Respiratory impact of local anaesthetic volume after interscalene brachial plexus block with extrafascial injection: a randomised controlled double-blinded trial

Background

We have previously demonstrated that an extrafascial injection of 20 ml of local anaesthetic for interscalene brachial plexus block (ISB) reduces the rate of hemidiaphragmatic paralysis by 70% compared with an intrafascial injection, with similar efficacy. In this double-blind trial, we tested the hypothesis that a local anaesthetic volume of 10 ml injected extrafascially would reduce the rate of hemidiaphragmatic paralysis vs a volume of 20 ml, while providing similar analgesia.

Methods

Sixty ASA physical status 1–3 patients scheduled for elective shoulder surgery under general anaesthesia were randomised to receive ultrasound-guided extrafascial ISB using ropivacaine 0.75% 20 ml (control group) or 10 ml (low-volume group) injected lateral to the brachial plexus sheath. The primary outcome was incidence of hemidiaphragmatic paralysis (diaphragmatic excursion reduction of >75%), measured by M-mode ultrasonography, at 30 min after the procedure. Secondary outcomes included duration of analgesia and i.v. morphine consumption at 24 h after surgery.

Results

The 30-min hemidiaphragmatic paralysis rate was 80% (95% confidence interval [CI] 61–91%) in the control group and 19% (95% CI 8–40%) in the low-volume group (P<0.001). Participants in the low-volume vs control group had a shorter duration of analgesia (550 vs 873 min; P<0.01) and higher i.v. morphine consumption (20 vs 12 mg; P=0.03).

Conclusions

A low volume of local anaesthetic injected extrafascially reduced the rate of hemidiaphragmatic paralysis, but at the expense of a shorter duration of analgesia compared with standard-dose extrafascial anaesthetic injection.

Clinical trial registration

NCT04726280.