Optimal bispectral index exists in healthy patients undergoing general anesthesia: A validation study.

PURPOSE: Continuous cerebrovascular reactivity monitoring in both neurocritical and intra-operative care has gained extensive interest in recent years, as it has documented associations with long-term outcomes (in neurocritical care populations) and cognitive outcomes (in operative cohorts). This has sparked further interest into the exploration and evaluation of methods to achieve an optimal cerebrovascular reactivity measure, where the individual patient is exposed to the lowest insult burden of impaired cerebrovascular reactivity. Recent literature has documented, in neural injury populations, the presence of a potential optimal sedation level in neurocritical care, based on the relationship between cerebrovascular reactivity and quantitative depth of sedation (using bispectral index (BIS)) - termed BISopt. The presence of this measure outside of neural injury patients has yet to be proven. METHODS: We explore the relationship between BIS and continuous cerebrovascular reactivity in two cohorts: (A) healthy population undergoing elective spinal surgery under general anesthesia, and (B) healthy volunteer cohort of awake controls. RESULTS: We demonstrate the presence of BISopt in the general anesthesia population (96% of patients), and its absence in awake controls, providing preliminary validation of its existence outside of neural injury populations. Furthermore, we found BIS to be sufficiently separate from overall systemic blood pressure, this indicates that they impact different pathophysiological phenomena to mediate cerebrovascular reactivity. CONCLUSIONS: Findings here carry implications for the adaptation of the individualized physiologic BISopt concept to non-neural injury populations, both within critical care and the operative theater. However, this work is currently exploratory, and future work is required.

Patient Selection Criteria in Ambulatory Spine Surgery: Single Canadian Provincial Experience.

BACKGROUND: Ambulatory spinal surgery is a care delivery model meant to improve patient outcomes and reduce in-hospital length of stay (LOS). We reviewed the experience of implementing an outpatient spine surgery program in Manitoba, Canada and highlight elements that can be used to reduce LOS and re-presentation to hospital. METHODS: This is a retrospective cohort study using data from the Canadian Spine Outcomes and Research Network and independent chart review of adult patients undergoing outpatient spinal surgery between 2015 and 2018. Patient demographics, comorbidities, perioperative course, LOS, and readmissions were analyzed. RESULTS: We included 217 patients in this analysis. The mean LOS was 36.2 hours; 71.98% of patients had a LOS <24 hours. A Kruskal-Wallis test by ranks analysis was conducted and identified 7 elements that correlated with prolonged length of stay (>1 day): age older than 55 (P = 0.027), body mass index >25 (P = 0.045), uncontrolled diabetes (P = 0.015), preoperative use of opioid medication (P = 0.024), American Society of Anesthesiologists classification of 3 (P = 0.023), non-minimally invasive surgical approach, and multilevel procedures. Most (94.1%) of the patients with none of these elements (i.e., age <55, low body mass index, normal/controlled diabetes, minimal preoperative opioid use, American Society of Anesthesiologist classification <3, minimally invasive surgical procedure) had a favorable LOS, <24 hours, compared with 84.8% with 1 risk factor, 80.4% of those with two, 69.8% with three, 53.1% with four, and 31.2% with 5 or more. A small number of patients (14.98%) presented to an emergency department within 90 days of their operation, and there was a 6.28% readmission rate. CONCLUSIONS: We identified several patient and surgical criteria that correlate with prolonged length of stays following planned ambulatory spine surgery. Our work provides some empiric evidence to help guide surgeons on which patients and approaches are ideal for ambulatory surgery.

Case report: Continuous spinal cord physiologic monitoring following traumatic spinal cord injury-A report from the Winnipeg Intraspinal Pressure Study (WISP).

