Effect of moderate hypothermia on systemic and internal jugular plasma IL-6 levels after traumatic brain injury in humans

Moderate hypothermia may reduce subsequent neuronal damage after traumatic brain injury. Interleukin (IL)-6 may have a role in the pathogenesis of tra umatic neuronal damage or repair. Using the enzyme-linked immunological sor bent assay (ELISA), we serially measured IL-6 levels in plasma obtained fro m the radial artery (systemic) and internal jugular vein (regional) in 13 c erebral trauma patients who underwent hypothermia of 32-33 degrees C ranged from 4-9 days postinjury and 10 head-injured patients who were maintained at normothermic levels (36-37 degrees C). In both patient populations, surf ace cooling was used since even in the normothermic group, cooling was need ed to maintain patient temperature in the normothermic range. All patients were mechanically ventilated after injection of midazolam and vecuronium. T he administration of these agents were continued until the end of the study . Hypothermia was typically maintained for four days, however, in some case s based upon CT findings and/or intra-cranial pressure change, the duration was prolonged. No significant differences were found between the two group s in age, gender and Glasgow Coma Scale upon admission. Further, no differe nces were found in terms of the classification of computed tomography findi ngs or the occurrence of pupillary abnormalities on admission. The patients in this study had not sustained either abdominal or thoracic trauma. Befor e inducing hypothermia, IL-6 levels in the arterial and internal jugular ve nous blood exceeded the normal range. Specifically, the internal jugular pl asma levels were significantly higher than those in the arterial plasma. Wh ile IL-6 levels in the normothermic group did not decrease even at 4 days p ostinjury, the plasma cytokine levels fell at both sites sharply after mode rate hypothermia. The cytokine suppression found in the hypothermic group c ontinued even after rewarming in these patients showing an improved clinica l course, but not in those whose condition worsened. In addition to these c hanges in cytokine levels, the Glasgow Outcome Scale at 6 months postinjury was significantly higher in the hypothermic group than in the normothermia group. Based on the above, this clinical study with its small patient samp le size suggests the need for further prospective randomized studies to exa mine the role of cytokine suppression in the beneficial effects of moderate hypothermia in patients with traumatic brain injury.