Newswise — Will reducing the volume of local anesthetic prevent the incidence of hemidiaphragmatic paresis (HDP) in patients receiving an ultrasound-guided supraclavicular block? Unfortunately, no, say researchers from New York Presbyterian Hospital–Weill Cornell Medicine in New York.

HDP is a condition in which one side of the diaphragm is weakened, resulting in shortness of breath and reduced respiratory function. It can occur when a patient is given regional anesthesia for shoulder surgery, using a nerve block called the supraclavicular block. Researchers are trying to determine the right amount of anesthesia to use in the supraclavicular block so that the block still works but the chances of developing HDP are low.

A team lead by Dr. Tiffany Tedore, which includes Dr. Hannah Lin, Dr. Kane Pryor, Ms. Virginia Tangel, Dr. Daniel Pak, Ms. Hannah Oden-Brunson, Ms. Jenna Yousif, and Ms. Kaitlyn Sbrollini received a Best of Meeting Abstract Award for their abstract of the study, “Dose-Response Relationship of Local Anesthetic Volume and Diaphragmatic Paresis Following Ultrasound-Guided Supraclavicular 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. 

No previous studies have looked at the dose-response relationship curve (DRC) between local anesthetic volume in a supraclavicular block and the degree of HDP, but studies investigating dosing in ultrasound-guided supraclavicular blocks have found HDP at various doses.

In their study, Lin et al. evaluated anesthetic dose levels ranging from 5 cc to 35 cc in 21 patients undergoing a supraclavicular block as the primary anesthetic for right upper-extremity surgery. The study used an up-down methodology which would help prevent patients from receiving unnecessary subtherapeutic anesthetic doses. The researchers prepared a 2:1 mixture of mepivacaine 1.5% and bupivacaine 0.5% in 5 mL increments and began administering it during supraclavicular block at a dose of 35 mL to the first three participants. If none of the subjects experienced HDP, they would administer 40 mL to the next three participants. But if any of the patients receiving 35 mL developed HDP, the researchers would drop the dose to 30 mL for the next three patients. The study was to be stopped when (1) HDP was observed at the lowest dose of 5cc, (2) a total of 30 patients were enrolled, or (3) the dose escalated or de-escalated to a previously tested level, and a total of six consecutive patients at that dose exhibited no HDP. This study was halted after meeting the first stopping criteria.

The researchers monitored patients’ respiratory function using a bedside negative inspiratory force (NIF) meter at baseline and 30 minutes after performing the block and assessed motor and sensory function at 15 and 30 minutes post-block. Fourteen patients experienced HDP at all dose levels, including at the lowest level of 5 mL, although none required respiratory intervention. Three patients had ineffective combined block scores at 30 minutes post-block (two at 15 mL and one at 5 mL).

“Our study defined a DRC for HDP after supraclavicular block and emphasized that there is likely no clinically relevant dose at which HDP can be avoided when utilizing this technique,” Lin et al. concluded. “In our patient population, which is without baseline respiratory impairments, HDP and its statistically significant effects on respiratory function via NIF and oxygen saturation were well tolerated.”

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