Spinal cord blood flow and ischemic injury after experimental sacrifice of thoracic and abdominal segmental arteries

Objective: Spinal cord blood flow (SCBF) after sacrifice of thoracoabdominal aortic segmental arteries (TAASA) during thoracoabdominal aortic aneurysm (TAAA) repair remains poorly understood. This study explored SCBF for 72 h after sacrifice of all TAASA. Methods: Fourteen juvenile Yorkshire pigs underwent complete serial TAASA sacrifice (T4-L5). Six control pigs underwent anesthesia and cooling to 32 °C with no TAASA sacrifice. In the experimental animals, spinal cord function was continuously monitored using motor evoked potentials (MEPs) until 1 h after clamping the last TAASA. Fluorescent microspheres enabled segmental measurement of SCBF along the entire spinal cord before, and 5 min, 1 h, 5 h, 24 h and 72 h after complete TAASA sacrifice. A modified Tarlov score was obtained for 3 days after surgery. Results: All the pigs with complete TAASA sacrifice retained normal cord function (MEP) until 1 h after TAASA ligation. Seven pigs (50%) with complete TAASA sacrifice recovered after 72 h; seven pigs suffered paraparesis or paraplegia. Intraoperatively, and until 1 h postoperatively, SCBF was similar among the three groups along the entire cord. Postoperatively, SCBF did not decrease in any group, but significant hyperemia occurred at 5 h in controls and recovery animals, but did not occur in pigs that developed paraparesis or paraplegia in the T8-L2 segments (p = 0.0002) and L3-S segments (p = 0.0007). At 24 h, SCBF remained marginally lower from T8 caudally; at 72 h, SCBF was similar among all groups along the entire cord. SCBF in the segments T8-L2 at 5 h predicted functional recovery (p = 0.003). Conclusions: This study suggests that critical spinal cord ischemia after complete TAASA sacrifice does not occur immediately (intraoperatively), but is delayed 1-5 h or longer after clamping, and represents failure to mount a hyperemic response to rewarming and awakening. The short duration of low SCBF associated with spinal cord injury suggests that hemodynamic and metabolic manipulation lasting only 24-72 h may allow routine preservation of normal cord function despite sacrifice of all TAASA secondary to surgical or endovascular repair of large TAAA.