We studied how lowering a syringe pump and changing the outflow pressure could affect syringe pump output. We experimentally reduced the height of three different syringe pump systems by 80 cm (adult setting) or 130 cm (neonatal setting), as can happen clinically, using five flow rates. We measured the time of backward flow, no flow and the total time without flow. An exponential negative correlation was present between infusion rate and time without flow (r2=0.809 to 0.972, P<0.01). Minimum flow rates of 4.4 and 2.6 ml h(-1) respectively were calculated to give 60 and 120 s without infusion. The compliance of the different syringe pumps and their infusion systems was linearly correlated with the effective time without infusion (r2=0.863, P<0.05). We conclude that the height of the syringe pumps should not be changed during transportation. If vertical movement of the syringe pump is necessary, the drugs should be diluted so that the flow rate is at least 5 ml h(-1).

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We have compared motor block of the extraocular muscles produced by injections of 3% prilocaine and a mixture of equal parts of 2% lignocaine and 0.75% bupivacaine into the medial compartment of the orbit. A volume of 8 ml was used initially, and a vasoconstrictor and hyaluronidase were added to both solutions. Ninety patients undergoing cataract surgery were allocated randomly to one of two groups in double-blind study. Eight minutes after block insertion, the median ocular movement score in the prilocaine group was 1 and in the lignocaine-bupivacaine group 3. This difference was statistically significant (P = 0.016). Twenty of the patients who received prilocaine and 29 of the patients who received the lignocaine-bupivacaine mixture required an additional inferotemporal injection. This difference was not statistically significant (P = 0.094).

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