Background and Objectives. The authors recently determined that intravascular injection of an epinephrine test dose reliably produced an increase in heart rate ≥ 20 beats/min in young individuals. 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 after intravascular injection of epinephrine.

Methods. Heart rate and systolic blood pressure were recorded during randomized and double-blind injections of 3 mL lidocaine plain or lidocaine with 10 or 15 μg epinephrine in 30 elective surgical patients between 21 and 81 years old.

Results. Increasing age was associated with smaller increases in HR after intravascular injection of epinephrine. The reduction in HR increase was statistically significant after 10 μg (P = .006, r ² = .24), but not after 15 μg (P = .25, r ² = .05) of epinephrine. Heart rate increases were of greater magnitude for patients younger than 40 years old (P = .01 for 10 μg epinephrine, and P = .03 for 15 μg epinephrine). One patient (of 11) over 60 did not respond to the 15 μg test dose with tachycardia. Aging did not alter systolic blood pressure increases after 10 or 15 μg 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 injection of epinephrine. The results suggest that to detect an intravascular injection in healthy people, a test dose containing 10 μg epinephrine will suffice before the age of 40. However, even 15 μg epinephrine will not be totally reliable in older patients, owing to decreased beta-adrenergic responsiveness.