Effect of chronic β-blockade on the utility of an epinephrine-containing test dose to detect intravascular injection in nonsedated patients.

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 P 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.