Intraoperative Neuromonitoring during Peripheral Arteriovenous Malformation Embolization.

PURPOSE: To evaluate whether intraoperative neuromonitoring (IONM), including pre-embolization lidocaine injection challenge ("provocative testing") is associated with reduced risk of irreversible nerve injury during embolization of peripheral arteriovenous malformations (AVMs). MATERIALS AND METHODS: Medical records of patients with peripheral AVMs who underwent embolotherapy with IONM with provocative testing between 2012 and 2021 were reviewed retrospectively. Data collected included patient demographic characteristics, AVM location and size, embolic agent used, IONM signal changes after lidocaine and embolic agent injections, postprocedural adverse events, and clinical outcomes. Decisions regarding whether embolization would proceed at specific locations were based on IONM findings after the lidocaine challenge and as embolization proceeded. RESULTS: A cohort of 17 patients (mean age, 27 years ± 19; 5 women) who underwent 59 image-guided embolization procedures with adequate IONM data was identified. No permanent neurologic deficits occurred. Transient neurologic deficits were observed in 3 patients (4 sessions), comprising skin numbness (2 patients), extremity weakness (1 patient), and extremity weakness and numbness (1 patient). All neurologic deficits resolved by postoperative day 4 without additional treatment. CONCLUSIONS: IONM, including provocative testing, during AVM embolization may minimize potential nerve injury.

Integration of Stable Ionic Liquid-Based Nanofluids into Polymer Membranes. Part II: Gas Separation Properties toward Fluorinated Greenhouse Gases.

Membrane technology can play a very influential role in the separation of the constituents of HFC refrigerant gas mixtures, which usually exhibit azeotropic or near-azeotropic behavior, with the goal of promoting the reuse of value-added compounds in the manufacture of new low-global warming potential (GWP) refrigerant mixtures that abide by the current F-gases regulations. In this context, the selective recovery of difluorometane (R32, GWP = 677) from the commercial blend R410A (GWP = 1924), an equimass mixture of R32 and pentafluoroethane (R125, GWP = 3170), is sought. To that end, this work explores for the first time the separation performance of novel mixed-matrix membranes (MMMs) functionalized with ioNanofluids (IoNFs) consisting in a stable suspension of exfoliated graphene nanoplatelets (xGnP) into a fluorinated ionic liquid (FIL), 1-ethyl-3-methylpyridinium perfluorobutanesulfonate ([C2C1py][C4F9SO3]). The results show that the presence of IoNF in the MMMs significantly enhances gas permeation, yet at the expense of slightly decreasing the selectivity of the base polymer. The best results were obtained with the MMM containing 40 wt% IoNF, which led to an improved permeability of the gas of interest (PR32 = 496 barrer) with respect to that of the neat polymer (PR32= 279 barrer) with a mixed-gas separation factor of 3.0 at the highest feed R410A pressure tested. Overall, the newly fabricated IoNF-MMMs allowed the separation of the near-azeotropic R410A mixture to recover the low-GWP R32 gas, which is of great interest for the circular economy of the refrigeration sector.

Artifact reduction by using alternating polarity stimulus pairs in intraoperative peripheral nerve action potential recording.

Intraoperative nerve action potential (NAP) recording permits direct study of an injured nerve for functional assessment of lesions in continuity. Stimulus artifact contamination often hampers NAP recording and interferes with its interpretation. In the present study, we evaluated the artifact reduction method using alternating polarity in peripheral nerve recording. Our study was conducted under controlled conditions in laboratory animals. NAPs were recorded from surgically exposed median or ulnar nerves. For the artifact reduction method with alternating polarity, two sequential recordings, one with normal and one with reversed stimulus polarity, were acquired and the signals from this recording pair were averaged. Simulation was also performed to further evaluate the effects of alternating polarity on the waveforms. The results are as follows: First, we found that this method worked for recordings with unsaturated electrical stimulus artifacts. Second, slightly unequal latencies occurred in an NAP pair, and this inequality contributed to a minimal loss of NAP amplitudes when averaging the two recordings. Third, perfect artifact cancelation and minimal signal loss were also demonstrated by simulation. Finally, we applied the method during nerve inching and demonstrated its usefulness in intraoperative NAP recordings as the method made the recording more resilient to short conduction distances. Thus, our findings demonstrate that this artifact reduction method can be used as a supplemental tool together with our previously described bridge grounding technique or the nonlifting nerve recording configuration to further improve intraoperative peripheral nerve recording. The method can be applied in clinical settings.

Solutions to the technical challenges embedded in the current methods for intraoperative peripheral nerve action potential recordings.

