Efficacy of Isoproterenol as a Marker of Epidural Test Dose in Patients Anesthetized with Enflurane

Kim, Keon Sik; Kang, Wha Ja; Lee, Doo Ik

Abstract

BACKGROUND: Epidural test doses containing epinephrine are an incomplete marker for the detection of inadvertent intravascular injection. Therefore, many investigators have attempted to find a more reliable marker as an alternative to epinephrine in adult patients anesthetized with enflurane. The present study was designed to test whether two different simulated intravenous test doses of isoproterenol could be used as a reliable marker for the detection of inadvertent intravascular injection in adult patients anesthetized with O2-N2O-enflurane.
METHODS
Forty healthy adult patients were anesthetized with 1% end-tidal enflurane and nitrous oxide after endotracheal intubation and were randomized to one of two groups according to the dose of isoproterenol. Group 1 and 2 (n = 20 each) received 3 ml of 1.5% lidocaine with 3 and 5 g isoproterenol intravenously, respectively, to simulate an intravascularly administered test dose. Heart rate (HR) and systolic blood pressure (SBP) were measured at 20-second intervals for 4 min after injection.
RESULTS
Mean maximal HR increases were 24+/-17, 35+/-11 bpm (P<0.05), mean maximal SBP increases were 14+/-8, 13+/-9 mmHg and mean maximal SBP decreases 20+/-11, 22+/-9 mmHg following the IV injection of 3, 5ng isoproterenol, respectively. The incidence of hypotension was similar in both groups. Isoproterenol 3 and 5ng produced 75%, 100% sensitivity in the HR criteria (>or=20 bpm increase) and 60%, 70% sensitivity in the SBP criteria (>or=15 mmHg), respectively.
CONCLUSIONS
These results indicate that based on the HR response, the epidural test dose containing 5ng isoproterenol to simulate an intravascular administration is a more reliable marker than 3ng isoproterenol in adult healthy patients during enflurane anesthesia.