93 - Factors Influencing the Determination of Dosing Weight in the NICU

Poster Number: 93
Publication Number: 93.438

Cassandra R. Montoya, Northwestern University The Feinberg School of Medicine, Chicago, IL, United States; Janine Y. Khan, Ann & Robert H. Lurie Children's Hospital of Chicago, Chicago, IL, United States; Delphine Nelson, Children's Hospital of Richmond at VCU, Richmond, VA, United States; Gustave Falciglia, Northwestern University, Chicago, IL, United States

Background: Dosing weight (DW) is a functional weight that differs from most recent measured weight (MW). In the neonatal intensive care unit (NICU), the DW can be used to account for variations in fluid status, growth, or measurement error. Although DW is routinely used for nutrition and medication calculations, the infant and unit factors used to determine DW have not been explored.

Objective: To describe how DW compares to birth weight (BW) and MW, and whether DW is influenced by comorbid conditions or signs of fluid overload.

Design/Methods: An existing level IV NICU database of very low birth weight infants in the first six weeks of life and chart review were used. Data included: gestational age (GA), BW, MW, DW, comorbid conditions, lowest sodium (Na), and highest creatinine (Cr). Number of days to regain BW was determined, defined as the first of three consecutive days with MW at or above BW. Before regaining BW, MW and BW percent difference was calculated and compared to infant and unit factors using ordinary least squares regression and Wilcoxon rank-sum test. After regaining BW, DW and MW percent difference was calculated and compared to similar factors using mixed effects linear regression. The frequency of DW updates was compared using mixed effects logistic regression.

Results: There were 115 infants and 4,643 infant days, with a median BW of 1060g and GA 28 weeks. Time to regain BW was 10.5 +/- 4.2 days. On average, DW was defined once prior to regaining BW and did not differ from BW, however, variation existed that did not correlate with any known factor (Figure 1). After regaining BW, DW averaged 3.9% (p < 0.0005) less than MW (Figure 2). Every 1mg/dL increase in Cr was associated with a further 5.6% decrease in DW (p < 0.0005). Every 10meq/L decrease in Na was associated with an additional 1% decrease in DW. Regardless of comorbid condition or Cr, the only factor associated with the frequency of DW update was day of the week (Figure 3).Conclusion(s): The fact that DW decreased referent to MW in infants with high Cr suggests that clinicians adjusted for fluid overload. Therefore, DW fell into three categories: BW, “dry” weight to correct for fluid overload, and practical weight for medication dosing. Use of DW rather than MW in infants with normal renal function would result in 4% less nutrition intake and should be avoided. We did not see a difference in DW adjustment in any remaining comorbid conditions. Further evaluation is needed to optimize the selection of DW.
Figure 1: Dosing & Birth Weight Difference Distribution
Figure 2: Dosing & Daily Weight Difference