DRG Category: 644
Mean LOS: 4.3 days
Description: Medical: Endocrine Disorders With Complication or Comorbidity
Syndrome of inappropriate antidiuretic hormone (SIADH), a disorder of the posterior pituitary gland, is a condition of excessive release of antidiuretic hormone (ADH) that results in excessive water retention and hyponatremia. Hyponatremia is the most common electrolyte imbalance that occurs while patients are in the hospital, and SIADH is a common cause. SIADH occurs when ADH secretion is activated by factors other than hyperosmolarity (increased concentration of solutes in the blood) or hypovolemia (decreased blood volume), which usually controls ADH secretion. The excess ADH secretion increases renal tubular permeability and reabsorption of water into the circulation, resulting in excess extracellular fluid volume, reduced plasma osmolality, decreased serum sodium levels, and increased glomerular filtration rates. The hyponatremia in this syndrome is not related to sodium loss but rather to water excess and the movement of water into the brain. In the process, brain cells lose potassium and amino acids. Without treatment, SIADH can lead to life-threatening complications. Water intoxication accompanied by sodium deficit and cerebral edema lead to complications such as seizures, coma, and death.
Several conditions contribute to SIADH. Central nervous system (CNS) responses to fear, pain, psychoses, and acute distress are known to increase the rate of ADH secretion by the posterior pituitary gland. Physiological conditions that increase intracranial pressure, such as acute CNS infections, brain trauma, anoxic brain death, stroke, and brain surgery, may lead to SIADH. Other conditions associated with SIADH include peripheral neuropathy, delirium tremens, and Addison disease. Certain medications, such as analgesics, anesthetics, thiazide diuretics, opiates, chlorpropramide, carbamezapine, vincristine, and nicotine, are also associated with SIADH. Some tumors have been associated with ADH production, such as cancer of the lungs, pancreas, and prostate as well as Hodgkin disease. Risk factors include head trauma, stroke, cardiopulmonary arrest, cancer of the lung, pneumonia, positive pressure ventilation, meningitis, alcohol withdrawal, low body weight, and certain medications (as listed previously).
No clear genetic contributions to susceptibility have been defined.
Both children and adults are at risk, but being a hospitalized patient over age 30 years is a risk factor, as is low body weight, which may result in more women than men being affected. Women are also are more affected by drug-induced and exercise-induced hyponatremia than men, who are more prone to develop mild hyponatremia. Typical childhood conditions that can lead to SIADH include pneumonia, meningitis, head trauma, and subarachnoid bleeding. In adults, the condition is most commonly associated with CNS disorders. The very old and very young develop symptoms with smaller decreases in serum sodium levels than adults.
Ethnicity, race, and sexual/gender minority status have no known effect on the risk for SIADH.
While SIADH and hyponatremia occur around the world, no prevalence data are available.
PLANNING AND IMPLEMENTATION
Collaborative
Restoration of normal electrolyte and fluid balance and normal body fluid concentration are the treatment goals. Treatment involves correction of the underlying cause and correction of hyponatremia. If the patient's life is not in danger from airway compromise or severe hyponatremia, the physician often restricts fluids initially to 600 to 800 mL or less per 24 hours. With fluid restriction, the hormone aldosterone is released by the adrenal gland and the patient begins to conserve sodium in the kidneys. As serum sodium increases, SIADH gradually corrects itself. The patient needs assistance to plan fluid intake, and a dietary consultation is also required for consistency in fluid management.
If fluid restriction is unsuccessful, the physician may prescribe an IV infusion of a 3% to 4.5% saline solution. Correction of hyponatremia is done carefully, because fluid could move rapidly from the brain into the circulation by osmosis, causing damage to the brain. In complicated cases, consultation with a neurologist may be important because of the risk of neurological deficits if correction is not done carefully. Use caution in administering these hypertonic solutions and always place them on an infusion control device to regulate the infusion rate precisely. Correction of the serum sodium levels by 6 mEq/L in 24 hours is recommended by many experts, or if in an emergency, 6 mEq/L in 6 hours and then cease correction for the rest of the day. Monitor the patient carefully because sodium and water retention may also result, leading to pulmonary congestion and shortness of breath.
Diuretics to remove excess fluid volume may be used in patients with cardiac symptoms if they are symptomatic.
| Medication or Drug Class | Dosage | Description | Rationale |
|---|
| Vasopressin receptor antagonists | Varies with drug | Conivaptan; tolvaptan | Block vasopressin receptors; used for hypervolemic and euvolemic (normal volume) hyponatremia when serum sodium level < 125 mEq/L, when hyponatremia is symptomatic, and when there has been inadequate response to fluid restriction |
| Diuretics | Varies with drug | Thiazide diuretics; loop diuretics (furosemide) | Remove excess fluid volume (may be used in patients with cardiac symptoms) |
Other Drugs: Osmotic diuretics mannitol and urea; tetracycline derivative demeclocycine is no longer recommended because of its delayed mechanism of action and nephrotoxic side effects.
Independent
If the patient is at risk for airway compromise because of low serum sodium levels or seizure activity, maintaining a patent airway is the primary nursing concern. Insert an oral or nasal airway if the patient is able to maintain breathing or prepare the patient for endotracheal intubation if it is needed. If the patient is able to maintain airway and breathing, consider positioning the patient so that the head of the bed is either flat or elevated no more than 10 degrees. This position enhances venous return and increases left atria filling pressure, which, in turn, reduce the release of ADH.
Explore with the patient methods to maintain the fluid restriction. If thirst and a dry mouth cause discomfort, try alternatives such as hard candy (if the patient is awake and alert) or chewing gum. Allocate some of the restricted fluids for ice chips to be used throughout the day at the patient's discretion. Work with the patient to determine the amount of fluid to be sent on each tray so that fluid intake is spread equitably throughout the day. If the patient is receiving fluids in IV piggyback medications, consider those volumes as part of the 24-hour intake. Work with the pharmacy to concentrate all medications in the lowest volume that is safe for the patient.
Promote range-of-motion exercises for patients who are bedridden, and turn and reposition them every 2 hours to limit the complications of immobility. Initiate seizure precautions to ensure the patient's safety.
Evidence-Based Practice and Health Policy
Mentrasti, G., Scortichini, L., Torniai, M., Giamperi, R., Morgese, F., Rinaldi, S., & Berardi, R. (2020). Syndrome of inappropriate antidiuretic hormone secretion (SIADH): Optimal management. Therapeutics and Clinical Risk Management, 16, 663–672.
- The authors note that while hyponatremia (sodium concentration < 135 mEq/L) is the most common electrolyte balance disorder in clinical practice, SIADH is the most relevant in hospitalized patients. The author describes the pathophysiology and clinical aspects and biochemical tests related to SIADH.
- Management strategies include fluid restriction of 500 to 800 cc per day, infusion of hypertonic saline (3%) with a bolus of 100 to 150 mL over 10 minutes, and the administration of tolvaptan, an arginine vasopressin (AVP) antagonistic agent. The authors note that the decrease of serum sodium levels lowers quality of life and leads to poorer survival in some critical medical conditions, such as congestive heart failure, hepatic cirrhosis, and renal disease, especially in older patients in treatment.