Retrograde venous perfusion with hypothermic saline and adenosine for protection of the ischemic spinal cord

Purpose: Spinal cord injury and the resultant postoperative paraplegia are devastating complications of thoracic aortic surgery, for which no widely accepted protective interventions exist. We hypothesized that retrograde venous perfusion-cooling of the spinal cord with a hypothermic saline and adenosine solution would protect it from ischemic injury caused by thoracic aortic occlusion. Methods: Adult domestic swine of either sex (weight range, 20 to 30 kg) were intubated and ventilated. A left thoracotomy was performed. The accessory hemiazygous vein was divided, and a catheter was inserted distally. The aorta was clamped at the left subclavian artery. The venous catheter was not used in the animals in the control group (n = 7); in the animals in the experimental group (n = 7), a cold (4°C) saline and adenosine solution was infused into the accessory hemiazygous vein. After 30 minutes, the clamp and catheter were removed, and the chest was closed. A blinded observer evaluated the animals' hind-leg motor activity 24 hours later. The Tarlov scale was used: 0, complete paralysis; 1, minimal movement; 2, stands with assistance; 3, stands alone; 4, weak walk; 5, normal gait. The animals' rectal temperatures were measured at the end of the experiment, and blood pressure was measured throughout. Two other groups were studied to assess the effect of the intervention on spinal cord temperature. Results: The animals in the control group had a mean Tarlov score of 1.7 ± 0.6; the animals in the experimental group had a mean Tarlov score of 4.9 ± 0.1 (P < .01). The animals in the experimental group had a significantly greater drop in spinal cord temperature than those in the control group (4.05 ± 0.6°C vs 0.58 ± 0.12°C; P < .01). No significant difference in rectal temperatures was found, nor did any arrhythmias or hypotensive episodes occur in either group. Perfusion of the spinal cord was confirmed with angiography by using this approach. Conclusion: Retrograde venous perfusion-cooling of the spinal cord with a hypothermic saline and adenosine solution protects the cord from ischemic injury caused by clamping of the thoracic aorta.