Does alkalinization of 0.75% ropivacaine promote a lumbar peridural block of higher quality?

Abstract

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 (NaHCO(3)), 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. It was determined in the laboratory that 0.012 and 0.015 mEq of NaHCO(3), 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 NaHCO(3) (solution B), and 10 mL of 0.75% ropivacaine (with adrenaline) plus 0.015 mEq of NaHCO(3) (solution C). The pH, PCO(2) (partial CO(2) pressure), and the nonionized fractions of the 0.75% ropivacaine solutions were compared before and after the addition of 0.9% NaCl or NaHCO(3) or adrenaline plus NaHCO(3). The motor and sensory onsets, block spread, and the duration of the block were evaluated. The values of the pH, PCO(2), 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. This study indicates that the quantity of NaHCO(3) 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 NaHCO(3) 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.