Test doses: optimal epinephrine content with and without acute beta-adrenergic blockade

Area of Science:

• Anesthesiology
• Pharmacology
• Cardiovascular Physiology

Background:

• Epidural anesthesia commonly uses test doses to detect accidental intravascular injections.
• Epinephrine is often included in test doses to elicit cardiovascular responses.
• Beta-adrenergic blockade can alter cardiovascular responses to epinephrine.

Purpose of the Study:

• To determine the optimal epinephrine concentration in an epidural test dose.
• To establish criteria for identifying intravascular injections with and without beta-adrenergic blockade.

Main Methods:

• Nine healthy subjects received intravenous infusions of saline or esmolol.
• Subjects were given randomized, double-blind injections of saline, lidocaine, or lidocaine with varying epinephrine concentrations (5, 10, 15 mcg).
• Injections were repeated after propranolol administration to simulate beta-adrenergic blockade.

Main Results:

• Without beta-blockade, epinephrine injections significantly increased heart rate and systolic blood pressure compared to plain lidocaine.
• With esmolol, epinephrine still caused significant increases in heart rate and blood pressure.
• After propranolol, epinephrine caused a decrease in heart rate but an increase in blood pressure.
• An increase in heart rate ≥ 20 beats/min was 100% sensitive and specific for intravascular injection of 10 or 15 mcg epinephrine without beta-blockade.

Conclusions:

• An increase in heart rate of ≥ 20 beats/min is a reliable indicator of intravascular injection of 10-15 mcg epinephrine.
• These findings aid in optimizing epidural test dose strategies and patient safety.