Abstracts

Rationale: A recent study (Loddenkemper et al., 2007) raised questions about the test-retest reliability of the Wada procedure based on findings from repeated intracarotid amobarbital tests (IAT) in which patients often performed better on retest. However, the majority of the patients included in that study were reportedly obtunded during the initial trial, limiting conclusions about IAT reliability. The purpose of this study was to assess the utility of repeating the Wada test under different retest conditions to determine how test circumstances impact retest performance.Methods: One hundred consecutive Wada tests utilizing methohexital as an anesthesia (i.e., intracarotid methohexital test, IMT) were reviewed retrospectively, yielding 24 cases in which the IMT was repeated (18 left injections, 6 right injections). Methohexital has been shown to have a shorter period of sedation, thus allowing for repeated injections on the same day without further obtundation (Buchtel et al., 2002), and most retests included in this study (96%) were performed on the same day. Language dominance was determined based on presence of aphasia whereas memory performance was assessed based on recognition of 8 objects presented during unilateral anesthesia.Results: Fourteen (58%) injections were repeated because the patient was inattentive during the registration of memory items, 4 (17%) because hemiplegia was not adequately established, and 6 (25%) because a reverse asymmetry was found despite an otherwise valid trial. All repeated injections were judged to be valid trials, although changes in methohexital dosages were utilized in some cases. Language functioning was unchanged upon repeat injection across all cases. Repeat Wada memory performance, in contrast, varied based on the reason for repeating the IMT. When patients were inattentive during the initial injection (mean 1st injection score = 2.2), their performance improved by a mean of 3.19 points. In contrast, when the trial was repeated for lack of hemiplegia (mean 1st injection score = 7.7) or due to reversed findings in a valid trial (mean 1st injection score = 2.8), scores remained more stable (0.12 points and 1.4 points improved, respectively).Conclusions: The stability of IMT memory scores across repeat injection varied according to the reason for repeating the injection, with the greatest change associated with inattentiveness during the initial trial. Modifications in medication dosing (e.g., injecting 2 + 2 mg vs. 3 mg) can effectively manage obtundation and allow for a more valid repeat trial. In contrast, reversed scores on otherwise valid trials or when hemiplegia is not established are not as susceptible to change when the trial is repeated. Based on these findings, repeating an IMT injection that was compromised by inattentiveness is necessary for proper interpretation of Wada findings, particularly since repeat IMT injections can be performed on the same day, minimizing some of the risks associated with repeating the injection.