Superior Trunk Block versus Interscalene Block for Postoperative Analgesia and Diaphragmatic Function in Patients Undergoing Shoulder Arthroscopy under General Anaesthesia: A Prospective Observational Study

Abstract

Background: Shoulder arthroscopy, although minimally invasive, is associated with intense early postoperative pain. The interscalene brachial plexus block (ISB) is the traditional gold standard for analgesia but carries a high incidence of ipsilateral hemidiaphragmatic paresis owing to phrenic nerve involvement. The superior trunk block (STB) targets the brachial plexus at a more distal, lateral level and may spare the phrenic nerve, yet direct real-world comparative data on functional analgesic duration and rescue-analgesic burden remain limited.

Aim: To compare the analgesic efficacy, rescue-analgesic requirement, diaphragmatic function and safety profile of STB and ISB in patients undergoing shoulder arthroscopy under general anaesthesia.

Methods: A prospective observational cohort study was conducted over 18 months at the Bone and Joint Hospital, an associated hospital of Government Medical College, Srinagar. Sixty adults (ASA I–II, 21–50 years) undergoing elective shoulder arthroscopy were allocated to ultrasound-guided STB (n = 30) or ISB (n = 30) according to the attending anaesthesiologist’s clinical judgement. The primary outcome was the duration of analgesia (time to first pain requiring rescue, visual analogue scale [VAS] > 5). Secondary outcomes were 24-hour rescue-analgesic consumption, diaphragmatic excursion on ultrasonography, VAS/NRS pain scores, block characteristics, complications and patient satisfaction. Data were analysed using the chi-square test, independent t-test and Mann–Whitney U test, with p < 0.05 considered significant.

Results: The groups were comparable in age, sex, height, ASA status and surgical diagnosis, although the STB group had a higher mean weight and body mass index (p = 0.032 and p = 0.021, respectively). Early pain scores (up to 6 hours) were comparable, but from 9 hours onward the STB group reported significantly lower VAS scores (9 hours, p = 0.015; 12, 24 and 48 hours, p < 0.0001). The mean time to first pain was significantly longer with STB (12.88 ± 1.30 vs 10.38 ± 1.19 hours; p < 0.001), and escalation to triple-drug rescue analgesia was far less frequent (3.3% vs 33.3%; p = 0.003). Although ISB produced a longer sensory (12.07 ± 1.79 vs 10.14 ± 1.55 hours) and motor (15.24 ± 2.29 vs 12.98 ± 1.88 hours) block (p < 0.001), this did not translate into superior late analgesia. Diaphragmatic excursion was significantly better preserved with STB at 30 minutes and 6 hours (p < 0.001), and complete hemidiaphragmatic paresis occurred in 63.3% of ISB versus 13.3% of STB patients (p < 0.001). Patient satisfaction was significantly higher in the STB group (p < 0.001); haemodynamic parameters were comparable.

Conclusion: In this cohort, STB provided early analgesia equivalent to ISB and superior late analgesia with a lower rescue-analgesic burden, while markedly preserving diaphragmatic function and improving patient satisfaction. Despite producing a longer measured block, ISB conferred no late analgesic advantage. STB represents a clinically valuable phrenic-sparing alternative for shoulder arthroscopy under general anaesthesia..