Do infusions of midazolam and propofol pose an infection risk to critically ill patients?

In order to investigate bacterial contamination of i.v. anaesthetic agents, given by infusion to critically ill patients, we have cultured residual infusion fluid from infusion syringes, 50 containing midazolam and 50 propofol. The infusions had been prepared with routine aseptic precautions and had been running for between 0.75 and 21.25 h. Only scanty growths of Staphylococcus epidermidis were isolated from seven syringes (four midazolam and three propofol). Small volume samples were more likely to produce bacterial growth than large volume specimens. Midazolam infusions made up in 5% glucose were more likely to be contaminated than those made up in 0.9% saline. Antibacterial activity was detected in 18 midazolam and one propofol filtrate. Midazolam infusions inhibited the growth of all seven of the S. epidermidis isolates, whereas propofol supported similar rates of multiplication to that obtained with control broth medium. The results of this study imply that contamination of the infusions probably occurred after they were disconnected from the patient. Despite the ability of propofol to support microbial multiplication, we have no evidence to suggest that this is clinically significant when infusions are prepared with conventional aseptic precautions.