Newswise — Interscalene blocks are used to relieve pain during and after shoulder surgery. They involve injecting local anesthetic into nerves in the side of the neck. The phrenic nerve originates in spinal nerves in the neck and provides motor control of the diaphragm, the primary muscle for breathing. Interscalene blocks are associated with a high risk of phrenic nerve blockade, which creates complications for patients.

Researchers are looking at how to reverse this phrenic nerve blockade using normal saline while maintaining the interscalene nerve block. Earlier research had indicated that the use of 30 mL saline can restore this phrenic nerve function while maintaining numbness in the interscalene area. However, at that level, patients may experience rebound pain. Researchers at Stanford University experimented with a smaller amount of saline (10 mL) and found that it was not enough to reverse the phrenic nerve blockade. Further research is important so that anesthesiologists can find the best approach for maintaining patients’ comfort and safety.

Lynn Ngai Gerber, Lisa Sun, Wen Ma, Shruthi Basireddy, Nan Guo, John Costouros, Emilie Cheung, Jan Boublik, Jean-Louis Horn, and Ban Tsui received a Resident/Fellow Travel Award for their abstract of the study, “10-Milliliter Normal Saline Washout Aliquots Are Insufficient to Reliably Reverse Phrenic Blockade From Interscalene Nerve Block,” which was accepted for the 45th Annual Regional Anesthesia and Acute Pain Medicine Meeting. The meeting was scheduled for April 23-25 but was cancelled due to COVID-19. 

Although an effective regional anesthesia technique for upper-extremity surgeries, the interscalene nerve block is associated with a high rate of phrenic nerve blockade, which can lead to complications such as respiratory distress in those with underlying pulmonary pathology, and sometimes unveiling respiratory issues in those without. Gerber et al.’s previous research suggested that normal saline washouts may restore phrenic nerve function while preserving the nerve block’s analgesic effect.

For the current study, Gerber et al. randomized 16 participants undergoing ultrasound-guided interscalene nerve blocks to receive either three doses of 10 mL normal saline washouts (n = 8) or sham washouts (n = 8) through their in situ nerve block catheters, after a postsurgical local anesthetic bolus. They found no clinically significant difference in reversal of diaphragmatic paralysis in patients who received the normal saline or sham washout. However, in a sub-analysis stratifying the results by the degree of paralysis, there was a significant difference in the number of patients who ultimately displayed partial versus full paralysis of the diaphragm, representing a difference in the degree of blockade between the two groups. In addition, there was no significant difference in participants’ pain scores or PACU opioid requirement in either group. Secondary outcome measures also showed no differences in brachial plexus motor and sensory exams between the two groups at baseline, post-intervention, or when comparing individual change in exam scores.

“This randomized clinical trial shows that normal saline washout in 10 mL increments has no clinically beneficial effect on reversing phrenic nerve blockade; however, it may reduce the degree of blockade and also does not lead to a reduction in analgesic effect,” Gerber et al. said. “In contrast to our and other experts’ previous experience in successfully reversing phrenic block using larger volumes (ie, 30 mL) of normal saline, perhaps our intent of minimizing potential rebound pain from the washout by using smaller incremental volumes was insufficient to unveil a clinically beneficial effect."

Gerber said more patients in the washout group showed an improvement from full to partial paralysis, suggesting that a larger bolus dose of normal saline may be sufficient to completely reverse diaphragmatic paralysis. Further investigations may use this as a dose-finding study in determining the minimum volume of normal saline washout needed to produce a reversal of phrenic nerve blockade while preserving analgesia, similar to results seen in previous case reports.

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45th Annual Regional Anesthesia and Acute Pain Medicine Meeting