Hypophosphatemia in Critical Care Causes

Hypophosphatemia is caused by inadequate intake (malnutrition or intestinal binding), excessive loss (diuretics) or redistribution within the body (catecholamines/refeeding).

 Hypophosphatemia is caused by inadequate intake, excessive loss or redistribution within the body. Inadequate intake may relate to malnutrition or to interference with absorption. Agents that bind with phosphate may reduce it’s absorption – examples include magnesium and aluminium antacids and the sucralfate (which contains aluminium). Any disease process causing malabsorption will have a similar effect – short bowel syndrome, tropical sprue, celiac and Crohn’s disease, radiation enteritis etc.

Excessive loss of phosphate is associated with diuresis and dialysis. The most phosphaturic diuretics are carbonic anhydrase inhibitors. One must be very careful that patients on continuous dialysis modes do not become profoundly hypophasphatemic (I usually add potassium phosphate to the dialysate). Osmotic diuretics and hyperglycemia cause increase urinary loss, as does throphylline and acetaminophen in overdose.

There are a number of reasons why phosphate may redistribute into cells. Phosphate is, after all, a predominantly intracellular cation: agents that cause this shift include – catecholamines, beta-receptor agonists, insulin, increased blood sugar, alkalosis and sodium bicarbonate administration.

Malnutrition

Phosphate binding antacids

Malabsorption syndromes – Crohn’s disease, celiac disease

Vitamin E deficiency

2) Increased Loss

Diuretics

Steroids

Alcoholism

Renal transplantaion

Hyperparathyroidism

Volume expansion

Metabolic acidosis

Pancreatitis

Burns

3) Redistribution

Shifts from serum into cells – carbohydrate infusions, hyperglycemia

Hormonal effects – Catecholamines (epinephrine, dopamine, terbutaline, albuterol), Insulin, Glucagon, Calcitonin

Respiratory alkalosis – hyperventilation – panic attacks, salicylate poisoning

Rapid cellular uptake – refeeding syndrome, leukemic blast cell crises, hungary bone syndrome.

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