Anesthetic effects on evoked potentials

Tailored Approach and Multimodal Intraoperative Neuromonitoring in Cerebellopontine Angle Surgery

The cerebellopontine angle (CPA) is a highly complex anatomical compartment consisting of numerous nervous and vascular structures that present mutual and intricate spatial relationships. CPA surgery represents, therefore, a constant challenge for neurosurgeons. Over the years, neurosurgeons have developed and refined several solutions with the aim of maximizing the surgical treatment effects while minimizing the invasiveness and risks for the patient. In this paper, we present our integrated approach to CPA surgery, describing its advantages in treating pathologies in this anatomical district. Our approach incorporates the use of technology, such as neuronavigation, along with advanced and multimodal intraoperative neuromonitoring (IONM) techniques, with the final goal of making this surgery safe and effective.

Inhalational Versus Intravenous Anesthetic Conditioning for Subarachnoid Hemorrhage-Induced Delayed Cerebral Ischemia

BACKGROUND

Inhalational anesthetics were associated with reduced incidence of angiographic vasospasm and delayed cerebral ischemia (DCI) in patients with aneurysmal subarachnoid hemorrhage (SAH). Whether intravenous anesthetics provide similar level of protection is not known.

METHODS

Anesthetic data were collected retrospectively for patients with SAH who received general anesthesia for aneurysm repair between January 1, 2014 and May 31, 2018, at 2 academic centers in the United States (one employing primarily inhalational and the other primarily intravenous anesthesia with propofol). We compared the outcomes of angiographic vasospasm, DCI, and neurological outcome (measured by disposition at hospital discharge), between the 2 sites, adjusting for potential confounders.

RESULTS

We compared 179 patients with SAH receiving inhalational anesthetics at one institution to 206 patients with SAH receiving intravenous anesthetics at the second institution. The rates of angiographic vasospasm between inhalational versus intravenous anesthetic groups were 32% versus 52% (odds ratio, 0.49 [CI, 0.32-0.75]; P=0.001) and DCI were 21% versus 40% (odds ratio, 0.47 [CI, 0.29-0.74]; P=0.001), adjusting for imbalances between sites/groups, Hunt-Hess and Fisher grades, type of aneurysm treatment, and American Society of Anesthesiology status. No impact of anesthetics on neurological outcome at time of discharge was noted with rates of good discharge outcome between inhalational versus intravenous anesthetic groups at (78% versus 72%, P=0.23).

CONCLUSIONS

Our data suggest that those who received inhalational versus intravenous anesthetic for ruptured aneurysm repair had significant protection against SAH-induced angiographic vasospasm and DCI. Although we cannot fully disentangle site-specific versus anesthetic effects in this comparative study, these results, when coupled with preclinical data demonstrating a similar protective effect of inhalational anesthetics on vasospasm and DCI, suggest that inhalational anesthetics may be preferable for patients with SAH undergoing aneurysm repair. Additional investigations examining the effect of inhalational anesthetics on other SAH outcomes such as early brain injury and long-term neurological outcomes are warranted.

An approach to using pharmacokinetics and electroencephalography for propofol anesthesia for surgery in infants

Safe and effective techniques for propofol total intravenous anesthesia (TIVA) in infants are not well imbedded into clinical practice, resulting in practitioner unfamiliarity and potential for over- and under-dosing. In this education article, we describe our approach to TIVA dosing in infants and toddlers (birth to 36 months) which combines the use of pharmacokinetic models with EEG multi-parameter analysis. Pharmacokinetic models describe propofol and remifentanil effect site concentrations (Ce) over time in different age groups for a given dosing regimen. These models display substantial biological variability between individuals within age groups, impeding their application to clinical practice. Nevertheless, they reveal that younger infants require a higher propofol loading dose, a lower propofol maintenance dose, and a higher remifentanil dose compared with older infants. Proprietary EEG indices (eg, Bispectral Index) can serve as a biomarker of propofol Ce in adults and children to guide dosing to the individual patient; however, they are not recommended for infants as their validity remains uncertain this population. In our experience, EEG waveforms and processed parameters can reflect propofol Ce in infants, reflected by spectral edge frequency (SEF), density spectral array (DSA), and waveform patterns. In our practice, we use a "lookup table" of age-based dosing regimens or target-controlled infusion (TCI) based on the pharmacokinetic models to deliver a target propofol Ce and co-administer remifentanil and/or regional technique for analgesia. We analyze Electroencephalogram (EEG) waveforms, SEF, and DSA to adjust the propofol dose or TCI target concentration to the individual infant. EEG analysis mitigates against biological variability inherent in the pharmacokinetic models and has improved our experience with TIVA for infants.

