Hyperoxia may be beneficial

The current practice of mechanical ventilation comprises the use of the least inspiratory O-2 fraction associated with an arterial O-2 tension of 55 to 80 mm Hg or an arterial hemoglobin O-2 saturation of 88% to 95%. Early goal-directed therapy for septic shock, however, attempts to balance O-2 delivery and demand by optimizing cardiac function and hemoglobin concentration, without making use of hyperoxia. Clearly, it has been well-established for more than a century that long-term exposure to pure O-2 results in pulmonary and, under hyperbaric conditions, central nervous O-2 toxicity. Nevertheless, several arguments support the use of ventilation with 100% O-2 as a supportive measure during the first 12 to 24 hrs of septic shock. In contrast to patients without lung disease undergoing anesthesia, ventilation with 100% O-2 does not worsen intrapulmonary shunt under conditions of hyperinflammation, particularly when low tidal volume-high positive end-expiratory pressure ventilation is used. In healthy volunteers and experimental animals, exposure to hyperoxia may cause pulmonary inflammation, enhanced oxidative stress, and tissue apoptosis. This, however, requires long-term exposure or injurious tidal volumes. In contrast, within the timeframe of a peri-operative administration, direct O-2 toxicity only plays a negligible role. Pure O-2 ventilation induces peripheral vasoconstriction and thus may counteract shock-induced hypotension and reduce vasopressor requirements. Furthermore, in experimental animals, a redistribution of cardiac output toward the kidney and the hepato-splanchnic organs was observed. Hyperoxia not only reverses the anesthesia-related impairment of the host defense but also is an antibiotic. In fact, perioperative hyperoxia significantly reduced wound infections, and this effect was directly related to the tissue O-2 tension. Therefore, we advocate mechanical ventilation with 100% O-2 during the first 12 to 24 hrs of septic shock. However, controlled clinical trials are mandatory to test the safety and efficacy of this approach. (Crit Care Med 2010; 38[Suppl.]:S559-S568)