Cell death can terminate in plasma membrane rupture to release potent pro-inflammatory intracellular contents thereby contributing to inflammatory diseases. Cell rupture is an active process, mediated by the membrane protein ninjurin-1 (NINJ1) in pyroptosis, post-apoptosis lysis, ferroptosis, and forms of necrosis. Once activated, NINJ1 clusters into large oligomers within the membrane to initiate cellular lysis. Recent preclinical studies have demonstrated that inhibiting NINJ1 is a new strategy for treating immune-mediated diseases. Indeed, both small molecule inhibitors and neutralizing antibodies can target NINJ1 clustering to preserve plasma membrane integrity and mitigate disease pathogenesis. In this Perspective, we provide a summary of the current state of knowledge and recent developments in targeting cellular integrity during cell death through NINJ1 inhibition to treat inflammatory disease, with a focus on liver injury. As these NINJ1-mediated cell death pathways are pivotal in maintaining health and contribute to disease pathogenesis when dysregulated, the studies discussed within have broad implications across the immunologic basis of molecular medicine.

NINJ1 is the terminal executioner of cellular rupture in multiple lytic cell death pathways through its clustering in the plasma membrane. Its activation trigger, however, remains unknown. We found that NINJ1-mediated plasma membrane rupture depends on calcium influx into the cell, which suffices to induce NINJ1-mediated rupture. Using genetic and pharmacologic approaches in macrophages, we show calcium drives membrane rupture through phospholipid scrambling by the calcium-activated scramblase TMEM16F. We next tested whether this calcium-activated NINJ1 mechanism is the elusive pathway by which extracellular ATP stimulates cellular rupture. We show that ATP-stimulation of P2X7R induces NINJ1-mediated cell lysis via calcium influx and TMEM16F lipid scrambling, independently of inflammasomes, pannexins and gasdermin D. Our work reveals the mechanism of NINJ1 activation and solves the long-standing mystery of ATP-induced cytolysis. ### Competing Interest Statement The authors have declared no competing interest.

First recognized more than 30 years ago, glycine protects cells against rupture from diverse types of injury. This robust and widely observed effect has been speculated to target a late downstream process common to multiple modes of tissue injury. The molecular target of glycine that mediates cytoprotection, however, remains elusive. Here, we show that glycine works at the level of NINJ1, a newly identified executioner of plasma membrane rupture in pyroptosis, necrosis, and post-apoptosis lysis. NINJ1 is thought to cluster within the plasma membrane to cause cell rupture. We demonstrate that the execution of pyroptotic cell rupture is similar for human and mouse NINJ1 and that NINJ1 knockout functionally and morphologically phenocopies glycine cytoprotection in macrophages undergoing lytic cell death. Next, we show that glycine prevents NINJ1 clustering by either direct or indirect mechanisms. In pyroptosis, glycine preserves cellular integrity but does not affect upstream inflammasome activities or accompanying energetic cell death. By positioning NINJ1 clustering as a glycine target, our data resolve a long-standing mechanism for glycine-mediated cytoprotection. This new understanding will inform the development of cell preservation strategies to counter pathologic lytic cell death.

BACKGROUND:The COVID-19 pandemic has yielded an unprecedented quantity of new publications, contributing to an overwhelming quantity of information and leading to the rapid dissemination of less stringently validated information. Yet, a formal analysis of how the medical literature has changed during the pandemic is lacking. In this analysis, we aimed to quantify how scientific publications changed at the outset of the COVID-19 pandemic.METHODS:We performed a cross-sectional bibliometric study of published studies in four high-impact medical journals to identify differences in the characteristics of COVID-19 related publications compared to non-pandemic studies. Original investigations related to SARS-CoV-2 and COVID-19 published in March and April 2020 were identified and compared to non-COVID-19 research publications over the same two-month period in 2019 and 2020. Extracted data included publication characteristics, study characteristics, author characteristics, and impact metrics. Our primary measure was principal component analysis (PCA) of publication characteristics and impact metrics across groups.RESULTS:We identified 402 publications that met inclusion criteria: 76 were related to COVID-19; 154 and 172 were non-COVID publications over the same period in 2020 and 2019, respectively. PCA utilizing the collected bibliometric data revealed segregation of the COVID-19 literature subset from both groups of non-COVID literature (2019 and 2020). COVID-19 publications were more likely to describe prospective observational (31.6%) or case series (41.8%) studies without industry funding as compared with non-COVID articles, which were represented primarily by randomized controlled trials (32.5% and 36.6% in the non-COVID literature from 2020 and 2019, respectively).CONCLUSIONS:In this cross-sectional study of publications in four general medical journals, COVID-related articles were significantly different from non-COVID articles based on article characteristics and impact metrics. COVID-related studies were generally shorter articles reporting observational studies with less literature cited and fewer study sites, suggestive of more limited scientific support. They nevertheless had much higher dissemination.

Objective: LDL (low-density lipoprotein) transcytosis across the endothelium is performed by the SR-BI (scavenger receptor class B type 1) receptor and contributes to atherosclerosis. HMGB1 (high mobility group box 1) is a structural protein in the nucleus that is released by cells during inflammation; extracellular HMGB1 has been implicated in advanced disease. Whether intracellular HMGB1 regulates LDL transcytosis through its nuclear functions is unknown. Approach and Results: HMGB1 was depleted by siRNA in human coronary artery endothelial cells, and transcytosis of LDL was measured by total internal reflection fluorescence microscopy. Knockdown of HMGB1 attenuated LDL transcytosis without affecting albumin transcytosis. Loss of HMGB1 resulted in reduction in SR-BI levels and depletion of SREBP2 (sterol regulatory element-binding protein 2)—a transcription factor upstream of SR-BI. The effect of HMGB1 depletion on LDL transcytosis required SR-BI and SREBP2. Overexpression of HMGB1 caused an increase in LDL transcytosis that was unaffected by inhibition of extracellular HMGB1 or depletion of RAGE (receptor for advanced glycation endproducts)—a cell surface receptor for HMGB1. The effect of HMGB1 overexpression on LDL transcytosis was prevented by knockdown of SREBP2. Loss of HMGB1 caused a reduction in the half-life of SREBP2; incubation with LDL caused a significant increase in nuclear localization of HMGB1 that was dependent on SR-BI. Animals lacking endothelial HMGB1 exhibited less acute accumulation of LDL in the aorta 30 minutes after injection and when fed a high-fat diet developed fewer fatty streaks and less atherosclerosis. Conclusions: Endothelial HMGB1 regulates LDL transcytosis by prolonging the half-life of SREBP2, enhancing SR-BI expression. Translocation of HMGB1 to the nucleus in response to LDL requires SR-BI.

