Early postoperative substitution procedure of the antioxidant ascorbic acid (AA) in postoperative intensive care unit (ICU) patients

A postoperatively reduced concentration of AA in plasma (<45.5 μmol/l) is common due to increased metabolic requirements. Positive effects of AA in the postoperative period are well known (e.g. radical scavenger activity); hence there is an indication for the substitution of AA. However, the dosage commonly recommended for substitution during clinical nutrition is not adequate. Therefore, a postoperative AA substitution procedure 'overnight' to normal values in plasma was investigated in this randomized, prospective study on a postoperative ICU in a university hospital.

Fifty-seven electively operated patients were assigned to a control group or an intervention group. In all patients the AA plasma concentration was analysed preoperatively and on the first three postoperative days. Patients of the intervention group received AA intravenously 'overnight' up to four times within 12 hours depending upon the initial AA concentration (< 34.1 μmol/l [4 × 500 mg AA]; < 56.8 μmol/l [2 × 500 mg AA]; < 68.2 μmol/l [1 × 500 mg AA]).

The preoperative and postoperative AA values on the first postoperative day did not differ between both groups. However, the postoperative plasma concentration was lowered (< 45.5 μmol/l) in 82.4% of all patients.

In the intervention group, the dosage regime increased the AA plasma concentration to > 45.5 μmol/l in 89.6% overnight.

In conclusion, the investigated substitution procedure is sufficient to increase the AA plasma concentration overnight to high normal values in postoperative ICU patients.