EPINEPHRINE PROLONGS DURATION OF SUBCUTANEOUS INFILTRATION OF LOCAL-ANESTHESIA IN A DOSE-RELATED MANNER

Background and Objectives. Epinephrine is frequently combined with loc al anesthesia to prolong analgesia. Determination of the minimal conce ntration and the dose of epinephrine that produces prolongation of ana lgesia is important in the face of epinephrine's potential for systemi c and local toxicity. The authors undertook this study to determine a dose-response curve of epinephrine on duration of analgesia of both 1% lidocaine and 0.25% bupivacaine after local infiltration. In order to determine whether epinephrine-induced vasoconstriction affected durat ion of analgesia, the authors correlated duration of analgesia with ma gnitude of local vasoconstriction as measured with laser Doppler flowm etry. ii?Methods. Six volunteers were studied in a randomized double-b lind manner. Ten skin wheals of 0.2 mL solution were subcutaneously in jected into both forearms of each volunteer. The solutions consisted o f 1% lidocaine with epinephrine concentrations of 0, 1:50,000, 1:200,0 00, 1:800,000, and 1:3,200,000, and 0.25% bupivacaine with the same ep inephrine concentrations. Duration of loss of sensation Co pinprick at each wheal was recorded. Skin wheals with 0.2 mt of these same soluti ons were also subcutaneously injected into the abdomen of the same 6 v olunteers, and laser Doppler flowmetry readings of skin blood flow wer e measured for 6 hours after injection. Results. Epinephrine prolonged duration of analgesia for both lidocaine and bupivacaine in a dose-re lated manner (P < .001). All concentrations of epinephrine attenuated the vasodilation observed in the first 15 minutes after injection with plain local anesthesia (P = .03), and blood flow returned to baseline by 30 minutes after injection of either plain or epinephrine-containi ng solutions. Duration of analgesia correlated with magnitude of vasoc onstriction only al the 15-minute measurement (r = .53 and .57, P = .0 03 and 0.001 for lidocaine and bupivacaine, respectively). Conclusions . Epinephrine prolongs duration of analgesia after local infiltration in a dose-related manner. Addition of epinephrine in concentrations of 1:50,000 or 1:200,000 increases duration of analgesia after local inf iltration by approximately 200%. Addition of doses as dilute as 1:3,20 0,000 still increases duration of analgesia by approximately 100%. Dur ation of analgesia appears to correlate with magnitude of epinephrine- induced vasoconstriction using laser Doppler flowmetry. Based on study data, the use of epinephrine in concentrations from 1:200,000 to 1:3, 200,000 is recommended for prolongation of analgesia after local infil tration.