Primary outcomes and anticipated effect sizes in randomised clinical trials assessing peripheral and truncal nerve...

Peripheral and truncal nerve blocks provide effective analgesia facilitating perioperative care. However, thresholds for clinically relevant effects remain undetermined and are left for clinicians to choose. These choices are fundamental for sample size calculations and interpretation of study results. This systematic scoping review aimed to create an overview of primary outcomes and anticipated effect sizes in randomised clinical trials assessing peripheral and truncal nerve blocks.

We searched Cochrane Library's CENTRAL, Medline, and Embase for randomised trials in English in 10 major anaesthesia journals investigating single-injection ultrasound-guided peripheral and truncal nerve blocks for adults undergoing surgery. The primary outcome was the anticipated effect sizes for primary outcomes. Secondary outcomes included reporting of sample size calculations and statistically significant primary outcomes below anticipated effect sizes.

The most frequently reported primary outcomes were postoperative pain, analgesic consumption, quality of recovery, mobilisation, and block performance. Median anticipated effect sizes were: 0-24 h opioid consumption: 9 mg i.v. morphine equivalents; pain at rest and during movement: 2 points on Numeric Rating Scale 0-10; quality of recovery: 10 points on Quality of Recovery-40 scale and 8 points on Quality of Recovery-15 scale. Adequate sample size calculations were reported in 85% (156/183) and 91% (29/32) of trials assessing continuous outcomes and dichotomous outcomes, respectively. Statistically significant primary outcomes failed to reach anticipated effect sizes in 24% (24/99) of trials, and only one trial addressed this disparity in the trial conclusion.

The presented outcomes and effect sizes from published trials on peripheral and truncal nerve block literature can be used in future trials to increase homogeneity in regional anaesthesia research.