Less pain on injection by a new formulation of propofol?

Background. Pain on injection is a major disadvantage of propofol, experien ced by the vast majority of patients. Since the traditional formulation has almost normal osmolality and pH, it is hypothesised that the concentration of free propofol in the aqueous phase of the emulsion is responsible for t he pain and that reducing the amount of free propofol would also reduce the frequency and intensity of pain on injection. This study was designed to i nvestigate whether pain on injection can be reduced in frequency and intens ity by a new formulation of propofol. Methods. We performed a monocentre, controlled, randomised, double-blind st udy to compare the pain produced by intravenous injection of a new propofol preparation (propofol-MCT/LCT) with standard propofol in patients undergoi ng elective surgical procedures. A total of 184 non-premedicated patients r eceived either 1% propofol prepared in a mixture of medium and long chain t riglycerides (Propofol-MCT/LCT, Propofol-(R) Lipuro, B. Braun Melsungen AG) or standard 1% propofol prepared exclusively in long chain triglycerides ( Propofol-LCT; Disoprivan (R) ,AstraZeneca) into a vein of the dorsal hand f or induction of anaesthesia. Anaesthesia was maintained by TIVA with propof ol and remifentanil. Pain on injection was recorded and graded as none, mil d, moderate or severe. Results. Patients receiving propofol-MCT/LCT had a significantly lower inci dence of pain on injection compared to the standard propofol group (37% vs 64%) with the intensity of pain also being less severe. There were no diffe rences between both groups in propofol dosage for induction (3.2 +/-0.8 mg/ kg vs 3.3 +/-0.9 mg/kg) and maintenance of anaesthesia (3.4 +/-0.6 mg/kg/h vs 3.2 +/-0.5 mg/kg/h), remifentanil dosage (25 +/-6 mug/kg/h vs. 24 +/-6 N g/kg/h), intraoperative hemodynamics,recovery parameters and postoperative patient satisfaction. Postoperative thrombophlebitis at the injection site for propofol was not observed in any of the patients. Conclusions. Propofol -MCT/LCT produced significantly less pain on injection when compared to sta ndard propofol in ASA I and II patients undergoing elective surgery. Pain w as also significantly less severe,with both effects presumably being due to the lower concentration of free propofol in the MCT/LCT-preparation. With regard to injection pain propofol-MCT/LCT offers significant a advantage ov er standard propofol.