Acute respiratory distress syndrome secondary to cardiopulmonary bypass: Do compromised plasma iron-binding antioxidant protection and thiol levels influence outcome?

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Abstract
Objectives Cardiopulmonary bypass (CPB) surgery is often associated with mild lung injury and in some patients leads to acute lung injury and acute respiratory distress syndrome (ARDS). Aberrant plasma iron chemistry (increased iron loading of transferrin and/or the presence of redox-active low molecular mass iron) and increased plasma thiol levels are features of this type of surgery and represent a potential pro-oxidant risk for oxidative damage. Oxidative damage is a feature of ARDS, and we hypothesized that pro-oxidant forces may contribute to the onset and progression of ARDS. Design Prospective, single center, observational study. Setting University-affiliated tertiary referral cardiothoracic center. Patients A total of 19 patients with ARDS secondary to CPB surgery and 64 patients with ARDS secondary to a variety of other predisposing causes. Interventions Supportive techniques appropriate to the treatment of ARDS. Measurements and Main Results Blood samples were collected into lithium heparin tubes for all patient groups on the first day of the admission of patients to the intensive care unit immediately after the diagnosis of ARDS. Plasma was immediately assayed for thiol content and total protein and albumin levels. Plasma from patients with ARDS secondary to CPB surgery was also assayed for changes in iron chemistry. Nonsurviving patients with ARDS secondary to CPB surgery displayed significantly greater levels of aberrant iron chemistry (elevated levels of iron saturation of transferrin) with decreased iron-binding antioxidant protection and elevated plasma thiol levels than did survivors. Plasma thiol levels in patients with ARDS secondary to other predisposing causes were (with the exception of lung-surgery patients) significantly elevated in survivors compared with those in nonsurvivors of the syndrome. Conclusions Increased levels of plasma thiol appear to be associated with mortality in patients with ARDS secondary to CPB surgery.