Hypophosphatemia is defined as a phosphate level of less than 2.5 mg/dL (0.8 mmol/L). Phosphate is critical for a remarkably wide array of cellular processes.ypophosphatemia has been reported in up to 15% of geriatric patients undergoing refeeding. Hypophosphatemia has also been reported in up to 35% of adult patients undergoing open heart surgery and is associated with prolonged mechanical ventilation, increased use of cardiovascular drugs, and prolonged hospitalization.