Practice guidelines for the supervising professional: intraoperative neurophysiological monitoring

The American Society of Neurophysiological Monitoring (ASNM) was founded in 1989 as the American Society of Evoked Potential Monitoring. From the beginning, the Society has been made up of physicians, doctoral degree holders, Technologists, and all those interested in furthering the profession. The Society changed its name to the ASNM and held its first Annual Meeting in 1990. It remains the largest worldwide organization dedicated solely to the scientifically-based advancement of intraoperative neurophysiology. The primary goal of the ASNM is to assure the quality of patient care during procedures monitoring the nervous system. This goal is accomplished primarily through programs in education, advocacy of basic and clinical research, and publication of guidelines, among other endeavors. The ASNM is committed to the development of medically sound and clinically relevant guidelines for the performance of intraoperative neurophysiology. Guidelines are formulated based on exhaustive literature review, recruitment of expert opinion, and broad consensus among ASNM membership. Input is likewise sought from sister societies and related constituencies. Adherence to a literature-based, formalized process characterizes the construction of all ASNM guidelines. The guidelines covering the Professional Practice of intraoperative neurophysiological monitoring were initially published January 24th, 2013, and subsequently that document has undergone review and revision to accommodate broad inter- and intra-societal feedback. This current version of the ASNM Professional Practice Guideline was fully approved for publication according to ASNM bylaws on February 22nd, 2018, and thus overwrites and supersedes the initial guideline.

The EC90 of remifentanil for blunting cardiovascular responses to head fixation for neurosurgery under total intravenous anesthesia with propofol and remifentanil based on bispectral index monitoring: estimation with the biased coin up-and-down sequential method

Background

Head fixation can induce hemodynamic instability. Remifentanil is commonly used with propofol for total intravenous anesthesia (TIVA) during neurosurgery. This study investigated the 90% effective concentration (EC₉₀) of remifentanil for blunting of cardiovascular responses to head fixation during neurosurgery via bispectral index (BIS) monitoring.

Methods

Fifty patients undergoing neurosurgery requiring head fixation were enrolled. This study was performed using the biased coin up-and-down design sequential method (BCD). After tracheal intubation, the effect-site target concentration (Ce) of remifentanil was adjusted to achieve hemodynamic stability and reset to the level preoperatively assigned to each patient, according to the BCD method, approximately 10 min before head fixation. Baseline hemodynamic values were recorded before head fixation. An ineffective response was defined as a case with a > 20% increase in hemodynamic values from baseline. Otherwise, the response was determined to be effective. The EC₉₀ of remifentanil was calculated as a modified isotonic estimator.

Results

Forty-three patients completed this study. The EC₉₀ of remifentanil for blunting cardiovascular responses to head fixation was estimated to be 6.48 ng/mL (95% CI, 5.94–6.83 ng/mL).

Conclusions

Adjustment of the Ce of remifentanil to approximately 6.5 ng/mL before head fixation could prevent noxious cardiovascular responses in 90% of neurosurgical ASA I-II patients aged 20 to 65 years old during propofol target-controlled infusion titrated to maintain BIS between 40 and 50.

Trial registration

ClinicalTrials.gov Identifier NCT01489137, retrospectively registered 5 December 2011.

A case of left frontal high-grade glioma diagnosed during pregnancy

Background

As pregnancy accelerates glioma growth, therapeutic abortion has been recommended prior to tumor resection. Additionally, it has also been suggested that the extent of glioma resection is closely correlated with patient survival.

