Continuous Optical Monitoring of Spinal Cord Oxygenation and Hemodynamics during the First Seven Days Post-Injury in a Porcine Model of Acute Spinal Cord Injury

Spinal cord lesion MRI and behavioral outcomes in a miniature pig model of spinal cord injury: exploring preclinical potential through an ad hoc comparison with human SCI

STUDY DESIGN

prospective case series of Yucatan miniature pig spinal cord contusion injury model with comparison to human cases of spinal cord injury (SCI).

OBJECTIVES

to describe magnetic resonance imaging (MRI) measures of spinal cord lesion severity along with estimates of lateral corticospinal tracts spared neural tissue in both a less severe and more severe contusion SCI model, as well as to describe their corresponding behavioral outcome changes.

SETTING

University laboratory setting.

METHODS

Following a more severe and less severe SCI, each pig underwent spinal cord MRI to measure lesion characteristics, along with locomotor and urodynamics outcomes testing.

RESULTS

In the pig with more severe SCI, locomotor and urodynamic outcomes were poor, and both the spinal cord lesion volume and damage estimates to the lateral corticospinal tracts were large. Conversely, in the pig with less severe SCI, locomotor and urodynamic outcomes were favorable, with the spinal cord lesion volume and damage estimates to the lateral corticospinal tracts being less pronounced. For two human cases matched on estimates of damage to the lateral corticospinal tract regions, the clinical presentations were similar to the pig outcomes, with more limited mobility and more limited bladder functional independence in the more severe case.

CONCLUSIONS

Our initial findings contribute valuable insights to the emergent field of MRI-based evaluation of spinal cord lesions in pig models, offering a promising avenue for understanding and potentially improving outcomes in spinal cord injuries.

A Clinical Practice Guideline for the Management of Patients With Acute Spinal Cord Injury: Recommendations on Hemodynamic Management

STUDY DESIGN

Clinical practice guideline development following the GRADE process.

OBJECTIVES

Hemodynamic management is one of the only available treatment options that likely improves neurologic outcomes in patients with acute traumatic spinal cord injury (SCI). Augmenting mean arterial pressure (MAP) aims to improve blood perfusion and oxygen delivery to the injured spinal cord in order to minimize secondary ischemic damage to neural tissue. The objective of this guideline was to update the 2013 AANS/CNS recommendations on the hemodynamic management of patients with acute traumatic SCI, acknowledging that much has been published in this area since its publication. Specifically, we sought to make recommendations on 1. The range of mean arterial pressure (MAP) to be maintained by identifying an upper and lower MAP limit; 2. The duration of such MAP augmentation; and 3. The choice of vasopressor. Additionally, we sought to make a recommendation on spinal cord perfusion pressure (SCPP) targets.

METHODS

A multidisciplinary guideline development group (GDG) was formed that included health care professionals from a wide range of clinical specialities, patient advocates, and individuals living with SCI. The GDG reviewed the 2013 AANS/CNS guidelines and voted on whether each recommendation should be endorsed or updated. A systematic review of the literature, following PRISMA standards and registered in PROSPERO, was conducted to inform the guideline development process and address the following key questions: (i) what are the effects of goal-directed interventions to optimize spinal cord perfusion on extent of neurological recovery and rates of adverse events at any time point of follow-up? and (ii) what are the effects of particular monitoring techniques, perfusion ranges, pharmacological agents, and durations of treatment on extent of neurological recovery and rates of adverse events at any time point of follow-up? The GDG combined the information from this systematic review with their clinical expertise in order to develop recommendations on a MAP target range (specifically an upper and lower limit to target), the optimal duration for MAP augmentation, and the use of vasopressors or inotropes. Using methods outlined by the GRADE working group, recommendations were formulated that considered the balance of benefits and harms, financial impact, acceptability, feasibility and patient preferences.

RESULTS

The GDG suggested that MAP should be augmented to at least 75-80 mmHg as the "lower limit," but not actively augmented beyond an "upper limit" of 90-95 mmHg in order to optimize spinal cord perfusion in acute traumatic SCI. The quality of the evidence around the "target MAP" was very low, and thus the strength of this recommendation is weak. For duration of hemodynamic management, the GDG "suggested" that MAP be augmented for a duration of 3-7 days. Again, the quality of the evidence around the duration of MAP support was very low, and thus the strength of this recommendation is also weak. The GDG felt that a recommendation on the choice of vasopressor or the use of SCPP targets was not warranted, given the dearth of available evidence.

