Peripheral nerve blocks induce blockade of sensory innervation through the injection of local anesthetic into a targeted location, thereby providing pain relief for procedures and operations which would, otherwise, require more systemic forms of analgesia (e.g., opioid-based analgesia concomitant with, or requiring, general anesthesia).1 They are generally well tolerated with absolute contraindications, including allergy to the local anesthetic being administered, patient refusal, and inability to cooperate.1 As with all interventions, however, there are some risks associated with peripheral nerve blocks.
One risk associated with peripheral nerve blocks is direct peripheral nerve injury, usually as a result of needle-to-nerve interaction or secondary compression from an aspect of the procedure (e.g., injectate pressure or displacement of nearby structures resulting in nerve impingement).2 Although it is difficult to quantify this risk, it is generally accepted that the risk is low, with a reported incidence around three in every 10,000 blocks.2
Another potential complication of peripheral nerve blocks is local anesthetic systemic toxicity (LAST). LAST is a potentially life-threatening condition that manifests from toxic systemic levels of local anesthetic. Its effects are primarily mediated through the central nervous and cardiovascular systems. Symptoms of LAST range from tinnitus, perioral numbness, metallic taste, agitation, and confusion to seizures and cardiovascular collapse. While uncommon, with reports estimating an incidence of 2–4 per 10,000 (or similar low-range estimates depending on the source), the severity of presentation warrants continuously monitoring patients for signs of its onset.
In addition to the previously stated risks, a concept known as the double crush phenomenon or theory is a clinically relevant concern for physicians when administering peripheral nerve blocks. This phenomenon is predicated on the concept that pre-existing neurologic damage along a specific neuronal distribution can precipitate neurologic deficits out of proportion to the prior injury in the presence of a second, neurologic insult along that same distribution.5 For example, pre-existing, minor neurologic damage to a nerve that provides sensation to a specific finger and specific impingement of that same nerve may produce disproportionately severe deficits at a different site during peripheral nerve blockade.
Like all procedures, peripheral nerve blocks carry risks. These risks can generally be classified as directly due to the procedure as it is performed (e.g., nerve impingement, direct or indirect); secondary, as in the case of systemic absorption of the injected local anesthetic and the consequences of its systemic absorption (e.g., LAST); or due to pre-existing neurologic disease which may lead to neurologic damage out of proportion to what would be expected. While this is not an exhaustive list, these insults represent the more common forms of neurologic injury and the risks associated with peripheral nerve blocks.
References
1. Chang A, Dua A. Peripheral Nerve Blocks. In: StatPearls. StatPearls Publishing; 2026. Accessed April 12, 2026. http://www.ncbi.nlm.nih.gov/books/NBK459210/
2. O’Flaherty D, McCartney CJL, Ng SC. Nerve injury after peripheral nerve blockade-current understanding and guidelines. BJA Educ. 2018;18(12):384-390. doi:10.1016/j.bjae.2018.09.004
3. Song K, Blankenship RB, Derian A. Local Anesthetic Toxicity. In: StatPearls. StatPearls Publishing; 2026. Accessed April 12, 2026.http://www.ncbi.nlm.nih.gov/books/NBK499964/
4. Neal JM, Barrington MJ, Fettiplace MR, et al. The Third American Society of Regional Anesthesia and Pain Medicine Practice Advisory on Local Anesthetic Systemic Toxicity: Executive Summary 2017. Reg Anesth Pain Med. 2018;43(2):113-123. doi:10.1097/AAP.0000000000000720
5. Molinari WJ, Elfar JC. The double crush syndrome. J Hand Surg. 2013;38(4):799-801; quiz 801. doi:10.1016/j.jhsa.2012.12.038