Relationship between duration of spinal cord ischemia and postoperative neurologic deficits in animals. Stagnara wake-up tests, blood flow measures, somatosensory evoked potentials (SEPs), and neurogenic-motor evoked potentials (NMEPs) were elicited from 20 hogs before and after spinal cord overdistraction at L3-L4. Overdistraction was maintained from 5 to 30 minutes after loss of NMEPs. Results suggest that the longer the duration of overdistraction the greater the likelihood of paraplegia. Blood flow measures indicated that reduced perfusion was greatest at the distraction site but extended proximally and distally. Finally, NMEPs were more sensitive to onset of overdistraction and a more valid indicator of paraplegia than SEPs. NMEPs should provide the surgeon with more time for initiation of intervention techniques than SEPs. Because NMEPs and SEPs provide information regarding different spinal cord tracts, the authors continue to use both methods for monitoring the functional integrity of the human spinal cord during corrective spine surgery. 