BACKGROUND:Twitter is a web-based social media platform that allows instantaneous sharing of user-generated messages (tweets). We performed an infodemiology study of the coronavirus disease 2019 (COVID-19) Twitter conversation related to anesthesiology to describe how Twitter has been used during the pandemic and ways to optimize Twitter use by anesthesiologists. METHODS:This was a cross-sectional study of tweets related to the specialty of anesthesiology and COVID-19 tweeted between January 21 and October 13, 2020. A publicly available COVID-19 Twitter dataset was filtered for tweets meeting inclusion criteria (tweets including anesthesiology keywords). Using descriptive statistics, tweets were reviewed for tweet and account characteristics. Tweets were filtered for specific topics of interest likely to be impactful or informative to anesthesiologists of COVID-19 practice (airway management, personal protective equipment, ventilators, COVID testing, and pain management). Tweet activity was also summarized descriptively to show temporal profiles over the pandemic. RESULTS:Between January 21 and October 13, 2020, 23,270 of 241,732,881 tweets (0.01%) met inclusion criteria and were generated by 15,770 accounts. The majority (51.9%) of accounts were from the United States. Seven hundred forty-nine (4.8%) of all users self-reported as anesthesiologists. 33.8% of all tweets included at least one word or phrase preceded by the # symbol (hashtag), which functions as a label to search for all tweets including a specific hashtag, with the most frequently used being #anesthesia. About half (52.2%) of all tweets included at least one hyperlink, most frequently linked to other social media, news organizations, medical organizations, or scientific publications. The majority of tweets (67%) were not retweeted. COVID-19 anesthesia tweet activity started before the pandemic was declared. The trend of daily tweet activity was similar to, and preceded, the US daily death count by about 2 weeks. CONCLUSIONS:The toll of the pandemic has been reflected in the anesthesiology conversation on Twitter, representing 0.01% of all COVID-19 tweets. Daily tweet activity showed how the Twitter community used the platform to learn about important topics impacting anesthesiology practice during a global pandemic. Twitter is a relevant platform through which to communicate about anesthesiology topics, but further research is required to delineate its effectiveness, benefits, and limitations for anesthesiology discussions.

PURPOSE: Under times of supply chain stress, the availability of some medical equipment and supplies may become limited. The current pandemic involving severe acute respiratory syndrome coronavirus 2 has highlighted limitations to the ordinary provision of personal protective equipment (PPE). For perioperative healthcare workers, N95 masks provide a stark example of PPE in short supply necessitating the creation of scientifically valid protocols for their decontamination and reuse. METHODS: We performed a systematic literature search of MEDLINE, Embase, Cochrane CENTRAL databases, and ClinicalTrials.gov to identify peer-reviewed articles related to N95 mask decontamination and subsequent testing for the integrity of mask filtration and facial seal. To expand this search, we additionally surveyed the official statements from key health agencies, organizations, and societies for relevant citations. RESULTS: Our initial database search resulted in five articles that met inclusion criteria, with 26 articles added from the expanded search. Our search did not reveal any relevant randomized clinical trials or cohort studies. We found that moist mask heating (65-80°C at 50-85% relative humidity for 20-30 min) and vaporous hydrogen peroxide treatment were supported by the literature to provide consistent viral decontamination without compromising mask seal and filtration efficiency. Other investigated decontamination methods lacked comprehensive scientific evidence for all three of these key criteria. CONCLUSIONS: N95 mask reprocessing using either moist heat or vaporous hydrogen peroxide is recommended to ensure healthcare worker safety.

To the Editor:The importance of the immune system in pulmonary arterial hypertension (PAH) pathogenesis is increasingly recognized by clinicians and scientists (1).Immune cells are recruited to the lungs of patients with PAH (2), and preclinical studies have demonstrated their requirement for disease progression (3).The importance of the human immune system in PAH pathogenesis is underscored by our recent finding that mice, which do not develop robust experimental pulmonary hypertension, are rendered susceptible to severe disease when reconstituted with human immune tissue (4).Consequently, several clinical trials are investigating immunomodulation as PAH treatment (1).The ubiquitously expressed damage-associated molecular pattern HMGB1 (high-mobility group box-1) is gaining recognition as a mediator of PAH.HMGB1 can be secreted from immune cells in response to stress, and it mediates many paracrine and autocrine effects in inflammatory conditions (5).HMGB1, by binding TLR4 (Toll-like receptor 4), activates macrophages and lymphocytes; induces TNF (tumor necrosis factor), IL-6, and IL-1b; and triggers autoimmunity (5).All of these factors are hallmarks of PAH (1).Expression of both HMGB1 and TLR4 is elevated in lungs of patients with PAH (6), and HMGB1 is secreted in response to hypoxia (7).Conversely, mice treated with neutralizing antibodies against HMGB1 (6) or deficient in TLR4 are protected from hypoxia-induced pulmonary hypertension (8).Although targeting HMGB1/TLR4 signaling may be a promising new treatment for PAH, this strategy can be expected to come at a cost, given the multiple roles of these molecules in infection and immunity.In this study, we first consolidated the critical role of HMGB1 in PAH in human samples and animal models.Next, we tested the therapeutic efficacy of a novel peptide, P5779, which specifically targets extracellular HMGB1 in its disulfide form, disrupting its interaction with the TLR4 adaptor MD-2 (9).Hence, P5779 does not affect the epigenetic functions of intracellular HMGB1 or non-HMGB1-mediated TLR4 signaling, thus minimizing potential off-target effects of anti-HMGB1 therapies for PAH.Some of these results were previously reported in abstract form (10).

