Nerve stimulator polarity and brachial plexus block

Area of Science:

• Anesthesiology
• Neurology
• Surgical Procedures

Background:

• Peripheral nerve blocks are essential for surgical anesthesia and analgesia.
• Accurate nerve localization is critical for effective peripheral nerve blocks.
• Nerve stimulator use is standard for guiding needle placement in peripheral nerve blocks.

Purpose of the Study:

• To investigate the impact of needle polarity on nerve stimulation thresholds during peripheral nerve blocks.
• To determine if positive or negative needle polarity influences the current required for muscle contraction.
• To optimize nerve localization techniques in regional anesthesia.

Main Methods:

• A randomized, double-blinded study involving 10 patients undergoing axillary block.
• An insulated needle was used to assess minimum current for muscle contraction.
• Measurements were taken at initial and maximal stimulation points with both positive and negative needle polarity.

Main Results:

• Significantly higher currents were needed for stimulation with positive needle polarity compared to negative polarity at both tested positions (P < 0.001).
• The ratio of positive to negative threshold current was significantly greater at maximal stimulation point (3.11) than at initial stimulation point (2.37) (P < 0.05).
• Positive needle polarity required substantially more current, potentially hindering accurate nerve identification.

Conclusions:

• Needle polarity significantly affects nerve stimulation thresholds during peripheral nerve blocks.
• Attaching the negative terminal of the nerve stimulator to the stimulating electrode is vital for reliable nerve localization.
• Incorrect polarity may lead to failed blocks or missed neural contacts, emphasizing the importance of correct electrode connection.