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REGIONAL ANESTHESIA

T-Wave Amplitude as an Indicator for Detecting Intravascular Injection of Epinephrine Test Dose in Awake and Anesthetized Elderly Patients

Department of Anesthesia, Akita University School of Medicine, Akita-city, Japan

Address correspondence and reprint requests to Makoto Tanaka, MD, Department of Anesthesia, Akita University School of Medicine, Hondo 1-1-1, Akita-city 010-8543, Japan. Address email to mtanaka{at}med.akita-u.ac.jp

Aging is associated with reduced heart rate (HR) responsiveness to a simulated IV test dose containing epinephrine. We tested the hypothesis that a more contemporary T-wave criterion (positive if there was a 25% decrease in T-wave amplitude) was applicable in both awake and anesthetized older patients. Sixteen healthy patients 65 yr old first received 3 mL of normal saline IV, followed 4 min later by 1.5% lidocaine 3 mL containing 15 µg epinephrine (1:200,000) IV in the supine position when awake, and they were anesthetized with stable 2% end-tidal sevoflurane and 67% nitrous oxide. HR, systolic blood pressure (SBP) determined invasively, and lead II of the electrocardiogram were continuously recorded for 4 min after the IV injections of saline and the test dose. A sensitivity of 88% and a negative predictive value of 89% were obtained in awake patients on the basis of the conventional HR criterion (positive if there was a 20 bpm increase), whereas a sensitivity of 81% and a negative predictive value of 84% were obtained during sevoflurane anesthesia on the basis of the modified HR criterion (positive if there was a 10 bpm increase). However, sen-sitivities, specificities, and positive and negative predictive values were all 100% on the basis of the SBP (positive if a 15 mm Hg increase was recorded with an arterial line) and the T-wave criteria for both awake and anesthetized conditions. These results suggest that the SBP and T-wave criteria should be applied in awake and anesthetized elderly patients for detecting accidental intravascular injection of the epinephrine-containing test dose.

IMPLICATIONS: To determine whether an epidural catheter is in a blood vessel, an epidural test dose containing 15 µg epinephrine is often used. We found that an increase in systolic blood pressure and a decrease in T-wave amplitude, but not an increase in heart rate, seem to be reliable indicators for detecting accidental intravascular injection in both awake and sevoflurane-anesthetized patients 65 yr old.

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