Poor reporting quality may contribute to irreproducibility of results and failed 'bench-to-bed-side' translation. Consequently, guidelines have been developed to improve the complete and transparent reporting of in vivo preclinical studies. To examine the impact of such guidelines on core methodological and analytical reporting items in the preclinical anesthesiology literature, we sampled a cohort of studies. Preclinical in vivo studies published in Anesthesiology, Anesthesia & Analgesia, Anaesthesia, and the British Journal of Anaesthesia (2008-2009, 2014-2016) were identified. Data was extracted independently and in duplicate. Reporting completeness was assessed using the National Institutes of Health Principles and Guidelines for Reporting Preclinical Research. Risk ratios were used for comparative analyses. Of 7615 screened articles, 604 met our inclusion criteria and included experiments reporting on 52 490 animals. The most common topic of investigation was pain and analgesia (30%), rodents were most frequently used (77%), and studies were most commonly conducted in the United States (36%). Use of preclinical reporting guidelines was listed in 10% of applicable articles. A minority of studies fully reported on replicates (0.3%), randomization (10%), blinding (12%), sample-size estimation (3%), and inclusion/exclusion criteria (5%). Statistics were well reported (81%). Comparative analysis demonstrated few differences in reporting rigor between journals, including those that endorsed reporting guidelines. Principal items of study design were infrequently reported, with few differences between journals. Methods to improve implementation and adherence to community-based reporting guidelines may be necessary to increase transparent and consistent reporting in the preclinical anesthesiology literature.

Learning objectivesBy reading this article, you should be able to:•Discuss the common modalities for intraoperative neuromonitoring (IONM) and the evidence that supports their implementation in paediatric spine surgery.•Explain the influence of anaesthetic agents and physiological variations on IONM monitoring.•Work as a team with surgeons, neuromonitoring professionals, and anaesthetists to respond to changes in IONM signals.Key points•The most common indications for intraoperative neuromonitoring (IONM) in paediatric surgery are for spinal deformities, intra- and extramedullary tumour resection, and spinal dysraphisms.•Modalities of IONM include motor-evoked potentials, somatosensory-evoked potentials, EMG, and EEG.•Anaesthetic and analgesic agents can affect IONM signals and must be selected in consultation with the neurophysiologist.•An IONM alert should prompt the surgeon to assess for possible mechanical injury and the anaesthetist to optimise MAP as first-line therapies.•Communication between the anaesthetist, neurophysiologist, surgeons, and nursing staff is fundamental to the effective use of IONM. By reading this article, you should be able to:•Discuss the common modalities for intraoperative neuromonitoring (IONM) and the evidence that supports their implementation in paediatric spine surgery.•Explain the influence of anaesthetic agents and physiological variations on IONM monitoring.•Work as a team with surgeons, neuromonitoring professionals, and anaesthetists to respond to changes in IONM signals. •The most common indications for intraoperative neuromonitoring (IONM) in paediatric surgery are for spinal deformities, intra- and extramedullary tumour resection, and spinal dysraphisms.•Modalities of IONM include motor-evoked potentials, somatosensory-evoked potentials, EMG, and EEG.•Anaesthetic and analgesic agents can affect IONM signals and must be selected in consultation with the neurophysiologist.•An IONM alert should prompt the surgeon to assess for possible mechanical injury and the anaesthetist to optimise MAP as first-line therapies.•Communication between the anaesthetist, neurophysiologist, surgeons, and nursing staff is fundamental to the effective use of IONM. Surgical procedures of the spine have an inherent risk of damage to important neural structures and may result in postoperative neurological deficits. In paediatric spinal scoliosis correction, this risk varies with the type and underlying aetiology of the scoliosis. Although the risks remain relatively low, severe neurological deficits are devastating.1Reames D.L. Smith J.S. Fu K.M. et al.Complications in the surgical treatment of 19,360 cases of pediatric scoliosis: a review of the Scoliosis Research Society Morbidity and Mortality database.Spine. 2011; 36: 1484-1491Crossref PubMed Scopus (279) Google Scholar Intraoperative neuromonitoring (IONM) techniques have been developed to provide feedback on the integrity of vulnerable neural structures and improve the safety of these surgical procedures. The benefit of IONM has long been acknowledged. Some of the first modalities of IONM, including the ankle clonus and Stagnara wake-up tests, had limited clinical utility and required intraoperative emergence from anaesthesia, which may be fraught with danger and difficulty, especially in children. The advent of newer and complementary intraoperative methodologies to assess specific, at-risk neural pathways, such as the corticospinal tracts, dorsal columns, and nerve roots, has made IONM standard practice in many paediatric and adult institutions. Nevertheless, a consensus on the use of IONM has not been established. There is a significant variation in practice between institutions; protocols vary depending on the technology and alert criteria used, and anaesthesia and surgical management. In this article, we review the methods, indications, and evidence for the use of the IONM techniques commonly used in paediatric spinal surgery. The considerations of IONM relevant to anaesthesia for spinal surgery in paediatric practice are discussed, with an emphasis on the impact of various anaesthetic and analgesic agents on IONM. Further information and figures describing IONM modalities, along with an additional bibliography, are provided in the accompanying online supplement. The clinical scenario presentation provides a review of IONM used commonly and a framework for dealing with intraoperative IONM alerts.Clinical scenario: crisis resource management and intraoperative neuromonitoring alertsA 15-yr-old with idiopathic scoliosis arrived for correction of her curvature. Before induction of anaesthesia, the surgeon, anaesthetist, nurses, and neurophysiologist participated in a preoperative huddle to confirm the intraoperative plan and discuss any concerns that may affect intraoperative neuromonitoring (IONM).After induction of anaesthesia, appropriate upper-extremity IONM responses confirmed that prone positioning had not caused pressure or stretch on the brachial plexus.As the case proceeded, the skull-femoral traction application corresponded with