The Combination of Epinephrine and Isoproterenol as a Simulated Epidural Test Dose in Isoflurane-Anesthetized Adults

During isoflurane anesthesia, an epinephrine-containing test dose produces unreliable heart rate (HR) responses with a high incidence of hypertension, whereas an isoproterenol-containing test dose results in a high incidence of hypotension. We designed this study to determine whether different combination doses of epinephrine and isoproterenol produce reliable HR changes without overt fluctuations of systolic blood pressure (SBP). Seventy-five healthy patients were anesthetized with 1% end-tidal isoflurane after endotracheal intubation and randomized to one of five groups (n = 15 each) according to the combination dose given IV: epinephrine 15 [micro sign]g, epinephrine 15 [micro sign]g + isoproterenol 1.5 [micro sign]g, epinephrine 7.5 [micro sign]g + isoproterenol 3 [micro sign]g, isoproterenol 3 [micro sign]g, and saline. HR and SBP were measured at 20-s intervals for 4 min after injection. Based on the conventional HR criterion (positive if >or=to20 bpm increase), the epinephrine 15 [micro sign]g + isoproterenol 1.5 [micro sign]g, the epinephrine 7.5 [micro sign]g + isoproterenol 3 [micro sign]g, and the isoproterenol 3 [micro sign]g groups yielded 100% sensitivities, specificities, and positive and negative predictive values, whereas all groups yielded 100% efficacy according to the modified HR criterion (positive if >or=to10 bpm increase). Four (27%) and three patients (20%) in the epinephrine 15 [micro sign]g and the epinephrine 15 [micro sign]g + isoproterenol 1.5 [micro sign]g groups, respectively, developed systolic hypertension (SBP >or=to180 mm Hg), whereas four (27%) patients in the isoproterenol 3 [micro sign]g group developed systolic hypotension (SBP <or=to80% of the preinjection value). We conclude that epinephrine 7.5 [micro sign]g + isoproterenol 3 [micro sign]g provides the most reliable HR changes with the least SBP fluctuations. Implications: To test whether an epidural catheter may be in a blood vessel, various vasoactive drugs are administered during general anesthesia. The authors found that the combination of epinephrine 7.5 [micro sign]g and isoproterenol 3 [micro sign]g produced the most reliable heart rate changes with minimal blood pressure fluctuations. (Anesth Analg 1998;86:1312-7)