476

Abstract

Introduction: The primary aim of our study was to determine the association between calculated total body exchangeable solute, sodium plus potassium (Na-K) and chloride (Cl), the main determinant of extracellular fluid volume, and measured blood volume (BV). Hypothesis: The calculated total body exchangeable solute, Na-K and Cl, will be highly correlated with measured BV. Methods: This retrospective study was approved by the University of Washington IRB. All adult patients in whom a BV was measured while in the neuroscience ICU of a large academic medical center were included. BV was measured as part of routine care using I-131 labeled albumin injection and the BVA-100 (Daxor Corp, New York, NY). Total body exchangeable solute was estimated at the time of BV measurement by multiplying the calculated total body water (TBW) by the sum of the serum Na-K and Cl. TBW on admit was estimated with Watson’s formula (http://www.medcalc.com/tbw.html) accounting for the patient’s sex, height and weight. Daily water balance was estimated using nurse entered daily fluid balances. Data were analyzed with Prism v5.0a (GraphPad Software, San Diego, CA). The correlation coefficient (r) and coefficient of determination (r-squared) between total body exchangeable solute and BV were examined using Pearson correlation calculations and linear regression, respectively. Significance was defined as a two-sided p-value <0.05. Results: Fifty-five patients underwent BV analyses. On the day of the test, TBW was 39 ± 10 L, serum Na-K and Cl were 142 ± 6 and 106 ± 6 mEq /L respectively. Total body Na-K and Cl were 5611 ± 1480 and 4182 ± 1092 mEq. Measured BV was 4845 ± 1421 mL. r and r-squared were 0.74 (p<0.01) and 0.57 for total body Na-K and 0.7 (p<0.01) and 0.48 for total body Cl, respectively. Conclusions: Total body exchangeable solute is highly correlated with actual measured BV and can be calculated using information readily available at the bedside (body weight, height, gender, fluid balance, serum chemistries). The utility of having this information automatically calculated and available at the bedside should be explored.