Regional Anesthesia and Acute Pain

Background and Objectives: Epinephrine is usually administered in concert with a lipid emulsion during local anesthetic toxicity. However, the timing and role of epinephrine administration in combination with a lipid emulsion remain unclear. Specifically, the temporal association of epinephrine and lipid emulsion administration with related changes in pulmonary vascular pressures that may lead to pulmonary edema and hemorrhage needs to be determined. Methods: This study consisted of 2 parts, experiments A and B. In experiment A, 24 adult male Sprague-Dawley rats were randomly divided into 3 groups (n = 8) to receive 1 of 3 treatments. All rats were anesthetized with an intraperitoneal injection of chloral hydrate, and anesthesia was maintained by sevoflurane. Each treatment group was initially given an infusion of bupivacaine (15 mg/kg) in order to produce cardiac depression. Group 1 (A-LEN) received a 30% lipid infusion (3 mL/kg) followed by a rapid epinephrine bolus (10 μg/kg), which was then followed by a normal saline infusion (3mL/kg). Group 2 (A-NEL) first received a normal saline infusion (3 mL/kg) followed by a rapid epinephrine bolus, which was then followed by a 30% lipid emulsion. Group 3 (A-NEN, considered a control group) first received a normal saline infusion (3 mL/kg) followed by a rapid epinephrine bolus (10 μg/kg), which was then followed by another normal saline infusion (3 mL/kg). Lipid and normal saline infusions were administered over 1 minute, whereas epinephrine was injected rapidly. The continuous monitoring of blood pressure, heart rate, pulmonary arterial pressure, and pulmonary venous pressure occurred for 30 minutes. After the 30-minute monitoring period, lung tissue was sampled, and bronchoalveolar lavage fluid was collected. In experiment B, the experimental model and resuscitation protocol were similar to experiment A (B-LEN and B-NEL groups). In this arm of the experiment, bupivacaine concentrations of cardiac tissue were determined after the second minute of normal saline infusion. Results: The A-LEN group produced the best rate pressure product when compared with the A-NEL or A-NEN group (P = 0.045, P = 0.011, respectively). In regard to pulmonary venous pressure, the A-LEN group was lower than the A-NEL or A-NEN group (P = 0.031, P = 0.006,