Two electrodes were attached to the radial side of dominant forearm. In the active TENS group, TENS was delivered via two electrodes on the venous cannulation site

Two electrodes were attached to the radial side of dominant forearm. In the placebo group the TENS device had no current output although the power "on" indicator light remained active.

In the active TENS group, TENS at 80 pulsed currents per second (PPS) with a pulse duration of 200 μs were delivered for 20 minutes. Current amplitude was slowly increased until a level was reached that participants reported was the maximum level they could tolerate below pain threshold without noticeable muscle contraction and maintained this intensity.

One hundred patients were allocated randomly to two groups: In the active TENS group TENS was delivered via two electrodes on the venous cannulation site (radial side of the wrist of dominant forearm) 20 min prior to venous cannulation and control group received placebo (no current) TENS. Venous cannulation with a 22 gage cannula was performed. One minute after venous cannulation the pain intensity (0 = no pain, 10 = worst pain imaginable) was measured. Any side effects during study periods were recorded