Pain on injection of propofol: effects of concentration and diluent.

The emulsion formulation of propofol (Diprivan) evokes pain on i.v. injection, although its pH and osmolality are close to those of blood. The pain induced by serial dilutions of propofol in Intralipid and 5% glucose was examined in isolated vein segments and after intracutaneous injection. Propofol evoked pain in a concentration-related manner in six of eight subjects after i.v. perfusion and in all eight subjects after intracutaneous injections. Pain was maximal with propofol 56 x 10(-3) mol litre-1 when visual analogue pain scale was 60% of maximum (range 20-92%) for venous perfusion and 89% (range 66-100%) for intracutaneous injection. Dilution with 10% Intralipid reduced pain more than that with 5% glucose. We conclude that the intensity of pain after i.v. injection of propofol was related to its free aqueous concentration.