CONCLUSION

We provide new recommendations for blood pressure management after acute SCI that acknowledge the limitations of the current evidence on the relationship between MAP and neurologic recovery. It was felt that the low quality of existing evidence and uncertainty around the relationship between MAP and neurologic recovery justified a greater range of MAP to target, and for a broader range of days post-injury than recommended in previous guidelines. While important knowledge gaps still remain regarding hemodynamic management, these recommendations represent current perspectives on the role of MAP augmentation for acute SCI.

The 2023 AO Spine-Praxis Guidelines in Acute Spinal Cord Injury: What Have We Learned? What Are the Critical Knowledge Gaps and Barriers to Implementation?

STUDY DESIGN

Narrative summary of the 2023 AO Spine-Praxis clinical practice guidelines for management in acute spinal cord injury (SCI).

OBJECTIVES

The objective of this article is to summarize the key findings of the clinical practice guidelines for the optimal management of traumatic and intraoperative SCI (ISCI). This article will also highlight potential knowledge translation opportunities for each recommendation and discuss important knowledge gaps and areas of future research.

METHODS

Systematic reviews were conducted according to accepted methodological standards to evaluate the current body of evidence and inform the guideline development process. The summarized evidence was reviewed by a multidisciplinary guidelines development group that consisted of international multidisciplinary stakeholders. The Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) approach was used to rate the certainty of the evidence for each critical outcome and the "evidence to recommendation" framework was used to formulate the final recommendations.

RESULTS

The key recommendations regarding the timing of surgical decompression, hemodynamic management, and the prevention, diagnosis, and management of ISCI are summarized. While a strong recommendation was made for early surgery, further prospective research is required to define what constitutes sufficient surgical decompression, examine the role of ultra-early surgery, and assess the impact of early surgery in different SCI phenotypes, including central cord syndrome. Furthermore, additional investigation is required to evaluate the impact of mean arterial blood pressure targets on neurological recovery and to determine the utility of spinal cord perfusion pressure measurements. Finally, there is a need to examine the role of neuroprotective agents for the treatment of ISCI and to prospectively validate the new AO Spine-Praxis care pathway for the prevention, diagnosis, and management of ISCI. To optimize the translation of these guidelines into practice, important barriers to their implementation, particularly in underserved areas, need to be explored. Ultimately, these recommendations will help to establish more personalized approaches to care for SCI patients.

CONCLUSIONS

The recommendations from the 2023 AO Spine-Praxis guidelines not only highlight the current best practice in the management of SCI, but reveal critical knowledge gaps and barriers to implementation that will help to guide further research efforts in SCI.

Non-contrast ultrasound image analysis for spatial and temporal distribution of blood flow after spinal cord injury

Ultrasound technology can provide high-resolution imaging of blood flow following spinal cord injury (SCI). Blood flow imaging may improve critical care management of SCI, yet its duration is limited clinically by the amount of contrast agent injection required for high-resolution, continuous monitoring. In this study, we aim to establish non-contrast ultrasound as a clinically translatable imaging technique for spinal cord blood flow via comparison to contrast-based methods and by measuring the spatial distribution of blood flow after SCI. A rodent model of contusion SCI at the T12 spinal level was carried out using three different impact forces. We compared images of spinal cord blood flow taken using both non-contrast and contrast-enhanced ultrasound. Subsequently, we processed the images as a function of distance from injury, yielding the distribution of blood flow through space after SCI, and found the following. (1) Both non-contrast and contrast-enhanced imaging methods resulted in similar blood flow distributions (Spearman's ρ = 0.55, p < 0.0001). (2) We found an area of decreased flow at the injury epicenter, or umbra (p < 0.0001). Unexpectedly, we found increased flow at the periphery, or penumbra (rostral, p < 0.05; caudal, p < 0.01), following SCI. However, distal flow remained unchanged, in what is presumably unaffected tissue. (3) Finally, tracking blood flow in the injury zones over time revealed interesting dynamic changes. After an initial decrease, blood flow in the penumbra increased during the first 10 min after injury, while blood flow in the umbra and distal tissue remained constant over time. These results demonstrate the viability of non-contrast ultrasound as a clinical monitoring tool. Furthermore, our surprising observations of increased flow in the injury periphery pose interesting new questions about how the spinal cord vasculature reacts to SCI, with potentially increased significance of the penumbra.

