Phrenic-sparing strategies for shoulder surgery: balancing respiratory safety and block completeness

Phrenic-sparing regional anesthesia for shoulder surgery has expanded in response to concerns that interscalene block (ISB) frequently causes hemidiaphragmatic paresis (HDP). This review examines the balance between respiratory safety and block completeness, emphasizing patient selection, technique modification, and clinically meaningful outcomes.

Contemporary evidence supports a spectrum of approaches. Low-volume, lower-concentration, and extrafascial ISB techniques can reduce but may not eliminate HDP and may not provide consistent analgesia. Superior trunk and supraclavicular approaches may preserve some pulmonary function while maintaining analgesia, but diaphragm paresis remains possible, and surgical anesthesia may be less reliable than with ISB. Distal strategies, particularly suprascapular nerve block, combined with anterior axillary or infraclavicular block, offer true phrenic sparing while preserving shoulder analgesia. The risk is concentrated in patients with limited respiratory reserve, including those with pulmonary disease, obesity, obstructive sleep apnea, heart failure, low baseline oxygen saturation, and advanced age.

Most blocks above the clavicle provide better analgesia but have a nonzero risk of HDP. Those distal to the clavicle provide slightly less analgesia, but the risk of HDP approaches zero. Phrenic-sparing strategies should not be viewed as universal replacements for ISB. Block choice should be individualized according to respiratory reserve, surgical requirements and analgesic goals.