Comparison of the Interscalene Block Alone Versus Combined With Superior Truncus Block During Shoulder Surgery in Diaphragmatic Function

Regional anesthesia is central to modern shoulder surgery because it provides excellent perioperative analgesia, reduces opioid consumption, and facilitates early rehabilitation. The interscalene brachial plexus block (ISB) has long been considered the gold-standard single-shot regional technique for shoulder procedures due to its reliable analgesia and surgical anesthesia. However, ISB commonly causes ipsilateral hemidiaphragmatic paresis (HDP) from unintended phrenic nerve blockade, which can produce clinically important declines in pulmonary function and may be poorly tolerated in patients with limited respiratory reserve.

To minimize phrenic involvement while preserving analgesic effectiveness, more selective approaches have been proposed. The superior trunk block (STB) - performed at the level where C5-C6 fibers form the superior trunk - aims to anesthetize the shoulder innervation more distally and thus reduce spread to the phrenic nerve. A landmark randomized trial and subsequent studies reported that STB provides analgesia comparable to ISB while greatly lowering the incidence of HDP (for example, ISB 71% vs STB 5% in one trial). Systematic reviews and meta-analyses since then have reinforced STB as an effective phrenic-sparing alternative for many shoulder procedures.

Despite encouraging data for STB, the literature is not entirely uniform. Some randomized trials and observational reports have found either reduced anesthetic quality with STB or smaller-than-expected reductions in phrenic involvement, particularly when block technique, local anesthetic volume, or patient anatomy differ. Moreover, combining blocks (for example, ISB with selective superior-trunk targeting or other modifications) has been proposed as a strategy to balance surgical anesthesia and respiratory safety, but comparative prospective data examining the effect of ISB alone versus ISB combined with STB on diaphragmatic function are limited. This uncertainty is important because even partial diaphragmatic paresis can degrade postoperative pulmonary mechanics and increase complications in vulnerable patients.

• Evaluation of the interscalene block alone versus combined with superior truncus block during shoulder surgery on the pulmonary function [Time frame: Assessment of pulmonary function by a handheld spirometer to measure forced vital capacity (FVC), forced expiratory volume ( FEV1, FEV2) with patients in an upright-seated position pre-block and 30 minutes post-block as well as 2-hours post-surgery]
• Duration of the sensory and motor block onset, duration of the interscalene block alone versus combined with superior truncus block during shoulder surgery [Time frame: Sensory, motor block onset time every minute. Sensory, Motor block duration every hour in 1st 6 hours , every 2 hours in 2nd 6 hours]
• Evaluation of postoperative analgesic consumption [Time frame: 12 hours]
• Evaluation of any complications or side effects during shoulder surgery [Time frame: 24 hours]