Hypophosphatemia in critically ill patients: Incidence, Patient Characteristics, Trajectory, Treatment and Outcomes

Abstract

Abstract Introduction: Hypophosphatemia is common in critically ill patients. We have described the epidemiology of hypophosphatemia in patients admitted to the Intensive Care Units. Methods: A multicentre, retrospective cohort study of 12 ICUs in Queensland, Australia using clinical information systems. All adult patients admitted from January 1st, 2015, or from the commencement of the clinical information system to December 31st, 2021, were included. Patients on renal replacement therapy and those admitted with palliative intent or transferred from other ICUs were excluded. Patients were classified into four groups based on severity of serum phosphate (PO4) derangement: “None” (PO4: ≥ 0.81 mmol/L, ``Mild” (PO4: ≥ 0.50 mmol/L & < 0.81 mmol/L) “Moderate” (PO4: ≥ 0.30 mmol/L & < 0.50 mmol/L) and “Severe” (PO4: < 0.30 mmol/L). Results: Of the 89,776 patients admitted, 77,310 patients were included in this study, with 26,409 (34.2%) having at least an episode of hypophosphatemia with onset mostly on ICU Day-2 in all groups. The proportion of ICU days with low phosphate was highest in the severe group (Mild: 0.33; Moderate: 0.40; Severe: 0.5). Groups received phosphate administration to varying extents (None: 1031(2%), Mild 13343 (59%); Moderate: 2658 (91%); Severe: 583 (97%)). The serum phosphate concentration normalised by Day-3 in all groups. There was substantial variation among participating ICUs in the percentage of hypophosphatemic patients who received phosphate replacement, the threshold for replacement and the route by which it was administered. Conclusion: Hypophosphatemia, while common, was mostly mild and occurred on day 2 with early normalisation of serum phosphate. Phosphate replacement practices were variable among ICUs in dose, route, threshold for administration and duration of replacement.