CHANGES IN CEREBROSPINAL-FLUID PRESSURE AND LACTATE CONCENTRATIONS DURING THORACOABDOMINAL AORTIC-ANEURYSM SURGERY

Background: Although ischemic injury to the spinal cord is a well-know n complication of aortic surgery, no metabolic markers have been ident ified as predictors of an adverse outcome. This study evaluated the ef fect of cerebrospinal fluid (CSF) drainage, with and without distal fe moral perfusion or moderate hypothermia on blood and CSF lactate conce ntrations and CSF pressure during thoracoabdominal aortic aneurysm sur gery. Methods: Three nonconcurrent groups of patients were studied pro spectively: patients with normal body temperature (35 degrees C) but w ithout distal femoral bypass (n = 6), patients with normal body temper ature with bypass (n = 7), and patients with hypothermia (30 degrees C ) and bypass (n = 8). In all patients, CSF pressure was recorded befor e, during, and after aortic cross-clamping. During the surgical repair , CSF drainage was performed using a 4-Fr intrathecal silicone cathete r. Blood and CSF lactate concentrations were measured throughout the o peration. Results: Significant increases in blood (490%) and CSF (173% ) lactate concentrations were observed during and after thoracic aorti c occlusion in patients with normothermia and no bypass (P < 0.02 and 0.05, respectively). Distal perfusion attenuated the increase in both blood and CSF lactate (P < 0.01), and a further reduction was achieved with hypothermia of 30 degrees C (P < 0.001). Patients who became par aplegic showed a greater increase in CSF lactate concentrations after aortic clamp release compared with those who suffered no neurological damage (275% vs. 123% of baseline; P < 0.05). Increased CSF pressure o f 42-60% (P < 0.005) was noted soon after thoracic aortic occlusion, b oth with and without distal femoral bypass. Conclusions: Incremental r eductions in CSF lactate concentrations were achieved using distal fem oral bypass and hypothermia. The reduction in CSF lactate correlated w ith the methods used to protect the spinal cord during thoracoabdomina l aortic aneurysm surgery and was associated with better outcome. Deco mpression by distal bypass of the hemodynamic overload caused by aorti c occlusion was insufficient to eliminate the acute increase in CSF pr essure. Cerebrospinal fluid lactate measurements during high aortic su rgery may accurately represent the spinal cord metabolic balance.