Spatial differences in corneal electroretinogram potentials measured in rat with a contact lens electrode array.

PURPOSE: It has been known for several decades that the magnitude of the corneal electroretinogram (ERG) varies with position on the eye surface, especially in the presence of focal or asymmetric stimuli or retinal lesions. However, this phenomenon has not been well-characterized using simultaneous measurements at multiple locations on the cornea. This work provides the first characterization of spatial differences in the ERG across the rat cornea. METHODS: A contact lens electrode array was employed to record ERG potentials at 25 corneal locations simultaneously following brief full-field flash stimuli in normally sighted Long-Evans rats. These multi-electrode electroretinogram (meERG) responses were analyzed for spatial differences in a-wave and b-wave amplitudes and implicit times. RESULTS: Spatially distinct ERG potentials could be recorded reliably. Comparing relative amplitudes across the corneal locations suggested a slight non-uniform distribution when using full-field, near-saturating stimuli. Amplitudes of a- and b-waves were approximately 3 % lower in the inferior quadrant than in the superior quadrant of the cornea. CONCLUSIONS: The present results comprise the start of the first normative meERG database for rat eyes and provide a basis for comparison of results from eyes with functional deficit. Robust measures of spatial differences in corneal potentials will also support optimization and validation of computational source models of the ERG. To fully utilize the information contained in the meERG data, a detailed understanding of the roles of the many determinants of local corneal potentials will eventually be required.

Impact of intraoperative direct cortical stimulation dynamics on perioperative seizures and afterdischarge frequency in patients undergoing awake craniotomy.

OBJECTIVE: Intraoperative stimulation is used as a crucial adjunct in neurosurgical oncology, allowing for greater extent of resection while minimizing morbidity. However, limited data exist regarding the impact of cortical stimulation on the frequency of perioperative seizures in these patients. METHODS: A retrospective chart review of patients undergoing awake craniotomy with electrocorticography data by a single surgeon at the authors' institution between 2013 and 2020 was conducted. Eighty-three patients were identified, and electrocorticography, stimulation, and afterdischarge (AD)/seizure data were collected and analyzed. Stimulation characteristics (number, amplitude, density [stimulations per minute], composite score [amplitude × density], total and average stimulation duration, and number of positive stimulation sites) were analyzed for association with intraoperative seizures (ISs), ADs, and postoperative clinical seizures. RESULTS: Total stimulation duration (p = 0.005), average stimulation duration (p = 0.010), and number of stimulations (p = 0.020) were found to significantly impact AD incidence. A total stimulation duration of more than 145 seconds (p = 0.04) and more than 60 total stimulations (p = 0.03) resulted in significantly higher rates of ADs. The total number of positive stimulation sites was associated with increased IS (p = 0.048). Lesions located within the insula (p = 0.027) were associated with increased incidence of ADs. Patients undergoing repeat awake craniotomy were more likely to experience IS (p = 0.013). Preoperative antiepileptic drug use, seizure history, and number of prior resections of any type showed no impact on the outcomes considered. The charge transferred to the cortex per second during mapping was significantly higher in the 10 seconds leading to AD than at any other time point examined in patients experiencing ADs, and was significantly higher than any time point in patients not experiencing ADs or ISs. Although the rate of transfer for patients experiencing ISs was highest in the 10 seconds prior to the seizure, it was not significantly different from those who did not experience an AD or IS. CONCLUSIONS: The data suggest that intraoperative cortical stimulation is a safe and effective technique in maximizing extent of resection while minimizing neurological morbidity in patients undergoing awake craniotomies, and that surgeons may avoid ADs and ISs by minimizing duration and total number of stimulations and by decreasing the overall charge transferred to the cortex during mapping procedures.

Feasibility of Full Neuromuscular Blockade During Transcranial Motor Evoked Potential Monitoring of Neurosurgical Procedures.

BACKGROUND: Transcranial motor evoked potential (TcMEP) monitoring is conventionally performed during surgical procedures without or with minimal neuromuscular blockade (NMB) because of its potential interference with signal interpretation. However, full blockade offers increased anesthetic management options and facilitates surgery. Here, the feasibility of TcMEP interpretation was assessed during full NMB in adult neurosurgical patients. METHODS: Patients undergoing cervical or lumbar decompression received a rocuronium bolus producing 95% or greater blockade by qualitative train-of-four at the ulnar nerve. TcMEPs were recorded in bilateral thenar-hypothenar and abductor hallucis muscles. Adequacy of response for reliable signal interpretation was determined on the basis of repeatability and clarity, assessed by coefficient of variation and signal-to-noise ratio, respectively. RESULTS: All patients had at least 3 of 4 measurable TcMEP limb responses present during full NMB, and 70.8% of patients had measurable responses in all 4 limbs. In total, 82.2% of thenar-hypothenar responses and 62.8% of abductor hallucis responses were robust enough for reliable signal interpretation on the basis of clarity. In addition, 97.8% of thenar-hypothenar responses and 79.1% of abductor hallucis responses met the criteria for reliable signal interpretation on the basis of consistency. Patient demographics, medical comorbidities, and preoperative weakness were not predictive of absent responses during full NMB. CONCLUSIONS: TcMEP interpretation may be feasible under greater levels of NMB than previously considered, allowing for monitoring with greater degrees of muscle relaxation. Consideration for monitoring TcMEP during full NMB should be made on a case-by-case basis, and baseline responses without blockade may predict which patients will have adequate responses for interpretation.

Pediatric tethered cord release: an epidemiological and postoperative complication analysis.

