Single-shot versus slow infusion interscalene block and its impact on diaphragmatic function in patients undergoing...

The Interscalene block offers adequate anesthesia and analgesia to the shoulder. Ipsilateral phrenic nerve paralysis is a common and generally well-tolerated consequence of the interscalene block. However, it may become clinically significant in patients with pre-existing respiratory conditions or limited pulmonary reserve. We hypothesized that a slow infusion of an interscalene block over 10 min would reduce the incidence of a complete phrenic nerve block.

This randomized controlled trial included 83 patients who underwent arthroscopic shoulder surgery. Patients were randomly allocated into one of two groups: single shot (n = 42), who received an interscalene block as a 10 mL 0.5% bupivacaine over 1 min, or slow infusion (n = 41), who received 10 mL 0.5% bupivacaine over 10 min via an indwelling catheter using a syringe pump. An experienced operator examined the corresponding hemidiaphragm for diaphragmatic excursion at baseline and 10-minute intervals for 30 min after the interscalene block. The main outcome variable was the incidence of complete phrenic nerve block.

Eighty-three patients were included in the final analysis. Demographic data, including age, body mass index, sex, type, and duration of surgery, were not significantly different between the groups. The slow-infusion and single-shot groups showed 7% and 83% complete phrenic nerve block, respectively. Additionally, Forced Expiratory Volume at 1 s (FEV1) and Forced Vital Capacity (FVC) at 30 min after block administration were significantly lower in the single-shot group. Notably, 24 h resting NRS score and morphine consumption were comparable between the groups, indicating preserved 24 h postoperative analgesic efficacy.

In adult patients undergoing arthroscopic shoulder surgery, slow infusion interscalene block reduced the incidence of complete phrenic nerve block to 7% compared to 83% in the single-shot block with comparable 24 h postoperative analgesic efficacy. Additionally, it preserved pulmonary function in terms of FEV1 and FVC without reducing analgesic efficacy compared with the single-shot approach.

ClinicalTrials.gov (NCT06820853).