Cardio-renal recovery of hypoxic newborn pigs after 18%, 21% and 100% reoxygenation

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 PaO2 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.