An increasing number of cases of target-controlled infusion (TCI) of propofol have substituted 2% propofol for 1% due to the concerns about lipid deposition and the practical convenience. However, 2% propofol may possess a higher proportion of free aqueous propofol because of the relatively decreased lipid-solvent ratio as compared to that for 1% propofol. We performed a prospective, randomized, double-blind trial to evaluate the pain of 1% and 2% propofol TCI. The efficacy of lidocaine pretreatment to abolish the pain was also tested for each concentration of propofol.

Two hundred adult patients were randomly allocated to 4 groups according to the pretreatment drugs and propofol concentrations; placebo (normal saline) and 1% propofol group (group 1), placebo and 2% propofol group (group 2), lidocaine and 1% propofol group (group 1L), and lidocaine and 2% propofol group (group 2L). Administration of pretreatment drug was followed by TCI with using each concentration of propofol. Pain was assessed using a four-point scale during propofol infusion.

Propofol pain was more frequent (82% vs. 63%, respectively, P = 0.026), and severe (P = 0.002) for the group 2 than for group 1. Pain was significantly reduced by lidocaine pretreatment in the group 2L (48%) and group 1L (19%), as compared with group 2 (82%) and group 1 (63%), respectively (P < 0.001, both). However, group 2L still showed considerable pain that was similar to the pain of group 1.

TCI of 2% propofol caused more frequent and severe pain despite of lidocaine pretreatment.