A 63-year-old female with past medical history of hypertension, obesity, and obstructive sleep apnea, was transferred from an outpatient surgery center in acute respiratory distress after the placement of an interscalene brachial plexus block prior to right shoulder surgery. A previous traumatic injury had left her with chronic shoulder pain and paresthesias. These symptoms had led to a decrease in her normal level of activity in the time leading up to her surgery.
Preoperatively an interscalene brachial plexus block had been placed with the position confirmed by nerve stimulation testing. Adequate regional anesthesia was accomplished and no apparent complications were initially observed. When the patient was moved to the operating room, she experienced acute dyspnea and her oxygen saturation (SpO2) fell to 85% on room air. This improved with supplemental oxygen, but her dyspnea continued and breath sounds were noted as absent on the right side. Due to the concern for iatrogenic pneumothorax, the patient was urgently transferred to the emergency department (ED) for further evaluation.
In the ED, she continued to require supplemental oxygen, while the rest of her vital signs included a heart rate of 77, respiratory rate of 20, and a blood pressure of 187/98. On examination, breath sounds decreased bilaterally, right greater than the left. Chest X-ray demonstrated a mildly elevated right hemidiaphragm with mild bibasilar atelectatic opacities (Fig. 1). No radiographic evidence of pneumothorax was appreciated. The patient’s EKG was unchanged from previous, with no findings suggestive of ischemia. Initial labs, including a CBC, basic metabolic panel, and cardiac markers were within the normal limits. The initial differential diagnosis included the possibility of pulmonary embolism, occult pneumothorax, hemidiaphragm paralysis secondary to the interscalene block, and acute coronary syndrome.
While awaiting CT angiography to assess for the possibility of pulmonary embolism, bedside ultrasound was performed and revealed good pleural sliding without evidence of pneumothorax. Ultrasound evaluation of the right diaphragm showed no movement with inspiration, including forcible inspiration and expiration by the patient (Fig. 2). This finding supported the diagnosis of phrenic nerve palsy secondary to the interscalene block. At this point, the patient started to improve clinically. Her dyspnea had decreased and she no longer needed supplemental oxygen.
Given the ultrasound diagnosis of hemidiaphragm paralysis and the patient’s clinical improvement, as the short acting component of the nerve block was wearing off, consideration was given to canceling the CT angiography. However, it was felt that the patient’s initial hypoxemia was difficult to attribute to an isolated hemidiaphragm paralysis in the absence of significant lobar atelectasis. With the persistent concern for coexistent pulmonary pathology, a CT angiography was obtained. A small, sub-acute, sub-segmental pulmonary embolus was found in the upper posterior right lung. Heparin was started in the ED, and the patient was admitted for observation and conversion to oral anticoagulation therapy.