Fifteen anaesthetists were observed while providing anaesthesia for 15 pairs of adult cardiac surgical operations, using conventional methods for one of each pair and a new drug administration system designed to reduce error for the other. Aspects of each method were rated by users on 10-cm visual analogue scales (10 being best). The new system was rated more favourably than conventional methods in terms of safety (median [range] = 8.1 [6.8-9.7] vs. 7.1 [2.6-9.3] cm; p = 0.001) and usability (8.5 [5.9-9.4] vs. 7.5 [3.2-9.8] cm; p=0.027). The new system saved preparation time both before anaesthesia (median [range] = 180 [32-480] vs. 360 [120-600] s; p=0.013) and during anaesthesia (10 [2-38] vs. 12 [10-60] s; p=0.009). Prefilled syringes for the new system increased costs by euro 23.00 per anaesthetic (p = 0.041), but this increase is likely to be offset by the potential of the new system to decrease costly iatrogenic harm by preventing drug error.