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Departments of
*Anesthesiology and Intensive Care B, and
Anesthesiology and General Intensive Care A, University of Vienna, School of Medicine, Vienna, Austria
Address for correspondence and reprints to Sibylle A. Kozek-Langenecker, MD, Department of Anesthesiology and General Intensive Care, University of Vienna, 1820 Währinger Gürtel, 1090-Vienna, Austria.
| Abstract |
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25%, SBP increase
15 mm Hg, and HR increase
10 bpm. By using the T wave, SBP, and HR criteria, a positive response rate to epinephrine was 100%, 95%, and 71%, respectively, during sevoflurane, and 90%, 71%, and 71%, respectively, during halothane anesthesia administration. These data suggest that the T wave criterion is superior to conventional hemodynamic criteria, and that sevoflurane attenuates T wave and SBP responses less than halothane; however, chronotropic responses are similar to halothane. Implications: We found a greater reliability of the T wave criterion over conventional hemodynamic criteria for detecting intravascular injection of a simulated epidural test dose. Sevoflurane may increase the likelihood of recognition of an accidental intravascular injection of epinephrine-containing solutions in clinical practice compared with halothane.
| Introduction |
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Previous reports suggested that changes in T wave morphology induced by epinephrine could serve as a marker of intravascular injection during epidural test dosing in children (3,7). Recently, the efficacy of the T wave criterion (defined as a change in T wave amplitude
25%) for detecting IV injection of a simulated test dose consisting of lidocaine and epinephrine has been documented in sevoflurane-anesthetized children (8). It remains uncertain whether similar changes in T wave amplitude could be elicited by an IV test dose during halothane anesthesia administration. Accordingly, we determined the efficacy of the HR, SBP, and the T wave criterion for diagnosis of IV epinephrine in children under stable halothane and sevoflurane anesthesia in a prospective, randomized, double-blinded study.
| Methods |
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15.0 mg) 30 min before the induction of anesthesia. By using computer-generated tables, patients were randomly assigned to be anesthetized with either halothane (n = 21) or sevoflurane (n = 21). Anesthesia was induced with a face mask by using 70% nitrous oxide in oxygen and incremental dosing of anesthetics every three to five breaths. Halothane was begun at 0.5% and increased by increments of 0.5% to 1%, whereas sevoflurane was begun at 1% and increased by increments of 1.5% until the patient was unconscious. The fresh gas flow exceeded 4 L/min. A standard anesthesia machine (Cicero; Draegerwerk AG, Luebeck, Germany) with a sevoflurane and halothane vaporizer (Draeger-Vapor 19.1; Draegerwerk AG) exclusively calibrated for each anesthetic was used for delivery. Inhaled anesthesia via a face mask was continued by using assisted or controlled ventilation, and an IV catheter was inserted for infusion of 5 mL/kg lactated Ringers solution, followed by a continuous infusion administered at a rate of 5 mL · kg-1 · h-1 throughout the study period. Neuromuscular blocking drugs and atropine pretreatment were not administered because the latter it is no longer routinely used in pediatric patients undergoing general anesthesia (9). After inserting a laryngeal mask, ventilation was controlled to maintain an ETCO2 tension between 30 and 35 mm Hg, and an end-tidal anesthetic concentration of 1.0 minimum alveolar anesthetic concentration (MAC) of inhaled anesthetic adjusted for age in 70% nitrous oxide and 30% oxygen (10,11). End-tidal gas concentrations were sampled at the proximal end of the laryngeal mask at a rate of 50 mL/min and were recorded continuously. Rectal temperature was maintained between 36°C and 37°C. Electrocardiogram (ECG) lead II (Megacart; Siemens-Elema AB, Solma, Sweden) and pulse oximetry were monitored continuously throughout the study period. Electrocardiograph records were subsequently analyzed for changes in T wave amplitude measured from the isoelectric P-QRS line to the peak of the T wave. Automated noninvasive oscillometric blood pressure (HP Model 68S; Hewlett Packard, Boebingen, Germany) was recorded in 30-s intervals throughout the study. When hemodynamic variables and end-tidal gas concentrations were stable for 10 min, each patient received two test doses injected via a peripheral arm vein to simulate the intravascular administration of an epidural test dose. The volume of the test injections was standardized at 0.2 mL/kg. One test injection consisted of epinephrine 0.5 µg/kg. The dose of epinephrine used represents the recommended contents in an epidural test dose (12,13). The other test injection consisted of saline. The sequence of test doses was assigned randomly. The second test dose was administered either 5 min after the previous injection when there was no change in HR, or 5 min after the HR had returned to baseline in response to the previous injection. The data-collecting investigator and the investigator analyzing the ECG records were blinded to the anesthetic group and the sequence of test injection. Measurements were performed before surgical incision.
