1.1 - Hyponatremia & Hypernatremia

Question 1

What is hyponatremia?

Answer 1

Hyponatremia is defined is a decreased serum sodium of less than 135 mEq/L where the normal range is 135-145 mEq/L. To maintain a normal serum sodium, water intake must equal water excretion.

Question 2

What is/causes hypotonic hyponatremia?

Answer 2

• It occurs when there is a low serum osmolality (SOsm).
• Serum Na less than 135 mEq/L and SOsm less than 270 mOsm/kg (normal is 280-295 mOsm/kg;SOsm = 2 x Serum Na)​
• There is an excess of body water with both intra- and extracellular fluid (ECF) dilution. The patient’s clinical signs occur from the excess water that causes cell swelling.

Question 3

What is/causes isotonic hyponatremia?

Answer 3

• Occurs when there is a normal sodium osmolality (SOsm), but a low serum sodium level <135 mEq/L.
• It occurs when there is a laboratory artifact, hyperlipidemia (triglycerides (1000-1500 mg/dl) that is extreme or hyperproteinemia (greater than 12-15 grams/dl) that displaces water in the lab sample.
• The patient’s body water is normal and they are asymptomatic.

Question 4

What is/causes hypertonic hyponatremia?

Answer 4

• It occurs when there is a serum Na less than 135 mEq/L but a high (290 mOsm/kg​)​ sodium osmolality (SOsm).
• There is a dilution of extracellular fluid sodium by the water shifting from cells into high concentrations of non-sodium solute (e.g. glucose or mannitol).
  
  • **Each 100 mg/dl increment in serum glucose above 100 mg/dl decreases serum Na by approximately 1.6 mEq/L**
• The patient’s clinical signs occur from the primary disorder and not from the redistribution of water

Question 5

What is/causes Hypervolemic hyponatremia?

Answer 5

It is an edematous state of excess total body sodium content with or without hemodynamic compromise. ADH secretion is stimulated. Examples include

• congestive heart failure
• hepatic cirrhosis causing peripheral vasodilation
• nephrotic syndrome with massive edema

Question 6

What is/causes Hypovolemic hyponatremia?

Answer 6

It may result from any cause of sodium loss, it is a state of deficient total body sodium content, ADH secretion is stimulated. Examples include:

• Blood loss
• Non renal causes: GI fluid loss (vomiting, diarrhea, tube loss)
• renal fluid loss through diuresis or aldosterone deficiency (adrenal insufficiency), impaired renal tubular function leadings to salt and water loss
• Skin fluid loss (insensible loss)
• Thiazide diuretics

Question 7

What is/causes euvolemic hyponatremia?

Answer 7

It occurs when there is a normal body sodium content, no edema, normal hemodynamics Examples include:

• SIADH – most frequent cause
• use of diuretics
• renal failure both acute and chronic,
• Moderate to severe hypothyroidism
• water ingestion exceeding excretion

Question 8

What are the symptoms associated with hyponatremia?

Answer 8

Neurological symptoms –primary symptoms; related to brain swelling from water excess

• Severity parallels fall in serum sodium
• More pronounced with acute (1-2 days) state versus chronic state
• Acute hyponatremic encephalopathy can result in acute cerebral edema and is considered a medical emergency

Question 9

Describe the symptoms associated with hyponatremia and their correlation with serum sodium levels

Answer 9

Serum Na = 120-125 mEq/L

• Acute: Nausea, malaise, gait instability
• Chronic: none to gait instability (fall risk in elderly)

Serum Na = 110-120 mEq/L

• Acute : headache, confusion, lethargy, nausea
• Chronic: Occasionally none to mild confusion or lethargy

Serum Na less than 110 mEq/L

• Acute: nausea, seizures, coma
• Chronic: Rarely none, greater confusion or lethargy

Question 10

What are some physical findings associated with hyponatremia?

Answer 10

• General neurologic depression, rarely focal
• Major findings may reflect the underlying conditions, look at medications closely
• Cardiovascular focus: Hyper – or hypovolemia may stimulate ADH release
  
  • Hypervolemia: edema, ascites, pulmonary crackles, cardiac gallop, JVD
  • Hypovolemia: Postural fall in BP with rise in pulse, jugular venous collapse
  • Euvolemia: normal exam

Question 11

How does hypotonic hyponatremia affect urine osmolality (UOsm) concentrations?

Answer 11

If the Urine osmolality (UOsm) is less than serum osmolality in a hyponatremic state, there is a pathological cause:

• UOsm less than 100 mOsm/L: is due to water intake at rate or volume that exceeds normal renal excretion
• UOsm greater than 100 mOsm/L: may be due to ADH effect or decrease in renal ability to form water free of solutes

Question 12

How does hypotonic hyponatremia affect urine sodium (UNa) concentrations?

Answer 12

Changes in Urine sodium (UNa) in hypotonic hyponatremia are due to:

• UNa less than 20 mEq/L is seen in decreased renal blood flow, hypervolemic or hypovolemic states
• UNa greater than 40 mEq/L is seen with SIADH, diuretics, renal failure, hypothyroidism and adrenal insufficiency

Question 13

In general, what does the treatment of hyponatremia revolve around?

Answer 13

• Therapy is guided by symptoms, level of serum sodium and rapidity of development
• Rate of correction is critical to avoid CNS insult
• Only hypotonic hyponatremia requires treatment directed at serum sodium itself

Question 14

How do you treat patients with seizures or coma with serum Na less than 120 mEq/L, acute or chronic?

