[Effect of concentration on counting numbers on pain induced by injection of propofol].

Background: One of the concerns in the use of propofol is the pain on injection of the drug. Many attempts were made to prevent such pain, none of which has been reasonably successful. We hypothesized that the pain is attenuated when the patient is directed to concentrate on counting numbers while propofol is injected.

Methods: Ninety-one patients undergoing elective surgery under general anesthesia were enrolled. They were randomly assigned to counting or non-counting group. Patients in counting group were instructed to verbally count numbers backwards starting 100 when propofol was injected, while patients in non-counting group were injected propofol without any instructions. The size of the i.v. cannula, the temperature of the drug, and speed by which the drug was injected were controlled. No premedication was given. We interviewed the patients after the surgery and scored the pain on propofol injection, the pain on the placement of the iv cannula, and the anxiety level on entering the operating room.

Results: There was no significant difference in the incidence of pain on injection of propofol (34% and 33% in the counting and the non-counting group, respectively). A multiple logistic-regression analysis revealed that the significant factors to cause pain on the injection of propofol were age and the degree of pain on inserting intravenous line.

Conclusions: Intensive counting did not reduce the incidence of pain on injection of propofol. Age and the degree of pain on inserting intravenous cannula can be a useful predictor for an intolerable pain on injection of propofol.