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Abstract: FR-PO276

Phosphorous and Magnesium Nadirs Following Continuous Renal Replacement Therapy (CRRT) Initiation Are Associated with Mortality

Session Information

Category: Fluid and Electrolytes

  • 902 Fluid and Electrolytes: Clinical


  • Griffin, Benjamin, University of Colorado, Aurora, Colorado, United States
  • Arruda, Nigel, University of Colorado, Aurora, Colorado, United States
  • Ambruso, Sophia L., University of Colorado, Aurora, Colorado, United States
  • Teixeira, Joao Pedro, University of Colorado, Aurora, Colorado, United States
  • Jovanovich, Anna Jeanette, Denver VA / University of Colorado, Denver, Colorado, United States
  • Faubel, Sarah, University of Colorado Denver, Denver, Colorado, United States

Severe acute kidney injury (AKI) requiring continuous renal replacement therapy (CRRT) is common in the intensive care unit, complicating 5% of all admissions. As CRRT therapy fluids typically contain no phosphorus and low magnesium concentrations, CRRT is known to rapidly deplete these electrolytes, and their repletion during CRRT is often required. Studies examining the impact of these electrolyte losses on patient mortality have been inconclusive. The purpose of this study was to examine the impact of phosphorous and magnesium levels on mortality in the setting of CRRT.


We conducted a retrospective analysis of adult patients initiated on CRRT at the University of Colorado Hospital between July 2015 and September 2016. Patients were excluded if they died within 24 hours of CRRT initiation. Phosphorous and magnesium levels were collected at CRRT initiation and every 8 hours thereafter. The primary outcome was in-hospital mortality. Logistic regression was used to adjust for SOFA score, body mass index, and gender.


A total of 155 cases were included in the analysis. Mean phosphorous and magnesium levels at the time of CRRT initiation were 5.4 ± 2.7 mg/dL and 2.28 ± 0.58 mg/dL, respectively. Neither baseline levels nor changes from baseline were associated with mortality. However, higher nadir levels of both phosphorous and magnesium were independently associated with mortality, even after adjusting for confounders.


While baseline phosphorous and magnesium values were not associated with mortality, nadir levels were. We expected lower nadir levels to be associated with mortality, but observed the opposite. Lower nadir levels may have been indicative of higher dose or higher quality of CRRT. The frequency and quantity of electrolyte repletion were not evaluated in this study. Further investigation into the role of phosphorous and magnesium in AKI requiring CRRT is warranted.

Table 1. Final multivariate models for in-hospital mortality
VariableOR (95% CI)p value
Final Phosphorous Model*
Initial Phosphorous1.06 (0.88 - 1.26)0.6
Nadir Phosphorous1.60 (1.13 - 2.24)0.007
Final Magnesium Model*
Initial Magnesium0.94 (0.44 - 2.00)0.9
Nadir Magnesium6.78 (1.64 - 28.02)0.008

* Final model was adjusted for SOFA score, body mass index, and gender


  • Other NIH Support