Plasma antioxidant capacity in critical polytraumatized patients?: methods, severity, and anatomic location

Oxidative stress (OS) has been invoked as a relevant factor in the evolution and outcome of critical care patients. Indeed, antioxidant therapies have been used in critical care patients [1] but with controversial results [2]. This may be explained by assuming OS as a homeostatically regulated parameter and both its excess and its deficit influencing severity progression. Nonetheless, antioxidant agents could mask an OS signaling role, blocking otherwise physiological responses aimed at recovery of homeostasis [3]. We have evaluated plasma total antioxidant capacity (TAC) in traumatized patients in an ICU, and we determined its potential relationship with severity and trauma location. In a prospective observational study of ICU polytraumatized patients (n = 73, mean Acute Physiology and Chronic Health Evaluation II (APACHE II) score of 11 ± 6) of the Hospital Arnau de Vilanova (Lleida, Spain), we measured (in the first 48 hours) plasma TAC by two different methods: the ferric reducing activity/antioxidant power (FRAP) and the capacity for neutralization of the free radical 2,2′-azino-bis (3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) as previously described [4]. For control subjects, we used age- and gender-matched volunteers (n = 102). We also evaluated the contribution of antioxidant molecules (uric acid, bilirubin, and albumin) to these values. The protocol was approved by the institutional ethics committee of the Arnau de Vilanova Hospital and followed Declaration of Helsinki guidelines for studies with human individuals. All participants (or their legal representatives) gave their consent for the study.

As shown in Figure 1, polytraumatized patients show differences in TAC with reference to control subjects, but these differences are dependent on the technique used. Thus, ICU polytraumatized patients show higher FRAP values but lower ABTS capacity. Notably, APACHE II score influenced FRAP values (Table 1). Indeed, we found that FRAP values were inversely correlated with APACHE II score (r = -0.266, P <0.01) suggesting that, in trauma patients, increased antioxidant response, as measured by FRAP assay, could be a pathophysiological response to stress. Albumin and uric acid concentrations reproduced the FRAP trend with severity. Reinforcing the importance of the technique and the specificities across different antioxidant assessment methods, data for the relationship of APACHE II score with ABTS do not show a significant trend (r = 0.040, P = 0.568). These results also contrast with those obtained in other ICU patients, such as those with sepsis [5].

In the multiple linear regression, FRAP values in trauma ICU patients are independently influenced by age (β = 0.271, P <0.021), APACHE II score (β = -0.356, P <0.002), and head trauma (β = -0.219, P <0.045). These results accentuate the influence of trauma location and severity in TAC changes.

Our results not only stress the importance of the method used for TAC measurement but also show that age, status severity, and anatomical location of trauma influence TAC response in ICU patients, reinforcing the need for an adequate tailoring of treatments aimed at their recovery, such as antioxidant therapies.