Renal injury in perinatal hypoxia: ultrasonography and changes in renal function

We studied 12 hypoxaemic neonates (5 mature newborns, birth weight 2850-4200 g, gestational age 37-41 weeks; and 7 premature newborns, birth weight 770-1850 g, gestational age 27-34 weeks;) with repeated urine and blood chemistry on the 1st and 3rd days of life. Nephrosonographical examinations on the 1st, 3rd and 5-7th days of life were also performed. As controls, 12 healthy infants were examined (gestational age 36-42 weeks; birth weight 24504200 g). Hypoxic neonates had higher serum creatinine and blood urea nitrogen levels. Tubular markers also demonstrated renal tubular damage. Neonates in both hypoxic groups were hyperuricaemic and hyperuricosuric, and had higher urinary protein concentrations. All these infants exhibited an increased echogenicity of the renal cortex, and 11/12 showed the same finding in the medullary area. These findings disappeared within 1 week in all infants. Among the 12 healthy control infants, no cortical hyperechogenicity was found and only three of these infants displayed transient medullary renal hyperechogenicity.

Since the hypoxaemic infants demonstrated greatly increased urinary concentrations of uric acid and protein, we suggest that a temporary precipitation of these two agents may be responsible for the ultrasonographic findings. Circulatory redistribution might play a role in the phenomenon of cortical hyperechogenicity.