The Changes of Propofol Concentration with Time-Course in the

Lidocaine-Propofol or Ketamine-Propofol Mixtures

Ho-Yeong Kil, M.D., Bong-Soo Chae, M.D. and Dae-Woo Kim, M.D.*

Department of Anesthesiology, College of Medicine, Hallym University and

Korea Catholic University,* Seoul, Korea

Background: Propofol is widely used for induction and maintenance of anesthesia, but pain on injection is one of the sujective source of patient unsatisfaction. Of the methods, pretreatment or addition of lidocaine or ketamine have been reported to reduce pain on injection. But it is not yet known that stability of propofol following the addition of lidocaine or ketamine.

Methods: After mixing 9 ml of propofol(1%) and 0, 5, 10, 15, 20 mg of lidocaine(2%) or 10, 20 mg of ketamine, the sample(0.9ml) were divided into 10 glass vials and stored at room temperature. Macroscopic changes, microscopic changes, and propofol concentrations were measured at 0, 15, 30 min, every 1hr for 6 hrs, and at 24 hr.

Results: Macroscopic changes was only seen in addition of lidocaine 20 mg after 2 hr. Microscopic changes was first seen in addition of lidocaine 15, 20 mg at l hr and droplet size was increased in a time-dependant manner. In the mixture added lidocaine 15, 20 mg, propofol concentrations decreased linearly and significantly compared to control(time 0) in a time-dependant manner from 1hr to 24hr. But, propofol concentrations was not changed in the ketamine-propofol mixtures(Fig. 1)

Fig 1. Changes of Propofol Concentration after mixing of Lidocaine

Conclusions: Lidocaine(more than 15 mg), but not ketamine, added to 90 mg of propofol reduced propofol concentration significantly and showed microscopic change after 1hr. So, this mixtures seems to be inappropriate for longterm storage and thus ketamine-propofol mixtures are more appropriate for this purpose.

References: Lilley EMM, Isert PR, Carasso ML, Kennedy RA: The effect of the addition of lignocaine on propofol emulsion stability. Anaesthesia 1996; 51: 815-8.