Changes in Cerebrospinal Fluid Lactate During Thoracic Aortic Surgery

Abstract

Introduction: A serious complication of thoracoabdominal aortic surgery is either partial (paraparesis) or complete paralysis (paraplegia) of the lower body. The circulatory disturbance of the spinal cord occurring during aorta cross-clamping is responsible for this consequence. The ischemic tolerance time of the neurons can be increased by cooling to slow the metabolic processes, which reduces the oxygen demand of the neurons. Prophylactic use of neuroprotective drugs can also increase the biochemical defense of the neurons. Methods that can be used to monitor intraoperative spinal cord function include electrophysiology, intracranial pressure measuring, and analysis of the biochemical ischemic markers in the cerebrospinal fluid (CSF). The goal of our study was to determine if a biochemical marker such as lactate in CSF can predict postoperative spinal cord dysfunction. Method: We followed 35 patients prospectively who underwent surgical procedures on the thoracic aorta between January 2003 and August 2005. The number of elective and acute surgeries was almost equal (18 vs 19). The thoracic aorta was involved in 9 patients, whereas the thoracoabdominal part was involved in 26. The surgical method was graft interposition in most (n = 31) of the cases. The aorta cross-clamp time was relatively short (47 ± 17.7 minutes). We used mechanical circulatory support on 7 patients. For spinal cord protection, CSF drainage was implemented in 25 cases. The cerebrospinal fluid was analyzed before and in every 10 minutes during and after the aorta cross-clamping for pH, Po2, base excess, and lactate during the surgery. Results: Cerebrospinal fluid alkalosis was characteristic of every period. The CSF Po2 was more than 100 mm Hg continuously at all times, except once. That patient, whose result was less than 100 mm Hg, had mild disorientation postoperatively. The CSF base excess values slowly decreased during the procedure despite alkalosis. We observed elevated lactate levels of more than 4 mmol/L in 5 patients. One patient had lactate of more than 4 mmol/L before and after declamping, whereas all others had the increased lactate level after declamping. Three of 5 patients who had lactate of more than 4 mmol/L had some degree of postoperative paralysis, and only 1 patient with paralysis did not reach this value. The postoperative complications of those patients who had no CSF drainage were also analyzed. They had a higher incidence of central nervous system disturbances. Conclusion: Our practical observation is that CSF drainage has a mechanical protecting effect and also plays an important role as a medium for intraoperative biochemical monitoring of the spinal cord function. The values and the direction of the CSF lactate levels help predict the postoperative spinal cord dysfunction, allowing a chance for fast intervention.