(57) Correlation of Systemic Blood Pressure and Renal Tissue Oxygenation in Preterm Neonates During the First Two Weeks of Age

Background: Near-infrared spectroscopy (NIRS) allows for continuous monitoring of renal tissue oxygenation (RrSO₂) at the bedside and has been used safely and effectively in preterm neonates. However, the relationship between systemic blood pressure (BP) and RrSO₂ as measured by NIRS in neonates is not well known.

Objectives: To investigate the correlation of systemic blood pressure and RrSO₂ in preterm neonates during the first 14 days of age.

Design/Methods: A secondary, retrospective analysis of a prospective single center observational study of neonates < 32 weeks gestational age (GA) was performed. RrSO₂ was measured every one to six seconds from day of age two to 14 using INVOS 5100C NIRS monitors. Mean arterial pressure (MAP), systolic blood pressure (SBP), and diastolic blood pressure (DBP) were recorded either every six hours using a non-invasive oscillometric cuff or continuously via an umbilical artery catheter (UAC). Mean hourly RrSO₂ values were matched and compared to concurrent BP measurements on an hourly basis. Results were analyzed using an exchangeable generalized estimating equations (GEE) model.

Results: 104 participants with a median GA of 29 weeks and birth weight of 1210 grams were included (Table 1). 3511 matched pairs of BP and RrSO₂ were used for analysis. Total MAP, SBP, and DBP were found to have a non-significant, positive correlation with RrSO₂ (ß = 0.0512, p = 0.14; ß = 0.512, p = 0.19; ß = 0.030, p = 0.44, respectively) (Figure 1). A significant, positive correlation between MAP and RrSO₂ was found on day of age 5, 6, 7, and 8 (ß = 0.270, p < 0.01; ß = 0.320, p < 0.01; ß = 0.234, p = 0.02; ß = 0.318, p < 0.01, respectively) (Figure 2). MAP and RrSO₂ correlation did not vary significantly in neonates born < 28 weeks GA versus those born ≥ 28 weeks GA (ß = 0.053, p = 0.34; ß = 0.0175, p = 0.68, respectively) or by sex (ß = 0.0551, p = 0.68 male; ß = 0.0516, p = 0.28 female). The correlation of MAP and RrSO₂ was insignificant for varying MAP levels, but a negative association between MAP and RrSO₂ was found for bottom and upper 25% of MAP readings (β = -0.0165, p = 0.94; β = -0.0485, p = 0.53, respectively) (Figure 3).

Conclusions: Blood pressure was not consistently correlated with RrSO₂ in this secondary analysis, but was on days five through eight. Future steps include analyzing UAC BP measurements independent of cuff BP's.