Hepatic Vein Flow Index During Orthotopic Liver Transplantation as a Predictive Factor for Postoperative Early Allograft Dysfunction.

OBJECTIVES: The authors devised a hepatic vein flow index (HVFi), using intraoperative transesophageal echocardiography and graft weight, and investigated its predictive value for postoperative graft function in orthotopic liver transplant. DESIGN: Prospective clinical trial. SETTING,: Single-center tertiary academic hospital. PARTICIPANTS: Ninety-seven patients who had orthotopic liver transplant with the piggy-back technique between February 2018 and December 2019. MEASUREMENTS AND MAIN RESULTS: HVFi was defined with HV flow/graft weight. Patients who developed early graft dysfunction (EAD) had low HVFi in systole (HVFi sys, 1.23 v 2.19 L/min/kg, p < 0.01), low HVFi in diastole (HVFi dia, 0.87 v 1.54 L/min/kg, p < 0.01), low hepatic vein flow (HVF) in systole (HVF sys, 2.04 v 3.95 L/min, p < 0.01), and low HVF in diastole (HVF dia, 1.44 v 2.63 L/min, p < 0.01). More cardiac death, more vasopressors at the time of measurement, more acute rejection, longer time to normalize total bilirubin (TIME t-bil), longer surgery time, longer neohepatic time, and more packed red blood cell transfusion were observed in the EAD patients. All HVF parameters were negatively correlated with TIME t-bil (HVFi sys R = -0.406, p < 0.01; HFVi dia R = -0.442, p < 0.01; HVF sys R = -0.44, p < 0.01; HVF dia R = -0.467, p < 0.01). The receiver operating characteristic curve analysis determined the best cut-off levels of HVFi to predict occurrence of EAD (HVFi sys <1.608, HVFi dia <0.784 L/min/kg), acute rejection (HVFi sys <1.388, HVFi dia <1.077 L/min/kg), and prolonged high total bilirubin (HVFi sys <1.471, HVFi dia <1.087 L/min/kg). CONCLUSIONS: The authors' devised HVFi has the potential to predict the postoperative graft function.

The Recognition, Incidence, and Management of Spinal Cord Monitoring Alerts in Pediatric Cervical Spine Surgery.

BACKGROUND: Perioperative spinal cord injury and postoperative neurological deficits are the major complications in spinal surgery. Monitoring of spinal cord function is of crucial importance. Somatosensory evoked potentials and transcranial electric motor-evoked potentials are now widely used in cervical spine surgery. Although much has been written on spinal cord monitoring in adult spinal surgery, very little has been published on the incidence and management of monitoring of cervical spine surgery in the pediatric population. The goal of this research was to review the recognition, incidence, and management of spinal cord monitoring in pediatric patients undergoing cervical spine surgery over the course of twenty years in a single institution. We postulate spinal cord monitoring alerts in pediatric cervical spine surgery are underreported. METHODS: An IRB-approved retrospective single institution review of pediatric cervical spine cases from 1997 to 2017 was performed. Both the surgeon's dictated operative note and the neuromonitoring team's dictated note were reviewed for each case, and both were cross referenced and correlated with one another to ensure no alerts were missed. All monitoring changes were assumed to be significant and reported. The incidence of alerts, type of changes, and corrective maneuvers were noted. New postoperative neurological injuries were recorded. RESULTS: From 1997 to 2017 fifty-three patients underwent a total of 69 procedures involving the cervical spine. Fourteen procedures (20%) were not monitored, whereas 55 procedures were 80%. There were 12 procedures (21.8%) complicated by neuromonitoring alerts. CONCLUSIONS: The number of cases complicated by alerts doubles that previously reported, and it is important to note there were no new permanent neurological deficits recorded over the study period. Corrective strategies were implemented once the operating surgeon was notified of the neuromonitoring alert. Aborting the case was then considered if corrective strategies failed to restore baseline neurophysiology. LEVEL OF EVIDENCE: Level IV.

The Recognition, Incidence, and Management of Spinal Cord Monitoring Alerts in Early-onset Scoliosis Surgery.

BACKGROUND: The objective of the research was to study the relevance of intraoperative neuromonitoring throughout all stages of surgical management in patients with progressive early-onset scoliosis (EOS).The routine monitoring of spinal cord potentials has gradually become standard of practice among spinal surgeons. However, there is not a consensus that the added expense of this technique necessitates monitoring in all stages of surgical management. METHODS: A retrospective review of 180 surgical cases of 30 patients with EOS from July 2003 to July 2012 was performed. All monitoring alerts as judged by the neuromonitoring team were identified. Both somatosensory-evoked potentials and transcranial electric motor-evoked potentials were studied and no limiting thresholds for reporting electrophysiological changes were deemed appropriate. RESULTS: Of 150 monitored cases there were 18 (12%) monitoring alerts. This represented 40% of the patient cohort over the 9-year study period. CONCLUSIONS: Index versus routine lengthening rate of alerts showed no significant difference in incidence of monitoring alerts. Conversely, several patients whose primary implantation surgeries were uneventful had monitoring alerts later in their treatment course. Intraoperative neuromonitoring is warranted throughout all stages of surgical management of EOS. LEVEL OF EVIDENCE: Level IV. This study is a retrospective review of surgical cases of 30 patients with EOS.

