Test Doses

Abstract

The authors studied the optimal epinephrine content of an epidural test dose, and determined criteria to identify intravascular injections in subjects with or without beta-adrenergic blockade. Nine healthy nonpregnant subjects 25-36 years of age were given intravenous infusions of saline or esmolol in random order. During each infusion, they received a series of five injections (3 ml each) of either saline, 1% lidocaine or 1% lidocaine containing 5, 10, or 15 micrograms of epinephrine. Thirty minutes after completing these two infusions, propranolol was administered as a bolus injection, and the series of five injections repeated. All injections were double blind and randomized. During saline infusion, all injections containing epinephrine significantly increased heart rate (HR) by an average of 31-38 beats/min when compared with that following plain lidocaine (P less than 0.05), and increased systolic blood pressure by an average of 17-26 mmHg (P less than 0.05 for the 15-micrograms dose only). During esmolol infusion, epinephrine injections increased HR by an average of 23-31 beats/min (P less than 0.05), and increased systolic blood pressure by an average of 18-30 mmHg (P less than 0.05 for 10 and 15 micrograms). After propranolol injection, epinephrine injections caused a decrease in HR by an average of 21-28 beats/min (P less than 0.05), whereas systolic blood pressure increased by an average of 22-35 mmHg (P less than 0.05 for 10 and 15 micrograms only). Without beta-adrenergic blockade, an increase in HR greater than or equal to 20 beats/min was 100% sensitive and specific for intravascular injection of 10 or 15 micrograms of epinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)