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 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.

The systemic, pulmonary and regional hemodynamic recovery of asphyxiated newborn piglets resuscitated with 18%, 21% and 100% oxygen.

OBJECTIVES: The increase in oxidative stress following neonatal hypoxia-reoxygenation can be related to subsequent cardiovascular deficits. We compared the acute systemic, pulmonary and regional hemodynamic recovery in hypoxic newborn pigs reoxygenated by low (18%) or high (100%) concentration of oxygen with that by 21% oxygen. STUDY DESIGN: Pigs (1-3 days, 1.5-2.5 kg) were acutely instrumented to continuously measure pulmonary artery flow (surrogate for cardiac index), mean and pulmonary artery pressures, common carotid, superior mesenteric and renal artery flow indices. After 1h of normocapnic alveolar hypoxia (8-10% oxygen), animals were randomized to receive 18%, 21% or 100% oxygen for 1h then 21% oxygen for 3 h (n=7 per group). Sham-operated pigs (n=6) had no hypoxia-reoxygenation. RESULTS: Severe hypoxia caused significant compromises in systemic and regional hemodynamics and oxygen delivery (vs. shams). Despite reoxygenation, mean arterial pressure remained significantly lower than that of shams with no difference among hypoxic-reoxygenated groups. There was an oxygen-dependent recovery of pulmonary artery pressure. Cardiac index improved with reoxygenation but deteriorated over time in the 100% group. Both 18% and 100% groups had lower systemic oxygen delivery. Regional flows and oxygen delivery in all hypoxic-reoxygenated piglets were similarly reduced in all groups. CONCLUSIONS: In this swine model of neonatal hypoxia-reoxygenation, resuscitation with 18% and 100% oxygen results in differential compromises in systemic and pulmonary circulations when compared with 21% oxygen.