AGING REDUCES THE RELIABILITY OF EPIDURAL EPINEPHRINE TEST DOSES

Background and Objectives. The authors recently determined that intrav ascular injection of an epinephrine test dose reliably produced an inc rease in heart rate greater than or equal to 20 beats/min in young ind ividuals. However, aging is associated with a significant reduction in beta-adrenergic responsiveness. This study was designed to determine whether aging decreases the magnitude of heart rate (HR) increase afte r intravascular injection of epinephrine. Methods. Heart rate and syst olic blood pressure were recorded during randomized and double-blind i njections of 3 mL lidocaine plain or lidocaine with 10 or 15 mu g epin ephrine in 30 elective surgical patients between 21 and 81 years old. Results. Increasing age was associated with smaller increases in HR af ter intravascular injection of epinephrine. The reduction in HR increa se was statistically significant after 10 mu g (P = .006, r(2) = .24), but not after 15 mu g (P = .25, r(2) = .05) of epinephrine. Heart rat e increases were of greater magnitude for patients younger than 40 yea rs old (P = .01 for 10 mu g epinephrine, and P = .03 for 15 mu g epine phrine). One patient (of 11) over 60 did not respond to the 15 mu g te st dose with tachycardia. Aging did not alter systolic blood pressure increases after 10 or 15 mu g epinephrine (P = .27, r(2) = .04 and P = .4, r(2) = .03, respectively). Conclusions. Aging is associated with a reduction in the magnitude of HR increase after intravenous injectio n of epinephrine. The results suggest that to detect an intravascular injection in healthy people, a test dose containing 10 mu g epinephrin e will suffice before the age of 40. However, even 15 mu g epinephrine will not be totally reliable in older patients, owing to decreased be ta-adrenergic responsiveness.