Bilateral transversus abdominis plane (TAP) block with 24 hours ropivacaine infusion via TAP catheters: A randomized trial in healthy volunteers

BACKGROUND The analgesic effect of a TAP block has been investigated in various surgical settings. There are however limited information about block level and block duration. Furthermore, there is a lack of information about continuous TAP block after ultrasound-guided posterior TAP blocks.The aim of this double-blind randomized study was therefore to investigate the effect of an ultrasound-guided posterior TAP block with 24 hours local anesthetic infusion via a TAP catheter. METHODS In this randomized study 8 male volunteers received a bilateral TAP block (20 mLs 0.5% ropivacaine) and were allocated to receive active infusion (ropivacaine 0.2% 5 mL/hr) via a TAP catheter on one side and placebo infusion on the other side. PRIMARY OUTCOME Dermatomal sensory block involvement after 24 hours evaluated with pinprick. SECONDARY OUTCOMES Sensory block involvement evaluated with cold test and heat-pain detection thresholds (HPDT) on the abdominal wall. Assessment points: 15 min before block performance and 1, 4, 8, 12 and 24 hours after block performance. RESULTS The TAP block primarily involved sensory changes in the Th10 to Th12 dermatomes. On the placebo side there was a decrease in extension beginning at 4-8 hours after block performance and with no detectable effect beyond 12 hours. Median number of dermatomes anesthetized (pinprick) at 24 hours after block performance was 1.5 (0-3) on the active side compared with 0 (0-0) on the placebo side (P = 0.039).There were no statistical significant between-side differences in HPDT measurements at 24 hours after block performance. CONCLUSIONS The spread of sensory block following ultrasound-guided posterior TAP block is partly maintained by a continuous 24 hour ropivacaine infusion through a TAP catheter. TRIAL REGISTRATION The study was registered at NCT01577940.