Effect of low versus standard local anesthetic volumes on phrenic nerve function in ultrasound-guided upper trunk block in shoulder surgeries

Background Shoulder surgeries usually result in intense postoperative pain, requiring the use of large doses of opioids and/or regional blocks. The current study aimed to detect phrenic nerve affection after upper trunk nerve block using different volumes of Bupivacaine (low volume vs. high volume). Settings and design This study was a randomized controlled trial. Patients and methods A total of 80 patients aged 18–50 years were eligible to study, ASA I and II admitted for shoulder surgery. Patients were randomly divided into: group L received 10 ml of 0.5% Bupivacaine ultrasound-guided upper trunk nerve block, while group H received 15 ml of 0.5% Bupivacaine. The excursion of the hemidiaphragm was measured using M-mode ultrasound before performing the block and again after extubation. Pain was assessed using the visual analogue scale (VAS), and recorded 30 min after the block, and subsequently in the ward 30 min, 2, 6, 8, 12, 16, 20, and 24 h postoperatively. Rescue analgesia (nalbuphine HCl 0.05 mg/kg IV) was administered when the VAS score was greater than or equal to 4 and was repeated every 30 min until the VAS score fell below 4. The total amount of nalbuphine administered during the first 24 h postoperatively was recorded. After completion of the block, motor blockade of the shoulder, elbow, and hand grip were assessed 30 min before induction of general anesthesia. Motor power was graded on a three-point scale, where 2=normal, 1=weakness, 0=complete loss of power. Any postoperative complication occurring within the first 24 h was documented and managed appropriately. Results There was a statistically significant difference in hemidiaphragmatic affection between the two groups ( P <0.001). 25 (62.5%) patients in group L had normal diaphragmatic function compared with 18 (45%) patients in group H. 16 (40%) patients in group H had paresis versus only 12 patients in group L and six (15%) patients showed paralysis in group H, while only three (7.5%) patients in group L exhibited paralysis. Recovery of diaphragmatic function was observed earlier in group L, with normalization of diaphragmatic excursion noted at ∼ 2–4 h postoperative, compared with 4–6 h in group H. VAS scores showed no significant difference immediately after the block at 30 min ( P =0.86); however, from 2 h onwards, group L consistently reported significantly higher VAS scores than group H, with statistically significant differences at 2 ( P =0.013), 6 ( P =0.001), 8 ( P <0.001), 12 ( P <0.001), 16 ( P <0.001), 20 ( P <0.001), and 24 h ( P <0.001). The duration of analgesia was significantly longer in group H compared with group L ( P <0.001). The total dose of nalbuphine in 24 h was significantly higher in group L compared with group H ( P <0.001). There was no statistically significant difference between the two groups concerning elbow movement and shoulder movement at 30 min, where all patients had a score of 0. There was also no significant difference between the two groups regarding handgrip, where seven patients exhibited a score of 1 in group H and 33 patients had a score of 2, whereas all patients in group L had a score of 2 at 30 min (χ 2 =3.27, P =0.217). Both study groups (group L and group H) reported no complications or side effects during the study. Conclusion Postoperative analgesia was superior in the higher volume group, with lower VAS scores, longer duration before first rescue analgesia, and reduced total opioid consumption. Motor sparing was more evident in the low-volume group.