From the Guidelines
The use of Peripheral Nerve Stimulators (PNS) in conjunction with ultrasound guidance is recommended for nerve blocks in obese patients to improve accuracy and reduce complications. This approach is particularly useful in obese patients where ultrasound visualization may be compromised due to increased adipose tissue 1. When performing a nerve block, the practitioner should first utilize ultrasound to identify anatomical structures, and then advance the stimulating needle while applying a current of 1-2 mA at 2 Hz. As the needle approaches the target nerve, the current should be gradually reduced to 0.2-0.5 mA. A motor response at this low current confirms proximity to the nerve without intraneural placement.
Key considerations for successful nerve blocks in obese patients include:
- Using longer needles (100-150 mm) to reach deeper structures
- Employing lower frequency ultrasound probes (2-5 MHz) to improve tissue penetration and visualization
- Combining ultrasound guidance with PNS to compensate for decreased image quality and increase success rates
- Minimizing sedation during regional anesthesia to ensure patient safety and comfort, as recommended by the Association of Anaesthetists of Great Britain and Ireland 1.
By adopting this dual-guidance technique, practitioners can enhance the efficacy and safety of nerve blocks in obese patients, ultimately leading to better outcomes in terms of morbidity, mortality, and quality of life. The role of PNS is crucial in this context, as it provides an additional layer of confirmation for proper needle placement, even when ultrasound visualization is suboptimal.
From the Research
Role of Peripheral Nerve Stimulator in Ultrasound-Guided Nerve Block for Obese Patients
- The role of Peripheral Nerve Stimulator (PNS) in ultrasound-guided nerve block for obese patients is evolving, with studies suggesting that ultrasound guidance alone may be more effective in reducing procedural time and procedure-related pain 2.
- PNS can serve as a monitor against needle-nerve contact and may be useful in avoiding nerves that are in the needle trajectory during specific ultrasound-guided techniques 3.
- The use of PNS in combination with ultrasound guidance may not improve block success rates, except in cases where the nerves are challenging to view, such as the obturator nerve 3.
- Ultrasound guidance with nerve stimulation can reduce the time necessary for resident peripheral nerve blockade and improve block efficacy 4.
- PNS can be a useful adjunct in teaching novices ultrasound-guided regional anesthesia, especially when the position and or appearance of nerves may be variable 3.
Benefits of Ultrasound Guidance over PNS
- Ultrasound guidance can reduce the procedural time for peripheral nerve blocks compared to nerve stimulation, especially in obese patients 2.
- Ultrasound guidance can decrease the number of needle redirections and procedure-related pain, and increase patient satisfaction with the block procedure 2.
- Ultrasound guidance can reduce the risk of local anesthetic systemic toxicity following peripheral nerve blockade 5.