- Design
- Prospective blinded observational study
- Population
- 99 adults having shoulder surgery with interscalene or superior trunk block
- Primary outcome
- Change in diaphragm excursion and thickening fraction by ultrasound
- Effect
- Median reduction 42–82%; >50% weakness in three-quarters; one complete paralysis
A prospective, blinded observational study in Regional Anesthesia & Pain Medicine measured diaphragm function by ultrasound before and within 30 minutes of an ultrasound-guided interscalene or superior trunk block in 99 adults having shoulder surgery, using 15–20 mL of ropivacaine 0.5% or bupivacaine 0.25% with adrenaline. Block choice was not randomised.
The median fall in diaphragm function ranged from 42% to 82%, depending on block type, sex and method of measurement. Three in four patients had more than 50% weakness, and one had complete paralysis. Interscalene block and female sex were associated with greater weakness.
The study also compared ways of measuring. The classic subcostal view of the diaphragm dome could be obtained on the left in only about half of patients. Excursion and thickening at the lateral zone of apposition, using a linear probe on the side of the chest, worked bilaterally in every patient.
The practical change is twofold. First, a superior trunk block at these volumes should not be assumed to spare the diaphragm. Second, a quick lateral ultrasound before and after the block gives a usable measure of what has happened, which matters most in the patient with limited reserve.
- Assume substantial hemidiaphragm weakness after an interscalene or superior trunk block at 15–20 mL.
- Do not treat a superior trunk block as reliably diaphragm-sparing at these volumes.
- Use a linear probe at the lateral zone of apposition to measure diaphragm excursion before and after the block.
- Consider measuring in patients with limited reserve before discharge from recovery.
- Expect more weakness in women and with interscalene block.
Why it matters
It challenges the assumption that the superior trunk approach reliably protects the diaphragm.
Don't overread it
Block type was not randomised, so the comparison between interscalene and superior trunk blocks may be confounded.
The statistics, in plain English
The 42% to 82% range is several medians across different measurement methods and subgroups, not one estimate. Differences between block types come from an observational comparison, so they show association, not that one block causes less weakness.
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