Sodium

Question 1

1. What is normal serum Na concentration?

2. What is the function of Na?

Answer 1

1. 135 to 145 mEq/L.
   NB: Na is the principal cation in the ECF while potassium is the major intracellular cation.
2. Sodium functions as the major osmotic determinant in regulating ECF volume and water distribution in the body. Other functions include determining the membrane potential of cells and the active transport of molecules across the cell membrane.

Question 2

1. Define hypernatremia?
2. What level is considered clinical relevant hyponatremia?
3. At what level do we see clinical manifestations related to CNS dysfunction?

Answer 2

1. Hypernatremia is defined as

Question 3

Upon recognition of clinical relevant hyponatremia, what factors should be determined to identify the etiology and appropriate treatment options for patients?

Answer 3

Clinicians should determine serum osmolality and volume status to identify the etiology and appropriate treatment options for patients.

Question 4

1. Serum osmolality can be directly measured or calculated. what is the formula to calculate serum osmolality?
2. What is normal serum osmolality?

Answer 4

1. serum osmolality = 2 x [Na mEq/L] + [Glu mg/dl] / 18 + [BUN mg/dl] / 2.8
2. Normal serum osmolality is 275 to 290 mOsm/kg

Question 5

1. What is hypertonic hyponatremia?

2. What causes hypertonic hyponatremia?

Answer 5

1. Serum osmolality >290 mOsm/L
2. It is caused by the presence of osmotically active substances other than Na in the ECF. Common causes include hyperglycemia and mannitol administration. The correction of serum sodium due to hyperglycemia can be calculated-see calculator.

Question 6

1. What is isotonic hyponatremia?

2. How is it cause?

Answer 6

1. Serum osmolality within the normal range 275 to 290 mOsm/kg.
2. It occurs when there is a reduction in the fraction of serum that is composed of water (excess of plasma proteins or lipids).

Question 7

1. Hypotonic hyponatremia (

Answer 7

1. Assessment of volume status is reflected by hypervolemia, hypovolemia and euvolemia.

Question 8

1. In hypovolemic hypotonic hyponatremia, what is taking place in regards to sodium and water?
2. What is the urine osmolality in these pts? What does it indicate?

Answer 8

1. In this condition, pts lose more Na in relation to water. Therefore, it is critical to determine the source of water loss.
2. Urine conc is > 450 mOsm/L. This is indicative of concentrated urine and the body’s attempt to retain fluid.

Question 9

1. In hypovolemic hypotonic hyponatremia, fluid losses could be renal or extrarenal. What attributes to the fluid losses via renal and extrarenal?
2. What is the urine sodium concentration in both situations?

Answer 9

1. Fluid losses via renal are caused by diuretic use and identified by urine Na concentration > 20 mEq/L.
2. Extrarenal losses can be due to diarrhea, fistula output, excessive sweating, burns, open wounds, and fluid drains (e.g peritoneal, thoracic, pleural, biliary, or pancreatic drains) and are commonly associated with a urine Na concentration

Question 10

What is the treatment for both renal and extrarenal losses in hypovolemic hypotonic hyponatremia?

Answer 10

Both renal and extrarenal fluid losses associated with hyponatremia are treated with isotonic fluid to expand the ECF.

Question 11

1. What conditions occurs in hypervolemic hypotonic hyponatremia?
2. What is taking place in regards to water and sodium?
3. What is the treatment in this type of hyponatremia?

Answer 11

1. Some element of end-organ damage (renal failure, hepatic failure with ascites, heart failure) is present resulting in fluid retention or third spacing.
2. These patients retain more water than sodium.
3. Treatment consists of both fluid and sodium restriction.

Question 12

1. What condition is commonly associated with euvolemic hypotonic hyponatremia?
2. What are other causes of euvolemic hypotonic hyponatremia?

Answer 12

1. Syndrome of inappropriate antidiuretic hormone (SIADH). These patients have stable sodium intake/output but retain large amounts of water due to excess ADH.
2. Other causes are psychogenic polydipsia (the ingestion of large amounts of free water), hypothyroidism, and reset osmostat ( a variant of SIADH). Treatment involves correcting the underlying condition and fluid restriction.

Question 13

1. What are common causes of SIADH?

2. What is the treatment for SIADH?

Answer 13

1. Common causes include brain or CNS malignancies, head trauma, lung malignancies, and PNA.
2. Mainstay treatment is fluid restriction of 500 to 1000ml/day and the administration of exogenous salt.

Question 14

What is guideline for the rate of sodium correction?

Answer 14

The targeted rate of sodium correction should not exceed 5 to 10 mEq/L per day to prevent demyelination.

Question 15

Define hypernatremia?

Answer 15

Hypernatremia is define as > 145 mEq/L

Question 16

True or False. In hypernatremia, all patients will have an increased serum osmolality?

Answer 16

True.

Question 17

In hypovolemic hypernatremia, it is important to determine the source of fluid loss. What are common renal and extrarenal losses?

Answer 17

Renal losses include diuretics, solute diuresis due to hyperglycemia or azotemia, or acute tubular necrosis.
Extrarenal losses include diarrhea and excessive sweating.

Question 18

How do we treat hypovolemic hypernatremia?

Answer 18

Treatment of hypovolemic hypernatremia involves replacing these hypotonic fluids either via enteral or parenteral.

Question 19

1. What is the most common cause of euvolemic hypernatremia?

2. What is the treatment for euvolemic hypernatremia?

Answer 19

1. Diabetes Insipidus (DI). These patients have water loss that exceeds sodium losses.
2. Treatment requires replacing of water either via the enteral or parenteral route.

Question 20

1. What are common causes of hypervolemic hypernatremia?

2. What is the treatment for this condition?

Answer 20

1. Causes can be iatrogenic (excess administration of isotonic or hypertonic sodium) or due to mineralocorticoid excess.
2. Treatment involves correcting the underlying disorder, administering diuretics, and replacing the water.