Pectoral nerves I block is associated with a significant motor blockade with no dermatomal sensory changes: a prospective volunteer randomized-controlled double-blind study

Purpose The pectoral nerves ( PECS) I block, first described in 2011 for surgery involving the pectoralis muscle, has principally been used for breast cancer surgery. No formal evaluation of its differential motor- and sensory-blocking abilities has been reported. We hypothesize that the PECS I block will produce a motor block of the pectoralis muscles with diminished upper limb adduction strength as measured with a handheld dynamometer. Methods We conducted a PECS I block in a randomized placebo-controlled trial in six healthy subjects who received 0.4 mL·kg −1 of 0.9% saline (placebo) on one side and bupivacaine (0.25% with 1:400 000 epinephrine) on the other. We measured both upper limb adduction strength with a dynamometer and sensory skin levels over the thorax. Results The mean (standard deviation [SD]) adductor strength evaluated before the block was 119.4 (20.7) Newtons (N). After the PECS I block with bupivacaine, the mean (SD) strength of 54.2 (16.3) N was compared with 116.0 (30.4) N in the placebo group (difference in means 61.8 N; 95% confidence interval [CI], 27.8 to 95.8 N; P = 0.005), showing a 54.6% (95% CI, 43.6 to 65.6%) reduction in adductor strength. There was no difference in dermatomal skin sensory testing between the placebo and bupivacaine sides. Conclusions This study shows that a PECS I block produces motor blockade as shown by reduced upper limb adductor strength without any overlying dermatomal sensory loss. Trial registration www.clinicaltrials.gov (NCT03040167) 2 February 2017.