Introduction: Acute traumatic spinal cord injury is routinely managed by surgical decompression and instrumentation of the spine. Guidelines also suggest elevating mean arterial pressure to 85 mmHg to mitigate secondary injury. However, the evidence for these recommendations remains very limited. There is now considerable interest in measuring spinal cord perfusion pressure by monitoring mean arterial pressure and intraspinal pressure. Here, we present our first institutional experience of using a strain gauge pressure transducer monitor to measure intraspinal pressure and subsequent derivation of spinal cord perfusion pressure. Case presentation: The patient presented to medical attention after a fall off of scaffolding. A trauma assessment was completed at a local emergency room. He did not have any motor strength or sensation to the lower extremities. A computed tomography (CT) scan of the thoracolumbar spine confirmed a T12 burst fracture with retropulsion of bone fragments into the spinal canal. He was taken to surgery for urgent decompression of the spinal cord and instrumentation of the spine. A subdural strain gauge pressure monitor was placed at the site of injury through a small dural incision. Mean arterial pressure and intraspinal pressure were then monitored for 5 days after surgery. Spinal cord perfusion pressure was derived. The procedure was performed without complication and the patient underwent rehabilitation for 3 months where he regained some motor and sensory function in his lower extremities. Conclusion: The first North American attempt at insertion of a strain gauge pressure monitor into the subdural space at the site of injury following acute traumatic spinal cord injury was performed successfully and without complication. Spinal cord perfusion pressure was derived successfully using this physiological monitoring. Further research efforts to validate this technique are required.

The Winnipeg Intraspinal Pressure Monitoring Study (WISP): A protocol for validation of fiberoptic pressure monitoring for acute traumatic spinal cord injury.

BACKGROUND: Research efforts have been focused on limiting secondary injury after traumatic spinal cord injury by performing spinal decompression and early optimization of spinal cord perfusion. The Winnipeg Intraspinal Pressure Monitoring Study (WISP) was designed to validate the technique of intraspinal pressure monitoring at the site of injury using a fiberoptic pressure monitor placed at the site of injury. OBJECTIVES: To describe the design of the WISP study. STUDY DESIGN: Descriptive. METHODS: We explain the current limitations in the available scientific literature around the topic of blood pressure management for acute traumatic spinal cord injury and rational for the WISP study. Then, we describe the design of WISP including the patient selection criteria, study interventions, follow up schedules and outcome measurements. A multitude of future research avenues are also discussed. RESULTS: The WISP study is a single center pilot study designed to validate the technique of intraspinal pressure monitoring following acute traumatic spinal cord injury. The study involves the measurement of intraspinal pressure from within the subarachnoid space at the site of injury to derive a number of physiological parameters including spinal cord perfusion pressure, spinal cord blood volume, measures of spinal cord compliance and vascular reactivity indices. Twenty eligible patients will be recruited and followed for a period of 12 months with visits scheduled for the first 5 days and 1, 3, 6, and 12 months following surgical intervention. CONCLUSIONS: The WISP study will provide the first attempt in North America at validation of intraspinal pressure monitoring with a fiberoptic pressure monitor at the site of injury. Successful validation will lead to future studies to define optimal spinal cord perfusion pressure, relationships of neural injury biomarkers and outcomes as well as epigenetic studies. TRIAL REGISTRATION: This study has been registered at clinicaltrials.gov (registration# NCT04550117).

Hypertonic Saline for Moderate Traumatic Brain Injury: A Scoping Review of Impact on Neurological Deterioration.

Hypertonic saline (HTS) is a commonly administered agent for intracranial pressure (ICP) control in traumatic brain injury (TBI). The literature on its use is mainly in moderate/severe TBI where invasive ICP monitoring is present. The role of HTS in patients with moderate TBI (mTBI) outside of the intensive care unit (ICU) setting remains unclear. The goal of this scoping review was to provide an overview of the available literature on HTS administration in patients with mTBI without ICP monitoring, assessing its impact on outcome and transitions in care. We performed a scoping systematic review of the literature of MEDLINE, Embase, Scopus, BIOSIS, and the Cochrane Databases from inception to July 31, 2020. We searched for those published articles documenting the administration of HTS in patients with mTBI with recorded functional outcome or transitions in hospital care. A two-step review process was conducted in accordance with methodology outlined in the Cochrane Handbook for Systematic Reviews of Interventions. There were many studies with combined moderate/severe TBI populations. However, most failed to document subgroup analysis for patients with mTBI. Our search strategy identified only one study that documented the administration of HTS in mTBI in which subgroup analysis for mTBI and outcomes were provided. This retrospective cohort study assessed patients with mTBI who did/did not receive prophylactic HTS, finding that those not receiving HTS demonstrated a deterioration in Glasgow Coma Scale (GCS) score in the first 48 h. However, the HTS group did demonstrate a trend to longer hospital stay and pneumonia. Our scoping review identified a significant gap in knowledge surrounding the use of HTS for patients with mTBI without invasive ICP monitoring. The limited identified literature suggests prophylactic administration prevents clinical deterioration, although this is based on a single study with data available for mTBI sub-analysis. Further studies on HTS in non-monitored patients with mTBI are required.

