Background and Objectives We did not find clinical studies of the alkalization of ropivacaine in the literature. The objectives of this study were: (1) to determine the quantity of sodium bicarbonate (NaHCO₃), which alkalinizes 0.75% ropivacaine (with and without adrenaline); (2) to verify the physico-chemical alterations arising from this alkalization; and (3) to determine whether alkalinized ropivacaine produces a higher-quality epidural block measured via sensory-motor onset, block spread and anesthesia duration.

Methods It was determined in the laboratory that 0.012 and 0.015 mEq of NaHCO₃, respectively, alkalinized 10 mL of the 0.75% ropivacaine solutions without and with adrenaline (1:200,000). In the second phase, the study was random and double-blind and involved 60 patients divided into 3 groups of 20 (G1, G2, and G3). Via epidural lumbar blocks, these groups received, respectively, 10 mL of 0.75% ropivacaine plus 0.5 mL of 0.9% NaCl (solution A), 10 mL of 0.75% ropivacaine plus 0.0012 mEq of NaHCO₃ (solution B), and 10 mL of 0.75% ropivacaine (with adrenaline) plus 0.015 mEq of NaHCO₃ (solution C). The pH, PCO₂ (partial CO₂ pressure), and the nonionized fractions of the 0.75% ropivacaine solutions were compared before and after the addition of 0.9% NaCl or NaHCO₃ or adrenaline plus NaHCO₃. The motor and sensory onsets, block spread, and the duration of the block were evaluated.

Results The values of the pH, PCO₂, and nonionized fractions increased significantly in solutions B and C in relation to solution A. No differences among the groups were observed in relation to block spread and sensory-motor onset. The duration of the sensory blocks was significantly greater in the patients in groups G2 and G3.

Conclusions This study indicates that the quantity of NaHCO₃ needed to alkalize 10 mL of 0.75% ropivacaine at room temperature is 0.012 mEq. When the solution contains adrenaline 1:200,000 (mg · mL⁻¹), up to 0.015 mEq of NaHCO₃ may be added. The alkalization of the 0.75% ropivacaine solution did not cause a reduction of sensory-motor onset, but did provide a significant increase in the duration of the epidural block with no significant differences between the solutions with and without adrenaline.