Alternatives to sodium amobarbital in the Wada test

Changes in measures of consciousness during anaesthesia of one hemisphere (Wada test)

BACKGROUND

In the Wada test, one hemisphere is selectively anaesthetised by unilateral intracarotid injection of a fast-acting anaesthetic agent. This gives a unique opportunity to observe the functions and physiological activity of one hemisphere while anaesthetising the other, allowing direct comparisons between brain states and hemispheres that are not possible in any other setting.

AIM

To test whether potential measures of consciousness would be affected by selective anaesthesia of one hemisphere, and reliably distinguish the states of the anesthetised and non-anesthetised hemispheres.

METHODS

We analysed EEG data from 7 patients undergoing Wada-tests in preparation for neurosurgery and computed several measures reported to correlate with the state of consciousness: power spectral density, functional connectivity, and measures of signal diversity. These measures were compared between conditions (normal rest vs. unilateral anaesthesia) and hemispheres (injected vs. non-injected), and used with a support vector machine to classify the state and site of injection objectively from individual patient's recordings.

RESULTS

Although brain function, assessed behaviourally, appeared to be substantially altered only on the injected side, we found large bilateral changes in power spectral density for all frequency bands tested, and functional connectivity changed significantly both between and within both hemispheres. Surprisingly, we found no statistically significant differences in the measures of signal diversity between hemispheres or states, for the group of 7 patients, although 4 of the individual patients showed a significant decrease in signal diversity on the injected side. Nevertheless, including signal diversity measures improved the classification results, indicating that these measures carry at least some non-redundant information about the condition and injection site. We propose that several of these results may be explained by conduction of activity, via the corpus callosum, from the injected to the contralateral hemisphere and vice versa, without substantially affecting the function of the receiving hemisphere, thus reflecting what we call "cross-state unreceptiveness".

The Preoperative Evaluation of Drug-Resistant Epilepsy

Antiepileptic drugs afford good seizure control for approximately 70% of individuals with epilepsy. Epilepsy surgery is extremely helpful for appropriate individuals with drug resistance. Since antiquity, trephination was a crude and invasive technique to manage epilepsy. The late 1800s saw the advent of a more evidence-based approach with attempts to define seizure foci and determine areas of function. Seizure localization initially required direct brain stimulation during surgery before resection. Fortunately, improved knowledge of seizure semiology and advancements in preoperative investigations have enabled epilepsy specialists to better analyze the benefit of seizure reduction versus risk of functional harm. This preoperative phase and the investigative techniques used to analyze surgical candidacy will be discussed in this article.

The Optimal Dose of Amobarbital in the Wada Test for the Presurgical Evaluation of Patients With Temporal Lobe Epilepsy

OBJECTIVE

The use of amobarbital in the Wada test varied between epilepsy centers, with no unified dosing or protocols available in the literature to standardize its use. We aimed to determine the dose of amobarbital in the presurgical evaluations of patients with temporal lobe epilepsy.

METHODS

A retrospective study of patients with temporal lobe epilepsy seen between January 2004 and December 2018 in King Faisal Specialist Hospital and Research Centre in Jeddah, Saudi Arabia, was conducted, and those who successfully underwent a Wada test were studied. A neuropsychologist or a neurologist will assess the memory and language, using standardized testing.

RESULTS

A total of 90 patients were studied. The mean age was 30 years (range, 16-52 years), where 49 (57%) of them were men. All patients had a routine neurological examination, including language and memory. The average dose of amobarbital given was 10.1.1 mg (range, 65.7-150 mg). There was no statistical difference between the dosing given to patients who passed or failed the memory testing (101.4 mg vs 94.7 mg, P = 0.1). Multivariate regression analysis showed that amobarbital dose needed an adjustment to patient's weight only for those older than 30 years, (P < 0.05; 95% confidence interval, 0.1-0.5), where an increase in the dose by 0.3 mg·kg·y was required to execute Wada test successfully.

CONCLUSION

It was only the patient's age that could influence the modification of Amobarbital dose in the Wada test, yet establishing a universal protocol is challenging because of the lack of well-defined dose determinants.