Intrathecal Morphine Following Lumbar Fusion: A Randomized, Placebo-Controlled Trial.

BACKGROUND: Despite the potential for faster postoperative recovery and the ease of direct intraoperative injection, intrathecal morphine is rarely provided in lumbar spine surgery. OBJECTIVE: To evaluate the safety and efficacy of intrathecal morphine following lumbar fusion. METHODS: We randomly assigned 150 patients undergoing elective instrumented lumbar fusion to receive a single intrathecal injection of morphine (0.2 mg) or placebo (normal saline) immediately prior to wound closure. The primary outcome was pain on the visual-analogue scale during the first 24 h after surgery. Secondary outcomes included respiratory depression, treatment-related side effects, postoperative opioid requirements, and length of hospital stay. An intention-to-treat, repeated-measures analysis was used to estimate outcomes according to treatment in the primary analysis. RESULTS: The baseline characteristics of the 2 groups were similar. Intrathecal morphine reduced pain both at rest (32% area under the curves [AUCs] difference, P < .01) and with movement (22% AUCs difference, P < .02) during the initial 24 h after surgery. The risk of respiratory depression was not increased by intrathecal morphine (hazard ratio, 0.86; 95% confidence interval, 0.44 to 1.68; P = .66). Although postoperative opioid requirements were reduced with intrathecal morphine (P < .03), lengths of hospital stay were similar (P = .32). Other than a trend towards increased intermittent catheterization among patients assigned to intrathecal morphine (P = .09), treatment-related side effects did not significantly differ. The early benefits of intrathecal morphine on postoperative pain were no longer apparent after 48 h. CONCLUSION: A single intrathecal injection of 0.2 mg of morphine safely reduces postoperative pain following lumbar fusion.

Central nervous system blastomycosis diagnosed using the MVista® Blastomyces quantitative antigen enzyme immunoassay test on cerebrospinal fluid: A case report and review of the literature.

Blastomyces dermatitidis is a thermally dimorphic fungus that is capable of causing pulmonary and extra-pulmonary disease, including infections of the central nervous system (CNS). Diagnosis of CNS blastomycosis with non-invasive testing can be difficult, and a surgical biopsy may ultimately be required for microbiological and/or histopathological confirmation. A case of B. dermatitidis meningitis is presented where the diagnosis was made by testing cerebrospinal fluid (CSF) using the MVista® Blastomyces Quantitative Antigen Enzyme Immunoassay test. The utility of performing this test on CSF for diagnosis of CNS mass lesions/abscesses caused by B. dermatitidis in the absence of associated meningitis remains unclear. Cross reaction of the Blastomyces antigen test with other dimorphic fungi is a concern, necessitating that positive test results are interpreted in the context of the patient's exposure and travel history.

Oblique Intrathecal Injection in Lumbar Spine Surgery: A Technical Note.

OBJECTIVES: Intrathecal morphine (ITM) is an efficacious method of providing postoperative analgesia and reducing pain associated complications. Despite adoption in many surgical fields, ITM has yet to become a standard of care in lumbar spine surgery. Spine surgeons' reticence to make use of the technique may in part be attributed to concerns of precipitating a cerebrospinal fluid (CSF) leak. METHODS: Herein we describe a method for oblique intrathecal injection during lumbar spine surgery to minimize risk of CSF leak. The dural sac is penetrated obliquely at a 30° angle to offset dural and arachnoid puncture sites. Oblique injection in instances of limited dural exposure is made possible by introducing a 60° bend to a standard 30-gauge needle. RESULTS: The technique was applied for injection of ITM or placebo in 104 cases of lumbar surgery in the setting of a randomized controlled trial. Injection was not performed in two cases (2/104, 1.9%) following preinjection dural tear. In the remaining 102 cases no instances of postoperative CSF leakage attributable to oblique intrathecal injection occurred. Three cases (3/102, 2.9%) of transient CSF leakage were observed immediately following intrathecal injection with no associated sequelae or requirement for postsurgical intervention. In two cases, the observed leak was repaired by sealing with fibrin glue, whereas in a single case the leak was self-limited requiring no intervention. CONCLUSIONS: Oblique dural puncture was not associated with increased incidence of postoperative CSF leakage. This safe and reliable method of delivery of ITM should therefore be routinely considered in lumbar spine surgery.

