Low-flow lower body perfusion for spinal protection in a frozen elephant trunk simulation model

Objectives: The frozen elephant trunk (FET) procedure using isolated selective cerebral perfusion (SCP) at moderate hypothermia is associated with an increased risk for spinal cord ischaemia. The aim of this study was to evaluate the benefit of a combined selective cerebral and low-flow lower body perfusion (CLBP) in a porcine model.

Methods: Twenty pigs (46 ± 5 kg) were cooled on cardiopulmonary bypass (CPB) to 28°C. After aortic clamping and occlusion of the thoracic segmental arteries (TSA_T4-T13), a pressure-controlled SCP (50 mmHg) was established for 90 min. Randomly, in n = 10 animals, an additional lower body perfusion (LBP) was performed with 15 ml/kg/min (CLBP). Regional spinal cord blood flow (SCBF), cerebrospinal fluid pressure (CSFP) and motor-evoked potentials (MEPs) were registered at six time points. The animals were sacrificed after 120 min of weaning from CPB, and the spinal cord was analysed histologically using a schematic scoring system (0 = normal, 8 = total necrosis).

Results: Isolated SCP led to an SCBF decrease from 18.5 ± 9.4 to 0.9 ± 1.4 ml/min/100 g in the L1-L5 region (P = 0.005). CLBP preserved an almost physiological lumbar SCBF of 11.3 ± 5.3 ml/min/100 g. CSFP decreased in both groups during cooling and SCP/CLBP to 70-80% and increased during reperfusion to 150%, without showing significant differences between groups. The MEP amplitude decreased in both groups, with certain regional differences: T7-T11. MEP recording revealed a more pronounced amplitude decrease in the CLBP group (52.5 ± 2.0 vs 71.3 ± 0.9%), but MEP amplitudes recovered in both groups (SCP: 73.7 ± 0.5 vs CLBP: 82.6 ± 0.1%). During selective hypothermic perfusion, SCP-treated animals showed significant lower MEP amplitudes, when compared with CLBP-treated animals: 60 ± 9 vs 90 ± 3% (P < 0.001). After weaning, CLBP animals showed a better MEP recovery, especially in the L1-L5 region (99 ± 7 vs 70 ± 13%; P < 0.001). The histological analysis did not show significant differences in the necrosis extension in the thoracic spinal cord. A different situation was seen in the L1-L5 area: all animals with isolated SCP, but only 50% of the CLBP animals presented a score of >5. A higher grade of lumbar ischaemia could be seen after isolated SCP (score: 5.9 ± 0.6 vs 3.6 ± 2.9).

Conclusion: The prolonged SCP provides an insufficient lumbar spinal cord protection during the FET procedure at 28°C. The use of a low-flow LBP in addition to SCP may reduce functional and structural spinal damage.