Effect of Combined Selective Cerebral and Lower Body Perfusion at 28°C on Spinal Cord Protection in a Porcine 'Frozen Elephant Trunk' Simulation Model

Objective: The ‘frozen elephant trunk’ procedure (FET), represents the therapy of choice for complicated aortic diseases. Aim of our study was to analyze if a combined selective cerebral perfusion (SCP) and lower body perfusion (LBP) at 28°C offers supplementary spinal cord protection during and after permanent occlusion of the thoracic segmental arteries (TSA) in a porcine model.

Methods: 20 pigs (41 ± 3kg) were cooled on CPB to 28°C. After clamping of the aortic arch, the systemic perfusion was stopped and SCP established for 90 min. In n = 10 animals isolated SCP was performed (SCP-group), in n = 10 animals an additional low-flow LBP was established via direct cannulation of the descending aorta (SCLBP-group). The supradiafragmatic TSA were clipped in all animals. After reperfusion and CPB weaning, hemodynamic data were registered for 120 min. Spinal cord blood flow (SCBF), motor-evoked potentials (MEP) were monitored at baseline, reaching of 28°C, 60 and 90 minSCP, respectively at 60 and 120 min off-CPB. After sacrifice, the spinal cord was analyzed histologically using a 9-point schematic grading system.

Results: During isolated SCP the thoracic SCBF was maintained at baseline level (7.8 ± 6.9 ml/min/100 g) in the T4-T13 region, but showed a significant decrease (from 7.8 ± 5.4 to 1.2 ± 1.4 ml/min/100 g) in the L1-L5 region. SCLBP maintained almost baseline lumbar SCBF (7.0 ± 4.3 ml/min/100). During reperfusion SCBF increased, exceeding the baseline, with 2–3 × higher values in both, the SCP- and the SCLBP-group. At 28°C the MEP amplitude showed a decrease to 80–90% from baseline. After 90 min of SCP/SCLBP the MEP assessed in the m. masseter, used as stimulation control, didn't differ between groups. The m. external oblique (T7-T11) amplitude was comparatively lower, without significant differences between groups 76 ± 7% versus 74 ± 5%. MEP reached lower levels in the L1-L5 region in SCP-animals: 59 ± 7% versus 71 ± 15% (m. vastus medialis) and 48 ± 6% versus 60 ± 36% (m. tibialis anterior). MEP didn't recovered back to baseline in both groups. Histological analysis showed similar ischemia rate in the L1-L5 region in both groups.

Conclusion: SCP at 28°C provides sufficient protection for the thoracic spinal cord during FET-procedure, whereas the lumbar spinal cord may be damaged caused by the permanent TSA occlusion. SCLBP is practically feasible and provides temporary a more physiologic lumbar SCBF but doesn't offer a certain benefit for the lower spinal cord during FET.