Case presentation

A 162-cm, 61.4-kg, 30-year-old, right-handed primigravida was referred to our institution at 21 weeks gestation to obtain a second opinion. At 18 weeks gestation, the patient developed new-onset generalized convulsive seizures (GCSs), which were poorly controlled by anticonvulsant polytherapy, early in the second trimester. A 6-cm lesion located in her left frontal supplementary motor area (SMA) was suspected as a grade III glioma, classified according to the World Health Organization (WHO) guidelines. Due to the limited evidence on the use of adjuvant therapy during pregnancy, tumors causing neurological symptoms and seizures must be treated, in order to stabilize the maternal condition and enable a safe birth. In the case of pregnant patients, awake craniotomy using intraoperative magnetic resonance imaging (iMRI) is considered advantageous, achieving gross total resection with a reduction of direct cortical stimulation, which may induce seizure, and so reducing fetal exposure to anesthetics. The “Asleep-Awake-Asleep” technique was performed at 27 weeks and 2 days gestation. As use of propofol in pregnant patients is prohibited, general anesthesia was maintained through administration of sevoflurane and remifentanil until the first scan of iMRI, and was subsequently re-induced with dexmedetomidine when tumor removal had been accomplished. A supraglottic airway (SGA) was used until the patient’s cranium was opened. There were no complications during either the procedure or the post-operative period. At 35 weeks gestation, the patient delivered a healthy baby of 2317 g. Pathological examination of the patient, revealed an anaplastic astrocytoma, thus radiotherapy and chemotherapy began 2 months post-delivery. There is no evidence of tumor recurrence in the patient and the child did not show any medical or developmental concerns at the point of the 17-month follow-up.

Conclusions

Since evidence on the use of adjuvant therapy during pregnancy is limited, extensive resection with functional monitoring is recommended if a brain tumor is presumed to be malignant. Awake craniotomy is considered advantageous to pregnant patients because subjective movement preserves the patient’s motor function and reduces fetal exposure to anesthetics. Therefore, providing multidisciplinary discussion takes place within the decision-making process, as well as careful perioperative preparation, awake craniotomy should be considered, even in the case of pregnant patients.

Intraoperative neurophysiology of the motor system in children: a tailored approach

INTRODUCTION

Intraoperative neurophysiology has moved giant steps forward over the past 15 years thanks to the advent of techniques aimed to reliably assess the functional integrity of motor areas and pathways.

INTRAOPERATIVE NEUROPHYSIOLOGICAL TECHNIQUES

Motor evoked potentials recorded from the muscles and/or the spinal cord (D-wave) after transcranial electrical stimulation allow to preserve the integrity of descending pathways, especially the corticospinal tract (CT), during brain and spinal cord surgery. Mapping techniques allow to identify the motor cortex through direct cortical stimulation and to localize the CT at subcortical levels during brain and brainstem surgery. These techniques are extensively used in adult neurosurgery and, in their principles, can be applied to children. However, especially in younger children, the motor system is still under development, making both mapping and monitoring techniques more challenging. In this paper, we review intraoperative neurophysiological techniques commonly used in adult neurosurgery and discuss their application to pediatric neurosurgery, in the light of preliminary experience from our and other centers. The principles of development and maturation of the motor system, and especially of the CT, are reviewed focusing on clinical studies with transcranial magnetical stimulation.

Anesthesia and intraoperative neurophysiological monitoring in children

PURPOSE

Anesthesia for pediatric patients undergoing surgery where intraoperative neurophysiological monitoring (IONM) is performed is based on an understanding of the anesthetic influence on the neural pathways involved and the physiology that supplies nutrients to the neural systems. Anesthesia in pediatric patients may be different than in adults due to the specific anesthesia considerations in children, notably the propofol infusion syndrome (PRIS) and the need to monitor immature neural pathways. This review was done to determine if the anesthesia protocols used were different than those used in adults.

METHODS

After reviewing the implications of anesthetic action, a survey of pediatric anesthesia practitioners in 40 North American centers was conducted to determine the anesthesia protocols used in pediatric surgery with IONM and if these were specifically modified over concerns about PRIS.

RESULTS

Twenty-five centers responded with 35 different protocols used by practitioners. These protocols are similar to protocols used in adult patients. Although no centers specifically avoided propofol in all patients, several strategies were used to reduce the dosage, avoid its use in selected patients, or monitor for the onset of the syndrome.

CONCLUSION

Anesthesia for pediatric patients undergoing surgery where IONM is being performed is consistent with the practice and principles of anesthesia for adults. Although PRIS has not caused major alterations in most patients, concern has modified the practice of some anesthesiologists.