Background and objectives: A test dose containing epinephrine is routinely used during epidural blockade to detect accidental intravenous needle or catheter placement before the administration of local anesthetics to avert local anesthetic systemic toxicity. β-Blocker therapy may interfere with the expected hemodynamic response from an intravascular injection. This study describes a cohort of 24 patients and their response to an epinephrine test dose (ie, if expected increased heart rates during test-dose administration are valid in this population.)
Methods: Twenty-four nonsedated, chronically β-blocked patients were enrolled in a prospective, order-randomized, crossover, double-blind study with injections of both placebo and a 15-μg epinephrine test dose in each individual. After injection into a peripheral vein, we observed blood pressure and pulse rate for 5 minutes, injected the other remaining solution (placebo or epinephrine), and observed hemodynamic parameters in the same fashion.
Results: Epinephrine raised the heart rate 17.8 beats per minute (bpm) (95% confidence interval [CI], 15.5-20.1) versus placebo 2.0 bpm (95% CI, - 0.3-4.3 P < 0.001) and the systolic blood pressure 23 mm Hg (95% CI, 17.2-28.9) versus placebo 4.4 (95% CI, - 1.5-10.3); P < 0.001 in our chronically β-blocked population. A threshold increase of 20 bpm yielded a sensitivity of 37.5% (95% CI, 18.8%-59.4%) and specificity of 100% (95% CI, 85.8%-100%). Revising a threshold to include a change of 10 bpm or increase in systolic blood pressure of 15 mm Hg or greater yielded 100% (95% CI, 85.8%-100%) sensitivity and 87.5% (95% CI, 67.6%-97.3%) specificity.
Conclusions: Epinephrine test-dose administration in nonsedated, chronically β-blocked patients cannot distinguish intravenous injection at the classic threshold increase of 20 bpm. The response in individuals is varied, and thresholds for a positive test need revising for this population of patients on therapeutic β-blockers.