Effect of injection pressure on the success rate of peribulbar block

The aim of this prospective double-blind study was to evaluate the effect of the pressure on injection of local anaesthetic during peribulbar anaesthesia. Fifty patients scheduled for cataract surgery under peribulbar anaesthesia, with a two injection site technique, were randomly assigned to receive a mixture of 5 ml of etidocaine 1%, 4 ml of bupivacaine 0.5% and hyaluronidase 50 IU, injected under a constant pressure of either 140 g.cm-2 (group 1) or 250 g.cm-2 (group 2). After orbital compression, the degree of akinesia of the extra-ocular and orbicular muscles was graded by clinical assessment. A significantly higher rate of satisfactory akinesia of the extra-ocular muscles was found in group 2 (72% vs 28% in group 1) (p < 0.01). No significant relationship was found between the time taken to administer the anaesthetic mixture at constant pressure and the quality of the block.