Current trends in pedicle screw stimulation techniques: lumbosacral, thoracic, and cervical levels.

Unequivocally, pedicle screw instrumentation has evolved as a primary construct for the treatment of both common and complex spinal disorders. However an inevitable and potentially major complication associated with this type of surgery is misplacement of a pedicle screw(s) which may result in neural and vascular complications, as well as impair the biomechanical stability of the spinal instrumentation resulting in loss of fixation. In light of these potential surgical complications, critical reviews of outcome data for treatment of chronic, low-back pain using pedicle screw instrumentation concluded that "pedicle screw fixation improves radiographically demonstrated fusion rates;" however the expense and complication rates for such constructs are considerable in light of the clinical benefit (Resnick et al. 2005a). Currently, neuromonitoring using free-run and evoked (triggered) electromyography (EMG) is widely used and advocated for safer and more accurate placement of pedicle screws during open instrumentation procedures, and more recently, guiding percutaneous placement (minimally invasive) where the pedicle cannot be easily inspected visually. The latter technique, evoked or triggered EMG when applied to pedicle screw instrumentation surgeries, has been referred to as the pedicle screw stimulation technique. As concluded in the Position Statement by the American Society of Neurophysiological Monitoring (ASNM), multimodality neuromonitoring using free-run EMG and the pedicle screw stimulation technique was considered a practice option and not yet a standard of care (Leppanen 2005). Subsequently, the American Association of Neurological Surgeons/Congress of Neurological Surgeons (AANS/CNS) Joint Section on Disorders of the Spine and Peripheral Nerves published their "Guidelines for the Performance of Fusion Procedures for Degenerative Disease of the Lumbar Spine" (Heary 2005, Resnick et al. 2005a, Resnick et al. 2005b). It was concluded that the "primary justification" of intraoperative neuromonitoring"... is the perception that the safety and efficacy of pedicle screw fixation are enhanced..." (Resnick et al. 2005b). However in summarizing a massive (over 1000 papers taken from the National Library of Medicine), contemporary, literature review spanning nearly a decade (1996 to 2003), this invited panel (Resnick et al. 2005b) recognized that the evidence-based documents contributing to the parts related to pedicle screw fixation and neuromonitoring were "... full of potential sources of error ..." and lacked appropriate, randomized, prospective studies for formulating rigid standards and guidelines. Nevertheless, current trends support the routine use and clinical utility of these neuromonitoring techniques. In particular free-run and triggered EMG have been well recognized in numerous publications for improving both the accuracy and safety of pedicle screw implantation. Currently, treatment with pedicle screw instrumentation routinely involves all levels of the spine - lumbosacral, thoracic, and cervical. Significant historical events, various neuromonitoring modalities, intraoperative alarm criteria, clinical efficacy, current trends, and caveats related to pedicle screw stimulation along the entire vertebral column will be reviewed.

American Society of Neurophysiologic Monitoring and American Society of Neuroimaging joint guidelines for transcranial doppler ultrasonic monitoring.

The American Society of Neurophysiologic Monitoring (ASNM) and American Society of Neuroimaging (ASN) Guidelines Committees formed a joint task force and developed guidelines to assist in the use of transcranial Doppler (TCD) monitoring in the surgical and intensive care settings. Specifically, these guidelines: (1) delineate the objectives of TCD monitoring; (2) characterize the responsibilities and behaviors of the sonographer during monitoring; (3) describe methodological and ethical issues uniquely relevant to monitoring. The ASNM and ASN strongly support the positions that (1) acquisition and interpretation of intraoperative TCD ultrasonograms be performed by qualified individuals, (2) service providers define their diagnostic criteria and develop on-going self-validation programs of these performance criteria in their practices. We agree with the guidelines of other professional societies regarding the technical and professional qualifications of individuals responsible for TCD signal acquisition and interpretation (Class III evidence, Type C recommendation). On the basis of current clinical literature and scientific evidence, TCD monitoring is an established monitoring modality for the: (1) assessment of cerebral vasomotor reactivity and autoregulation; (2) documentation of the circle of Willis functional status; (3) identification of cerebral hypo- and hyperperfusion, recanalization and re-occlusion; and (4) detection of cerebral emboli (Class II and III evidence, Type B recommendation).

