hypophosphatemia
hypophosphatemia
[hi″po-fos″fah-te´me-ah]hy·po·phos·pha·te·mi·a
(hī'pō-fos'fă-tē'mē-ă),hypophosphatemia
Low blood phosphate Endocrinology Low serum phosphate which may be linked to management of DKA, starvation, etc. See Phosphate.hy·po·phos·pha·te·mi·a
(hī'pō-fos-fă-tē'mē-ă)Synonym(s): hypophosphataemia.
Hypophosphatemia
| DRG Category: | 642 |
| Mean LOS: | 4.6 days |
| Description: | MEDICAL: Inborn and Other Disorders of Metabolism |
Phosphorus is a major anion in the intracellular fluid that is measured in the serum; normal serum phosphorus levels range between 1.7 and 2.6 mEq/L (2.5 and 4.5 mg/dL). In children, the serum phosphorus level is higher, at 4 to 7 mg/dL. Hypophosphatemia occurs when the serum phosphorus levels fall below 1.7 mEq/L (2.5 mg/dL). Patients with moderate hypophosphatemia (1 to 2.5 mg/dL) are usually asymptomatic and require no treatment except to manage the underlying cause; patients with severe hypophosphatemia (< 1 mg/dL) need more aggressive treatment to prevent complications. The possible complications of hypophosphatemia are grave and include dysrhythmias, heart failure, shock, destruction of striated muscles, seizures, and coma. Hypophosphatemia occurs in approximately 1% to 5% of all hospitalized patients, 30% of patients admitted to critical care units, and 40% to 80% of patients with alcohol dependence, diabetic ketoacidosis, sepsis, or septic shock. Severe hypophosphatemia is rare and occurs in less than 1% of all hospitalized patients.
Approximately 85% of body phosphorus is in bone, and most of the remainder is intracellular. Only 1% is in the extracellular fluid. Phosphorus serves many functions in the body, such as maintenance of the normal nerve and muscle activity; formation and strength of bones and teeth; maintenance of cell membrane structure and function; metabolism of carbohydrates, proteins, and fats; maintenance of oxygen delivery to the tissue; maintenance of acid-base balance; and activation of the B complex vitamins. Phosphorus is excreted by the kidneys (90%) and gastrointestinal (GI) tract (10%). Regulation of phosphorus is controlled by parathyroid hormone (PTH). PTH stimulates a vitamin D derivative (calcitriol) to increase phosphorus absorption by the GI tract. PTH acts on the renal tubules to increase phosphate excretion.
Causes
The many causes of hypophosphatemia include dietary changes, GI abnormalities, drug interactions, hormonal changes, and cellular changes. Changes in the diet as a result of malnutrition or alcoholism can significantly reduce the serum phosphorus levels. Inadequate amounts of phosphorus in total parental nutrition may also lead to hypophosphatemia. GI problems that result in a phosphorus deficit include vomiting, chronic diarrhea, and intestinal malabsorption because of vitamin D deficiency. Two types of medications that most commonly decrease serum phosphorus are aluminum-containing antacids and diuretics. Aluminum binds with phosphorus in the GI tract, and most diuretics promote urinary excretion of phosphorus. Infusion of glucose also leads to phosphate depletion, as do increased levels of PTH, which increase the urinary excretion of phosphorus. Cellular changes in several disorders, such as diabetic ketoacidosis, burns, and acid-base disorders, lead to hypophosphatemia.
Genetic considerations
Familial hypophosphatemia (formerly vitamin D–resistant rickets) results in the inability of the kidney to effectively reabsorb phosphate. Low blood levels of phosphate can be seen beginning between 6 and 10 months. In most cases, transmission of the trait follows an X-linked dominant (from PHEX mutations) pattern, although autosomal recessive (via DMP1 mutations), autosomal dominant (from FGF23 mutations), and X-linked recessive transmissions have been reported. About one-third of cases involve a new mutation.
