Introduction
Antegrade selective cerebral perfusion (ASCP) has a widespread use today for cerebral protection during aortic arch surgery with increasing incorporation of moderate hypothermia (28°C) during lower body circulatory arrest (LBCA). Although a considerable amount of contribution has been made literally addressing the favorable effects of this technique questions remain regarding the protection of distal abdominal viscera and neuronal structures-namely the spinal cord- during lower body circulatory arrest with moderate hypothermia. The nervous tissue is very sensitive to ischemia and ensuing spinal cord complications can be devastating with a wide spectrum ranging from clinically undetected sensory loss to permanent paraplegia. Animal models of arch surgery at moderate hypothermia revealed insufficient spinal cord blood flow below thoracic 8 and 9 segment to sustain its viability with ASCP only 1. If distal perfusion is not included during arch surgery, concerns about the margins of the safe period for spinal cord ischemia during distal circulatory arrest exist.
Considering that a real time information system may help raise awareness of the team about ischemic insult of the spinal cord during thoracoabdominal interventions where there is a considerably high risk of paraplegia, pioneering experimental works with near infrared spectrometry (NIRS) yielded acceptable results 2-4. NIRS could reveal both ischemic and reperfusion related changes below midthoracic level (T7) in procedures involving the proximal descending thoracic aorta in a large animal model 5. In the clinical setting, after the feasibility of NIRS monitoring in both open, endovascular and hybrid thoracoabdominal interventions has been confirmed and the Leipzig group have reported upgrading their monitoring system to bilateral thoracic and lumbar paravertebral NIRS monitoring today it is used in both open and endovascular thoracoabdominal procedures 4,6,7. Regarding arch surgery, Kinoshita et al. were the first to use NIRS monitoring in a pilot study and reported that lower part of the spinal cord was not perfused sufficiently during ASCP 8. We use routine cerebral NIRS monitoring in arch surgery and had experience with spinal cord NIRS monitoring in patients with type B aortic dissection in our hospital previously9,10. We therefore planned to monitor spinal cord oxygenation with NIRS in our patients undergoing arch surgery to detect a warning sign regarding spinal cord ischemic insult and looked for a correlation between blood lactate, s100β values and NIRS levels.