Intraoperative magnetic resonance imaging and neuronavigation for transoral approaches to upper cervical pathology.

BACKGROUND: The transoral transpharyngeal surgical approach is a recognized technique for management of ventral lesions at the clivus and upper cervical spine. This report examines the use of neuronavigation and intraoperative magnetic resonance imaging as surgical adjuncts for lesions in this region. METHODS: A retrospective review of patients undergoing transoral transpharyngeal surgery in the intraoperative magnetic resonance imaging (iMRI) unit from 1997 to present was performed. Preoperative demographic data, clinical history, physical examination, and imaging studies were reviewed. Data were collected on surgical approach, pathology, postoperative management, and adverse events. RESULTS: Twenty patients underwent resection of ventral lesions at the craniovertebral junction through a transoral approach in the iMRI suite. Mean age at time of surgery was 50 years. A variety of pathologies were identified including neoplasms (n=7), congenital anomalies (n=7), and degenerative disease (n=6). Intraoperative imaging and neuronavigation allowed for tailoring of the surgical approach in each of our patients: 11 patients underwent transoral surgery without a palatal split or mandibulotomy; 9 patients underwent a palatal split and of these, 5 required a mandibulotomy. Interdissection images allowed for immediate confirmation of gross total resection in all cases. Postoperatively, patients were managed in the intensive care unit for an average of 7 days. Ninety-two percent of patients had neurological improvement at a mean of 1.8 years of follow-up (range 0.4-6 years). Two patients died from tumor progression and one died from renal failure. CONCLUSIONS: Intraoperative MRI and neuronavigation are valuable adjuncts that allow selective surgical exposure and confirmation of surgical objectives within the narrow surgical corridor provided by a transoral approach to the craniovertebral junction.

Rapid magnetic resonance imaging-guided reduction of craniovertebral junction deformities.

The authors demonstrate the utility of an MR imaging-compatible traction board for the rapid reduction of craniovertebral junction (CVJ) deformities. To choose the appropriate surgical management, patients with compressive CVJ deformities often undergo a trial of traction. Conventional traction trials require the treating surgeon to infer from plain radiographs the manner in which traction forces affect neural and ligamentous structures at the CVJ. To avoid overdistraction injury, low increments of weight are added in a gradual fashion, a process that typically requires 48-72 hours. The authors outline the use of an MR imaging-compatible traction board to determine reducibility safely and rapidly in 4 patients with compressive CVJ deformities. Four patients with advanced CVJ deformities underwent a trial of MR imaging-guided traction performed using an MR imaging-compatible spine board. Serial sagittal images were acquired at baseline and following each sequential addition of force. All patients tolerated traction without neurological worsening. The neural elements were seen to be adequately decompressed in all cases during a single MR imaging session. Patients subsequently underwent craniocervical stabilization and fusion. Postoperative imaging showed maintenance of the reduction without neural compression. An MR imaging-guided trial of traction can facilitate the rapid and safe determination of the reducibility of compressive lesions in patients with advanced CVJ deformities. Rapidly acquired sagittal MR images permit the surgeon to evaluate the effects of traction on the soft tissues at the CVJ, thereby expediting the traction trial and avoiding the risks of immobility in this often-fragile patient population.

The pore, not cytoplasmic domains, underlies inactivation in a prokaryotic sodium channel.

Kinetics and voltage dependence of inactivation of a prokaryotic voltage-gated sodium channel (NaChBac) were investigated in an effort to understand its molecular mechanism. NaChBac inactivation kinetics show strong, bell-shaped voltage dependence with characteristic time constants ranging from approximately 50 ms at depolarized voltages to a maximum of approximately 100 s at the inactivation midpoint. Activation and inactivation parameters for four different covalently linked tandem dimer or tandem tetramer constructs were indistinguishable from those of the wild-type channel. Point mutations in the outer part of the pore revealed an important influence of the S195 residue on the process of inactivation. For two mutants (S195D and S195E), the maximal and minimal rates of inactivation observed were increased by approximately 2.5-fold, and the midpoint of the steady-state inactivation curve was shifted approximately 20 mV in the hyperpolarizing direction, compared to the wild-type channel. Our data suggest that pore vestibule structure is an important determinant of NaChBac inactivation, whereas the inactivation mechanism is independent of the number of free cytoplasmic N- and C-termini in the functional channel. In these respects, NaChBac inactivation resembles C-type or slow inactivation modes observed in other voltage-gated K and Na channels.