OBJECTIVE: To determine xanthine oxidase activity, free radical concentrations, and lipid peroxidation in patients with sepsis syndrome compared with noninfected critically ill patients.

DESIGN: A prospective observational study.

SETTING: A nine-bed intensive care unit in a university teaching hospital trust.

PATIENTS: Fourteen consecutive patients who met the established criteria for sepsis syndrome with multiple organ dysfunction syndrome, and ten noninfected critically ill patients were studied.

INTERVENTIONS: None.

MEASUREMENTS AND MAIN RESULTS: Xanthine oxidase activity was increased in septic patients compared with both healthy volunteers (p < .01) and noninfected patients (p < .05), and was highest in the six patients who survived (p < .05). Lipid peroxides were increased in both septic patients (p < .001) and nonseptic controls (p < .001). Xanthine oxidase activity did not relate to the Acute Physiology and Chronic Health Evaluation (APACHE) II score or to the presence of organ dysfunction. The mean ascorbyl radical concentration (arbitrary units) determined by electron paramagnetic resonance following spin trapping was increased in patients compared with healthy subjects (p < .05).

CONCLUSIONS: Patients with sepsis have xanthine oxidase activation, high free-radical concentrations, and evidence of free radical damage. The finding that xanthine oxidase activity was lower in those patients who died, coupled with increased lactate concentrations implies more severe ischemia with incomplete reperfusion resulting in less xanthine oxidase "wash out" into the circulation. Increased ascorbyl radical concentrations may be due to an increased radical generation and oxidant scavenging, but appears to be unrelated to xanthine oxidase activity within the circulation.