Peripheral Neuroanatomy, Human Anatomy, USMLE Step 1 - Full Vignette with Extended Explanations

A 41-year-old woman with severe COPD symptoms, chronic smoking history, and significant shoulder trauma presents with a painful anterior shoulder dislocation, positional hypoxemia, and signs of respiratory compromise. After an initial regional anesthesia attempt, her oxygen levels worsen when supine. What aspects of her respiratory and neurological exam should guide the choice of further shoulder analgesia, and how do you approach regional anesthesia in patients with limited pulmonary reserve?

VIDEO INFO
Category: Peripheral Neuroanatomy, Human Anatomy, USMLE Step 1
Difficulty: Hard - Advanced level - Challenges experienced practitioners
Question Type: Treatment Failure
Case Type: Emergency - Emergency scenario requiring urgent decision-making

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QUESTION
A 41-year-old woman is rushed to a United States emergency department after slipping at work and sustaining a painful anterior shoulder dislocation while carrying equipment up a flight of stairs. EMS recorded an oxygen saturation of 81% on a finger probe in a cold, windy stairwell. On arrival, saturation is 86% on room air and rises to 93-95% on 2 L/min nasal cannula when upright, but it dips to 88-90% with attempts to place her supine for procedures....

OPTIONS
A. Ultrasound-guided superior trunk block using a low-volume, single-injection technique (e.g., 5 mL of 0.5% ropivacaine at the C5-C6 trunk in-plane) to provide shoulder analgesia while minimizing hemidiaphragmatic dysfunction risk during ED reduction.
B. Ultrasound-guided superior trunk block using a standard-volume, single-injection technique (e.g., 15 mL of 0.5% ropivacaine at the superior trunk) immediately before reduction despite increased phrenic involvement at higher volumes.
C. Combined posterior suprascapular nerve block plus selective axillary nerve block (each 10 mL of 0.5% ropivacaine under ultrasound) in the monitored ED bay, assuming this will always equal interscalene-level shoulder coverage without respiratory effects.
D. Ultrasound-guided supraclavicular brachial plexus block with 20 mL of 0.5% ropivacaine to anesthetize the upper limb for reduction, presuming negligible impact on ipsilateral diaphragmatic motion.

CORRECT ANSWER
A. Ultrasound-guided superior trunk block using a low-volume, single-injection technique (e.g., 5 mL of 0.5% ropivacaine at the C5-C6 trunk in-plane) to provide shoulder analgesia while minimizing hemidiaphragmatic dysfunction risk during ED reduction.

EXPLANATION
"Ultrasound-guided superior trunk block using a low-volume, single-injection technique (e.g., 5 mL of 0.5% ropivacaine at the C5-C6 trunk in-plane) to provide shoulder analgesia while minimizing hemidiaphragmatic dysfunction risk during ED reduction." This is the best next regional strategy after an interscalene block attempt in a patient with limited pulmonary reserve and position-dependent desaturation. Compared with interscalene, the superior trunk block (STB) deposits local anesthetic distal to the point where the phrenic nerve runs closely along the anterior scalene. Randomized data show STB substantially reduces hemidiaphragmatic paresis and preserves pulmonary function for shoulder anesthesia; furthermore, lower volumes reduce phrenic involvement even more....


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