Adverse Effect of Neurogenic, Infective, and Inflammatory Fever on Acutely Injured Human Spinal Cord

This study aims to determine the effect of neurogenic, inflammatory, and infective fevers on acutely injured human spinal cord. In 86 patients with acute, severe traumatic spinal cord injuries (TSCIs; American Spinal Injury Association Impairment Scale (AIS), grades A-C) we monitored (starting within 72 h of injury, for up to 1 week) axillary temperature as well as injury site cord pressure, microdialysis (MD), and oxygen. High fever (temperature ≥38°C) was classified as neurogenic, infective, or inflammatory. The effect of these three fever types on injury-site physiology, metabolism, and inflammation was studied by analyzing 2864 h of intraspinal pressure (ISP), 1887 h of MD, and 840 h of tissue oxygen data. High fever occurred in 76.7% of the patients. The data show that temperature was higher in neurogenic than non-neurogenic fever. Neurogenic fever only occurred with injuries rostral to vertebral level T4. Compared with normothermia, fever was associated with reduced tissue glucose (all fevers), increased tissue lactate to pyruvate ratio (all fevers), reduced tissue oxygen (neurogenic + infective fevers), and elevated levels of pro-inflammatory cytokines/chemokines (infective fever). Spinal cord metabolic derangement preceded the onset of infective but not neurogenic or inflammatory fever. By considering five clinical characteristics (level of injury, axillary temperature, leukocyte count, C-reactive protein [CRP], and serum procalcitonin [PCT]), it was possible to confidently distinguish neurogenic from non-neurogenic high fever in 59.3% of cases. We conclude that neurogenic, infective, and inflammatory fevers occur commonly after acute, severe TSCI and are detrimental to the injured spinal cord with infective fever being the most injurious. Further studies are required to determine whether treating fever improves outcome. Accurately diagnosing neurogenic fever, as described, may reduce unnecessary septic screens and overuse of antibiotics in these patients.

Evaluation of transcutaneous near-infrared spectroscopy for early detection of cardiac arrest in an animal model

Sudden cardiac arrest (SCA) is a leading cause of mortality worldwide. The SCA-to-resuscitation interval is a key determinant of patient outcomes, highlighting the clinical need for reliable and timely detection of SCA. Near-infrared spectroscopy (NIRS), a non-invasive optical technique, may have utility for this application. We investigated transcutaneous NIRS as a method to detect pentobarbital-induced changes during cardiac arrest in eight Yucatan miniature pigs. NIRS measurements during cardiac arrest were compared to invasively acquired carotid blood pressure and partial oxygen pressure (PO₂) of spinal cord tissues. We observed statistically significant decreases in mean arterial pressure (MAP) 64.68 mmHg ± 13.08, p < 0.0001), spinal cord PO₂ (38.16 mmHg ± 20.04, p = 0.0028), and NIRS-derived tissue oxygen saturation (TSI%) (14.50% ± 3.80, p < 0.0001) from baseline to 5 min after pentobarbital administration. Euthanasia-to-first change in hemodynamics for MAP and TSI (%) were similar [MAP (10.43 ± 4.73 s) vs TSI (%) (12.04 ± 1.85 s), p = 0.3714]. No significant difference was detected between NIRS and blood pressure-derived pulse rates during baseline periods (p > 0.99) and following pentobarbital administration (p = 0.97). Transcutaneous NIRS demonstrated the potential to identify rapid hemodynamic changes due to cardiac arrest in periods similar to invasive indices. We conclude that transcutaneous NIRS monitoring may present a novel, non-invasive approach for SCA detection, which warrants further investigation.

