The procedure

  • Test the function of the nerve stimulator. 
  • Disinfect the skin, create a skin weal and, if necessary, infiltrate puncture channel. When blocking superficial nerves (e.g. brachial plexus, femoral nerve), infiltrate the puncture site cautiously, as otherwise the effect of stimulation may be reduced by a premature partial block. 
  • Place an injection line with NaCl 0.9% syringe, rinse the injection line and needle, connect the current line and create a connection to the neutral electrode. 
  • Pierce the skin with the stimulation needle and advance it into the subcutaneous tissue. 
  • Switch on the stimulator and select the pulse duration (0.1 ms for mixed nerves), pulse frequency (2 Hz) and stimulation current (1 mA). Check to make sure that the selected stimulation current corresponds to the actual current reading. If the actual stimulation current deviates markedly from the pre-selected value, check to electrode and the stimulator once more. 
  • Advance the stimulation needle towards the nerve until the first muscle contractions occur in the area of the target muscle. While monitoring the stimulatory response, reduce the stimulation current incrementally until the threshold electrical current (>0.2<0.3 ma="" is="" reached="" and="" contractions="" are="" still="" visible="" to="" rule="" out="" a="" too="" close="" needle="" position="" the="" amplitude="" reduced="" further="" until="" muscle="" response="" disappears="" if="" stimulatory="" triggered="" at="" 0="" 2="" must="" be="" retracted="" slightly="" here="" it="" important="" that="" anaesthesiologist="" assistant="" co-ordinate="" their="" activities="" only="" one="" of="" them="" may="" make="" adjustments="" either="" changes="" stimulation="" or="" adjusts="" current="" li="">
  • If visible contractions of the target muscle continue to occur at the threshold current, perform a negative aspiration test and then inject the local anaesthetic. 
  • Turn the stimulation current back up to 1.0 mA after the first 10 ml of the local anaesthetic have been injected. This is done to rule out an accidental intravascular position. If the needle is inadvertently positioned intravascularly, the local anaesthetic will be washed away and any increase in the stimulation current would lead to renewed and strong muscle contractions. Aspiration checks should be performed repeatedly throughout the entire injection. 
  • When using the catheter technique, it is advisable to make a stab incision of the injection site with a steel needle or lancet before puncturing. This will make it easier to advance the fine Teflon introducer mounted on the stimulation needle through the skin. We usually inject the full dose through the stimulation needle. This dilates the connective tissue surrounding the nerve, thereby facilitating placement of the catheter. After the stimulation needle is fixated, the capillary is released from the screw adapter by turning it clockwise and then the needle removed.