Modulation of Peroxynitrite Reduces Norepinephrine Requirements in Ovine MRSA Septic Shock

Vascular hypo-responsiveness to vasopressors during septic shock is a challenging problem. This study is to test the hypothesis that reactive nitrogen species (RNS), such as peroxynitrite, are major contributing factors to vascular hypo-responsiveness in septic shock. We hypothesized that adjunct therapy with peroxynitrite decomposition catalyst (PDC) would reduce norepinephrine requirements in sepsis resuscitation. Fourteen female Merino sheep were subjected to a "two-hit" injury (smoke inhalation and endobronchial instillation of live methicillin-resistant Staphylococcus aureus [1.6-2.5 × 10 CFUs]). The animals were randomly allocated to control: injured, fluid resuscitated, and titrated norepinephrine, n = 7; or PDC: injured, fluid resuscitated, titrated norepinephrine, and treated with PDC, n = 7. One-hour postinjury, an intravenous injection of PDC (0.1 mg/kg) was followed by a continuous infusion (0.04 mg/kg/h). Titration of norepinephrine started at 0.05 mcg/kg/min based on their mean arterial pressure. All animals were mechanically ventilated and monitored in the conscious state for 24 h. The mean arterial pressure was well maintained in the PDC with significantly less norepinephrine requirement from 7 to 23 h after injury compared with control. Total norepinephrine dose, the highest norepinephrine rate, and time on norepinephrine support were also significantly lower in PDC. Modified sheep organ failure assessment scores at 6 to 18 h postinjury were significantly lower in PDC compared with control. PDC improved survival rate at 24 h (71.4% vs. 28.6%). PDC treatment had no adverse effects. In conclusion, the modulation of RNS may be considered an effective adjunct therapy for septic shock, in the case of hypo-responsiveness to norepinephrine.