The Changes of Propofol Concentration over Time in a Propofol-Lidocaine or Propofol-Ketamine Mixtures

Chae, Bong Soo; Kil, Ho Yeong

Abstract

BACKGROUND: Pretreatment or addition of lidocaine or ketamine have been reported to reduce pain on injection. However, the stability of propofol following the addition of lidocaine or ketamine is not yet known. Therefore, we checked compatibility and stability of propofol-lidocaine or propofol-ketamine mixtures.
METHODS
After mixing 9 ml of 1% propofol and 0, 5, 10, 15, or 20 mg of 2% lidocaine or 10, 20 mg of ketamine, the samples (0.9 ml) were divided into 10 glass vials and stored at room temperature. Macroscopic and microscopic changes, and propofol concentrations were measured at 0, 1/4, 1/2, 1, 2, 3, 4, 5, 6, and 24 hours after mixing. Premedicated 100 ASA classification I or II patients scheduled for elective surgery were randomly allocated into one of three groups(Group 1: propofol only, Group 2: propofol + lidociane 20 mg, Group 3: propofol + ketamine 10 mg). Intensity and frequency of injection pain was checked during induction (150 ml/hr). Intensity of injection pain was evaluated with a pain score (1: no pain, 2: mild, 3: moderate 4: severe).
RESULTS
Macroscopic and microscopic changes were only seen in propofol-lidocaine mixtures (more than 15 mg after 1 hour) in a time-dependent manner. In the mixtures with lidocaine 15 or 20 mg, the propofol concentration decreased linearly and significantly compared to the control (time 0) in a time-dependent manner from 1 hour to 24 hours. However, the propofol concentration was not changed in the propofol-ketamine mixtures. The pain score at 20 mg of lidocaine or 10 mg of ketamine were significantly lower than propofol only group and there was no difference in pain score between group 2 and group 3.
CONCLUSIONS
Lidocaine (more than 15 mg), but not ketamine, added to 90 mg of propofol reduced the propofol concentration linearly in a time-dependent manner and showed microscopic changes from l hour after mixing. Therefore, this mixture seems to be inappropriate for long-standing storage and thus propofol-ketamine mixtures are more appropriate for this purpose.