Outpatients on chronic dialysis usually have trouble with hyperphosphatemia, requiring high doses of oral phosphorus binders to block absorption of dietary phosphate. In the intensive care setting, the opposite situation—hypophosphatemia—is often encountered in patients on dialysis for several reasons including higher frequency of dialysis and relative malnutrition. It is critical to check the serum phosphate level daily in the intensive care unit (ICU) patient on hemodialysis. A level that may have been quite high prior to dialysis can plummet to critical values if unmonitored. Severe (<1.5 mg/dL) hypophosphatemia can cause diaphragmatic weakness, apnea, cardiac instability, rhabdomyolysis, or hemolysis.

Conventional intermittent hemodialysis is intrinsically very effective at phosphate removal, but the overall treatment time (usually 2 to 4 hours) is often not enough to cause profound hypophosphatemia, since extracellular stores are rapidly repleted from intracellular reserve. In the ICU setting it is common to use sustained, high-intensity dialysis, usually in the form of a continuous renal replacement therapy such as continuous venovenous hemofiltration (CVVH) or continuous venovenous hemodiafiltration (CVVHDF). A retrospective study showed that CVVHDF curbs hyperphosphatemia better than intermittent hemodialysis, but at an increased risk of hypophosphatemia. In addition to continuous renal replacement therapy, other risk factors for hypophosphatemia in the ICU include parenteral nutrition, diarrhea, and profound renal phosphate wasting due to tubular cell injury.