Gender, ethnic/racial, and life span considerations
Hypophosphatemia can occur at any age, across both sexes, and in all races and ethnicities. Identifying high-risk groups—such as individuals with alcoholism, diabetes, malnourishment, or parathyroid disease—is critical. Children begin to show signs of hypophosphatemia from the genetic syndromes in infancy or childhood, whereas acquired hypophosphatemia occurs in late adolescence or adulthood. Adolescents who develop the condition may have eating disorders, whereas with aging, hypophosphatemia is usually associated with alcohol dependence, cancerous tumors, malabsorption syndrome, or vitamin D deficiency.
Global health considerations
No data are available.
Assessment
History
Ask patients about their diet and if they have had any nausea, vomiting, diarrhea, or loss of appetite. Inquire about medications, especially aluminum-containing antacids and diuretics. Determine if the patient is a diabetic or has a history of alcoholism, hyperparathyroidism, or a serious recent burn.
Physical examination
Symptoms do not usually occur unless there is total body depletion of phosphorus or the serum level drops below 1 mg/dL. With acute hypophosphatemia, the patient appears apprehensive. Ask if the patient has any chest pain, muscle pain, or paresthesia. With chronic hypophosphatemia, an accurate history may be difficult to obtain because often there is memory loss. The patient may report a history of anorexia, muscle and bone pain, and paresthesia.
Hypophosphatemia generally creates neuromuscular, cardiopulmonary, hematological, and GI abnormalities. Perform a thorough neuromuscular assessment; assess the patient’s hand grasp and leg strength and note tremors of the extremities. Assess the deep tendon reflexes; often hyporeflexia is found. Neurological deficits include paresthesia, dysarthria, confusion, stupor, seizures, and coma. The patient’s voice may be weak and shaky. Assess the patient’s ability to swallow and the gag reflex. Auscultate the heart; the pulse may be weak and irregular. Assess the respiratory status, and note if the respirations are rapid and shallow because of impaired diaphragmatic function. Weigh the patient and assess for signs and symptoms of malnutrition, such as pallor, dull hair, poor skin turgor, weight loss, and fatigue.
Psychosocial
The patient with hypophosphatemia may be anxious and concerned about the muscular weakness, paresthesia, and ability to perform activities of daily living. Assess coping skills and family support and ability to assist with care.
Diagnostic highlights
| Test | Normal Result | Abnormality With Condition | Explanation |
|---|---|---|---|
| Serum phosphorus | 2.5–4.5 mg/dL | Moderate: 1–2.5 mg/dL; severe: < 1 mg/dL; critical value: < 1.1 mg/dL | Reflects phosphorus deficit |
| Urine phosphorus | 400–1,300 mg/day | 100 mg/day when patient is hypophosphatemic | Reflects excessive renal loss of phosphorus |
Other Tests: Electrocardiogram, serum total calcium, serum ionized calcium, parathyroid hormone level, urine amino acids, blood urea nitrogen, creatinine, serum vitamin D assays
Primary nursing diagnosis
Diagnosis
Altered nutrition: Less than body requirements related to alcoholism, dietary changes, GI abnormalitiesOutcomes
Nutritional status: Nutrient intake; Electrolyte and acid-base balance; Cardiac pump effectiveness; Knowledge: Medication and treatment proceduresInterventions
Electrolyte management: Hypophosphatemia; Nutrition management; Nutrition monitoring; Vital signs monitoring; Medication management; Venous access devices maintenance; Teaching: IndividualPlanning and implementation
Collaborative
The most important goals are to replace the phosphorus and to correct the underlying cause of the phosphorus deficit. Phosphorus is replaced either by dietary intake or by oral administration of phosphate salt tablets or capsules. If hyperphosphatemia inadvertently occurs, hypocalcemia is also likely. Assess for tetany and be sure the patient has an open airway, adequate breathing, normal circulation, and an adequate urine output. Routine serum phosphate and calcium levels are ordered to determine the effectiveness of the replacement. Monitor the IV site for infiltration because potassium phosphate can cause tissue sloughing and necrosis.