Guidelines for intraoperative neuromonitoring using raw (analog or digital waveforms) and quantitative electroencephalography: a position statement by the American Society of Neurophysiological Monitoring.

BACKGROUND CONTEXT: Electroencephalography (EEG) is one of the oldest and most commonly utilized modalities for intraoperative neuromonitoring. Historically, interest in the EEG patterns associated with anesthesia is as old as the discovery of the EEG itself. The evolution of its intraoperative use was also expanded to include monitoring for assessing cortical perfusion and oxygenation during a variety of vascular, cardiac, and neurosurgical procedures. Furthermore, a number of quantitative or computer-processed algorithms have also been developed to aid in its visual representation and interpretation. The primary clinical outcomes for which modern EEG technology has made significant intraoperative contributions include: (1) recognizing and/or preventing perioperative ischemic insults, and (2) monitoring of brain function for anesthetic drug administration in order to determine depth of anesthesia (and level of consciousness), including the tailoring of drug levels to achieve a predefined neural effect (e.g., burst suppression). While the accelerated development of microprocessor technologies has fostered an extraordinarily rapid growth in the use of intraoperative EEG, there is still no universal adoption of a monitoring technique(s) or of criteria for its neural end-point(s) by anesthesiologists, surgeons, neurologists, and neurophysiologists. One of the most important limitations to routine intraoperative use of EEG may be the lack of standardization of methods, alarm criteria, and recommendations related to its application. Lastly, refinements in technology and signal processing can be expected to advance the usefulness of the intraoperative EEG for both anesthetic and surgical management of patients. OBJECTIVE: This paper is the position statement of the American Society of Neurophysiological Monitoring. It is the practice guidelines for the intraoperative use of raw (analog and digital) and quantitative EEG. METHODS: The following recommendations are based on trends in the current scientific and clinical literature and meetings, guidelines published by other organizations, expert opinion, and public review by the members of the American Society of Neurophysiological Monitoring. This document may not include all possible methodologies and interpretative criteria, nor do the authors and their sponsor intentionally exclude any new alternatives. RESULTS: The use of the techniques reviewed in these guidelines may reduce perioperative neurological morbidity and mortality. CONCLUSIONS: This position paper summarizes commonly used protocols for recording and interpreting the intraoperative use of EEG. Furthermore, the American Society of Neurophysiological Monitoring recognizes this as primarily an educational service.

Electrical artifact during intraoperative electromyographic neuromonitoring.

Acoustic electromyography is a commonly employed neuromonitoring modality for protecting cranial and peripheral nerves for a variety of neck, cranial, and spinal surgeries. An artifact resembling an electromyographic (EMG) response caused by contact between two metal instruments within the surgical field may contaminate the interpretation of mechanically-elicited activity that occurs from neural irritation during surgery. This artifact has been casually referred to as the "crossed swords" effect and has not been adequately described. A series of manipulations were devised to determine if this artifact: 1) required an electrolytic medium for its occurrence, 2) could be produced between a metal and nonmetal object, 3) could be detected in a control channel outside the surgical site, 4) could be detected in background waveforms using parameters for averaging a somatosensory evoked potential (SSEP), and lastly 5) could be quantified electrically. The metal-to-metal artifact could be produced when instruments made contact in a fluid medium. In contrast, metal-to-nonmetal contact did not produce the artifact in or outside a fluid medium. This artifact was not detected on a control channel from surface electrodes over the deltoid muscle. When tapped or rubbed, the artifact sounded like an EMG response, but the morphology was unique. Only when the two metals were rubbed together were the morphologies and acoustic "signatures" similar to an EMG response. Metal-to-metal contact in a fluid medium did not produce an artifact that could be detected in the background activity recorded using parameters for SSEPs. The electrical potential discharge was approximately 100 mV after the instruments stayed in solution and made contact after 150 seconds. This artifact is likely attributable to current discharge when two metals contact each other, a phenomenon referred to as a galvanic couple.

Cerebral oximetry does not correlate with electroencephalography and somatosensory evoked potentials in determining the need for shunting during carotid endarterectomy.

