Objective: To assess the effect of the duration of spontaneous hypoxic episodes and variations in hemodynamic parameters on cerebral and renal tissue oxygenation in clinically stable preterm infants.
Design: Observational study.
Setting: Neonatal intensive care unit of a university-affiliated children’s hospital.
Patients: Cerebral and renal tissue oxygenation (rSO2C and rSO2R) and hemodynamic parameters were recorded for 2-3 hours (1-2 times) in clinically stable preterm neonates (n=10) using near-infrared spectroscopy (NIRS), GE DASH 4000 and Bedmaster Software.
Main outcome measures: rSO2C and rSO2R and fractional oxygen extraction (FOE-C and FOE-R) in association with the duration of pulse oximetry desaturation (SaO2 <84%), bradycardia (heart rate <90 beats per minute) and hypotension (mean blood pressure, MBP <30 mm Hg).
Results: Among the 14 sets of recorded measurements, 128 hypoxic episodes with 5-10 (n=41), 15-20 (n=26), 25-30 (n=78), 35-40 (n=14), 45-50 (n=25), and >55 seconds (n=16) duration were identified. Prolongation of hypoxic episodes for more than 30 seconds was associated with major reductions in SaO2, rSO2C, and rSO2R without significant changes in the regional FOE. Bradycardia occurred during 43.8% of hypoxemic episodes of >55 seconds duration (P<0.01) and impacted the severity of the tissue deoxygenation. Decreased renal tissue oxygenation and increased FOE-R were observed in association with mild hypotension irrespective of the systemic oxygenation status.
Conclusions: Prolongation of hypoxemia contributes to the severity of the deoxygenation (systemic and regional) and development of bradycardia. In stable preterm neonates, mild decreases in mean blood pressure can independently from the hypoxemia affect the renal but not cerebral tissue oxygenation and oxygen utilization.
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