Emergency Department Care
Treatment of hypophosphatemia is twofold: (1) correct any precipitating causes of hypophosphatemia, and (2) replace total body phosphates.
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Depending on the clinical situation, replacement options include dietary phosphate, oral phosphate preparations, and IV phosphate.
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Replacement of phosphate is recommended through the intravenous (IV) route in patients with severe hypophosphatemia and for patients that concomitantly have cardiac dysfunction, respiratory failure, muscle weakness, or impaired tissue oxygenation. [32]
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Hypophosphatemia and hypokalemia can coexist in certain disorders like diabetic ketoacidosis and alcoholism, so replacement with the potassium salt is most appropriate in these settings.
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The most important consideration in choosing replacement therapy is whether the patient has signs or symptoms of phosphate depletion. Patients with decreased renal function require one half of the suggested dose.
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Mild to moderately severe, asymptomatic hypophosphatemia
Mild to moderately severe, asymptomatic hypophosphatemia may require oral phosphate replacement; however, correcting factors that led to hypophosphatemia usually is sufficient. Mild hypophosphatemia in DKA and gastrointestinal losses often corrects with resolution of the underlying cause.
In most asymptomatic patients, the serum phosphate level spontaneously normalizes over several days when factors inducing hypophosphatemia are corrected.
In patients with minimal symptoms or moderate hypophosphatemia (serum phosphate 1-2 mg/dL), providing oral phosphate replacement may be desirable.
It is recommended that oral phosphate replacement be used in patients who are symptomatic and have phosphate levels between 1.0-1.9 mg/dL.
For patients who are symptomatic and have a serum phosphate level less than 1.0 mg/dL, IV replacement is recommended, followed by oral replacement once serum phosphate levels reach greater than 1.5 mg/dL.
The average adult consumes 1 gram of phosphorus daily. A quart of cow's milk provides this amount of phosphorus (1 mg phosphorus/mL). Dairy products have an additional advantage of supplying absorbable calcium, which can help avoid the hypocalcemia that may result with more aggressive replacement regimens.
Phosphorus preparations with sodium and potassium are available, but they have disadvantages, including causing osmotic diarrhea, volume overload, or hyperkalemia.
Usual starting doses are 2-3 grams of elemental phosphorus in divided doses.
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Severe/symptomatic hypophosphatemia
Patients with symptoms of hypophosphatemia or with serum phosphate levels less than 1 mg/dL require IV phosphate replacement.
IV replacement can be dangerous for the patient, causing an electrolyte disturbances including hypocalcemia, renal failure from calcium phosphate precipitating in the kidneys, and fatal arrhythmias.
Serum phosphate concentration should be monitored every 6 hours if replacement is given through the IV route.
Once serum phosphate levels reach 1.5 md/dL, therapy should be switched to oral replacement.
The intracellular nature of phosphate makes interpreting a low serum phosphate level difficult and predicting the amount required to replenish cellular stores nearly impossible.
Accordingly, recommendations for IV phosphate in the literature are varied and based on therapeutic experiences with limited numbers of patients.
Avoid hyperphosphatemia when replacing phosphorus intravenously, as this can lead to hypocalcemia (leading to tetany) and calcium-phosphate deposition in tissues (eye, heart, kidney, lung).
Urinary phosphate wasting is more difficult to treat, as increasing serum phosphate levels result in increased urinary excretion. Dipyridamole may result in urinary phosphate reabsorption, but further study is required for use in patients with urinary excretion of phosphate. [33]
Consultations are based on any underlying or suspected etiologies.