Pharmacologic highlights
| Medication or Drug Class | Dosage | Description | Rationale |
|---|---|---|---|
| Phosphate supplements |
|
| Replace phosphorus; often capsules are preferred because the tablet form may cause nausea; if the deficit is severe, IV infusion of potassium phosphate is needed |
Note: The response to IV phosphorus supplementation is variable and may lead to hyperphosphatemia and hypocalcemia. When using potassium phosphate as a supplement, monitor the potassium level and note that hyperkalemia may limit amount of phosphate that can be given safely. Other Drugs: Analgesics may be ordered for bone pain. Monitor the effectiveness of the pain medications. Avoid administering antacids that contain aluminum. If the patient develops alcohol withdrawal, the treatment of choice is the benzodiazepine class of medications.
Independent
Maintain an open airway and adequate breathing. Keep an artificial airway, manual resuscitator bag, and suction at the bedside at all times. If you hear stridor or see respiratory distress, notify the physician immediately, insert an oral or nasal airway if appropriate, and keep the airway clear with oral or nasal suction. If the patient is unresponsive, use the jaw lift or chin thrust to maintain the airway until a decision is made whether to intubate the patient.
Maintain a safe environment. The patient may need assistance with ambulation and activities of daily living. Orient the patient as needed. Encourage patient involvement in self-care as much as possible. If the patient develops signs of alcohol withdrawal (restlessness, insomnia, thirst, and tremors progressing to fever, hallucinations, and combative and irrational behavior), notify the physician and decrease stimulation as much as possible. Place the patient in a quiet, darkened room with a cool temperature. Provide frequent sips of water and fruit juices, but avoid fluids with caffeine. Place the patient in a room where she or he can be monitored frequently to decrease the risk of injury.
Evidence-Based Practice and Health Policy
Foley, R.N., Collins, A.J., Herzog, C.A., Ishani, A., & Kalra, P.A. (2009). Serum phosphorus levels associate with coronary atherosclerosis in young adults. Journal of the American Society of Nephrology, 20(2), 397–404.
- Investigators conducted a 15-year prospective study among 3,015 healthy young adults to determine the effects of phosphorus on cardiovascular risk and found that each 0.5 mg/dL increase in phosphorus levels at baseline was associated with a 13% decreased risk of coronary artery calcification (95% CI, 0.77 to 0.99; p = 0.0332). The mean phosphorus level for the entire sample at baseline was 3.6 mg/dL (SD, ± 0.5 mg/dL; range, 1.3 to 5.7 mg/dL).
- In this sample, 3.2% had minimal coronary artery calcification, 4.8% had mild calcification, 1.1% had moderate calcification, and 0.5% had severe calcification at year 15.
Documentation guidelines
- Laboratory: Maintain a flowsheet on serum electrolytes for easy day-to-day comparisons
- Physical responses: Adequacy of airway, breathing, and circulation; vital signs, noting any respiratory difficulties such as rapid, shallow breathing patterns; cardiac rhythm; intake and output; presence of any neuromuscular twitching, tetany, or seizure activity; ability to swallow; presence or absence of gag reflex
- Any signs of alcohol withdrawal; management of the symptoms; response to treatment
- Duration, intensity, location, and frequency of pain; effectiveness of analgesics
Discharge and home healthcare guidelines
Instruct the patient on all medications regarding dosage, route, action, and adverse effects. Instruct the patient to avoid antacids that contain aluminum and about the higher risk for recurrence if he or she is taking diuretics. Instruct the patient to eat foods high in phosphorus, such as meats (kidney, liver, and turkey), milk, whole-grain cereals, dried fruits, seeds, and nuts. Many carbonated drinks are high in phosphate as well. Discuss with the patient how to prevent reoccurrence of hypophosphatemia.
hy·po·phos·pha·te·mi·a
(hī'pō-fos-fă-tē'mē-ă)Synonym(s): hypophosphataemia.