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Changes of mean arterial pressure affect spinal cord oxygenation as monitored by an implantable near-infrared spectroscopy sensor in an animal model of acute spinal cord injury (Conference Presentation)

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.