ± 2.2 kg (mean ± SD). Each lamb was administered four treatments for brachial plexus block (BPB): lidocaine 2% (5 mg kg−1) (LID), lidocaine 2% combined with morphine (0.1 mg kg−1) (LIDMO), lidocaine 2% combined with tramadol (1 mg kg−1) (LIDTR) or bupivacaine 0.5% (1.25 mg kg−1) (BUP), for a total treatment volume of 0.25 mL kg−1. The brachial plexus was located with a peripheral nerve stimulator, and the treatment volume was injected in increments. Treatments were randomized and separated by at least 7 days. Onset and duration of a sensory block of the distal thoracic limb were evaluated using superficial and deep pin pricks and pinching of the skin with haemostatic forceps. The mean duration of sensory block was 100 ± 38 minutes in LID, 103 ± 35 minutes in LIDMO, 79 ± 28 minutes in LIDTR, and 335 ± 134 minutes in BUP. The mean duration of sensory and motor blocks in BUP were significantly longer compared with other treatments (p < 0.05). No clinical signs of local anaesthetic toxicity were noticed, and the rectal temperature did not differ significantly from baseline values in any treatments. The addition of morphine or tramadol to lidocaine did not affect the duration of antinociception of lidocaine for brachial plexus block in fat-tailed lambs. Administration of bupivacaine provided a prolonged duration of action without obvious adverse effects.