Evaluation of Serum Phosphate Levels in ICU Patients Undergoing Continuous Renal Replacement Therapy Katherine Fonfara, Eric Pyles, Rebecca Falter AdventHealth Orlando, Orlando, FL Background: Severe hypophosphatemia is associated with serious adverse effects such as skeletal muscle weakness, respiratory insufficiency, cardiac rhythm disturbances, and delirium. These complications have been linked to worsening clinical outcomes including failed extubations, increased time on mechanical ventilation, and increased intensive care unit (ICU) and hospital length of stay. Patients on continuous renal replacement therapy (CRRT) are at increased risk of experiencing hypophosphatemia and the corresponding complications.
Iatrogenic hypophosphatemia represents a modifiable risk factor that may potentially improve patient outcomes. This study aims to evaluate phosphate replacement strategies in critically ill patients on CRRT and characterize incidence and severity of hypophosphatemia.
Methods: This evaluation was a single-center, retrospective study comparing rates of hypophosphatemia in adult patients requiring CRRT and those not on CRRT admitted to the ICU at a large community hospital. Patients who were admitted to an ICU and receiving CRRT for 24 hours or more were included in the treatment group. The control group included patients admitted to an ICU and not requiring CRRT. Patients with end-stage renal disease on chronic dialysis, nocturnal CRRT/sustained low-efficiency dialysis (SLED), or with confounding metabolic conditions were excluded from either group. The primary outcome was the percentage of hypophosphatemic levels, defined as serum phosphate level less than 1.9 mg/dL. Secondary outcomes included percentage of severe hypophosphatemic levels, defined as serum phosphate level less than 1.0 mg/dL, in-hospital mortality, hospital length of stay, ICU length of stay, and time requiring mechanical ventilation. A post-hoc subgroup analysis was conducted to compare the primary outcome based on average CRRT flow rates.
Results: A total of 100 patients were included in the study, with 50 patients included in each group. The baseline demographics were similar between both groups except home diuretic use, and baseline phosphorus and serum creatinine levels. In the control group, the median baseline phosphorus level was 3.1 mmol/L (IQR 2.6-3.8), and the median baseline serum creatinine was 1.0 mg/dL (IQR 0.8-1.2). In the CRRT group, the median baseline phosphorus level was 5.4 mmol/dL (IQR 4.2-6.4), and the median baseline serum creatinine was 2.9 mg/dL (IQR 2.2-4.1).
Regarding the primary outcome, the CRRT group had a significantly higher median percentage of hypophosphatemic levels compared with the control group (10.8% [0-29.3] vs 0% [0], p < 0.001). For the secondary outcomes, there was no difference in the median percentage of severely hypophosphatemic levels between groups (0% [0] in both groups, p = 0.317). The median hospital length of stay was longer in the CRRT group compared with the control group (14 days [7-24.8] vs 4.5 days [3-9.5], p < 0.001). Similarly, the median ICU length of stay was longer in the CRRT group (8 days [5-14] vs 3 days [2-7], p < 0.001). The median ventilator duration was also significantly longer in the CRRT group (4 days [3-8] vs 1 day [1-2], p < 0.001). In-hospital mortality was significantly higher in the CRRT group with 62% of patients dying during admission compared with 18% in the control group (p < 0.001). In the subgroup analysis of the CRRT group, there was no difference in percentage of hypophosphatemic levels across flow rate groups (< 20 ml/kg/h, 20-25 ml/kg/h, and > 25 ml/kg/h).
Conclusions: Patients receiving CRRT were associated with a significantly greater percentage of hypophosphatemic phosphate measurements compared with control group. The CRRT group had higher phosphate levels at baseline and was associated with increased phosphate depletion. No association was observed between CRRT dialysate flow rate and the percentage of hypophosphatemic levels. These findings support the need for close phosphorus monitoring as well as early phosphorus supplementation.
