Monitoring of motoneuron activity for spinal cord ischemia

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The F-wave/polysynaptic responses complex (FPC) which is recorded on a plantar region after electric stimulation of the tibial nerve is a group of potentials reflecting the excitement of the anterior horn cells at the L-5 level of spinal cord. We evaluated the utility of FPC monitoring for spinal cord ischemia in the context of thoracic aortic surgery, experimentally and clinically.Twenty four dogs were subjected to the balloon catheter occlusion of both the distal thoracic aorta and the left internal mammary artery under pentobarbital anesth esia. Half of the dogs were treated with no muscle relaxants and the other half were with a non-depolarizing muscle relaxant, pancuronium. The FPCs were well monitored even if the muscle relaxant was used and were lost within 3 minutes after the completion of the balloon arterial occlusion in all dogs. They were divided into four groups, A,B,C, and D, according to arterial occlusion time after the loss of the FPCs, 20,30,40, and 50 minutes, respectively. Incidence of paraplegia was 0% (0/6) in Group A, 33% (2/6) in Group B, 83% (5/6) in Group C (A vs C : P<0.01), and 100% (6/6) in Group D.The FPCs were monitored in 13 patients who underwent graft replacement for thoracic or thoracoabdominal aortic aneurysms. The operations were performed with temporary bypass or partial cardiopulmonary bypass. The FPCs were lost in 7 patients after aortic clamping or intercostal artery ligation. Paraplegia or paraparesis occurred in two of three patients that aortic reconstruction was completed in beyond twenty minutes after the loss of the FPCs.In conclusion, FPC monitoring is a usefull method for detection of spinal cord ischemia and reconstruction of the spinal cord blood flow within 20 minutes after the loss of the FPC may prevent postoperative paraplegia nearly completely.