Multiple injection axillary brachial plexus block: influence of obesity on failure rate and incidence of acute complications.

Background: Obesity has been associated with an increased failure rate in regional anesthesia, but specific block techniques have not been evaluated. We hypothesized that obesity decreases the success rate of axillary brachial plexus block.

Methods: We prospectively studied axillary brachial plexus blocks performed by experienced anesthesiologists in patients scheduled for upper limb surgery. A triple-injection technique was given to block the musculocutaneous and the median nerves with 6 mL and 10 mL ropivacaine 0.5%, respectively, and the radial nerve with 20 mL ropivacaine 0.5%. For the median and radial nerves, distal motor responses (wrist or fingers) were identified. Success was defined as adequate anesthesia allowing surgery to be performed without additional medications. Acute complications were noted. Before leaving the postanesthesia care unit, patient's satisfaction with anesthesia was collected.

Results: Of 605 patients, 85 were obese (body mass index > or = 30 kg/m(2)). The success rate was 97% overall, 91% in the obese and 98% in the non-obese patients (P = 0.003). Additional nerve blocks at the elbow were performed more frequently in obese (7%) than in non-obese patients (2%; P = 0.007). Acute complications (mainly vascular puncture) were more frequent in obese than in non-obese patients (27% vs 9%; P < 0.001). Patient satisfaction was 87% in the obese and 94% in the non-obese patients (P = 0.03).

Conclusions: Obesity increased the failure rate and immediate complications of axillary brachial plexus block. Furthermore, more obese patients were dissatisfied with their anesthesia.