Abstract 2662: Hypoxic, Normoxic and Hyperoxic Resuscitation of Hypoxic Newborn Pigs: The Hemodynamic and Histopathologic Comparisons
Background: The optimal oxygen concentration used in the neonatal resuscitation is uncertain. Hypothesis: In a survival model of neonatal hypoxia-reoxygenation (HR), the resuscitation with 18% or 21% would be as effective as 100%O2 on the recovery of the heart, intestine and kidneys.
Methods: In a blinded randomized fashion, 18 pigs (1– 4d, 1.7–2.5kg) received alveolar normocapnic hypoxia (FiO2=0.15)(2h) and reoxygenated with either 18%, 21% or 100%O2(1h) then 21%O2(n=6/group). Sham-operated pigs had no HR (n=6). Systemic arterial pressure, heart rate, left renal and superior mesenteric (SMA) arterial flows were monitored for 4 post-HR days (D). Oxygen transport, plasma troponin I and creatinine levels were studied. Histology of left ventricle, small intestine and right kidney was analyzed by 2 pathologists using established grading criteria for HR-induced damage.
Results: There was moderate hypoxemia (PaO2 27–33 mmHg), mild metabolic acidosis (pH 7.20–7.24), tachycardia and hypotension (44–50 mmHg)(p<0.05 vs. sham, ANOVA) but cardiac work did not decrease (Rate-pressure-product=15–16x103). Heart rate normalized by 0.5h of reoxygenation in 18% and 21% groups but not the 100% HR group. There were no differences in systemic and regional hemodynamics and oxygen transport between groups from early reoxygenation through post-HRD4. Four HR piglets died (1 in the 18% group due to cardiopulmonary arrest; 1 in the 21% and 2 in the 100% due to necrotizing enterocolitis on post-HRD1–3). While plasma troponin I levels were not different between groups, the 100% HR group had the most cardiac HR-induced injury (myocardial architectural disruption and necrosis)(p<0.05 vs. sham and 18%, p=0.21 vs. 21% HR groups; X2 test). The animals fed well, gained weight and had normal renal function with no differences between groups including the HR injury score. Neurofunction improved gradually from HR with no difference from shams after post-HRD2.
Conclusions: Systemic and regional hemodynamic recovery, the intestinal and renal injury are similar in the resuscitation of hypoxic newborn pigs with 18%, 21% or 100%O2. Given the striking myocardial histopathologic injury in the 100% HR group, neonatal resuscitation with 100%O2 appears sub-optimal as the first line therapy.