F+E: SIADH vs Diabetes Insipidus

What hormone, also known as vasopressin, is secreted by the posterior pituitary gland in response to changes in blood osmolality?

Antidiuretic hormone (ADH)

What effect does decreased water intake have on blood osmolality, and how does ADH respond to restore normal levels?

Decreased water intake increases blood osmolality, which stimulates ADH release. ADH then increases water reabsorption in the kidneys, helping return blood osmolality to normal.

What happens to ADH secretion and kidney function with excess water intake?

ADH secretion is suppressed, leading to decreased water reabsorption in the kidney tubules and resulting in diuresis (increased urine volume).

What does a dilute urine with a fixed specific gravity of ~1.010 or a fixed osmolality of ~300 mOsm/L indicate?

An inability to concentrate and dilute urine, which is a common early sign of kidney disease.

Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

results from a failure of the negative feedback system that regulates the release and inhibition of ADH. Too much ADH!!!

SIADH Can occur secondary to 

Brain trauma/ surgery, infection, tumor, small cell lung cancer, malignances

Risk Factors for SIADH:

CNS disorders

• Head traumas

• Brain tumors

Malignancy

• Lung cancer

Pulmonary disorders

• Viral PNA

• Bacterial PNA

SIADH Symptoms

Weight gain, hypertension

Sodium Under 130:

• Muscle cramps & weakness

• Fatigue

• Anorexia

• Vomiting & abdominal cramps

Sodium under 120:

• Twitching & seizures

• Lethargy

• Confusion

• Cerebral edema

• Increased body weight

SIADH Lab Symptoms:

Low: urine output, blood osmolality, serum sodium(hyponatremia)

High: Urine specific gravity (>1.030), urine osmolality

Treatment of SIADH:

Loop Diuretics, vasopressin antagonists, hypertonic saline

Nursing Interventions for SIADH:

• Strict I&O

• Daily weights

• Fluid restriction

• Neuro checks

• Seizure precautions

Diabetes Insipidus (DI)

A water metabolism problem caused by an ADH deficiency (either decrease in ADH synthesis or an inability of the kidneys to respond to ADH).

What is the result of ADH deficiency on urine output?

It causes the excretion of large volumes of dilute urine.

What happens in the kidneys without ADH?

The distal tubules and collecting ducts do not reabsorb water, leading to polyuria and dehydration.

How does dehydration lead to the sensation of thirst?

Water loss stimulates osmoreceptors, which relay a thirst sensation to the cerebral cortex.

What does thirst promote?

Increased fluid intake

What happens if the thirst mechanism is absent or diminished?

Dehydration becomes more severe and can lead to death.

Why can’t diabetes insipidus be controlled by limiting fluid intake?

Because the high-volume loss of urine continues even without fluid replacement.

Diabetes Insipidus signs & symptoms

Skin Manifestations Poor skin turgor-- Dry mucous membranes

Neurologic Manifestations- Increased sensation of thirst- Irritability- Decreased cognition

Cardiovascular Manifestations- Hypotension-Tachycardia- Weak peripheral pulses- Hemoconcentration: Increased hemoglobin • Increased hematocrit

Renal Manifestations- Increased urine output Dilute, low specific gravity

Diabetes Insipidus labs signs & symptoms

Low: Urine Specific Gravity, Urine osmolality

High: Urine output, blood osmolality, serum sodium, hemoglobin, hematocrit

7 D’s of DI:

D-Diurese

D-Diluted

D-Dry inside

D-Drinking

D-Dehydrated

D-Decreased BP

D-Desmopressin

Nursing Interventions for DI:

• Strict I&O

• Daily weights

• Monitor VS&EKG

• Monitor electrolytes and urine specific gravity

• Neuro checks

• Dehydration assessment

Treatments for DI:

Desmopressin (DDAVP), vasopressin, hypotonic fluids