a reduction in motor-evoked potentials (MEPs) of 70%, suspicious for stretching of the anterior spinal artery. In response, the MAP was increased to >85 mm Hg. Despite this, the responses did not fully recover, prompting the surgeon to reduce the applied traction. With this manoeuvre, the responses recovered to their baseline values. Consulting a 'checklist for the response to IONM changes' (Fig. 1) was beneficial in identifying all possible causes of IONM alerts.During insertion of a left-sided pedicle screw, a unilateral loss of the left lower-extremity MEPs and somatosensory-evoked potentials of 80% and 50%, respectively, were noted, raising concerns of a Brown-Séquard spinal-cord injury. In response, the surgeon paused all manipulations. The responses did not recover, despite working through the checklist and taking all measures to improve the situation. The patient was given steroids, and a decision was made to limit the extent of the surgery.As the surgeons began their closure, the anaesthetist titrated the TIVA infusion to allow for prompt emergence based on the patient's depth of anaesthesia as interpreted from the EEG signal. The patient was returned to the supine position and the trachea extubated without complication. A postoperative examination revealed mild left-sided lower-extremity motor and sensory deficits, which recovered after a few weeks.The dynamic perioperative exchange between the surgeon, anaesthesiologist, and neurophysiologist highlights the importance of good communication in order to mitigate the risk of neurological injury. A 15-yr-old with idiopathic scoliosis arrived for correction of her curvature. Before induction of anaesthesia, the surgeon, anaesthetist, nurses, and neurophysiologist participated in a preoperative huddle to confirm the intraoperative plan and discuss any concerns that may affect intraoperative neuromonitoring (IONM). After induction of anaesthesia, appropriate upper-extremity IONM responses confirmed that prone positioning had not caused pressure or stretch on the brachial plexus. As the case proceeded, the skull-femoral traction application corresponded with a reduction in motor-evoked potentials (MEPs) of 70%, suspicious for stretching of the anterior spinal artery. In response, the MAP was increased to >85 mm Hg. Despite this, the responses did not fully recover, prompting the surgeon to reduce the applied traction. With this manoeuvre, the responses recovered to their baseline values. Consulting a 'checklist for the response to IONM changes' (Fig. 1) was beneficial in identifying all possible causes of IONM alerts. During insertion of a left-sided pedicle screw, a unilateral loss of the left lower-extremity MEPs and somatosensory-evoked potentials of 80% and 50%, respectively, were noted, raising concerns of a Brown-Séquard spinal-cord injury. In response, the surgeon paused all manipulations. The responses did not recover, despite working through the checklist and taking all measures to improve the situation. The patient was given steroids, and a decision was made to limit the extent of the surgery. As the surgeons began their closure, the anaesthetist titrated the TIVA infusion to allow for prompt emergence based on the patient's depth of anaesthesia as interpreted from the EEG signal. The patient was returned to the supine position and the trachea extubated without complication. A postoperative examination revealed mild left-sided lower-extremity motor and sensory deficits, which recovered after a few weeks. The dynamic perioperative exchange between the surgeon, anaesthesiologist, and neurophysiologist highlights the importance of good communication in order to mitigate the risk of neurological injury. Common IONM modalities used in paediatric spine surgery include somatosensory-evoked potentials (SEPs), motor-evoked potentials (MEPs), EMG and EEG. The neural pathways monitored by these modalities are summarised in Table 1.Table 1Intraoperative neuromonitoring modalities.SEPMEPEMGEEGStimulation sitePeripheral sensory nervesTranscranial motor cortexTriggered (or none)(None)Recording siteCorticalExtremity muscleMuscleScalpAdvantagesSensory specificity; continuous signal captureMotor specificity; large-amplitude signalContinuous monitor; allows for surgical correlation with pedicle screw stimulationMonitors cerebral integrity and anaesthetic depthLimitationsLow amplitude; requires averaging (possible introduction of delays)TIVA preferable; intermittent signal; variable stimulation thresholds with ageNo neuromuscular block; difficulty distinguishing innocuous from serious injury; insensitive to complete nerve injury Open table in a new tab SEPs were developed to monitor the posterior columns of the spinal cord by evaluating signals from sensory cortical neurones generated in response to stimulation of peripheral nerves, typically the ulnar, median, and posterior tibial nerves. Upon stimulation, the signal propagates up the dorsal spinal column with some contribution from the spinothalamic tract before moving through the medulla and thalamus to arrive in the somatosensory cortex. Notably, SEP monitoring does not provide any information on the descending corticospinal tract or spinal-cord grey matter. The integrity of the sensory pathway is evaluated by intermittently monitoring the amplitude and latency of the SEP waveforms to assess for intraoperative changes from baseline. This procedure relies on averaging responses in order to improve reliability. Current technologies have mitigated, but not removed this limitation, which also inherently introduce some degree of feedback delay. Changes in somatosensory-evoked potentials may arise from trauma to the dorsal columns. For example, insertion of a sublaminar hook can directly traumatise the spinal cord, producing a Brown-Séquard injury and an abrupt reduction in the SEP amplitudes on the affected side without affecting the contralateral signals. Supplementary Fig 1 shows a stereotypical example of these signal changes. Once an alert is identified, diagnosis of the underlying cause is paramount. Clinical response to a signal change can include removal of offending implants and increasing the mean arterial pressure in an effort to aide recovery.2Vitale M.G. Skaggs D.L. Pace G.I. et al.Best practices in intraoperative neuromonitoring in spine deformity surgery: development of an intraoperative checklist to optimise response.Spine Deform. 