Electrocerebral Recovery During the Intracarotid Amobarbital Procedure: Influence of Interval Between Injections

Abstract

Summary: Purpose and Methods: During the intracarotid amobarbital procedure (IAP) at the University of Michigan, continuous scalp EEG monitoring guides the timing for presentation of memory items and postinjection testing. Most of our patients have undergone bilateral injections. The interval between injections varied from 22 to 60 min, depending on the test and recovery time, as well as the time to catheterize the second side. After noting a trend toward prolonged electrographic recovery following the second injection, we tested our clinical impression that recovery of the second hemisphere may be influenced by (a) the time between injections and (b) which hemisphere is injected first (epileptogenic or nonepileptogenic).To study these questions, we analyzed EEG recovery data from 48 consecutive IAPs. Approximately half the patients had the epileptogenic side injected first. Results: We found that (a) electrographic recovery after the second injection is prolonged if the interval between bilateral injections is less than 40 minutes and (b) electrographic recovery is more rapid after injection of the epileptogenic hemisphere.Conclusions: We now recommend waiting at least 45 min between injections. The pathophysiology of more prolonged amobarbital effect on the nonepileptogenic hemisphere than on the epileptogenic hemisphere remains unclear. Key Words: Amobarbital-Intracarotid-Epilepsy-Temporal lobeMemory-Epilepsy partial-Injections-Intraarterial.For more than a decade, Wada's intracarotid amobarbital test was used exclusively to localize language function (1). In 1962, Milner (2) proposed that the procedure be used to identify patients at risk for anterograde global amnesia after anterior temporal lobectomy (ATL). While the role of the intracarotid amobarbital procedure (IAP) in localizing language function has remained largely unchanged, significant controversy has arisen about the value of the IAP in (a) noninvasive lateralization of the epileptogenic zone (3-7) and (b) prediction of postoperative memory function (6,8,9). The role of the IAP in predicting both seizure outcome and postoperative cognition depends on consistent, accurate, bilateral memory testing during the procedure. To facilitate investigation of these issues, a standardized IAP protocol, with equivalent injections of the two hemispheres, must be developed. ing the extent of amobarbital effect in the hemisphere contralateral to injection. Previous studies have demonstrated an excellent correlation between the type of online visual analysis we perform and automated quantitative techniques (10). Data available during the IAP provide the most useful information for optimizing the timing of injections and behavioral testing. Qualitative EEG has some additional advantages while the patient is being tested: (a) it allows the electroencephalographer to evaluate different types of artifact effectively (including myogenic, kinesogenic and oculomotor), (b) it allows the electroencephalographer some degree of ability to distinguish between amobarbital-ind...

Sodium Methohexital (Brevital) as an Anesthetic in the Wada Test

“…With methohexital, time to motor recovery was the same for the left and right hemispheres [t(19) ‫ס‬ 1.0; p > 0.31]. As expected (14), the motor recovery times were slightly longer for the nonepileptogenic hemisphere (second injection) than for the epileptogenic hemisphere (first injection), but the difference was of borderline significance [t(19) ‫ס‬ 2.1; p ‫ס‬ 0.053, two-tailed]. Motor recovery from the effects of methohexital (259 ± 63) is clearly much faster than that with amobarbital [31 patients with bilateral injections in whom motor recovery times were recorded: 385 ± 108; t(49) ‫ס‬ 4.7; p < 0.0001].…”

“…Table 4 shows a comparison of EEG recovery times for the most recent 20 patients who had bilateral injections, compared with similar data with 120‐mg injections of amobarbital (from 14). As we already saw with amobarbital (14), EEG recovery after injection into the nonepileptogenic hemisphere (365 ± 89 s) took slightly longer than after injection into the epileptogenic hemisphere (344 ± 82 s), although the difference does not reach statistical significance [t(19) = 1.2; p > 0.2, two‐tailed]. In all but one of the methohexital cases, the epileptogenic hemisphere was injected first, so the effect of injecting the epileptogenic hemisphere first or second could not be independently assessed independent of order, as was done with amobarbital (14).…”

“…As we already saw with amobarbital (14), EEG recovery after injection into the nonepileptogenic hemisphere (365 ± 89 s) took slightly longer than after injection into the epileptogenic hemisphere (344 ± 82 s), although the difference does not reach statistical significance [t(19) = 1.2; p > 0.2, two‐tailed]. In all but one of the methohexital cases, the epileptogenic hemisphere was injected first, so the effect of injecting the epileptogenic hemisphere first or second could not be independently assessed independent of order, as was done with amobarbital (14). On average, the time to EEG baseline after methohexital (355 ± 76 s) is more rapid than that with amobarbital [42 patients with bilateral injections in whom EEG recovery times were recorded: 468 ± 110 s; t(60) = 4.1; p < 0.0001].…”

“…In addition, the patients recovered more completely after each injection, which allows multiple testings within a single session without the incremental drowsiness that is seen with amobarbital. Because it is not necessary to wait 45 min between injections, as had been the case with amobarbital (14), the entire procedure can be completed more efficiently with methohexital than with amobarbital; the time from the preinjection behavioral testing on the first side to completion of testing on the second side is usually <60 min. In our institution, the neuroradiologic team also prefers methohexital because it is an anesthetic that they already use in several other procedures, and the pharmacy here also has preferred not to handle amobarbital, which is a controlled substance used in small quantities by only one service.…”

“…However, amobarbital is associated with troublesome characteristics. In particular, successive injections must be separated by ≥45 min (14), and after two injections, a third injection is likely to lead to significant drowsiness, which limits the number of times the test can be carried out on a particular day (see 11). This problem is less severe at centers where the right and left hemisphere injections can be carried out on different days, but the number of such centers is small.…”