Electrocerebral recovery during the intracarotid amobarbital procedure: influence of interval between injections

Behavioral measures and EEG monitoring using the Brain Symmetry Index during the Wada test in children

EEG monitoring is used routinely during the Wada test in children. We quantified EEG asymmetry using the Brain Symmetry Index (BSI) to reduce subjectivity of EEG interpretation. Clinical and procedural variables were obtained and EEG data were retrieved from 46 patients with a total of 89 injections. The BSI, the absolute value of the relative difference of the average spectral density of the right and left hemisphere, was calculated over time for all EEGs. Lateralized slowing was correctly identified in all procedures. Asymmetry was minimal at baseline (BSI 0.16) and increased with injection of amobarbital (BSI 0.49). Various patterns of the BSI were seen in distinct clinical and procedural scenarios. In this retrospective analysis, the BSI could not predict an unsuccessful Wada procedure. Our results suggest application of the BSI during the Wada test in children is feasible. Real-time calculation of the BSI during EEG monitoring in the angiography suite is warranted for further validation.

Alternatives to sodium amobarbital in the Wada test

OBJECTIVE

To review the literature and identify alternatives to sodium amobarbital for use in the Wada test.

DATA SOURCES

A search of PubMed (1960-October 2010) was performed using the following key words alone or in combination: Wada test, intracarotid amobarbital procedure, intracarotid, intraarterial, sodium amobarbital, methohexital, Brevital, pentobarbital, etomidate, propofol, and alternative anesthetics. References of the identified articles were reviewed for relevant information.

STUDY SELECTION AND DATA EXTRACTION

All articles in English identified from the data sources were evaluated. Review included comparative, prospective, and retrospective studies along with case series and case reports.

DATA SYNTHESIS

Methohexital, pentobarbital, etomidate, and propofol have all been studied as alternatives to sodium amobarbital in the Wada test. Four controlled experimental trials, 1 uncontrolled experimental trial, 6 retrospective chart reviews, and 2 case reports were reviewed. Methohexital, pentobarbital, and propofol required a second injection due to their short duration of action. Etomidate was studied as a bolus injection followed by a continuous infusion until the critical speech and memory tests were administered, which differed from the standard Wada test procedure. Patients had an increased risk of seizures with methohexital, whereas 1 patient developed transient respiratory depression immediately after receiving pentobarbital. Furthermore, propofol caused increased tone with twitching and rhythmic movements, which interfered with the completion of the Wada test for 1 patient. All authors concluded that these agents were equivalent to amobarbital for the Wada test.

CONCLUSIONS

Methohexital, pentobarbital, etomidate, and propofol are viable alternatives to sodium amobarbital for use in the Wada test, but each has shortcomings.

Intracarotid propofol testing: a comparative study with amobarbital

Twenty-five consecutive patients who underwent the Wada test using propofol as anesthetic were compared with 15 randomly selected patients who were tested using amobarbital. Time to verbal and nonverbal responses and time to motor power 3/5 did not differ between the two groups (P>0.05). The number of doses received by each patient and the percentage of patients needing more than one dose were significantly greater in the propofol group (P<0.005). Only one patient developed confusion, combativeness, and agitation. Despite the need for multiple doses, our patients had no residual drowsiness within 10 to 15 minutes of the propofol injection. This allowed us to perform the test on both sides on the same day separated only by 45 minutes. Propofol is an effective alternative to amobarbital in the Wada test, and may be used successfully in multiple repeated injections within the same test without significant residual sedation or significant adverse effects.

Sodium methohexital (brevital) as an anesthetic in the Wada test

PURPOSES

We report our experience with sodium methohexital (Brevital) as an anesthetic used in the Wada test for language and memory in 86 epilepsy surgery patients (173 procedures).

METHODS

The methods are compared with those of the more commonly used anesthetic sodium amobarbital (Amytal).

RESULTS

Despite differences between the methohexital and amobarbital test protocols, the behavioral and neurologic effects of the two anesthetics are similar. Because of the brief duration of methohexital, two successive injections are made on each side rather than one, to lengthen the time available for testing both language and memory. Behavioral and EEG indices return to baseline more quickly and more completely with methohexital than with amobarbital, allowing several repetitions of the procedure without incremental drowsiness, and the total time taken for the procedure is less with methohexital than with amobarbital.

CONCLUSIONS

The results of language and memory testing in the Wada test are equivalent for amobarbital and methohexital, except that methohexital has a briefer duration of action and is associated with less sedation.

Wada difference a day makes: interpretive cautions regarding same-day injections

OBJECTIVE

To determine whether memory scores after second intracarotid amobarbital procedure (IAP) injections are affected by the time between the first and second injections.

METHODS

Sixty-two patients received their second IAP injection on the day after the first injection. Forty-three other patients received the second injection on the same day as the first injection. Both groups underwent similar IAP protocols and memory assessments, except for the timing of the second injection.

RESULTS

The second IAP memory scores in the two-day group were significantly higher (p < 0.05) than those in the one-day group. Timing of second injection was a significant correlate of second memory scores, but amobarbital dosage, first IAP memory score, and pre-IAP measures of memory and intelligence were not significant correlates.

CONCLUSION

One-day and two-day IAP protocols do not result in similar memory scores after the second injection. Nineteen percent of a subset of patients in the one-day protocol were misclassified, in terms of IAP memory ratings, because of the deleterious effect of having both injections on the same day. It is recommended that correction scores be considered, for some patients who receive two IAP injections on one day, to approximate what the second IAP memory score would have been had the second injection occurred on a second day.

Hemispheric asymmetries in arousal affect outcome of the intracarotid amobarbital test

Objective: To evaluate changes in arousal and their impact on memory performance during the intracarotid amobarbital test (IAT).

Methods: Along with memory measures, level of arousal was evaluated through clinical ratings and nonverbal self-ratings in epilepsy patients undergoing IAT before anterior temporal lobectomy.

Results: Irrespective of seizure focus, left-sided amobarbital injection resulted in decreased objective and subjective arousal more often than right-side injection. Impaired objective arousal was greater when the left hemisphere was injected second, because of the presumed additive effects of systemic amobarbital residual from the first injection. Decreased objective arousal was related to poorer performance on memory testing following left-hemisphere injection.

Conclusions: The IAT, as practiced in most centers, is biased, so patients with right temporal lobe seizure focus are more likely to “pass” the test, whereas patients with left seizure focus are more likely to “fail” the test. The significant impact of changes in arousal on memory testing needs to be considered when using IAT results to select patients for temporal lobectomy.