Ultrasound and Nerve Stimulator: A Combo Technique to Improve Safety During Nerve Blocks

Dear Editor, The nerve stimulator is a device that passes a small amount of electrical current at the tip of the needle during the performance of a nerve block. It can detect needle–nerve contact even if it is missed on ultrasound. It is important to use a nerve stimulator while performing a nerve block. Most pain practitioners do not consider it due to a lack of evidence. As the practice of nerve blocks using ultrasound alone is subjective and depends on the operator’s interpretation, image quality, and other factors, it exposes the practitioners to the risk of medico-legal scrutiny. In fact, the available data demonstrates that even experts may miss an intra-neural injury in almost 20% of the blocks using ultrasound as a sole monitoring tool.[1] Nerve stimulators can detect dangerous nerve positions and needle–nerve contact before the needle enters the nerve and causes potential harm. They can provide objective data that not only aids in patients’ safety but also offers protection against potential medico-legal issues. The working of nerve stimulators depends on the electrical current and frequency. For example, if the current is set at 0.5 mA and the frequency at 2 Hz, that is, every second, two of these pulses of 0.5 mA pass on the tip of the needle. If the needle encounters the nerve, there will be a motor response that occurs before it is seen on the ultrasound. Thus, it prevents further advancement of the needle and damage to the nerve. Therefore, while performing a block with ultrasound, if needle–nerve contact is visually missed, an unexpected motor response to nerve stimulation will guide regarding the closeness of the needle to the nerve, and give an opportunity to refocus on the ultrasound image. Neurological complications during nerve blocks are not uncommon. However, if a nerve stimulator is used and a loco-motor response is documented, it demonstrates that all the necessary precautions were taken to avoid nerve injury. In addition, coupling this with objective “injection pressure monitoring” during nerve blocks further improves safety, giving confidence in the face of any potential legal challenges.[2,3] To conclude, implementing objective measures such as nerve stimulation and injection pressure monitoring would not eliminate the risk of neurologic complications. However, it does assure the practitioners that everything has been done to mitigate the risk, documenting the presence or absence of motor response during nerve blocks. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.