Effects of N-acetylcysteine on tissue oxygenation in patients with multiple organ failure and evidence of tissue hypoxia

Covert tissue hypoxia, particularly of the splanchnic region, appears important in the pathogenesis of multiple organ failure (MOF). This investigation evaluates the effects of N-acetylcysteine (NAC) upon several measures of tissue oxygenation in 10 patients with severe MOF and evidence of splanchnic hypoxia (as suggested by a pathologically low value (< 7.32) of the pH of the gastric mucosa (pHi)). Patients were studied following a prospective, randomized, placebo-controlled, cross-over design. Measurements included pulmonary and systemic haemodynamics, cardiac output by thermodilution, arterial and mixed venous blood gas values, blood lactate concentration, whole-body oxygen uptake by analysis of the expired gases, and pHi by tonometry. A complete set of measurements was obtained before and 45 min after the infusion of NAC (150 mg.kg-1 in 250 mL of saline) and, also, before and 45 min after the infusion of an equivalent volume of saline. NAC increased the cardiac index and vasodilated the systemic circulation (p < 0.01). However, O2 delivery to the tissues did not increase because the arterial oxygen content fell after NAC (p < 0.01). Mean O2 extraction or lactate concentration did not change after NAC, and pHi fell slightly (from 7.11 +/- 0.21 to 7.07 +/- 0.21; p < 0.05). The infusion of saline did not modify any variable significantly. The O2 extraction fraction increased exponentially in those patients with reduced O2 transport to the tissues. These results argue against a beneficial effect of N-acetylcysteine upon tissue oxygenation in patients with severe multiple organ failure and evidence of splanchnic hypoxia. Furthermore, they suggest that the mechanisms controlling the extraction of oxygen by the peripheral tissues in these patients were not impaired.

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