Peripheral Nerve Blocks: Risks & Contraindications

RISKS & CONTRAINDICATIONS

Patient cooperation and participation are key to the success and safety of every regional anesthetic procedure; patients who are unable to remain still for a procedure may be exposed to increased risk. Examples include younger pediatric patients and some developmentally delayed individuals, as well as patients with dementia or movement disorders. Bleeding disorders and pharmacological anticoagu-lation heighten the risk of local hematoma or hem-orrhage, and this risk must be balanced against the possible benefits of regional block. Specific periph-eral nerve block locations warranting the most con-cern are posterior lumbar plexus and paravertebral blocks owing to their relative proximity to the retro-peritoneal space and neuraxis, respectively.

Placement of a block needle through a site of infection can theoretically track infectious mate-rial into the body, where it poses a risk to the target nerve tissue and surrounding structures. Therefore, the presence of a local infection is a relative contra-indication to performing a peripheral nerve block. Indwelling perineural catheters can serve as a nidus of infection; however, the risk in patients with sys-temic infection remains unknown.

Although nerve injury is always a possibil-ity with a regional anesthetic, some patients are at increased risk. Individuals with a preexisting condi-tion (eg, peripheral neuropathy or previous nerve injury) may have a higher incidence of complica-tions, including prolonged or permanent sensori-motor block. The precise mechanisms have yet to be clearly defined but may involve local ischemia from high injection pressure or vasoconstrictors, a neuro-toxic effect of local anesthetics, or direct trauma to nerve tissue.

Other risks associated with regional anesthesia include local anesthetic toxicity from intravascular injection or perivascular absorption. In the event of a local anesthetic toxic reaction, seizure activity and cardiovascular collapse may occur. Supportive mea-sures should begin immediately, including solici-tation of assistance with a code blue, the initiation of cardiopulmonary resuscitation, lipid emulsion administration to sequester local anesthetic, and preparation for cardiopulmonary bypass.

Site-specific risks should also be considered for each individual patient. In a patient with severe pul-monary compromise or hemidiaphragmatic paraly-sis, for example, a contralateral interscalene or deep cervical plexus block with resultant phrenic nerve block could be disastrous.