The Effects of Bupivacaine and Ropivacaine on Baroreflex Sensitivity With or Without Respiratory Acidosis and Alkalosis in Rats

Abstract

Systemic toxicity of local anesthetics causes cardiac and central nervous system (CNS) depression that could be enhanced in the presence of respiratory acidosis.We examined a potential suppression of baroreflex function with bupivacaine and ropivacaine during hypercapnic acidosis or hypocapnic alkalosis. Baroreflex sensitivity (BRS) was randomly tested in rats with one of 13 conditions during intravenous administration of saline (control), bupivacaine 1, 2, or 3 mg/kg, or ropivacaine 2, 4, or 6 mg/kg. The effects of bupivacaine (3 mg/kg) or ropivacaine (6 mg/kg) on BRS were also examined during hypercapnic acidosis or hypocapnic alkalosis. The BRS was assessed using a value of Delta heart rate/Delta mean arterial pressure after infusion of phenylephrine (3 micro g/kg). Both bupivacaine and ropivacaine (at the largest dose) significantly suppressed BRS. Acute respiratory acidosis (pH_a 7.24 +/- 0.04, PaCO₂ 63 +/- 4 mm Hg) enhanced BRS. The BRS enhanced during acidosis was also suppressed with bupivacaine and ropivacaine, but less so than in the absence of acidosis. The presence of hypocapnic alkalosis (pH_a 7.55 +/- 0.03, PaCO₂ 25 +/- 2 mm Hg) did not affect BRS and reversed BRS suppression caused by both drugs. Thus, bupivacaine and ropivacaine affect neuronal control mechanisms for maintaining cardiovascular stability, and acute changes of respiration could significantly modify such suppression. (Anesth Analg 1997;84:398-404)