Evaluation of kidney oxygenation monitoring with near infrared spectroscopy in preterm neonates: kidney location, depth, and laterality differences.

Introduction: Near infrared spectroscopy (NIRS) monitoring of preterm kidney oxygenation is increasing. We sought to evaluate kidney positioning and oxygenation differences between the right and left kidneys.

Methods: Preterm neonates <32 weeks' gestational age were enrolled in a prospective observational NIRS study. Two three-hour epochs of simultaneous bilateral kidney monitoring were performed (5-8 days, 9-14 days). Point of care kidney ultrasound was performed once between days 5 and 12.

Results: There were no right-left differences in skin to superior kidney depth (0.39 and 0.38 cm; p = 0.62) or spine to kidney distance (1.06 and 1.02 cm; p = 0.31). There was a difference in right-left skin to inferior kidney depth (2.15 and 2.04 cm; p = 0.02). There was higher oxygenation in the left kidney compared to the right (65.6 vs. 62.7%, p < 0.01). Hourly individual differences of >10% were seen in 37% of neonates.

Conclusions: Differences in kidney depth and right-left oxygenation exist in preterm neonates.