Continuous Monitoring of Cerebrospinal Fluid Oxygen Tension in Relation to Motor Evoked Potentials during Spinal Cord Ischemia in Pigs

Background Perioperative assessment of spinal cord oxygenation might guide measures to prevent neurologic deficits secondary to ischemic or traumatic damage of the spinal cord. Although cerebrospinal fluid (CSF) partial pressure of oxygen (Po2) measurement has been used to detect spinal cord ischemia (SCI), the diagnostic value and the temporal resolution of CSF Po2 measurement compared with functional assessment of the spinal cord is unknown. This study compared CSF Po2 with transcranial motor evoked potentials (tcMEPs) for detection of experimental SCI. Methods The aorta and segmental arteries were exposed in 10 sufentanil-ketamine-anesthetized pigs (weight, 40-50 kg). Myogenic tcMEPs were recorded from the upper and lower limbs, and continuous assessment of CSF Po2 was provided by two Clark-type microcatheters inserted in the lumbar and thoracic intrathecal space. Graded lumbar SCI was produced by sequential clamping of segmental arteries. The relation between CSF Po2 and tcMEP during graded SCI was determined using linear regression. Diagnostic characteristics of CSF Po2 values for clinical SCI were determined using different cutoff points of CSF Po2. Results Lumbar CSF Po2 (baseline, 44 [interquartile range, 38-54] mmHg) decreased below 50% in all animals and was linearly related to loss of tcMEP amplitude in all animals. The median lumbar CSF Po2 during reduction of tcMEP to less than 25% of baseline was 11 (4-29) mmHg, whereas thoracic CSF Po2 remained constant (40 [28-50] mmHg). During absence of the tcMEP signal, lumbar CSF Po2 was less than 20 mmHg in 80% of the animals. Optimal sensitivity and predictive values of CSF Po2 measurement for SCI were in the range of 40-60% of baseline. Conclusions The data indicate that intrathecal Po2 measurement is a sensitive monitoring technique to track real-time changes in local spinal cord oxygenation. Continuous monitoring of CSF Po2 might be applied for evaluation of patients who are at risk for direct or secondary SCI.