Higher Percent Fluid Overload in Lower-Weight Patients on Continuous Renal Replacement Therapy

Background: Intravenous fluids (IVF) are essential for many intensive care unit (ICU) patients, but fluid overload (FO) is associated with poor outcomes. Patients with lower weight develop FO, defined as a 5% increase in body weight from ICU admission, with smaller volumes of IVF, which can be exacerbated in oliguric acute kidney injury (AKI). We hypothesize that patients with lower weight are at higher risk for developing FO and its associated adverse outcomes. Methods: We conducted a single-center retrospective cohort study of ICU patients who received continuous renal replacement therapy (CRRT) for AKI. We collected data on demographics, daily volume balances, and inpatient mortality. Percent FO was calculated as net volume balance (intake minus output) divided by ICU admission weight x100 and reported as percent of weight. Volume balance and FO were analyzed 72 hours before and 7 days after CRRT initiation. Results: In a cohort of 1,242 AKI-CRRT patients, median(IQR) weight was 84.9kg(71.0-103.0). The median weight for the upper and lower halves of the cohort were 103.0kg(93.2-118.7) and 71.0kg(60.6-77.6). Patients in the lower weight group had higher FO 72 hours before CRRT and after 7 days of CRRT (Table). While mortality was similar between weight groups (61.5% vs 61.8%,p=0.93), FO during the study period was higher among non-survivors versus survivors in both the lower weight group (6.7%(-0.8-15.2) vs -2.6%(-9.9-5.0),p<0.001) and the higher weight group (4.0%(0-9.0) vs -1.8%(-6.3-2.9),p<0.001). Logistic regression showed that percent FO as a continuous variable (OR(95% CI) 1.06(1.05-1.08),p<0.001) and chronic kidney disease (1.31(1.02-1.68),p=0.032) were associated with mortality when adjusting for age, race, diabetes, and hypertension. Conclusion: Patients with lower ICU admission weight had higher FO prior to CRRT initiation and were less likely to achieve ultrafiltration (UF) rates sufficient to reverse FO after 7 days of CRRT. Future studies should investigate whether weight-based volume balance thresholds for initiation of CRRT and UF would be beneficial. Volume Balance and Percent Fluid Overload Based on ICU Admission Weight - Net Volume Balance (mL) Percent Fluid Overload (%) Time Point Below median weight (n = 619) Above median weight (n = 623) p-value Below median weight (n = 619) Above median weight (n = 623) p-value 72 hours prior to CRRT 959.1 (0-3263.9) 458.4 (0-2817.0) 0.065 1.34 (0-4.9) 0.42 (0-2.6) <0.001 Days 1-7 on CRRT 741.08 (-4571.4-5357.4) 664.6 (-4442.9-4832.1) 0.981 1.12 (-6.3-8.2) 0.60 (-3.9-4.7) 0.488 Combined 72 hours prior to CRRT through Day 7 on CRRT 2298.7 (-3441.3-8456.2) 2195.7 (-3696.8-7206.3) 0.794 3.20 (-4.9-12.3) 2.02 (-3.4-6.9) 0.041