Reliability and safety of Etomidate speech test in children with drug resistant focal epilepsy

PURPOSE

To review our experience with the Etomidate speech test (EST) for lateralizing language in children undergoing epilepsy surgery evaluation METHODS: This retrospective study included children (<18 years) with drug refractory focal epilepsy undergoing EST for bilateral or poorly reliable language representation on functional MRI. Data for consecutive children who underwent EST between January 2013 to June 2017 were reviewed.

RESULTS

Twenty-one children (mean age at EST, 13.1 ± 4.4 years) were studied, with 19-right hemispheric and 20 left hemispheric injections. Six patients had neurological co-morbidities. Duration of ipsilateral EEG slowing was sufficient for speech testing in all children with a single bolus of Etomidate per carotid artery. Language was lateralized to one hemisphere in 17 (80.9%) and bilateral in two cases. EST was unsuccessful in two patients because of diffuse EEG slowing. Contralateral transient frontal EEG slowing was seen in 14 (73.7%) cases. EST was well tolerated in all the patients.

CONCLUSIONS

The EST was found to be successful and safe in lateralizing language in most of our drug refractory pediatric epilepsy cohort.

Experience of adverse events with cerebral propofol testing in patients with drug resistant epilepsy

The aim of this study was to assess the type and frequency of adverse events during the Wada test conducted with propofol as an anaesthetic agent. In total, 122 patients with temporal lobe epilepsy underwent the Wada test with propofol between 2006 and 2016 as part of presurgical evaluation at the Department of Neurosurgery of the Medical University of Warsaw. The Wada test was conducted bilaterally on 118 patients (236 cases). In four cases, due to complications, the test was conducted only unilaterally, which resulted in a total of 240 cases. Those cases were further analysed for the presence of adverse events. In all cases, intracranial circulation angiography (via the transfemoral approach) was performed before memory and language testing. Of the 122 patients, adverse events were observed in 75 patients (61.4%). Serious complications were notably rare and observed only in two patients (1.6%): one patient had a carotid artery dissection, and the other had a pseudoaneurysm at the puncture site. Mild adverse events (e.g., shivers or pain of the eye) were highly common - we observed them in 71 patients (58%), but they were short-term and well-tolerated by the subjects. Two patients (1.6%) had a seizure during the Wada test. Most of the adverse events occurring during the Wada test with propofol were mild and short-lived. Considering a small risk of serious damage to health, this procedure can be perceived as a good method for assessing language and memory in a fraction of the epilepsy surgery candidates.

The safety and efficacy of propofol as a replacement for amobarbital in intracarotid Wada testing of presurgical patients with epilepsy

OBJECTIVE

The intracarotid sodium amytal procedure (the "Wada test") has for many years been the gold standard for language and memory lateralization and remains an important part of presurgical analysis for patients with medically intractable seizures. Due to shortages in the key sedative (amobarbital), neuropsychologists have turned to alternatives such as propofol. Our aim was to investigate the safety and efficacy of propofol relative to amobarbital in the Wada test.

METHODS

We performed a retrospective review of the 97 Wada procedures performed at University of Iowa Hospitals and Clinics from 2007 through mid-2015.

RESULTS

Propofol produced similar lateralization rates as amobarbital for both language and memory. Similar rates of patients in each group went on to have the resection surgery. With regard to safety, there were no differences found in average rate or severity of adverse effects. None of the demographic characteristics reviewed were predictive of increased risk for either drug.

SIGNIFICANCE

These findings support previous studies indicating that propofol is as safe and efficacious as amobarbital, and can continue to be used in Wada procedures with confidence.

An improved qEEG index for asymmetry detection during the Wada test

The Wada test is commonly used to evaluate language and memory lateralization in candidates for epilepsy surgery. The spatial Brain Symmetry Index (BSI) quantifies inter-hemispheric differences in the EEG. Its application has been shown to be feasible during Wada testing. We developed a method for the quantification of EEG asymmetry that matches visual assessments of the EEG better than BSI. Fifty-three patients' EEG data, with a total of 85 injections were analyzed. In a step-wise, data-driven manner, multiple electrode and frequency band combinations were evaluated. Eventually, BSI, calculated using only the frontal electrodes F3 and F4, was combined with a temporal measure of delta power in the central electrodes, C3 and C4, into a new measure: cBSI. Using the area under the ROC curve (AUC), we showed that cBSI performs significantly better relative to BSI (median AUC 0.98 versus 0.96, p=0.0015, Wilcoxon signed rank test). Our results showed that asymmetry detection was significantly improved by combining temporal with spatial qEEG measures. In the future, our combined qEEG measure could allow for a more objective way of monitoring EEG asymmetry, thereby increasing the feasibility of using EEG as a monitoring tool during the Wada test. Future studies should, however, validate our cBSI method in real time in the operating room or radiology suite.