2014; 2: 333-339Abstract Full Text Full Text PDF PubMed Scopus (97) Google Scholar A surgical pause may afford the spinal cord time to recover. A checklist, such as the one described in the clinical scenario accompanying this article (see Clinical scenario and Fig 1) can aid in the management of changes in IONM signals. The alert criteria for changes in SEP amplitude vary. For example, alert criteria can range from a 50% decrease relative to a stable baseline to an abrupt amplitude alteration, to a trend clearly exceeding trial-to-trial variability without a technical cause (see online Supplementary data for references to several studies that examine signal sensitivity). There is no consensus about what magnitude in a change from baseline constitutes a meaningful abnormality. In one recent retrospective study of a large cohort mostly comprising children, a persistent 50% reduction in amplitude or a prolonged latency >10% proved to have a 95.0% sensitivity, 99.8% specificity, 95% positive predictive value, and a 99.8% negative predictive value.4Thirumala P.D. Bodily L. Tint D. et al.Somatosensory-evoked potential monitoring during instrumented scoliosis corrective procedures: validity revisited.Spine J. 2014; 14: 1572-1580Abstract Full Text Full Text PDF PubMed Scopus (52) Google Scholar Whilst the specificity of SEPs is uniformly high across studies, sensitivity may be low. There are several reports of patients waking from anaesthesia with neurological deficits that had been undetected by SEP monitoring (see online Supplementary data for references). The differential receiver operating characteristics between sensory and motor pathways emphasise the need to integrate multiple IONM modalities. MEPs achieve motor specificity without the need for signal averaging. The MEP is elicited using a high-voltage short-duration stimulus applied to the scalp overlying the primary motor cortex. The transcranial impulse generates multiple electrical waves that propagate down the spinal cord and synapse of the neuromuscular junction, leading to depolarisation and muscle contraction. Monitoring the amplitude, latency, and morphology of the resultant compound muscle action potential provides an assessment of the motor pathway. Unlike SEPs, MEP monitoring in children has some unique differences to adult patients. Infants and toddlers require a greater delivered charge to obtain MEPs than adolescents, with reported reliability decreased in children aged <6 yrs. This is likely to be a result of the immaturity of the motor pathway, which does not fully develop until about 13 yrs of age.5Lieberman J.A. Lyon R. Feiner J. Diab M. Gregory G.A. The effect of age on motor evoked potentials in children under propofol/isoflurane anesthesia.Anesth Analg. 2006; 103: 316-321Crossref PubMed Scopus (63) Google Scholar More references describing motor pathway maturation are available in the online Supplementary data. MEP monitoring during spine surgery is both efficacious and safe (see online see online Supplementary data for references). Compared with SEPs, MEPs are more sensitive to reduced blood flow secondary to vascular insult or hypotension.6Schwartz D.M. Auerbach J.D. Dormans J.P. et al.Neurophysiological detection of impending spinal cord injury during scoliosis surgery.J Bone Jt Surg Am. 2007; 89: 2440-2449Crossref PubMed Scopus (282) Google Scholar In addition, MEPs change earlier than the SEP signal, which facilitates quicker diagnosis of impending spinal-cord injury.6Schwartz D.M. Auerbach J.D. Dormans J.P. et al.Neurophysiological detection of impending spinal cord injury during scoliosis surgery.J Bone Jt Surg Am. 2007; 89: 2440-2449Crossref PubMed Scopus (282) Google Scholar For example, during the reduction of kyphosis, stretch of the anterior spinal artery can limit the spinal-cord blood flow, a frequent cause of changes to the MEP response.7Lewis S.J. Gray R. Holmes L.M. et al.Neurophysiological changes in deformity correction of adolescent idiopathic scoliosis with intraoperative skull-femoral traction.Spine. 2011; 36: 1627-1638Crossref PubMed Scopus (42) Google Scholar In a case series, 19 of 37 instances of intraoperative skull-femoral traction were associated with MEP amplitude decreases greater than 50% related to the application of traction, all of which resolved with reduction of the traction weights.7Lewis S.J. Gray R. Holmes L.M. et al.Neurophysiological changes in deformity correction of adolescent idiopathic scoliosis with intraoperative skull-femoral traction.Spine. 2011; 36: 1627-1638Crossref PubMed Scopus (42) Google Scholar Notably, there were no observable SEP changes in each of these traction-related MEP decreases, indicative of spinal-cord compromise specifically to the area supplied by the anterior spinal artery. MEP changes during acute hypotension and skull-femoral traction during posterior spinal fusion surgery are shown in Supplementary Fig 2. Consensus guidelines recommend using a decrease in MEP signal >60% as a 'significant warning criteria' in spine deformity surgery.2Vitale M.G. Skaggs D.L. Pace G.I. et al.Best practices in intraoperative neuromonitoring in spine deformity surgery: development of an intraoperative checklist to optimise response.Spine Deform. 2014; 2: 333-339Abstract Full Text Full Text PDF PubMed Scopus (97) Google Scholar However, published warning criteria have ranged from a decrease of 60% amplitude to complete loss.6Schwartz D.M. Auerbach J.D. Dormans J.P. et al.Neurophysiological detection of impending spinal cord injury during scoliosis surgery.J Bone Jt Surg Am. 2007; 89: 2440-2449Crossref PubMed Scopus (282) Google Scholar Lack of concrete warning criteria unfortunately remains one of the principal limitations around the use of MEPs. This limitation partly reflects high sensitivity of MEPs to anaesthesia and marked trial-to-trial variability. The wide range of alert criteria highlight the difficulty in selecting optimal receiver operating characteristics and predicting new neurological deficits (NNDs): a low threshold leads to increased false-positive alerts; high thresholds risk false negatives and missed reversible NND. Illustrating these difficulties, in a study of paediatric spinal fusion surgery, alert criteria included a persistent unilateral or bilateral loss of ≥65% of MEP amplitude or ≥50% SEP amplitude decrease relative to a stable baseline.8Neira V.M. Ghaffari K. Bulusu S. et al.Diagnostic accuracy of neuromonitoring for identification of new neurologic deficits in pediatric spinal fusion surgery.Anesth Analg. 2016; 123: 1556-1566Crossref PubMed Scopus (10) Google Scholar In this study, sensitivities were estimated as 93.5%, 92.2%, and 46.7% for MEPs, combination (either MEPs or SEPs), and SEPs, respectively; however, sensitivity analyses demonstrated that the receiver-operator characteristics varied markedly depending on different assumptions related to the number of patients that would have otherwise experienced an NND without intervention.8Neira V.M. Ghaffari K. Bulusu S. et al.Diagnostic accuracy of neuromonitoring for identification of new neurologic deficits in pediatric spinal fusion surgery.Anesth Analg. 