Prevention of propofol injection pain with small-dose ketamine. 
Propofol is a popular i.v.  anesthetic induction drug that causes pain when given i.v.,  the incidence of which is between 28%-90%.  We plan to determine the optimal dose of ketamine in the prevention of propofol injection pain and compare it with lidocaine, the commonly proposed pre-treatment.  In a double-blind randomized study 500 Patients (ASA I, II) scheduled for elective strabismus surgery under general anesthesia were randomly allocated into five groups.  After obtaining the informed consent.,  patients received normal saline (Group NS), lidocaine 1 mg x kg(-1) (Group L), and different doses of ketamine 50-75-100 microg x kg(-1) (Group K50-K75-K100 respectively), immediately before the injection of 2.5 mg.kg(-1) propofol.  Each patient's pain scores were measured at five seconds intervals by a blinded anesthesiologist.  Statistical analysis were made by SPSS vs 11.5.  The incidence and intensity of pain in all study groups were significantly lower than placebo group (Group NS) (P < 0.005).  Patients in the K100 Group had significantly lower incidence of pain and lower pain scores compared with the K50 and L Groups (P < 0.0001).  There were no significant differences in hemodynamic parameters between groups.  Administration of ketamine 100 microg x kg(-1) immediately before propofol injection is a safe and effective method in preventing propofol injection pain.