Hypophosphatemia in Critically Ill Patients on Continuous Renal Replacement Therapy (CRRT)

Introduction: Hypophosphatemia has been reported in up to 80% of patients on CRRT. This retrospective review evaluated the incidence of hypophosphatemia in patients on CRRT and rates of successful phosphate repletion to normophosphatemia.


Methods: This single center, retrospective chart review included critically ill patients newly initiated on CRRT while in the intensive care unit (ICU) from January 1, 2024 to June 30, 2024. Patients with a history of end-stage renal disease (ESRD) requiring dialysis or CRRT duration of less than 3 days were excluded. The patients were categorized into groups based on their initial dialysate flow rate (DFR): less than 20 mL/kg/hr, 20-35 mL/kg/hr, and greater than 35 mL/kg/hr. The primary outcome was the incidence of hypophosphatemia during the first 7 days of CRRT. Secondary outcomes included successful phosphate repletion (serum phosphate level between 2.5-4.5 mg/dL following repletion) and severity of hypophosphatemia [mild (2-2.4 mg/dL), moderate (1-1.9 mg/dL), severe ( < 1 mg/dL)] between DFR groups. Descriptive statistics were used to summarize categorical data, and a Kruskal-Wallis test was used to compare the incidence of hypophosphatemia among the three DFR groups.


Results: Hypophosphatemia occurred in 75% (N=39/52) of patients during the first 7 days of CRRT treatment. Within this group, 107 low phosphate levels were identified, and 66% (N=71) were repleted within 6 hours following the initial low phosphate level. Only 35.3% (N=24/68) of these repletions were considered successful. No statistically significant difference was observed between DFR groups with respect to the severity of hypophosphatemia (p=0.56). In both the DFR less than 20 mL/kg/hr and 20-35 mL/kg/hr groups, successful phosphate repletions were associated with higher total mmol of phosphate.


Conclusions: Hypophosphatemia occurred frequently with low rates of successful repletion. No significant relationship was observed between DFR and hypophosphatemia severity, suggesting DFR variations may not meaningfully impact severity. These findings demonstrate the need for close phosphate monitoring and further research to identify strategies for improving phosphate management during CRRT.