Effect of procaine on the pH of buffered and unbuffered cardioplegic solutions

Changes in pH values were studied in two types of cardioplegic admixtures containing procaine 0.95 meq/L: an institutional formulation based on Ringer's injection and buffered with tromethamine injection 3.6%, and Plegisol (Abbott Laboratories) buffered with sodium bicarbonate injection 8.4%. Initial pH was measured in the buffered and unbuffered solutions before the addition of procaine and after the addition of 13 mL of procaine hydrochloride injection 2% or 260 mg of procaine hydrochloride powder (reference standard). Buffered 1-L admixtures containing procaine hydrochloride injection were stored (the institutional formulations in glass and the Plegisol admixtures in flexible plastic bags) at 3-5 degrees C or 25 degrees C. Plegisol admixtures were prepared with 10 mL (10 meq or 840 mg) of buffer as directed by the manufacturer or with 3 mL (3 meq) of buffer. Admixture pH was tested after various time intervals. Of the unbuffered solutions containing procaine, pH values were lower in Plegisol than in the institutional formulation. Of the procaine-containing buffered Plegisol solutions, only the admixture containing 3.0 mL of buffer and procaine prepared from powder had an initial pH in the acceptable range of 7.30-7.60. In all the stored solutions, pH changed rapidly; solution pH changed less under refrigeration. In the stored institutional admixtures, pH was acceptable for 96 hours at 3-5 degrees C and 24 hours at 25 degrees C. In the stored Plegisol admixtures to which 10 mL of buffer was added, pH was greater than 7.6 initially and continued to increase.(ABSTRACT TRUNCATED AT 250 WORDS)