OBJECTIVE: Several reports in the literature have described the value of regional cerebral oximetry (rSO(2)) as a neuromonitoring device during carotid endarterectomy (CEA). The use of rSO(2) is enticing because it is simpler and less expensive than other neuromonitoring modalities. This study was performed to compare the efficacy of rSO(2) with electroencephalography (EEG) and median nerve somatosensory evoked potentials (SSEP) in determining when to place a shunt during CEA. METHODS: From October 2000 to June 2006, 323 CEAs were performed under general anesthesia by six surgeons. Shunting was done selectively on the basis of EEG and SSEP monitoring under the auspices of an intraoperative neurophysiologist. All patients were retrospectively reviewed to see if significant discrepancies existed between EEG/SSEP and rSO(2). RESULTS: Twenty-four patients (7.4%) showed significant discrepancies. Sixteen patients showed no significant EEG/SSEP changes, but profound changes occurred in rSO(2), and no shunt was placed. In seven patients there was no change in rSO(2) but a profound change occurred in EEG/SSEP, and shunts were placed. In one patient early in the series, the EEG and SSEP were unchanged but the rSO(2) dropped precipitously, and a shunt was placed. In the 299 patients who showed no discrepancies, 285 were not shunted and 14 required a shunt. Two strokes occurred in the entire series (0.6%), none intraoperatively. Shunts were placed in 23 patients (7%). The sensitivity of rSO(2) compared with EEG/SSEP was 68%, and the specificity was 94%. This gave a positive-predictive value of 47% and a negative-predictive value of 98%. CONCLUSIONS: Relying on rSO(2) alone for selective shunting is potentially dangerous and might have led to intraoperative ischemic strokes in seven patients and the unnecessary use of shunts in at least 16 patients in this series. The use of rSO(2) adds nothing to the information already provided by EEG and SSEP in determining when to place a shunt during CEA.

Intraoperative neuromonitoring detects thrombotic occlusion of the left common iliac arterial bifurcation after anterior lumbar interbody fusion: case report.

Prompt recognition of acute or delayed vascular insults during anterior spinal reconstructive surgery of the lower lumbar levels is paramount for successful intervention and prevention of sequelae. Although surgical exposure of the lower lumbar levels requires mindful dissection and cautious retraction of abdominal vessels, ischemic insult due to partial or complete occlusion of the iliac arteries may go undetected without adequate surgical monitoring. We present a case of progressive thrombotic occlusion of the left common iliac artery detected by intraoperative spinal cord monitoring using somatosenory evoked potentials (SSEPs) at the peripheral and central levels. Surgical monitoring using palpation of vessels and pulse oximetry of the great toe were initially proposed as simple and relatively inexpensive modalities for routine surgical monitoring. Subsequently, monitoring cortical SSEPs were combined with great toe pulse oximetry to advance continuous routine surgical monitoring. However, using only cortical SSEPs predisposes such protocols to an inherently higher risk of false positives. Neuromonitoring protocols should rely heavily on the replication of waveforms recorded at multiple sites along the neural pathway.

Intraoperative monitoring of the recurrent laryngeal nerve using acoustic, free-run, and evoked electromyography.

The purpose of this study was to explore advantages and disadvantages of electrodes used for monitoring of the recurrent laryngeal nerve (RLN) and to determine the postoperative outcome in 135 patients. A pilot study examined 11 patients to compare the clinical performance of two commercially available recording electrodes and three stimulation electrodes for RLN neuromonitoring. After determining the most reliable and consistent stimulating/recording electrode combination, 124 patients were then monitored. In a total of 135 patients there was no permanent iatrogenic nerve damage to the RLN, although 2 patients developed transient vocal hoarseness that resolved shortly postoperatively. An initial "searching" current for evoked electromyography (EMG) was delivered at 0.7 mA and then decreased to a value of 0.35 mA, which reliably elicited RLN stimulation with a minimal incidence of false-positive results. The combination of auditory feedback from the mechanically elicited EMG and a control channel involving EMG monitoring of an additional peripheral muscle improved the detection of artifact and improved the clinical efficacy of intraoperative electromyography. A video camera showed the surgical manipulation on the EMG screen, allowing the neurophysiologist to correlate dissection with RLN status and location. Auditory responses from the nerve helped to determine the type of distress the RLN was encountering.

The Reliability of Computer-Processed EEG in the Determination of ECT Seizure Duration.

The reliability of single-channel analog EEG and two-channel, computer-processed EEG (cEEG) in determining seizure duration during electroconvulsive therapy (ECT) was studied in 144 consecutive individual treatment sessions of 14 hospitalized patients. Seizure durations determined by post hoc, blind readings of data generated by each method were compared. These estimates of seizure duration were also compared to those determined by the "cuff" method. We found that under our study conditions, the cEEG method was more reliable than the EEG method in two tests of reliability: the cEEG method had fewer readings with a discrepancy of 10 s or more between readers, and had a higher degree of correlation between readers. There was no difference, however, between the cEEG and EEG methods when comparing mean differences and the mean absolute difference between readers within the methods. We also found that the EEG and cEEG methods detected seizure durations that were substantially longer than those detected by the "cuff" method. We conclude that under our study conditions, cEEG was more reliable than analog EEG in certain measures of reliability.