Anesth Analg 2001;93:1612-1617
© 2001 International Anesthesia Research Society
REGIONAL ANESTHESIA
The Efficacy of Simulated Intravascular Test Dose in Sedated Patients
Makoto Tanaka, MD,
Masayoshi Sato, MD,
Tetsu Kimura, MD, and
Toshiaki Nishikawa, MD
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, Akita 010-8543, Japan. Address e-mail to mtanaka{at}med.akita-u.ac.jp
Sedation usually decreases the reliability of subjectively detecting an intravascular test dose, but the efficacies of objective hemodynamic and T-wave criteria remain undetermined. Sixty healthy patients were randomly assigned to receive IV midazolam in 1-mg increments until they were lightly sedated, fentanyl 2 µg/kg followed by incremental midazolam until they were similarly sedated, or no sedative (n = 20 each). Then, normal saline 3 mL was administered IV, followed 4 min later by 1.5% lidocaine 3 mL plus epinephrine 15 µg (1:200,000) in all subjects. Heart rate (HR), systolic blood pressure (SBP) measured by a radial arterial catheter, and lead II of the electrocardiogram were continuously recorded for 4 min after the saline and test dose injections. An IV test dose produced significant increases in HR and SBP and decreases in T-wave amplitude in all subjects. However, the mean maximum increase in HR in patients sedated with midazolam plus fentanyl (31 ± 14 bpm [mean ± SD]) was significantly less than in those administered midazolam alone or no sedative (42 ± 12 and 44 ± 10 bpm, respectively; P < 0.05). A sensitivity of 100% was obtained on the basis of the traditional HR criterion (positive if  20 bpm increase) in patients sedated with midazolam or no sedative, but it was 70% in those with midazolam plus fentanyl (P < 0.05 versus the other two groups). Irrespective of the treatment, sensitivities and specificities of 100% were obtained according to the SBP (positive if 15 mm Hg increase) and T-wave (positive if 25% decrease in amplitude) criteria. An increase in SBP and a decrease in T-wave amplitude are more reliable than an HR response for detecting accidental intravascular injection of the epinephrine-containing test dose in subjects sedated with midazolam and fentanyl.
IMPLICATIONS: To determine whether an epidural catheter is in a blood vessel, an epidural test dose containing 15 µg epinephrine is used. We found that an increase in systolic blood pressure and a decrease in T-wave amplitude seem to be more reliable than a heart rate change for detecting inadvertent intravascular injection of an epinephrine-containing test dose in patients sedated with midazolam and fentanyl.
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