Efficacy of simulated intravenous test dose in the elderly during general anesthesia

Reliability of detecting unintentional intravascular injection of the epinephrine-containing test dose is improved by decreasing the heart rate (HR) threshold to 10 beats/min during combined epidural and general anesthesia. We have tested whether this modified HR criterion is still applicable in the anesthetized elderly patients.

Forty healthy elderly patients, >65 years old, undergoing upper abdominal surgeries received epidural block to T4 or higher and were anesthetized with 67% nitrous oxide and 0.5-1.1% end-tidal sevoflurane in oxygen. They were randomly assigned to either test dose group (n = 20) receiving 3 mL 1.5% lidocaine plus epinephrine 15 microg (1/200,000), or saline group (n = 20) receiving 3 mL normal saline intravenously to simulate intravascularly administered test dose during surgery.

Intravenous test dose caused significant increases in both HR and systolic blood pressure (SBP), while no hemodynamic changes were seen in the saline group. In the test dose group, only 5 of 20 patients developed HR increases > or = 20 beats/min (conventional HR criterion), 14 developed HR increases > or = 10 beats/min (modified HR criterion), and all patients developed SBP increases > or = 15 mm Hg (conventional SBP criterion), while none of the saline group patients met these hemodynamic criteria. Therefore, sensitivity/negative predictive value based on the conventional and modified HR criteria, and the conventional SBP criterion were 25/57%, 70/77%, and 100/100%, respectively.

Our results indicate that the efficacy of the modified HR criterion using epinephrine-containing test dose is clinically applicable in most elderly patients, and the combination of the SBP and the modified HR criteria is reliable in detecting intravascular injection during combined epidural and general anesthesia.