RESUMO
OBJECTIVES: We examined the effects of 18%, 21% or 100% oxygen on the recovery of the heart and kidneys in a short-term survival model of neonatal hypoxia-reoxygenation (HR). DESIGN: Controlled, block-randomized animal study. SETTING: University animal research laboratory. SUBJECT: Large White piglets (1-3 days, 1.7-2.5 kg). INTERVENTIONS: Piglets received normocapnic hypoxia (15% oxygen) (2 h) and were reoxygenated with 18%, 21% or 100% oxygen (1 h) (n=7 per group) then 21% oxygen (2 h). Sham-operated pigs (n=7) had no HR. MEASUREMENTS AND RESULTS: Seventeen of 21 HR piglets recovered from moderate hypoxemia (mean PaO(2) 27-33 mmHg and pH 7.20-7.22, associated with tachycardia and hypotension). Systemic arterial pressure, heart rate, left renal arterial flow, oxygen transport, plasma troponin-I and creatinine levels were monitored and recovered with no differences among HR groups over 4 days after resuscitation. The 100% group had increased myocardial oxidative stress (oxidized glutathione levels) and the most cardiac HR-induced injury. There were no differences in renal oxidative stress and HR-induced injury among groups. Early oxygenation at 1 h after resuscitation correlated with the plasma troponin-I level at 6 h (r = -0.51 and 0.64 for SaO(2) and systemic oxygen extraction ratio, p<0.05, respectively) and renal HR-induced injury at 4 days (r =0.61 for renal oxygen delivery, p<0.05). CONCLUSIONS: In hypoxic piglets, 18%, 21% and 100% reoxygenation caused similar systemic and renal hemodynamic and functional recovery. The indicators of oxidative stress and HR injury in myocardial and renal tissues suggest that the reoxygenation with 100% oxygen appears sub-optimal and the use of 18% oxygen offers no further benefit, when compared with 21% oxygen.