Metabolic clearance of the antioxidant ascorbic acid in surgical patients.

BACKGROUND: A reduction of plasma ascorbic acid concentration in the post-operative period has been well documented and is associated with an increase in post-operative complications. The underlying reason for the decreased concentration of ascorbic acid in the plasma is not clear. However, only an increased post-operative requirement for ascorbic acid would justify a substitution. Therefore, we investigated the pre-operative and post-operative metabolic clearance of ascorbic acid. MATERIALS AND METHODS: We calculated the metabolic clearance subsequent to intravenous bolus injection of 6 mg ascorbic acid/kg body weight in 15 patients before and after they underwent major maxillofacial surgery. Blood samples were taken before and 5, 15, 30, 45, 60, 90, 120, and 240 min after administration of ascorbic acid before and after the operation. Urine was collected. Ascorbic acid in plasma and urine was analyzed using a high performance liquid chromatographic technique. RESULTS: The pre-operative metabolic clearance was 7.6 +/- 2.22 l/h (mean +/- SD), increasing significantly to 12.1 +/- 4.87 l/h on the first post-operative day (P < 0.001). Doses of approximately 1150 mg ascorbic acid would be necessary to compensate for the observed loss and to raise plasma ascorbic acid to high normal values. CONCLUSIONS: There is a significantly increased post-operative metabolic clearance of ascorbic acid that might be considered when framing future dose recommendations in post-operative patients.