Porcine spinal cord injury model for translational research across multiple functional systems

Animal models are necessary to identify pathological changes and help assess therapeutic outcomes following spinal cord injury (SCI). Small animal models offer value in research in terms of their easily managed size, minimal maintenance requirements, lower cost, well-characterized genomes, and ability to power research studies. However, despite these benefits, small animal models have neurologic and anatomical differences that may influence translation of results to humans and thus limiting the success of their use in preclinical studies as a direct pipeline to clinical studies. Large animal models, offer an attractive intermediary translation model that may be more successful in translating to the clinic for SCI research. This is largely due to their greater neurologic and anatomical similarities to humans. The physical characteristics of pig spinal cord, gut microbiome, metabolism, proportions of white to grey matter, bowel anatomy and function, and urinary system are strikingly similar and provide great insight into human SCI conditions. In this review, we address the variety of existing porcine injury models and their translational relevance, benefits, and drawbacks in modeling human systems and functions for neurophysiology, cardiovascular, gastrointestinal and urodynamic functions.

Sensor technology usage in orthopedic trauma

Medicine in general is quickly transitioning to a digital presence. Orthopaedic surgery is also being impacted by the tenets of digital health but there are also direct efforts with trauma surgery. Sensors are the pen and paper of the next wave of data acquisition. Orthopaedic trauma can and will be part of this new wave of medicine. Early sensor products that are now coming to market, or are in early development, will directly change the way we think about surgical diagnosis and outcomes. Sensor development for biometrics is already here. Wellness devices, pressure, temperature, and other parameters are already being measured. Data acquisition and analysis is going to be a fruitful addition to our research armamentarium with the volume of information now available. A combination of broadband internet, micro electrical machine systems (MEMS), and new wireless communication standards is driving this new wave of medicine. The Internet of Things (IoT) [1] now has a subset which is the Internet of Medical Devices [2-5] permitting a much more in-depth dive into patient procedures and outcomes. IoT devices are now being used to enable remote health monitoring, in hospital treatment, and guide therapies. This article reviews current sensor technology that looks to impact trauma care.

Porcine Model of Spinal Cord Injury: A Systematic Review

Spinal cord injury (SCI) is a devastating disease with limited effective treatment options. Animal paradigms are vital for understanding the pathogenesis of SCI and testing potential therapeutics. The porcine model of SCI is increasingly favored because of its greater similarity to humans. However, its adoption is limited by the complexities of care and range of testing parameters. Researchers need to consider swine selection, injury method, post-operative care, rehabilitation, behavioral outcomes, and histology metrics. Therefore, we systematically reviewed full-text English-language articles to evaluate study characteristics used in developing a porcine model and summarize the interventions that have been tested using this paradigm. A total of 63 studies were included, with 33 examining SCI pathogenesis and 30 testing interventions. Studies had an average sample size of 15 pigs with an average weight of 26 kg, and most used female swine with injury to the thoracic cord. Injury was most commonly induced by weight drop with compression. The porcine model is amenable to testing various interventions, including mean arterial pressure augmentation (n = 7), electrical stimulation (n = 6), stem cell therapy (n = 5), hypothermia (n = 2), biomaterials (n = 2), gene therapy (n = 2), steroids (n = 1), and nanoparticles (n = 1). It is also notable for its clinical translatability and is emerging as a valuable pre-clinical study tool. This systematic review can serve as a guideline for researchers implementing and testing the porcine SCI model.

Detection of hypoxia by near-infrared spectroscopy and pulse oximetry: a comparative study

SIGNIFICANCE

Pulse oximetry is widely used in clinical practice to monitor changes in arterial oxygen saturation (SpO2). However, decreases in SpO2 can be delayed relative to the actual clinical event, and near-infrared spectroscopy (NIRS) may detect alterations in oxygenation earlier than pulse oximetry, as shown in previous cerebral oxygenation monitoring studies.

AIM

We aim to compare the response of transcutaneous muscle NIRS measures of the tissue saturation index with pulse oximetry SpO2 during hypoxia.

APPROACH

Episodes of acute hypoxia were induced in nine anesthetized Yucatan miniature pigs. A standard pulse oximeter was attached to the ear of the animal, and a transcutaneous NIRS sensor was placed on the hind limb muscle. Hypoxia was induced by detaching the ventilator from the animal and reattaching it once the pulse oximeter reported 70% SpO2.

RESULTS

Twenty-four episodes of acute hypoxia were analyzed. Upon the start of hypoxia, the transcutaneous NIRS measures changed in 5.3 ± 0.4 s, whereas the pulse oximetry measures changed in 14.9 ± 1.0 s (p < 0.0001).

