SummaryTwentyfive patients undergoing elective cataract day surgery were studied after receiuing a dual-injection peribulbar block with a mixture consisting of equal volumes of 2% lignocaine and 0.75% bupivacaine with hyaluronidase. A maximum of' 10 mi of solution was used for the initial hlock; supplementary injections of up to lOml were given lo five patients. Venous blood was taken prior to the block and then 1, 10, 20, 30, 60 and 90min after the block. The peak mean concentrations of lignocaine (0.722 p g . m l~ ' ) and bupivacaine (0.353 pg.ml-' ) were found at I s 2 0 min after injection when no top-up was given and at 10 min after the top-up injection when required. AN measured serum concentrations of lignocaine and bupivacaine were below the accepted toxic levels of the two drugs. However, the highest individual toxicity score after a top-up was 0.915 which was very close to the toxicity threshold (= I) when a scoring system was used to assess the combined levels.

No abstract