B73-49 A Breathless Block: A Case Of Left-sided Hemidiaphragm Paralysis And Atelectasis After Interscalene Nerve Block

Introduction Interscalene nerve blocks are frequently used for shoulder and upper arm surgeries to provide effective anesthesia and postoperative analgesia. However, this intervention carries a recognized risk of phrenic nerve paresis, leading to transient diaphragmatic dysfunction. Although typically benign in healthy individuals, this complication can result in clinically significant hypoxemia in patients with underlying pulmonary disease. We present a case of transient hemidiaphragmatic paralysis following an interscalene block in a patient with chronic hypoxic respiratory failure, initially misinterpreted as pneumonia. Case Presentation A 74-year-old woman with chronic hypoxic respiratory failure (requiring 2 L oxygen with exertion), COPD, obstructive sleep apnea, hypertension, hyperlipidemia, and hypothyroidism underwent elective left shoulder arthroscopy for rotator cuff repair. A preoperative ultrasound-guided interscalene block was administered for anesthesia and postoperative analgesia without immediate complications.In the postoperative period, the patient’s oxygen saturation decreased to 88% on room air, requiring 3-4 L/min supplemental oxygen. She remained hemodynamically stable and denied dyspnea or chest discomfort. Chest radiography revealed a new left lower opacity, prompting initiation of empiric antibiotics for presumed pneumonia. Within 24 hours, her oxygenation returned to baseline and repeat imaging showed complete resolution of the opacity. Given the temporal association with the nerve block and rapid recovery, transient left hemi-diaphragmatic paralysis secondary to phrenic nerve involvement was thought to be the most likely cause. The diagnosis was supported by the absence of infectious symptoms and radiographic resolution. Antibiotics were discontinued, and the patient was discharged in stable condition at her baseline respiratory status. Discussion Phrenic nerve blockade occurs in up to 100% of interscalene blocks when standard volumes are used. Even with ultrasound guidance and low-volume techniques, diaphragmatic motion and pulmonary function can remain reduced. In patients with chronic lung disease, such transient dysfunction can mimic infectious processes radiographically, and can lead to unnecessary antibiotic exposure. Recognition of this predictable complication is important, particularly in those with limited pulmonary reserve. Alternative blocks such as suprascapular or infraclavicular approaches may reduce respiratory compromise. Conclusion Transient phrenic nerve paresis from an interscalene block can cause reversible hypoxemia and radiographic changes mimicking pneumonia. Clinicians should maintain a high degree of suspicion in postoperative patients with underlying respiratory disease to prevent misdiagnosis and enhance perioperative care.