A Novel Approach to Reverse and Titrate the Clinical Effects of a Nerve Block

Background and rationale Peripheral nerve blocks provide effective surgical anesthesia targeted to specific body regions while avoiding the unpleasant side-effects of general anesthesia. Additionally, infusion of local anesthetic (LA) solution through a perineural catheter can provide superior analgesia compared to opioid painkillers and reduces the incidence of opioid-associated side effects.

Most studies to date have focused on the efficacy of agents to extend block duration, thereby maximizing pain relief for patients receiving a nerve block. However, there are occasions when rapid and effective block reversal is needed. For example, interscalene brachial plexus block for upper extremity surgery frequently causes paralysis of the diaphragm due to inadvertent anesthesia of the phrenic nerve. A method to 'wash out' the local anesthetic around the phrenic nerve in these cases would be beneficial, especially for patients who have pre-existing pulmonary or respiratory diseases. Saline washout of LA may have an additional safety benefit since LAs are myotoxic; reducing the exposure of muscle to LA solutions while maintaining anesthesia would increase the safety of peripheral nerve blocks.

Several studies have demonstrated that epidural washout using normal saline (NS) or Ringer's lactate following epidural block facilitates more rapid recovery of motor function and sensation than letting the block resolve on its own. However, no studies to date have addressed whether washout is effective for reversal of peripheral nerve blocks. Our limited clinical experience suggests that a bolus of NS through a perineural catheter can rapidly and effectively restore phrenic nerve function following interscalene block, and preliminary laboratory experiments indicate that a continuous washout of 0.9% NS reduces by half the time required for normal diaphragm function following injection of lidocaine around the phrenic nerve. Unclear, however, is the mechanism by which NS is able to resolve the block. Thus, the investigators wish to investigate the optimal approach to block reversal and resolution.

Study objective To demonstrate that an infusion of NS can be used in a clinical setting to modify the properties of a nerve block in patients who have received a nerve block for surgery and post-operative analgesia.

Hypothesis The investigators hypothesize that NS can be delivered through a perineural catheter to 'wash out' a nerve block to the point that motor function is restored while maintaining anesthesia of sensory nerve fibers.