CONCLUSIONS

Transcutaneous muscle NIRS can detect the effects of hypoxia significantly sooner than pulse oximetry in the Yucatan miniature pig. A transcutaneous NIRS sensor may be used as an earlier detector of oxygen saturation changes in the clinical setting than the standard pulse oximeter.

Intraoperative Optical Monitoring of Spinal Cord Hemodynamics Using Multiwavelength Imaging System

The spinal cord is a major structure of the central nervous system allowing, among other things, the transmission of afferent sensory and efferent motor information. During spinal surgery, such as scoliosis correction, this structure can be damaged, resulting in major neurological damage to the patient. To date, there is no direct way to monitor the oxygenation of the spinal cord intraoperatively to reflect its vitality. This is essential information that would allow surgeons to adapt their procedure in case of ischemic suffering of the spinal cord. We report the development of a specific device to monitor the functional status of biological tissues with high resolution. The device, operating with multiple wavelengths, uses Near-InfraRed Spectroscopy (NIRS) in combination with other additional sensors, including ElectroNeuroGraphy (ENG). In this paper, we focused primarily on aspects of the PhotoPlethysmoGram (PPG), emanating from four different light sources to show in real time and record biological signals from the spinal cord in transmission and reflection modes. This multispectral system was successfully tested in in vivo experiments on the spinal cord of a pig for specific medical applications.

Characterization of the gut microbiome in a porcine model of thoracic spinal cord injury

BACKGROUND

The gut microbiome is a diverse network of bacteria which inhabit our digestive tract and is crucial for efficient cellular metabolism, nutrient absorption, and immune system development. Spinal cord injury (SCI) disrupts autonomic function below the level of injury and can alter the composition of the gut microbiome. Studies in rodent models have shown that SCI-induced bacterial imbalances in the gut can exacerbate the spinal cord damage and impair recovery. In this study we, for the first time, characterized the composition of the gut microbiome in a Yucatan minipig SCI model. We compared the relative abundance of the most dominant bacterial phyla in control samples to those collected from animals who underwent a contusion-compression SCI at the 2nd or 10th Thoracic level.

RESULTS

We identify specific bacterial fluctuations that are unique to SCI animals, which were not found in uninjured animals given the same dietary regimen or antibiotic administration. Further, we identified a specific time-frame, "SCI-acute stage", during which many of these bacterial fluctuations occur before returning to "baseline" levels.

CONCLUSION

This work presents a dynamic view of the microbiome changes that accompany SCI, establishes a resource for future studies and to understand the changes that occur to gut microbiota after spinal cord injury and may point to a potential therapeutic target for future treatment.

Duraplasty in Traumatic Thoracic Spinal Cord Injury: Impact on Spinal Cord Hemodynamics, Tissue Metabolism, Histology, and Behavioral Recovery Using a Porcine Model

After acute traumatic spinal cord injury (SCI), the spinal cord can swell to fill the subarachnoid space and become compressed by the surrounding dura. In a porcine model of SCI, we performed a duraplasty to expand the subarachnoid space around the injured spinal cord and evaluated how this influenced acute intraparenchymal hemodynamic and metabolic responses, in addition to histological and behavioral recovery. Female Yucatan pigs underwent a T10 SCI, with or without duraplasty. Using microsensors implanted into the spinal cord parenchyma, changes in blood flow (ΔSCBF), oxygenation (ΔPO₂), and spinal cord pressure (ΔSCP) during and after SCI were monitored, alongside metabolic responses. Behavioral recovery was tested weekly using the Porcine Injury Behavior Scale (PTIBS). Thereafter, spinal cords were harvested for tissue sparing analyses. In both duraplasty and non-animals, the ΔSCP increased ∼5 mm Hg in the first 6 h post-injury. After this, the SCP appeared to be slightly reduced in the duraplasty animals, although the group differences were not statistically significant after controlling for injury severity in terms of impact force. During the first seven days post-SCI, the ΔSCBF or ΔPO₂ values were not different between the duraplasty and control animals. Over 12 weeks, there was no improvement in hindlimb locomotion as assessed by PTIBS scores and no reduction in tissue damage at the injury site in the duraplasty animals. In our porcine model of SCI, duraplasty did not provide any clear evidence of long-term behavioral or tissue sparing benefit after SCI.