OBJECTIVE: Intraoperative nerve action potential (NAP) recording is a useful tool for surgeons to guide decisions on surgical approaches during nerve repair surgeries. However, current methods remain technically challenging. In particular, stimulus artifacts that contaminate or mask the NAP and therefore impair the interpretation of the recording are a common problem. The authors' goal was to improve intraoperative NAP recording techniques by revisiting the methods in an experimental setting. METHODS: First, NAPs were recorded from surgically exposed peripheral nerves in monkeys. For the authors to test their assumptions about observed artifacts, they then employed a simple model system. Finally, they applied their insights to clinical cases in the operating room. RESULTS: In monkey peripheral nerve recordings, large stimulus artifacts obscured NAPs every time the nerve segment (length 3-5 cm) was lifted up from the surrounding tissue, and NAPs could not be recorded. Artifacts were suppressed, and NAPs emerged when "bridge grounding" was applied, and this allowed the NAPs to be recorded easily and reliably. Tests in a model system suggested that exaggerated stimulus artifacts and unmasking of NAPs by bridge grounding are related to a loop effect that is created by lifting the nerve. Consequently, clean NAPs were acquired in "nonlifting" recordings from monkey peripheral nerves. In clinical cases, bridge grounding efficiently unmasked intraoperative NAP recordings, validating the authors' principal concept in the clinical setting and allowing effective neurophysiological testing in the operating room. CONCLUSIONS: Technical challenges of intraoperative NAP recording are embedded in the current methods that recommend lifting the nerve from the tissue bed, thereby exaggerating stimulus artifacts by a loop effect. Better results can be achieved by performing nonlifting nerve recording or by applying bridge grounding. The authors not only tested their findings in an animal model but also applied them successfully in clinical practice.

Intraoperative neuromonitoring for superior semicircular canal dehiscence and hearing outcomes.

BACKGROUND: Recent findings in patients with superior semicircular canal dehiscence (SCD) have shown an elevated ratio of summating potential (SP) to action potential (AP), as measured by electrocochleography (ECochG). Changes in this ratio can be seen during surgical intervention. The objective of this study was to evaluate the utility of intraoperative ECochG and auditory brainstem response (ABR) as predictive tools for postoperative hearing outcomes after surgical plugging via middle cranial fossa approach for SCD syndrome (SCDS). METHODS: This was a review of 34 cases (33 patients) in which reproducible intraoperative ECochG recordings were obtained during surgery. Diagnosis of SCDS was based on history, physical examination, vestibular function testing, and computed tomography imaging. Simultaneous intraoperative ECochG and ABR were performed. Pure-tone audiometry was performed preoperatively and at least 1 month postoperatively, and air-bone gap (ABG) was calculated. Changes in SP/AP ratio, SP amplitude, and ABR wave I latency were compared with changes in pure-tone average and ABG before and after surgery. RESULTS: Median SP/AP ratio of affected ears was 0.62 (interquartile range [IQR], 0.45-0.74) and decreased immediately after surgical plugging of the affected canal to 0.42 (IQR, 0.29-0.52; p < 0.01). Contralateral SP/AP ratio before plugging was 0.33 (IQR, 0.25-0.42) and remained unchanged at the conclusion of surgery (0.30; IQR, 0.25-0.35; p = 0.32). Intraoperative changes in ABR wave I latency and SP amplitude did not predict changes in pure-tone average or ABG after surgery (p > 0.05). CONCLUSION: This study confirmed the presence of an elevated SP/AP ratio in ears with SCDS. The SP/AP ratio commonly decreases during plugging. However, an intraoperative decrease in SP/AP does not appear to be sensitive to either the beneficial decrease in ABGs or the mild high-frequency sensory loss that can occur in patients undergoing surgical plugging of the superior semicircular canal. Future work will determine the value of intraoperative ECochG in predicting changes in vestibular function.

Near-dehiscence: clinical findings in patients with thin bone over the superior semicircular canal.

OBJECTIVE: To determine whether patients with thin bone over the superior semicircular canal can develop signs or symptoms of superior canal dehiscence syndrome (SCDS). STUDY DESIGN: Retrospective case series. SETTING: Tertiary referral center. PATIENTS: All patients from our institution found to have thin but not frankly dehiscent bone over the superior canal despite symptoms and signs of SCDS. MAIN OUTCOME MEASURES: Preoperative CT imaging, symptoms, audiometry, vestibular evoked myogenic potentials (VEMP), and intraoperative electrocochleography (ECochG) results were reviewed. Symptoms were assessed at least 1 month postoperatively in all patients, and postoperative physiologic data are presented when available. RESULTS: Ten patients (11 ears) had thin bone over the superior semicircular canal at surgery. All presented with autophony or sound- and/or pressure-induced vertigo, in addition to at least 1 physiologic measure consistent with SCDS. CT imaging was read as showing either dehiscence (36%) or marked thinning of bone overlying the affected canal (64%). Preoperative median low-frequency air-bone gap (ABG) was elevated (10.9 dB; interquartile range [IQR], 8.8-12.5), with 4 patients demonstrating negative bone conduction thresholds. Patients had elevated oVEMP amplitude (median, 20.7; IQR, 6.7-22.1) µV and ECochG SP/AP ratios (median, 0.59; IQR, 0.54-0.67). Postoperative ABG and SP/AP ratio decreased significantly compared with preoperative values (p < 0.05), and all patients reported symptomatic improvement. CONCLUSION: Symptoms typical of SCDS can occur in cases with thin but not dehiscent bone. Surgical plugging or resurfacing can reduce symptoms in such cases.