2016; 123: 1556-1566Crossref PubMed Scopus (10) Google Scholar In contrast, others have established that a single MEP signal with an 80% decrease in amplitude during a surgical action is an important warning criterion for neurological damage, whereas the persistence of any MEP recording at the time of surgical closure is associated with normal postoperative neurological function.9Langeloo D.D. Lelivelt A. Louis Journee H. Slappendel R. de Kleuver M. Transcranial electrical motor-evoked potential monitoring during surgery for spinal deformity: a study of 145 patients.Spine. 2003; 28: 1043-1050Crossref PubMed Scopus (205) Google Scholar Of note, the duration of MEP loss may be a predictor of outcome with weakness associated with MEP loss durations greater than 40–60 min.10Legatt A.D. Emerson R.G. Epstein C.M. et al.ACNS guideline: transcranial electrical stimulation motor evoked potential monitoring.J Clin Neurophysiol. 2016; 33: 42-50Crossref PubMed Scopus (72) Google Scholar Adverse effects of MEP monitoring are infrequent, but include tongue laceration (mitigated by the use of a bite block), scalp burn, and seizures (see online Supplementary data for reference). Continuous EMG monitors cranial nerve and nerve roots by placing needle electrodes into a given muscle group. Either visual or audible outputs are used to detect neurotonic discharges, which reflect irritation of a nerve innervating the muscle by mechanical, thermal, or metabolic stimuli. This modality is a sensitive indicator of nerve irritation, but not necessarily of injury, as innocuous surgical manoeuvres can cause irritation.11Nuwer M.R. Daube J. Fischer C. Schramm J. Yingling C.D. Neuromonitoring during surgery. Report of an IFCN committee.Electroencephalogr Clin Neurophysiol. 1993; 87: 263-276Abstract Full Text PDF PubMed Scopus (98) Google Scholar Accordingly, EMG has utility in providing the surgeon with information on nerve location. Notably, transection, avulsion, or severe nerve injury will abrogate firing. Therefore, the absence of an EMG signal does not necessarily preclude injury. For the anaesthetist, EMG activity may detect movement, which could represent inadequate depth of anaesthesia (DOA). In spinal fusion instrumentation, electrical stimulus can be applied to each pedicle screw. A screw in close proximity to a nerve root will activate the EMG at a lower threshold current, indicating its misplacement. Multiple confounding factors alter the triggered EMG signal, including prior root injury, the use of neuromuscular block, screw type, and location within the spinal column. The reliability and validity of stimulated EMG results do not appear to change in paediatric patients. References that elaborate on the characteristics of intraoperative EMG changes with specific injury patterns are available in the online Supplementary data. Raw and processed EEG monitors the integrity of the cerebral cortex to provide the operative team with information regarding cerebral perfusion and DOA. In the absence of cerebral blood flow, children may continue to display sustained low-amplitude EEG activity, and EEG should be interpreted with caution.12Ashwal S. Schneider S. Failure of electroencephalography to diagnose brain death in comatose children.Ann Neurol. 1979; 6: 512-517Crossref PubMed Scopus (74) Google Scholar Bispectral index (BIS) monitoring, a commercially available processed EEG monitor, is routinely used to evaluate DOA. It provides a dose–response relationship to anaesthetic depth with either hypnotic i.v. or inhalation agents. Processed EEG is most commonly used as a marker of DOA in the perioperative setting. Multiple conditions can preclude the BIS monitor from indicating the correct hypnotic state, including EMG activity, neuromuscular block, electrical interference, and patient-specific abnormal EEG patterns.13Dahaba A.A. Different conditions that could result in the bispectral index indicating an incorrect hypnotic state.Anesth Analg. 2005; 101: 765-773Crossref PubMed Scopus (254) Google Scholar In children, EEG features are also a function of age, and so commercial devices should accordingly be used with caution. Monitoring DOA in children can be achieved by using raw EEG waveforms. EEG waves are classified by frequency from high (8–15 Hz α-activity and 15–25 Hz β-activity) to low (1–3 Hz δ-activity and 4–7 Hz θ-activity). The progression from awake to anaesthetised follows a progression from a relative abundance of high-frequency components to a low-frequency prominence. This transition displays features that depend on both age and anaesthetic agent. Fig. 2 provides an illustration of the typical EEG changes seen under anaesthesia. Importantly, raw EEG may be more predictive in paediatric patients. Raw EEG has additional advantages compared with processed EEG, as it is not limited by a processing delay. It also allows for easy identification of pollution from EMG and electrocautery interference, which can be excluded during interpretation. Multichannel or bilateral hemisphere recordings are possible without the use of proprietary electrodes or special equipment. The accumulation of propofol after a prolonged exposure can cause motor neurone suppression and result in reduction of MEP responses. This will not only necessitate increased stimulating thresholds to elicit responses, but may also trigger false alerts. This phenomenon of 'anaesthetic fade' can be minimised by titrating to the appropriate DOA as indicated by the EEG response.14Lyon R. Feiner J. Lieberman J.A. Progressive suppression of motor evoked potentials during general anesthesia: the phenomenon of "anesthetic fade".J Neurosurg Anesthesiol. 2005; 17: 13-19PubMed Google Scholar Monitoring DOA with EEG may also prevent excessively long emergence times. The most common paediatric spinal surgical indications for IONM are spinal deformities, including kyphoscoliosis and spondylolisthesis, intra- and extramedullary tumour resection, and spinal dysraphisms. The online Supplementary data includes a brief history of the developments leading to our modern IONM methods. MAP <60 mm Hg is an important risk factor for spinal-cord injury during spinal deformity surgery. Autoregulation may not ensure adequate spinal-cord perfusion during the increased stress placed on the spinal cord with corrective surgery. Anatomically, a single anterior spinal artery supplies the ventral two-thirds of the spinal cord, which includes the motor neurones and the corticospinal tracts. The dorsal one-third of the spinal cord, which houses the dorsal columns transmitting proprioception and light touch, is fed by a pair of posterior spinal arteries. There is limited collateral flow between the anterior and posterior circulations. A diagram of the vascular supply of the spinal cord is available in the online supplement (Supplementary Fig 3). Patients with thoracic kyphoscoliosis are at particular risk for ischaemic cord injury during spinal deformity surgery. Almost 1% of patients undergoing scoliosis surgery have a degraded or complete loss of MEP responses caused by hypotension alone when the MAP decreases below 60 mm Hg. These changes resolve within 5 min of increasing the blood pressure.6Schwartz D.M. Auerbach J.D. Dormans J.P. et al.Neurophysiological detection of impending spinal cord injury during scoliosis surgery.J Bone Jt Surg Am. 2007; 89: 2440-2449Crossref PubMed Scopus (282) Google Scholar SEPs are largely resistant to profound hypotension to MAP <40 mm Hg.15Kottenberg-Assenmacher E. Armbruster W. Bornfeld N. Peters J. Hypothermia does not alter somatosensory evoked potential amplitude and global cerebral oxygen extraction during marked sodium nitroprusside-induced arterial hypotension.Anesthesiology. 