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AMBULATORY ANESTHESIA

Spinal Chloroprocaine Solutions: Density at 37° C and pH Titration

From the Department of Anesthesiology, Virginia Mason Medical Center, Seattle, Washington

Address correspondence to Dr. Kopacz, Department of Anesthesiology, Virginia Mason Medical Center, 1100 Ninth Avenue, B2-AN, PO Box 900, Seattle, WA 98111. Address email to anedjk{at}vmmc.org

The density and pH of a local anesthetic are important characteristics in its use as an intrathecal drug. Preservative- and antioxidant-free formulations of chloroprocaine are available and are being investigated for short-duration spinal anesthesia. In this study, we evaluated the pH and density (to 5 significant digits in g/mL, at 37.0°C) of these new chloroprocaine formulations. In addition to plain 2% and 3% chloroprocaine and 2% lidocaine, mixed solutions of 2% chloroprocaine with epinephrine or with bicarbonate were evaluated. Density was also measured after water dilution and after increasing amounts of added dextrose. Chloroprocaine, 2% or 3%, is hyperbaric relative to cerebrospinal fluid (CSF) before any addition of dextrose (density 1.00123 g/mL and 1.00257 g/mL, respectively). When diluted with water, all the solutions are hypobaric relative to CSF (density <1.00028 g/mL). Plain 2% lidocaine is the only dextrose-free solution measured to be hypobaric (density 1.00004 g/mL). Bisulfite-free 2-chloroprocaine remains very acidic (pH <4.0), but the pH can be increased to more than 7.0 with a small amount of bicarbonate (0.25–0.33 mL/10 mL). The increased density of plain chloroprocaine makes it a useful hyperbaric spinal drug without the addition of dextrose.

IMPLICATIONS: Dextrose-free 2-chloroprocaine is hyperbaric relative to cerebrospinal fluid at 37°C, and therefore can be used for spinal anesthesia without dextrose. Bisulfite-free 2-chloroprocaine remains very acidic (pH <4.0). The pH can be increased to more than 7.0 with a small amount of bicarbonate (0.25–0.33 mL/10 mL).

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