title: Effect of chronic β-blockade on the utility of an epinephrine-containing test dose to detect intravascular injection in nonsedated patients.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Anesthesiology, Virginia Mason Medical Center, Seattle, WA 98101, USA. ryan.pong@vmmc.org
authors.forename: Ryan P
authors.initials: RP
authors.lastname: Pong
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Bernards
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hejtmanek
authors.forename: April E
authors.initials: AE
authors.lastname: Slee
authors.forename: Manbir S
authors.initials: MS
authors.lastname: Batra
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000008:administration & dosage*; D000368:Aged; D001794:Blood Pressure / Q000187:drug effects* / Q000502:physiology; D002406:Catheterization, Peripheral / Q000379:methods; D015331:Cohort Studies; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004837:Epinephrine / Q000008:administration & dosage*; D005260:Female; D006339:Heart Rate / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D007275:Injections, Intravenous; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D016896:Treatment Outcome
chemical_list: D000319:Adrenergic beta-Antagonists; D004837:Epinephrine