Protective effect of hypothermia and left heart bypass on spinal ischemia in the dog.

OBJECTIVE: To test the hypothesis that systemic hypothermia (SH) to 30 degrees C in combination with partial left heart bypass (PLHB) at either a high or low distal arterial perfusion pressure (DAPP) following 45 minutes of cross-clamp (XC) occlusion of the thoracic aorta will protect against clinical and histological spinal cord ischemia in the dog. DESIGN: A blinded, prospective, randomized, and controlled experimental trial. SETTING: Tertiary care center animal laboratory. PARTICIPANTS: Seventeen adult mongrel dogs. INTERVENTIONS: The animals were randomized into 5 groups: control group 1: XC plus no protection (n = 3); control group 2; XC plus systemic normothermia plus PLHB, with a DAPP less than 20 mm Hg (n = 3); treatment group 1: XC plus systemic normothermia plus PLHB, with a DAPP greater than 20 mm Hg (n = 3); treatment group 2: XC plus SH plus PLHB, with a DAPP greater than 20 mm Hg (n = 3); treatment group 3: XC plus SH plus PLHB, with a DAPP less than 20 mm Hg (n = 5). MAIN OUTCOME MEASURES: Clinical and histological neurological injury evaluation by separate blinded observers. RESULTS: Control animals were neurologically and histologically ischemic. Treatment animals were neurologically and histologically normal. Partial left heart bypass with a DAPP greater than 20 mm Hg prevented paraplegia, with either systemic normothermia or SH. Systemic hypothermia plus PLHB, even with a DAPP less than 20 mm Hg, protected against spinal cord ischemia during thoracic aortic occlusion. CONCLUSION: Systemic hypothermia to 30 degrees C combined with PLHB at either a high or low DAPP prevented spinal cord ischemia following thoracic aortic XC occlusion in our canine model and merits clinical trial in patients.