Background and aims The QLB2 efficacy has been demonstrated both in major abdominal surgery and in cesarean section (CS). QLB2 safety in parturients has never been investigated. Adding epinephrine to local anesthetic (LA), by determining a delayed LA systemic reabsorption and a reduced plasmatic concentration, could improve QLB2 safety, as demonstrated for other blocks. Our primary outcome has been the assessment of the chronological changes in venous LA concentration after QLB2 with or without epinephrine. Secondary outcomes have been duration, efficacy and collateral effects of block.

Methods 20 parturients, at term, with singleton pregnancy, undergoing CS under SA have been enrolled and randomly allocated to receive at the end of surgery 20 ml for each side of 0,375% ropivacaine + 100 mcg epinephrine (QLB2-e group) or 0,375% ropivacaine alone (QLB2 group). After block, venous samples (2 ml each) have been performed at 10, 30, 45, 60, and 120 minutes. Symptoms of subjective neurological toxicity, block duration, total morphine consumption, pain scores and adverse events have also been recorded.

Results Venous ropivacaine concentration peaked earlier in QLB2 vs QLB2-e group (Tmax=10 vs 60 minutes) and higher (1.3225 [0.6744–1.3383] vs. 0.7634 [0.4858–0.8946]). Ropivacaine plasmatic concentrations were significantly lower in QLB2-e vs QLB2 at 10 minutes (0.5303 [0.2886–0.7176] vs 1.3225 mcg/ml [674.4–1338.3], p 0.04). the total morphine consumption after QLB2-e was lower than after QLB2 (3 mg [2–11.5] vs 5 mg [3–10], p=0.63).

Conclusions Adding epinephrine to QLB2 lowered the peak of venous ropivacaine concentration; this could increase safety of block in the obstetric population.