title: Does the addition of tris(hydroxymethyl) aminomethane to 0.5% bupivacaine delay epidural onset in parturients?
abstract: A rapid onset of epidural anesthesia may predispose a pregnant patient to hypotension during the first stage of labor. Sodium bicarbonate has been reported to hasten epidural onset of chloroprocaine, lidocaine and bupivacaine while tris(hydroxymethyl) aminomethane (THAM) has been shown to delay the onset of epidurally administered chloroprocaine in parturients. The purpose of this study was to determine whether the addition of THAM to bupivacaine affected the onset, cephalad spread and incidence of hypotension following epidural administration in healthy pregnant patients during the first stage of labor. Three groups each consisting of 20 ASA I or II patients were studied. Group I received 0.5% bupivacaine with saline (0.06 ml/10 ml). Group II received bupivacaine buffered with THAM (0.06 ml/10 ml) to a pH of 6.8. Group III received bupivacaine buffered to a pH of 6.8 with sodium bicarbonate (0.05 ml+0.01 ml saline/10 ml). Statistical analysis used one-way analysis of variance and the appropriate post hoc test for multiple comparisons. A [Formula: see text] value less than 0.05 was considered significant. The onset of analgesia, the cephalad spread, and the incidence of hypotension did not differ between the groups. It is concluded that THAM does not affect the pharmacodynamics of 0.5% bupivacaine administered epidurally.
authors.affiliation: Department of Anesthesia, University of Cininnati College of Medicine, Cincinnati, Ohio 45267-0531, USA.
authors.forename: W E
authors.initials: WE
authors.lastname: Ackerman
authors.forename: M M
authors.initials: MM
authors.lastname: Juneja