Estimating Vitamin C Status in Critically Ill Patients with a Novel Point-of-Care Oxidation-Reduction Potential Measurement

Abstract

Vitamin C deficiency is common in critically ill patients. Vitamin C, the most important antioxidant, is likely consumed during oxidative stress and deficiency is associated with organ dysfunction and mortality. Assessment of vitamin C status may be important to identify patients who might benefit from vitamin C administration. Up to now, vitamin C concentrations are not available in daily clinical practice. Recently, a point-of-care device has been developed that measures the static oxidation-reduction potential (sORP), reflecting oxidative stress, and antioxidant capacity (AOC). The aim of this study was to determine whether plasma vitamin C concentrations were associated with plasma sORP and AOC. Plasma vitamin C concentration, sORP and AOC were measured in three groups: healthy volunteers, critically ill patients, and critically ill patients receiving 2- or 10-g vitamin C infusion. Its association was analyzed using regression models and by assessment of concordance. We measured 211 samples obtained from 103 subjects. Vitamin C concentrations were negatively associated with sORP (R2 = 0.816) and positively associated with AOC (R2 = 0.842). A high concordance of 94-100% was found between vitamin C concentration and sORP/AOC. Thus, plasma vitamin C concentrations are strongly associated with plasma sORP and AOC, as measured with a novel point-of-care device. Therefore, measuring sORP and AOC at the bedside has the potential to identify and monitor patients with oxidative stress and vitamin C deficiency.

Keywords: antioxidant capacity; ascorbate; ascorbic acid; oxidation-reduction potential; oxidative stress; point-of-care device; reactive oxygen species; vitamin C deficiency.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1

Graphic representation of the methodological process.

Figure 2

Flowchart of included subjects and sample measurements.

Figure 3

Boxplots of plasma vitamin C concentrations (A), static oxidation reduction potential (sORP) (B) and antioxidant capacity (AOC) (C) in the vitamin C status study at day 1 and 3. The dashed line (A) represents the lower limit of normal plasma vitamin C concentrations (23 µmol/L). sORP and AOC were measured in non-acidified samples.

Figure 4

Boxplots of plasma vitamin C concentrations (A) and static oxidation reduction potential (sORP) (B) in the pharmacokinetic study at five different time points (hours). The dashed line (A) represents the lower limit of normal plasma vitamin C concentrations (23 µmol/L). Asterisks represent significant differences at p < 0.05. Vitamin C concentrations at T24 and T48 are trough concentrations. T72 represents a wash-out phase sample. sORP was measured in acidified samples.

Figure 5

Scatter plot of the association between plasma vitamin C concentration and concomitant static oxidation reduction potential (sORP) and antioxidant capacity (AOC) in the vitamin C status study (A+B) and pharmacokinetic study (C). A: sORP = −26.89 ln(plasma vitamin C concentration) + 198.69; B: AOC = 0.199 × e0.039(plasma vitamin C concentration); C: sORP = −21.74 ln(plasma vitamin C concentration) + 523.46.

Figure 6

Four-quadrant plots demonstrating the concordance between the changes in plasma vitamin C concentration and changes in sORP and AOC between day 1 and day 3 in the vitamin C status study (A and B respectively), and changes in sORP per day in the pharmacokinetic study (C).