Ten minutes interscalene block: An innovative administration technique for interscalene block in a 20-week pregnant woman with mitochondrial myopathy and proximal humerus fracture

To the Editor, Patients with neuromuscular disorders are vulnerable to muscle relaxants, which may cause prolonged weakness, hyperkalemia, malignant hyperthermia, or rhabdomyolysis.[1] Interscalene block offers a suitable alternative to general anesthesia for shoulder and proximal arm surgeries, although single-shot techniques carry a phrenic nerve block risk approaching 100% in some reports.[2] Mitochondrial myopathy, a genetic disorder of impaired skeletal muscle energy generation, presents with progressive weakness and recurrent myoglobinuria.[3] Here, we describe a successful interscalene block in a 28-year-old female, 20 weeks pregnant, weighing 67 kg, with a known case of mitochondrial myopathy scheduled for open reduction and internal fixation of the fracture of the right proximal humerus. She was hemodynamically stable, on no medications, and had preserved motor strength in the operative limb. Informed written consent was obtained for anesthesia and publication. Given the risks of general anesthesia in pregnancy and neuromuscular disease, regional anesthesia was selected. An interscalene block was chosen because it provides reliable anesthesia for the shoulder and proximal humerus. Under ultrasound guidance using the Versana Essential device (GE Medical Systems Co., Ltd., China), a 25-gauge needle was advanced into the interscalene groove between C5 and C6. A slow infusion technique was deliberately chosen, with bupivacaine administered at 1 mL/min over 10 min using a syringe pump. This approach allowed continuous visualization of the spread, minimized migration, and reduced phrenic nerve involvement. Moreover, the infusion pump provided precise control and enhanced safety in this high-risk patient with mitochondrial myopathy and pregnancy. Block success was confirmed by loss of shoulder abduction and sensory changes in the deltoid region. Surgery lasted 75 min uneventfully. Notably, the surgical field was limited to the proximal humerus and lateral shoulder, areas adequately covered by the interscalene block. The medial arm was not involved in the incision. Spirometry and diaphragmatic excursion were assessed at baseline and 30 min post-block. Forced vital capacity, forced expiratory volume in 1 s, and diaphragmatic excursion decreased by 12%, 15%, and 20%, respectively, indicating only mild compromise [Figure 1]. The surgical field was limited to the proximal humerus and lateral shoulder, areas adequately covered by the block. Postoperative analgesia was supplemented with systemic medications.Figure 1: Right diaphragmatic excursion. (a) before the interscalene block. (b) Thirty minutes after the interscalene blockA complete phrenic nerve block is defined as ≥75% reduction in excursion.[4] Alternative approaches such as selective upper trunk, low-volume, or extrafascial injections have been described. In our case, a conventional interscalene block with slow infusion achieved reliable anesthesia with only mild respiratory effects. Previous studies report phrenic nerve involvement in nearly all patients with standard single-shot injections, often with ≥75% excursion reduction.[5] In contrast, our patient demonstrated only minor changes, suggesting slow infusion may limit phrenic nerve blockade while maintaining efficacy. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that her name and initials will not be published and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.