Outcome and risk factors associated with perirenal subcapsular fluid collections in extremely preterm infants with acute kidney injury

Objectives: To investigate the incidence of, clinical outcome of, and risk factors for perirenal subcapsular fluid collections in extremely preterm infants with acute kidney injury (AKI). Methods: Extremely preterm infants with AKI who underwent renal ultrasonography (US) during neonatal intensive care unit stay were classified into two groups according to the presence of a perirenal subcapsular fluid collection at US. Clinical outcome was compared, and relevant data were analysed, including demographics and comorbidities of the infants, as well as maternal demographics. The risk factor of perirenal subcapsular fluid in infants with AKI was tested with univariate and multivariate logistic regression analysis. Results: A perirenal subcapsular fluid collection was detected in 7 of 56 (13%) extremely preterm infants with AKI (male to female ratio, 5:2; mean gestational age, 23.6 ± 1.4 weeks) and it appeared bilaterally in most cases (86%, 6/7). The mortality rate was higher in infants with perirenal subcapsular fluid collections and AKI (86%, 6/7) than with AKI alone (35%, 17/49) (p = 0.015). Infants with perirenal subcapsular fluid collections and AKI were of a lower gestational age, and more frequently showed episodes of intestinal perforation, use of medication having potential to impair renal function, and a history of maternal chorioamnionitis (p < 0.05). Multivariate analysis revealed a significantly higher risk for perirenal subcapsular fluid collections in extremely preterm infants who were treated with anti-fungal agents (OR, 13.2 (95% CI: 1.5, 119.4); p = 0.022). Conclusions: Although a perirenal subcapsular fluid collection occurred in a small proportion of extremely preterm infants with AKI, its presence was associated with high mortality. The use of anti-fungal agents was an independent risk factor for a perirenal subcapsular fluid collection. Key Points: • A perirenal subcapsular fluid collection may occur in association with acute kidney injury. • A perirenal subcapsular fluid collection has a grave prognostic implication in extremely preterm infants. • The use of anti-fungal agent might be associated with perirenal subscapular fluid collections in critically ill extremely preterm infants with AKI.