BACKGROUND: Tethered cord release (TCR) is a common procedure in pediatric neurosurgery. Despite a reputation for being relatively safe, the risk factors for postoperative complications are poorly understood. METHODS: In this study, the American College of Surgeons-National Surgical Quality Improvement Program Pediatric Database (ACS-NSQIP-P) was reviewed to identify the demographics, risk factors, and 30-day postoperative complications for tethered cord release using univariate and multivariate analysis. A detailed analysis of reasons for readmission and reoperation was also performed. RESULTS: Three thousand and six hundred eighty-two pediatric patients were studied. Males undergoing TCR were younger (5.6 vs. 6.1 years) and had a higher rate of pre-operative comorbidities but lower 30-day complication rate versus females. Patients who later developed complications were more likely to require a microscope intraoperatively, had longer operative times, and worse preoperative American Society of Anesthesiologists (ASA) class. CONCLUSIONS: Despite being a relatively safe procedure, TCR in the pediatric population carries a finite risk of complications. In this large, international database study, males were found to have a greater number of risk factors prior to TCR, while females exhibit a higher risk of developing postoperative complications. This paper provides a large sample size of multi institutional pediatric patients undergoing TCR and may serve as a contemporary "snapshot" for future studies.

Intracranial Electrode Placement for Seizures Before Temporal Lobectomy: A Risk-Benefit Analysis.

BACKGROUND AND OBJECTIVE: Anterior temporal lobectomy (ATL) is the most common surgical procedure for refractory temporal lobe epilepsy. When scalp electroencephalography cannot adequately identify an epileptogenic site, electrode implantation may be used to monitor epileptic activity and localize a target focus before surgical resection. Whether the advantage of improved seizure localization justifies the added risk of electrode placement remains unclear. : The present study uses an international surgical database to explore whether a 2wo-stage approach, electrode implant followed by ATL, has a reasonable safety profile and is clinically worthwhile versus ATL alone. METHODS: Data from the American College of Surgeons National Surgical Quality Improvement Program for 2005 to 2016 were queried to identify patients undergoing ATL or electrode implant for epilepsy. The 30-day postoperative outcomes were analyzed for the electrode implant and ATL groups, and individual and combined risk profiles were determined. RESULTS: Patients undergoing electrode implant followed by ATL had a predicted reoperation rate of 7.6%, readmission rate of 14.6%, and a 30-day mortality rate of 1.2%. The combined rate of patients having ≥1 medical complication for 2-staged procedures was higher, at 14.7%. The most common complications encountered were urinary tract infection (2.7%) and sepsis (2.7%). CONCLUSIONS: Intracranial electrode placement increases the risk of complications when added to ATL. The severity of complications from electrode placement are mild, however, and as intracranial electrode recording provides a potentially large reduction in the surgical failure risk, electrode placement may be advisable for all but the most convincing seizure foci.

Vagal Nerve Stimulation for Epilepsy in Adults: A Database Risk Analysis and Review of the Literature.

BACKGROUND: Epilepsy is one of the most common neurologic disorders and often remains refractory despite pharmacologic treatment. In patients who are not amenable to surgical resection of seizure foci, vagal nerve stimulation (VNS) may be beneficial. Multiple case series have attempted to construct a risk profile for VNS, but they are largely confined to pediatric or single-center populations. We aimed to compile a risk profile for adults undergoing VNS, using multicenter patient data from an international database. METHODS: The 30-day outcomes of adults undergoing VNS from 2005 to 2016 were collected from the American College of Surgeons National Surgical Quality Improvement Program database. Readmission rates, reoperation rates, length of hospital stay, operative time, and complications were assessed. A comprehensive literature search was performed to identify historically reported complication rates. RESULTS: Inclusion and exclusion criteria were met by 77 patients. A 30-day risk profile revealed low readmission (6.2%), reoperation (1.3%), and postoperative infection (1.3%) rates. Mean operative time was 81.7 minutes, and average length of stay was 0.27 days. Most (87.0%) patients were discharged on the day of operation. CONCLUSIONS: This study provides a current snapshot of risks and outcomes in VNS, revealing a safe 30-day risk profile. Greater use of VNS may be beneficial in this fragile population.

Three-Dimensional Model of Electroretinogram Field Potentials in the Rat Eye.

OBJECTIVE: The information derived from the electroretinogram (ERG), especially with regard to local areas of retinal dysfunction or therapeutic rescue, can be enhanced by an increased understanding of the relationship between local retinal current sources and local ERG potentials measured at the cornea. A critical step in this direction is the development of a robust bioelectric field model of the ERG. METHODS: A finite-element model was created to simulate ERG potentials at the cornea resulting from physiologically relevant transretinal currents. A magnetic resonance image of a rat eye was segmented to define all major ocular structures, tissues were assigned conductivity values from the literature. The model was optimized to multi-electrode ERG (meERG) data recorded in healthy rat eyes, and validated with meERG data from eyes with experimental lesions in peripheral retina. RESULTS: Following optimization, the simulated distribution of corneal potentials was in good agreement with measured values; residual error was comparable to the average difference of individual eyes from the measured mean. The model predicted the corneal potential distribution for eight eyes with experimental lesions with similar accuracy, and a measure of pre- to post-lesion changes in corneal potential distribution was well correlated with the location of the lesion. CONCLUSION: An eye model with high anatomical accuracy was successfully validated against a robust dataset. SIGNIFICANCE: This model can now be used for optimization of ERG electrode design, and to support functional mapping of the retina from meERG data via solving the inverse bioelectric source problem.