Fluid and Electrolyte Balance: ADH and Diabetes Insipidus

Fluid Volume Excess (Hypervolemia)

• Occurs when there is too much water in the body.
• If kidneys are working well, the body will compensate by diuresing (excreting excess water).
  • The urine will be dilute.
• Blood and urine usually reflect each other regarding concentration.

SIADH (Syndrome of Inappropriate Antidiuretic Hormone)

• Too much ADH is produced, leading to water retention.
• Water is retained in the vascular space.
• Blood becomes dilute (hyponatremia).
• Urine output decreases and becomes concentrated (high specific gravity).
• Sodium does NOT always follow water; if it did, SIADH and diabetes insipidus wouldn't exist.

Diabetes Insipidus (DI)

• Not enough ADH is produced, leading to excessive water loss (diuresis).
• Think "Diuresis" when you see "DI".
• Leads to fluid volume deficit and potential for shock (main concern).
• Not related to blood sugar levels; checking blood glucose is not a primary concern.
• Blood becomes concentrated due to water loss.
• Urine becomes dilute.
• Trauma patients in shock have decreased urine output due to poor kidney perfusion; DI patients in shock have increased urine output, worsening their condition.

ADH and the Pituitary Gland

• ADH is produced in the pituitary gland.
• ADH problems are often subtle and require a sharp nurse to identify.
• Conditions that can lead to ADH problems: Craniotomy, head injury, sinus surgery, transsphenoidal hypophysectomy, increased intracranial pressure.
• Transsphenoidal hypophysectomy: Surgical removal of the pituitary gland through the sphenoid sinus.
  • Trans: Across or through.
  • Sphenoid: Sphenoid sinus (a sinus in the skull).
  • Hypophysis: Pituitary gland.
  • Ectomy: Removal.
• Vasopressin or DDAVP may be used as an ADH replacement in diabetes insipidus, administered as a nasal spray.
  • DDAVP is also used for bedwetting (enuresis) to help retain water at night.

Scenario

• Post-sinus surgery patient voids 1800 cc of urine shortly after surgery.
• This is TOO much, raising suspicion.
• Assume the worst: Patient may be developing diabetes insipidus due to surgery affecting the pituitary.
• The patient is sleeping and feels cold later. Could indicate shock.

Signs and Symptoms of Fluid Volume Excess

• Distended neck and peripheral veins due to increased fluid volume.
• Peripheral edema and third spacing (fluid leaking out of vessels into tissues).
• Sacral edema in bedridden patients.
• Increased Central Venous Pressure (CVP) due to more volume and pressure in the right atrium.
• Wet lung sounds; patient may be short of breath.
  • Auscultate posteriorly (on the back) to best assess lung sounds.
  • Fluid accumulates in the bases of the lungs first.
• Polyuria (increased urine output) if kidneys are functioning.
• Increased pulse rate; bounding and full pulse.
• Increased blood pressure due to more volume and pressure.
• Weight gain: Acute gain/loss is usually fluid, not fat.
  • A gain of 5 pounds overnight is likely fluid retention.
  • Be aware of Heart problems when fluid retention occurs.
• Daily weights: Same time, same scales, same clothes, after voiding.

Treatment of Fluid Volume Excess

• Low sodium diet to reduce fluid retention.
• Diuretics to get rid of fluid.
  • Loop diuretics (e.g., Lasix/furosemide):
  • Bumex/bumetanide may be used if Lasix isn't effective.
  • Thiazide diuretics (e.g., hydrochlorothiazide): Cause potassium loss (hypokalemia).
• Potassium-sparing diuretics (e.g., Aldactone/spironolactone): Spares potassium, but can lead to hyperkalemia.
• Bed rest induces diuresis by increasing kidney perfusion when supine.

Hazards of Immobility

• Blood clots (thick blood).
• Pneumonia (thick pulmonary secretions).
• Constipation (thick bowel secretions).
• Kidney stones (concentrated blood).
• Push fluids unless contraindicated.

Interventions for Fluid Volume Excess

• Focused physical assessment (signs and symptoms).
• If the patient is improving:
  • Blood pressure decreases.
  • Pulse decreases.
  • CVP decreases.
  • Weight decreases.
  • Lung sounds clear.
• Give IV fluids slowly, especially to the elderly or very young, and patients with heart or kidney disease, to avoid pulmonary edema or fluid volume excess.
• Validate data when an LPN gets the admission history by looking at risk factors.

Hypovolemia (Fluid Volume Deficit)

• A deficit in fluid volume; severe deficit leads to shock.

Causes of Hypovolemia

• Loss of fluids from anywhere:
  • Thoracentesis, paracentesis (removing fluid from the chest or abdomen).
  • Vomiting, diarrhea.
  • Hemorrhage (obvious fluid loss).
  • NG tube hooked to suction (less obvious fluid loss).
• Third spacing: Fluid is in a place that does no good (not in the vascular space).
  • Burns: Fluid shifts to the interstitial space or outside the body.
  • Ascites: Fluid accumulates in the abdomen (peritoneum); causes breathing problems.
    • Measure abdominal girth daily.
    • Elevate patient; do not make them lie flat.
  • Intestinal obstruction: Fluid shifts into the intestines.

Diabetes and Particle Induced Diuresis

• Polyuria: Excessive urination, commonly seen in diabetes.
• Particle-induced diuresis (PID):
  • In diabetes, the vascular space is full of sugar particles.
  • Kidneys try to help by excreting the sugar, but particles must go out in fluid, leading to volume loss.
  • Polyuria can lead to shock.
  • This is why DKA patients may be in shock upon arrival to the ER.
• Kidneys failing.
• Polyuria can switch to oliguria (decreased urine output) or anuria (no urine output) as the kidneys become damaged due to trying to get rid of the amount of particles.
  • When kidneys are oliguric or anuric, number one concern is renal failure.

Signs and Symptoms of Hypovolemia

• Weight loss.
• Decreased skin turgor, dry mucous membranes.
• Decreased urine output as kidneys try to conserve fluid.
• Blood pressure decreases due to less volume, less pressure.
• Pulse increases as the heart tries to pump what little fluid is left.
• Weak and thready pulse.
  • Artery is very small, like a thread.
• Decreased CVP.
• Small peripheral and neck veins.
• Difficult IV insertion.
• Cool extremities.
  • Peripheral vasoconstriction shunts blood to vital organs.
• Concentrated urine (high specific gravity).

Treatment of Hypovolemia

• Mild deficit: Oral (PO) fluids.
• Severe deficit: Intravenous (IV) fluids.
  • Isotonic solutions: Stay in the vascular space.
    • Examples: Normal saline (0.9% NaCl), Lactated Ringer's (LR), D5W (Dextrose 5% in water).
    • Normal saline is used to irrigate NG tubes because it is isotonic and won't cause fluid shifts.
  • Hypotonic solutions: Go into the vascular space briefly, then move into the cells for rehydration; do not stay in the vascular space and won't drive up blood pressure.
  • Hypertonic solutions:
    • Packed with particles.
    • Examples: Hyperalimentation (TPN), hypertonic saline (3% NaCl), D50 (dextrose 50% in water).
    • TPN is packed with all kinds of particles.
    • Hypertonic saline is packed with sodium particles.
    • D50 is packed with sugar particles and used for unconscious patients with low blood sugar.