Comparison of lidocaine, lidocaine/epinephrine or bupivacaine for thoracolumbar paravertebral anaesthesia in fat-tailed sheep.

OBJECTIVE: To evaluate the speed of onset and duration of loss of sensation in the flank following paravertebral administration of lidocaine (with or without epinephrine) or bupivacaine. STUDY
DESIGN: Blinded, randomized experimental study. ANIMALS: Nine healthy fat-tailed male lambs (mean weight ± SD, 22.9 ± 3 kg). Each animal was used twice.
METHODS: Animals were allocated randomly to receive two of three treatments: lidocaine 2% (LID, n = 6), lidocaine with epinephrine 5 μg mL(-1) (LIDEP, n = 6) or bupivacaine 0.5% (BUP, n = 6). The sheep received a total volume of 9 mL (3 mL for each paravertebral nerve) of anaesthetic. Onset and duration of loss of sensation on the flank were evaluated using nociceptive stimuli (superficial and deep pin-prick and clamping with a haemostat). Values for heart (HR) and respiratory (f(R) ) rates, rectal and skin temperatures were recorded before and at predetermined intervals after paravertebral injection. Parameters were compared using anova followed by Duncan's test where relevant.
RESULTS: Mean ± SD times to onset of loss of flank sensation following paravertebral administration of LID, LIDEP or BUP were 1.8 ± 1.2, 2.0 ± 0.9 and 3.6 ± 1.3 minutes, respectively. Durations of action in minutes were 65 ± 18, 95 ± 46 and 303 ± 98, respectively. Onset and duration of effects after BUP treatment were significantly longer than after LID or LIDEP (p < 0.05), but did not differ significantly between LID and LIDEP. No clinical signs of local anaesthetic toxicity were noticed and HR and f(R) remained stable with all protocols. CONCLUSIONS AND CLINICAL RELEVANCE: Paravertebral administration of bupivacaine produces a longer duration of anaesthesia when compared to lidocaine with or without epinephrine and is indicated when prolonged flank surgery is to be performed.