Introduction: Current clinical guidelines recommend augmenting the mean arterial pressure (MAP) in acute spinal cord injury (SCI) patients to increase perfusion and oxygen delivery to the spinal cord, and potentially improve neurologic function. However, it is difficult for clinicians to hemodynamically manage acute SCI patients without real-time physiologic information about the effect of MAP augmentation within the injured cord. In this study, we investigated the utilization of a customized optical sensor, based on near-infrared spectroscopy (NIRS), to non-invasively monitor spinal cord oxygenation during the first week post-injury in a porcine model. Methods: Six Yucatan mini-pigs received a weight-drop T10 contusion-compression injury. A multi-wavelength NIRS system with a custom-made miniaturized sensor was placed directly onto the dura. The spinal cord tissue oxygenation index (TOI) and concentrations of oxygenated, deoxygenated, and total hemoglobin were monitored before and after SCI. To validate the NIRS measures, invasive intraparenchymal (IP) combined PO2/blood flow sensors were inserted into the spinal cord adjacent to the NIRS sensor. Episodes of MAP alteration and hypoxia were performed acutely after injury, 2 days post-injury, and 7 days post-injury to simulate the types of hemodynamic changes SCI patients experience post-injury. Results: Non-invasive NIRS monitoring identified changes in spinal cord oxygenation levels during the MAP alterations. Changes of TOI followed similar patterns of IP-derived oxygenation changes. Conclusion: Our novel NIRS sensor is feasible as a non-invasive technique to monitor real-time changes in spinal cord oxygenation 7 days post-injury in a porcine model of SCI.
Introduction: Current clinical practice guidelines for acute spinal cord injury (SCI) patients suggest that increasing the mean arterial pressure (MAP) to 85-90 mmHg may improve spinal cord (SC) hemodynamics and oxygenation. The purpose of this study was to examine this effect using an implantable Near Infra-Red Spectroscopy (NIRS) sensor.
Methods: Nine anesthetized Yorkshire pigs were studied. A multi-wavelength NIRS system with a custom-made miniaturized optical sensor was applied directly onto the SC dura at T9 to measure tissue oxygenation and hemodynamics within the SC non-invasively. To validate the NIRS measures, an invasive Intraparenchymal (IP) combined O2/blood flow sensor was inserted directly into the SC adjacent to the NIRS probe at T11. Using NIRS, the SC tissue oxygenation percentage (TOI%), as well as concentrations of oxygenated, deoxygenated and total hemoglobin, were monitored before, during and after episodes of MAP alterations. Using norepinephrine and nitroprusside, MAP was increased and decreased by 20mmHg for 30 min periods, simulating the types of hemodynamic changes that SCI patients experience post-injury.
Results: Changes in SC hemodynamics and oxygenation levels were detected in all subjects as measured by both the invasive IP and the non-invasive NIRS sensors. Changes of TOI% during MAP increase (1.64%, p<0.005) and decrease (-3.97%, p<0.005) were significant. A consistent decrease in TOI (-15.94%, p<0.005) was observed following SCI, indicating SC tissue hypoxia at the injury site.
Conclusions: Using a miniaturized SC NIRS sensor we have shown the significant effect of MAP alterations on tissue oxygenation within the injured SC.
Introduction: Sudden physical trauma to the spinal cord results in acute spinal cord injury (SCI), leading to spinal cord (SC) tissue destruction, acute inflammation, increased SC intraparenchymal pressure, and tissue ischemia, hypoxia, and cellular necrosis. The ability to monitor SC tissue viability at subcellular level, using a real-time noninvasive method, would be extremely valuable to clinicians for estimating acute SCI damage, and adjusting and monitoring treatment in the intensive care setting. This study examined the feasibility and sensitivity of a custommade near infrared spectroscopy (NIRS) sensor to monitor the oxidation state of SC mitochondrial cytochrome aa3 (CCO), which reflects the subcellular damage of SC tissue in an animal model of SCI.
Methods: Six anesthetized Yorkshire pigs were studied using a custom-made multi-wavelength NIRS system with a miniaturized optical sensor applied directly on the surgically exposed SC at T9. The oxidation states of SC tissue hemoglobin and CCO were monitored before, during and after acute SCI, and during mean arterial pressure alterations.
Results: Non-invasive NIRS monitoring reflected changes in SC tissue CCO, simultaneous but independent of changes in hemoglobin saturation following acute SCI. A consistent decrease in SC tissue CCO chromophore concentration (-1.98 ± 2.1 ab, p<0.05) was observed following SCI, indicating progressive SC cellular damage at the injury site. Elevation of mean arterial pressure can reduce SC tissue damage as suggested by different researchers and observed by significant increase in SC tissue CCO concentration (1.51 ± 1.7 ab, p<0.05) in this study.
Conclusions: This pilot study indicates that a novel miniaturized multi-wave NIRS sensor has the potential to monitor post-SCI changes of SC cytochrome aa3 oxygenation state in real time. Further development of this method may offer new options for improved SCI care.
Background: After an acute traumatic spinal cord injury (SCI), the spinal cord is subjected to ischemia, hypoxia, and increased hydrostatic pressure which exacerbate further secondary damage and neuronal deficit. The purpose of this pilot study was to explore the use of near infrared spectroscopy (NIRS) for non-invasive and real-time monitoring of these changes within the injured spinal cord in an animal model. NIRS is a non-invasive optical technique that utilizes light in the near infrared spectrum to monitor changes in the concentration of tissue chromophores from which alterations in tissues oxygenation and perfusion can be inferred in real time. Methods: A custom-made miniaturized NIRS sensor was developed to monitor spinal cord hemodynamics and oxygenation noninvasively and in real time simultaneously with invasive, intraparenchymal monitoring in a pig model of SCI. The spinal cord around the T10 injury site was instrumented with intraparenchymal probes inserted directly into the spinal cord to measure oxygen pressure, blood flow, and hydrostatic pressure, and the same region of the spinal cord was monitored with the custom-designed extradural NIRS probe. We investigated how well the extradural NIRS probe detected intraparenchymal changes adjacent to the injury site after alterations in systemic blood pressure, global hypoxia, and traumatic injury generated by a weight-drop contusion. Results: The NIRS sensor successfully identified periods of systemic hypoxia, re-ventilation and changes in spinal cord perfusion and oxygenation during alterations of mean arterial pressure and following spinal cord injury. Conclusion: This pilot study indicates that extradural NIRS monitoring of the spinal cord is feasible as a non-invasive optical method to identify changes in spinal cord hemodynamics and oxygenation in real time. Further development of this technique would allow clinicians to monitor real-time physiologic changes within the injured spinal cord during the acute post-injury period.
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