2003; 98: 1112-1118Crossref PubMed Scopus (29) Google Scholar The avoidance of low MAP during surgery and postoperative care is important for children with substantial thoracic kyphosis. In children older than 6 yrs old, the MAP is maintained at 70 (20) mm Hg.16Haque I.U. Zaritsky A.L. Analysis of the evidence for the lower limit of systolic and mean arterial pressure in children.Pediatr Crit Care Med. 2007; 8: 138-144Crossref PubMed Scopus (123) Google Scholar Arterial blood gas tensions can affect IONM signals through changes in tissue blood flow patterns and oxygen delivery. For example, mild hypocapnia depresses SEP latencies in both awake and anaesthetised patients, whilst more severe hypocapnia will alter cortical SEPs by stimulating cerebral vasoconstriction.17Kalkman C.J. Boezeman E.H. Ribberink A.A. Oosting J. Deen L. Bovill J.G. Influence of changes in arterial carbon dioxide tension on the electroencephalogram and posterior tibial nerve somatosensory cortical evoked potentials during alfentanil/nitrous oxide anesthesia.Anesthesiology. 1991; 75: 68-74Crossref PubMed Scopus (28) Google Scholar Hypercapnia has not been shown to influence IONM.18Seyal M. Mull B. Mechanisms of signal change during intraoperative somatosensory evoked potential monitoring of the spinal cord.J Clin Neurophysiol. 2002; 19: 409-415Crossref PubMed Scopus (69) Google Scholar Hypoxaemia, even before spinal-cord ischaemia, will compromise the IONM signal.18Seyal M. Mull B. Mechanisms of signal change during intraoperative somatosensory evoked potential monitoring of the spinal cord.J Clin Neurophysiol. 2002; 19: 409-415Crossref PubMed Scopus (69) Google Scholar To optimise IONM, the anaesthetist must ensure adequate arterial-oxygen-carrying capacity whilst targeting normocapnic ventilation. The most commonly used volatile anaesthetic agents produce dose-related decreases in the amplitude of MEPs. Therefore, TIVA techniques with propofol and opioid infusions are popular. Similarly, the neuromuscular block abolishes the MEP signal and is usually avoided when monitoring is in use. Regardless of the anaesthetic technique, a collaborative approach between anaesthetist and neurophysiologist is vital. Any changes in the choice or dosing of medications that can influence IONM should be communicated with the monitoring team so they can understand their impact on the signals. In the following sections, we provide a summary of the paediatric evidence for how commonly used perioperative medications impact IONM. We have limited our review to methods that have been studied in paediatric patients. The online Supplementary data reviews the use of lidocaine, magnesium and gabapentinoids, whose impact on IONM has not been studied in children, and makes an effort to infer an approach to their use in children based on the adult literature. One study compared 30 paediatric idiopathic spine corrective surgeries. Anaesthesia was maintained with either propofol or midazolam. There were no differences in SEPs between groups.19Laureau E. Marciniak B. Hebrard A. Herbaux B. Guieu J.D. Comparative study of propofol and midazolam effects on somatosensory evoked potentials during surgical treatment of scoliosis.Neurosurgery. 1999; 45: 69-75Crossref PubMed Scopus (31) Google Scholar Benzodiazepines are generally compatible with IONM modalities. Ketamine is often used as an adjunct to prevent postoperative pain, an important consideration in patients with scoliosis. Ketamine will increase SEP and MEP amplitudes, and has been useful in cases that would otherwise be unsuitable for monitoring because of low-amplitude, poorly defined MEP responses.20Frei F.J. Ryhult S.E. Duitmann E. Hasler C.C. Luetschg J. Erb T.O. Intraoperative monitoring of motor-evoked potentials in children undergoing spinal surgery.Spine. 2007; 32: 911-917Crossref PubMed Scopus (52) Google Scholar One observational case series describes the impact of ketamine on MEP monitoring during paediatric spine surgery. Frei and colleagues report 134 consecutive MEP monitoring sessions in 108 children.20Frei F.J. Ryhult S.E. Duitmann E. Hasler C.C. Luetschg J. Erb T.O. Intraoperative monitoring of motor-evoked potentials in children undergoing spinal surgery.Spine. 2007; 32: 911-917Crossref PubMed Scopus (52) Google Scholar Based on their institutional experience, balanced anaesthesia with propofol had occasionally resulted in a gradual decline in MEP signal, more often in younger patients. Their practice pattern included an intraoperative switch to ketamine at an initial dose of 2–3 mg kg−1 followed by a continuous infusion of 4 mg kg−1 h−1 to ameliorate the propofol-related attenuation in signal. In their series, they describe the details for 13 patients requiring intraoperative switch from propofol to ketamine. In all but one scenario, MEPs returned. In the case where the MEPs failed to return, there was persistent motor deficit after surgery. They advocate a propofol-free ketamine-based anaesthetic approach for children. Notably, the changes in MEPs seen with propofol infusion in this study could potentially have been resolved by reducing the propofol infusion rates in order to prevent accumulation. It is important to note that ketamine does not have a reliable effect on EEG or BIS, and makes DOA based on these methods more difficult to interpret. Dexmedetomidine, an α2 adrenergic agonist, is increasingly used as an adjunct to TIVA in procedures requiring IONM. A prospective clinical trial examining MEPs in 40 children that targeted various blood concentrations of dexmedetomidine and propofol using a factorial design demonstrated that the addition of dexmedetomidine caused a significant attenuation in amplitudes of MEP.21Mahmoud M. Sadhasivam S. Salisbury S. et al.Susceptibility of transcranial electric motor-evoked potentials to varying targeted blood levels of dexmedetomidine during spine surgery.Anesthesiology. 