Using a randomized blind cross-over design, the comparative efficacy of clonidine in prolonging tetracaine spinal anaesthesia was studied in six mongrel dogs. Lumbar subarachnoid injections (1 ml) of: tetracaine 4 mg with clonidine 150 μg, tetracaine 4 mg with epinephrine 200 μg, tetracaine 4 mg, clonidine 150 μg, epinephrine 200 μg, and five per cent dextrose in H2O (vehicle) were administered randomly to each animal at 5-7 day intervals. Subarachnoid tetracaine produced a motor blockade of 186 ± 58 (mean ± SEM) min. Both clonidine and epinephrine produced a similar prolongation of tetracaine motor blockade, 135 percent(p < 0.01 ) and 116 per cent (p < 0.05) respectively, compared with tetracaine alone. No motor blockade was observed in dogs receiving clonidine, epinephrine or five per cent dextrose in H2O. The addition of clonidine to tetracaine spinal anaesthesia produced a significant increase in duration of sensory blockade, 56 per cent (p<0.01) and 107 per cent (p < 0.01) respectively, when compared to tetracaine with and without epinephrine. Subarachnoid clonidine alone produced a sensory blockade of 76 ± 17minutes, while only one animal receiving subarachnoid epinephrine had a sensory blockade (40 minutes). No neurologic deficits were observed in any of the animals. The study concludes that during spinal anaesthesia with tetracaine in dogs, clonidine is as effective as epinephrine in prolonging motor blockade, but is more effective in prolonging sensory blockade.
- Adrenoceptor agonist: clonidine
- Catecholamines: epinephrine
- anaesthetic techniques: subarachnoid block
- anaesthetics, local: tetracaine
- sympathetic nervous system
ASJC Scopus subject areas
- Anesthesiology and Pain Medicine