As in the study by Fisher et al. (3), we defined an increase or decrease in T wave amplitude
25% as a positive T wave criterion. In addition, a positive response to intravascular injection of a test dose was defined as a HR increase of
10 bpm (HR criterion) (4,5) and an increase in SBP of
15 mm Hg (SBP criterion) occurring within 2 min of injection (13). Sensitivity (true-positives/[true-positives + false-negatives]), specificity (true-negatives/[true-negatives + false-positives]), and positive (true-positives/[true-positives + false-positives]) and negative predic- tive values (true-negatives/[true-negatives + false-negatives]) were calculated for each test criterion and all anesthesia groups. A power analysis based on a pilot study revealed that a minimal study size of 36 people would provide 80% power (0.05
, two-tailed, 0.20 ß, two-tailed) of detecting a change in T wave amplitude of 0.05 mV or greater in response to IV epinephrine 0.5 µg/kg in sevoflurane-anesthetized children. Differences in frequency distribution between the cardiovascular criteria and the two anesthetic groups were analyzed by using Cochrans Q and by
2 test. Correlations between baseline T wave amplitudes immediately before test dose injection and maximal changes in T wave amplitude were analyzed by using Pearsons correlation coefficient. Demographic data and hemodynamic data before test dose injections were expressed as mean ± SD and compared with the two anesthesia groups by using an unpaired Students t-test. Changes in T wave amplitude over time within each group were analyzed by using analysis of variance for repeated measures followed by paired Students t-test. A P < 0.05 was considered statistically significant.
| Results |
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IV injection of epinephrine caused changes in T wave amplitude, SBP, and HR, whereas cardiovascular variables remained stable during saline injection under stable sevoflurane and halothane anesthesia. Changes in T wave amplitude after IV epinephrine are shown in Figure 1. During sevoflurane anesthesia, mean maximal increase in T wave amplitude occurred 20 ± 8 s after injection and values returned to baseline until 1 min after test injections. During halothane anesthesia, mean maximal decrease in T wave amplitude occurred 51 ± 7 s after the injection and T wave amplitude remained decreased until 4 min after the injection.
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| Discussion |
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10 bpm in 100% of children anesthetized with sevoflurane at 1 MAC in nitrous oxide. The reason for the discrepancy between the latter study and our findings is unclear and may be related to the greater statistical power of our current study. Our results further demonstrate that the SBP criterion is more sensitive for detection of IV epinephrine during sevoflurane anesthesia (95%) compared with halothane anesthesia (71%). However, in agreement with previous investigators (4,5), we conclude that short-lived SBP increases may easily be missed in clinical practice unless noninvasive measurements of blood pressure are performed at the shortest intervals possible. Our study demonstrates that changes in T wave amplitude provide evidence of intravascular injection of epinephrine in children under both halothane and sevoflurane anesthesia. All children receiving sevoflurane anesthesia met the T wave criterion in response to direct IV injection of epinephrine without false-positive responses after saline injection, resulting in all sensitivity, specificity, and positive and negative predictive values being 100%. The T wave criterion identified IV epinephrine in 90% of children receiving halothane anesthesia. We observed higher baseline T wave amplitudes immediately before test dose injections in children during stable halothane anesthesia compared with sevoflurane anesthesia administration. However, we found no significant relationship between baseline T wave amplitude and peak change in T wave amplitude in any of the groups, suggesting that different baseline T wave amplitude does not influence the efficacy of the T wave criterion.
Both an increase as well as a decrease in T wave amplitude
25% has been proposed as a diagnostic criterion for intravascular injection in clinical practice (3). The IV injection of epinephrine induced an increase in T wave amplitude in the majority of patients receiving sevoflurane, whereas flattening or inversion of the T wave predominated in patients receiving halothane. Peak increases in T wave amplitude occurred almost within a circulation time, approximately 30 seconds earlier than those of maximal decreases in T wave amplitude and other hemodynamic alterations. It is not clear from our study why halothane and sevoflurane at 1 MAC differ in their effects on cardiac repolarization in the presence of epinephrine. Modifications of cardiac electrophysiologic properties (1518), basal sympathetic, and parasympathetic tone (19,20) may, in part, be responsible. Recently, an age-specific effect of IV epinephrine on T wave morphology has been reported (8,21). This phenomenon, however, cannot explain the difference in magnitude and time course of T wave changes we observed because groups were comparable with respect to patient age. Both positive and negative changes in T wave amplitude exceeding the threshold of 25% could be easily detected visually on the strip chart, as in previous studies (3,8). Epinephrine-induced T wave changes have a characteristic crescendo/decrescendo pattern, are sustained for more than four beats, and precede HR and SBP changes (3). Atropine pretreatment before test dosing has been found to reduce the incidence of flattening in favor of T wave increases during sevoflurane anesthesia (22). The effect of atropine on the T wave configuration under halothane remains to be determined.
One limitation of our study design is the use of a single dose of 0.5 µg/kg epinephrine recommended for epidural test dosing (13). Our observations cannot predict the reliability of the T wave criterion for detecting intravascular injection of an epidural test dose in clinical practice where only a fraction of the test dose may enter the vascular space. Although our study indicates the potential usefulness of the T wave as a marker for epidural test dosing in anesthetized children, this technique cannot be recommended until further studies have determined the dose-response relationship for epinephrine-induced changes in T wave amplitude, HR, and SBP.
The present results suggest that sevoflurane may be safer than halothane in combined general and regional anesthetic techniques in pediatric patients. Sevoflurane may increase the likelihood of recognition of accidental intravascular injection of epinephrine-containing solutions, thus preserving the efficacy of an epidural test dose. Sevoflurane appears to attenuate blood pressure and ECG responses to the mixed
- and ß-adrenergic agonist epinephrine (23) less than halothane and the chronotropic responses similar to halothane. Comparative studies between halothane and sevoflurane are not available; however, our findings indicate that sevoflurane preserves the potential for vasoconstriction and the positive inotropic response better than halothane, as suggested previously (24,25). The increased blood pressure stimulus during sevoflurane anesthesia may have induced greater reflex decreases in the cardiac R-R interval resulting in chronotropic responses similar to halothane. Further studies are warranted to substantiate the difference between sevoflurane and halothane on the efficacy of the epidural test dose containing epinephrine at varying MAC values in infants and children.
| Acknowledgments |
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| References |
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