Efficacy of simulated epidural test doses in adult patients anesthetized with isoflurane: a dose-response study

A recent study demonstrated that an epidural test dose containing 15 micrograms epinephrine was an imperfect marker for intravascular injection during isoflurane anesthesia based on the conventional heart rate (HR) criterion (positive if > or = 20 bpm increase). We have determined the effects of epinephrine doses and isoflurane concentrations on these efficacies in healthy adult patients during isoflurane anesthesia. Eighty patients were randomly assigned to one of four groups according to the simulated test dose injected intravenously (IV) under 1% end-tidal isoflurane and nitrous oxide after endotracheal intubation. The saline group (n = 20) received 3 mL normal saline; the epinephrine 7.5 group (n = 20) received 3 mL 1.5% lidocaine containing 7.5 micrograms epinephrine; the epinephrine 15 and epinephrine 22.5 groups (n = 20 each) received an identical dose and volume of lidocaine but containing 15 and 22.5 micrograms epinephrine, respectively. HR and systolic blood pressure (SBP) were monitored invasively for 4 min after IV injection of the study drug. Although none in the saline group developed a HR increase > or = 20 bpm, 2, 14, and 12 patients elicited positive responses in the epinephrine 7.5, 15, and 22.5 groups (10%, 70%, and 60% sensitivities), respectively. If a positive HR response was defined by an increase of 10 bpm, sensitivities were 55%, 100%, and 100% in the epinephrine 7.5, 15, and 22.5 groups, respectively. On the other hand, none in the saline group, 12 in the epinephrine 7.5 group, and all patients in the epinephrine 15 and 22.5 groups developed maximum SBP increases > or = 15 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)