2010; 112: 1364-1373Crossref PubMed Scopus (76) Google Scholar Recent unpublished data obtained from our institution show that infusion rates of 3 μg kg−1 h−1 caused significant reductions in MEPs in 14 of 28 patients undergoing spinal deformity correction for adolescent idiopathic scoliosis, with complete loss of signal in three cases. Clonidine administration has similarly been shown to depress MEPs significantly, but not SEPs.22Calderon P. Deltenre P. Stany I. et al.Clonidine administration during intraoperative monitoring for pediatric scoliosis surgery: effects on central and peripheral motor responses.Neurophysiol Clin. 2018; 48: 93-102Crossref PubMed Scopus (7) Google Scholar Accordingly, α2 adrenergic agonists should be used with caution whenever motor pathways are being monitored. Two clinical studies have examined how intrathecal (IT) opioids influence IONM in paediatric scoliosis correction. In one study, 10 patients aged 15–18 yrs received sufentanil 50 μg with morphine 20 μg kg−1 intrathecally after induction of anaesthesia.23Goodarzi M. Shier N.H. Grogan D.P. Effect of intrathecal opioids on somatosensory-evoked potentials during spinal fusion in children.Spine. 1996; 21: 1565-1568Crossref PubMed Scopus (16) Google Scholar None of these patients had significant changes in SEP compared with their baseline measurements. Another study examining MEPs showed no significant difference in amplitudes and latencies compared to age-matched controls up to 30 min after injection of morphine 3–16 μg kg−1 IT at the end of the operation.24Stricker P.A. Sestokas A.K. Schwartz D. et al.Effects of intrathecal morphine on transcranial electric motor-evoked potentials in adolescents undergoing posterior spinal fusion.Anesth Analg. 2012; 115: 160-169Crossref PubMed Scopus (4) Google Scholar Thus far, the available clinical data suggest that any negative impact of IT opioids is marginal. IONM is an important component of intraoperative management in paediatric spinal surgery. Nevertheless, anaesthetic and analgesic agents can impact on IONM signals, and must be selected in collaboration with the intraoperative neurophysiologist. As reviewed in the accompanying clinical scenario, any intraoperative IONM alert should prompt the surgeon to assess for possible mechanical injury and the anaesthetist to optimise MAP as first-line therapy. Effective communication between the anaesthetist, neurophysiologist, surgeons, and nursing staff is fundamental to the effective use of IONM and providing safe and optimal anaesthetic care to children undergoing spinal surgery.

Patients with pulmonary arterial hypertension (Group 1 pulmonary hypertension, including idiopathic, heritable, connective tissue disease–associated, congenital heart disease–associated pulmonary arterial hypertension, and others) present for noncardiac surgery with an exceptionally high risk of morbidity and mortality even when compared to patients with other forms of pulmonary hypertension.1 Current pulmonary arterial hypertension–specific therapies are primarily pulmonary vasodilators. Yet pulmonary vasoconstriction only partially explains disease pathology, and the development of better therapies necessitates a deeper understanding of pulmonary arterial hypertension pathogenesis. Indeed, evidence links the immune system to pulmonary arterial hypertension pathogenesis (see fig.) and has fundamentally shifted our understanding of the disease mechanism.2In pulmonary arterial hypertension lungs, endothelial apoptosis and the subsequent proliferation of an abnormal, reprogrammed subset of endothelial cells form a neointimal layer (fig. element 1). Smooth muscle cells hypertrophy and proliferate, leading to medial thickening and loss of vascular compliance (fig. element 2). Together, these phenomena narrow the vessel lumen, impeding blood flow. In the adventitia, lymphocytes, macrophages, dendritic cells, and mast cells form tertiary lymphoid tissue, which produces cytokines, autoantibodies, and other soluble mediators (fig. element 3). Release of these mediators from immune cells and activated fibroblasts further recruits immune cells (fig. element 4). These changes perpetuate vascular damage and drive pulmonary arterial hypertension. Protective elements of the immune system, however, including regulatory T cells,3 help dampen this response.Anesthesiologists will welcome agents for perioperative optimization of these high-risk patients.Support was provided from institutional and/or departmental sources, as well as a grant from the International Anesthesia Research Society, San Francisco, California, to Dr. Goldenberg.The authors declare no competing interests.

Patients with pulmonary arterial hypertension have exceptionally high perioperative risk. This review summarizes the clinical presentation and therapies for pulmonary arterial hypertension, and it highlights evidence for inflammation as a driver of disease pathogenesis and a therapeutic target.

Although widely studied as a neurotransmitter, T cell-derived acetylcholine (ACh) has recently been reported to play an important role in regulating immunity. However, the role of lymphocyte-derived ACh in viral infection is unknown. Here, we show that the enzyme choline acetyltransferase (ChAT), which catalyzes the rate-limiting step of ACh production, is robustly induced in both CD4+ and CD8+ T cells during lymphocytic choriomeningitis virus (LCMV) infection in an IL-21-dependent manner. Deletion of Chat within the T cell compartment in mice ablated vasodilation in response to infection, impaired the migration of antiviral T cells into infected tissues, and ultimately compromised the control of chronic LCMV clone 13 infection. Our results reveal a genetic proof of function for ChAT in T cells during viral infection and identify a pathway of T cell migration that sustains antiviral immunity.

Mammalian blood vessels are innervated by adrenergic neurons that increase blood pressure. The neurotransmitter mechanism is dependent upon norepinephrine that mediates contraction of vascular smooth cells to increase arterial resistance. Vasodilation is mediated by acetylcholine, which lowers blood pressure through a mechanism dependent upon relaxation of vascular smooth muscle cells in response to endothelial release of nitric oxide. Endothelial cells are not innervated by cholinergic neurons, and it was unknown whether acetylcholine release by lymphocytes might modulate blood pressure. Here, we observed lymphocytes expressing choline acetyltransferase (ChAT), the enzyme that catalyzes biosynthesis of acetylcholine, in the blood. Co-culture of ChAThi lymphocytes with endothelial cells significantly increased calcium concentration and phosphorylation of eNOS in endothelial cells (p<0.05 vs. ChATlow lymphocytes). Passive transfer of engineered ChAThi Jurkat T cells resulted in an immediate significant decrease in blood pressure in recipient mice to 83±5 % of baseline, while blood pressure after transfer of ChATlow Jurkat T was 104±4 % of baseline (p=0.02). Pre-treatment with the NO synthesis inhibitor L-NG-monomethyl arginine citrate prevented the blood pressure reduction by ChAThi Jurkat T cells, and blood pressure remained at 98%±5% of baseline in these animals (p=0.21). These findings suggest a novel mechanism of lymphocyte-mediated blood pressure regulation.