Conscious Intravenous Sedation in Dentistry: A Review of Current Therapy

Several sedation options are used to minimize pain, anxiety, and discomfort during oral surgery procedures. Minimizing or eliminating pain and anxiety for dental care is the primary goal for conscious sedation. Intravenous conscious sedation is a drug-induced depression of consciousness during which patients respond purposefully to verbal commands. No interventions are required to maintain a patent airway, and spontaneous ventilation is adequate as well as cardiovascular function. Patients must retain their protective airway reflexes, and respond to and understand verbal communication. The drugs and techniques used must therefore carry a broad margin of safety.

Propofol as a substitute for amobarbital in Wada testing

We describe a patient with equivocal findings on functional MRI (fMRI), who underwent a propofol Wada test, review the literature on this topic and suggest a protocol for the use of propofol for a Wada test. Although fMRI techniques can usually accurately lateralize language, the Wada test remains the gold standard for preoperative lateralization and is occasionally still required if there are non-diagnostic findings on fMRI. Amobarbital, the agent of choice for the Wada test, has become increasingly difficult to obtain and requires regulatory approval, which may delay definitive management and have an impact on patient outcomes. Propofol has been suggested as an alternative to amobarbital, and while there is some published data on this, there is no reported Australian experience to date.

Quantitative EEG is an objective, sensitive, and reliable indicator of transient anesthetic effects during Wada tests

The intracarotid amobarbital or Wada procedure is a component of the presurgical evaluation for refractory epilepsy, during which monitoring the onset and offset of transient anesthetic effects is critical. In this study, the authors characterized changes of 8 quantitative measures during 26 Wada tests, which included alpha, beta, theta, and delta powers, alpha/delta power ratio, beta/delta power ratio, median amplitude-integrated EEG, and 90% spectral edge frequency (SEF90), and correlated them with contralateral hemiplegia. The authors found that on the side of injection, delta and theta powers, alpha/delta power ratio, beta/delta power ratio, and SEF90 peaked within 1 minute after injection of 70 to 150 mg amobarbital or 4 to 7 mg methohexital. When contralateral arm strength returned to 3/5, delta power and amplitude-integrated EEG decayed on average 24% and 19%, respectively, for amobarbital, similar to that of methohexital (27% and 18%). Because delta power resolution most closely mirrored that of the hemiplegia and amplitude-integrated EEG had the highest signal/noise ratio, these quantitative values appear to be the best measures for decay of anesthetic effects. Increase in alpha power persisted longest, and therefore may be the best measure of late residual anesthetic effects.

The intracarotid etomidate Wada test: a 54-patient series

Hemispheric language dominance and isolated hemispheric memory function evaluation can be undertaken with the intracarotid injection of a general anesthetic agent (Wada test). Amobarbital has been traditionally used as the anesthetic agent, but legal and commercial constraints limit its use. We evaluated the use of etomidate as an alternative agent for the Wada test in a series of 54 consecutive adult patients with mesial temporal sclerosis undergoing presurgical evaluation for epilepsy surgery. Language lateralization and hemispheric memory function evaluation were successfully achieved in all cases. Side effects (somnolence, tremor, and dystonia) were infrequent, minor, and transient and did not require interruption of the procedure. Etomidate appears to be a safe and effective alternative agent to amobarbital in the Wada test. Similarly to the amobarbital Wada test, the ability of the etomidate Wada test to predict postoperative memory decline remains unclear.

A comparison of propofol and amobarbital for use in the Wada test

129 Wada procedures were reviewed to examine the suitability of propofol (n=54) as a replacement to amobarbital (n=75) for use as an anaesthetic in the Wada test. Suitability was considered with respect to length of hemiplegia induced, the frequency of side effects and patient memory scores. Data was retrospectively collected from records of patients who had undergone the Wada procedure between 2004 and 2009 in Beaumont Hospital, Dublin. No significant differences were found between the two drugs on any of the measures. The results suggest that propofol represents a suitable alternative to amobarbital for use in the Wada procedure.