Answer 14

1. 3% hypertonic saline to increase serum Na by only 1-2 mEq/L/hr until Na rises by 12-15 mEq/L OR to a level of 120 mEq/L
   
   • Max correction rate is 8-12 mEq/L/24 hr or 25 mEq/L/48 hrs
2. Restrict water or total fluid intake to 1000ml/24 hours or less
3. Discontinue drugs that enhance sodium excretion
4. Treat the underlying condition
5. Serum Na should be monitored every 2-4 hours in all symptomatic patients​

Question 15

How do you treat patients with moderate symptoms or serum Na less than 115 mEq/L?

Answer 15

1. 3% hypertonic saline to increase serum Na by only 1-2 mEq/L/hr until Na rises by 12-15 mEq/L OR to a level of 120 mEq/L
   
   • Max correction rate is 8-12 mEq/L/24 hr or 25 mEq/L/48 hrs
   • OR treat on basis of volume status
2. Restrict water or total fluid intake to 1000ml/24 hours or less
3. Discontinue drugs that enhance sodium excretion
4. Treat the underlying condition
5. Serum Na should be monitored every 2-4 hours in all symptomatic patients

Question 16

How do you treat patients with hyponatremia with mild/no symptoms?

Answer 16

• If the patient is hypovolemic, give NS to correct the volume status. ADH secretion will stop, kidneys will excrete the excess water
• If the patient is Hypervolemic, administer loop diuretics. Lasix 40-80 mg IV or PO is the usual treatment. ADH stops, kidneys excrete extra water

Question 17

What are 3 conditions that cause hyponatremia and how do you treat them?

Answer 17

1. Hypothyroidism – replacement as indicated
2. Adrenal insufficiency – cortisol therapy
3. SIADH – treatment is geared at blocking the ADH effect in the kidney
   
   • Conivaptan – used in the hospitalized patient with hypervolemic or euvolemic hyponatremia only. A loading dose of 20 mg is given followed by a continuous infusion
   • Tolvaptan – Used in Hypervolemic or euvolemic hyponatremic patients only. Must be initiated in the hospital starting at 15 mg daily. Titrate to max dose of 60 mg daily, limit to 30 day course.
   • Demeclocycline – 150-300 mg PO Q6H for long-term therapy

Question 18

What is hypernatremia?

Answer 18

• _Serum Na greater than 146 mEq/_L and SOsm greater than 300 mOsm/L
• represents a state of hyper osmolality
• Always indicates hyper osmolality or a deficit of total body water
• May also be caused by a primary Na gain in addition to a water deficit which is more common

Question 19

What are 3 causes for hypernatremia?

Answer 19

1. Primary water loss can be either:

• Central (pituitary) diabetes insipidus; lack of ADH secretion
• Nephrogenic (renal) diabetes insipidus; failed response to ADH

2. Occurs when water loss exceeds sodium loss in:

• Renal osmotic diuresis seen in glucosuria of DM, Mannitol or glycerol infusion or high urea excretion in catabolic states such as burns
• GI fluid loss through persistent diarrhea or postsurgical drainage
• Cutaneous fluid loss in burns or profuse sweating

3. Excessive administration of hypertonic saline solutions

• Hypertonic sodium bicarbonate (NaHCO3) in CPR or lactic acidosis
• 3% saline infusions

Hypernatremia is a “water problem” – either excess water loss or inability to acquire water. More common in debilitated elderly, infants, handicapped

Question 20

What are the symptoms associated with hyponatremia?

Answer 20

• Abnormal findings are mostly neurologic
  
  • Related to brain cell shrinkage from water loss
  • Severity is relative to the degree and rapidity of development of hypernatremia
• Patient complaints may be thirst and polydipsia along with polyuria and nocturia (indicative of renal basis. You will see this with DI patients or patients experiencing an osmotic diuresis as in uncontrolled DM
• Hypotension, tachycardia or oliguria if the patient is volume depleted
• The major finding may reflect the underlying cause or the primary disorder than is the cause of the elevated serum Na

Question 21

Describe the symptoms associated with hypernatremia and their correlation with serum sodium levels

Answer 21

The CNS symptoms correlate with the serum Na:

• Serum Na 146-150 mEq/L – usually asymptomatic
• Serum Na 151-160 mEq/L – depends on the time frame of development. If acute you may see nausea, weakness, lethargy, confusion. If chronic condition there may be no or mild CNS symptoms
• Serum Na greater than 160 mEq/L – If it develops acutely may see stupor and coma. If it is chronically this elevated will see moderate to severe CNS symptoms

Question 22

What are some urine osmolality values seen in hypernatremia, and what does each value suggest?

Answer 22

• UOsm less than 300 mOsm/L suggests central or nephrogenic DI
• UOsm = 300-400 mOsm/L suggests osmotic diuresis
• UOsm greater than 400 mOsm/L suggests GI, cutaneous or insensible fluid losses

Question 23

How do you manage a patient with hypernatremia?

Answer 23

1. A more rapid correction of serum Na is indicated for acute, symptomatic hypernatremia but no faster than 1-2 mEq/L to avoid cerebral edema
2. Slower correction is indicated for chronic hypernatremia – maximum rate of correction should not exceed 0.5 mEq/L/hr
3. Estimate water deficit at approximately 0.4 x Body wt (kg) x {(serum Na/140)-1}
4. Discontinue any excess NS administration
5. Replace water at rate calculated to reduce serum sodium by approximately 1mEq/L in acute hypernatremia. In chronic, reduce serum sodium by half of excess above 140 mEq/L over 24 hours
6. Oral water is preferred if patient is conscious
7. Use IV therapy guidelines
8. Monitor serum Na every 2-4 hr in acute hypernatremia, every 4-6 hrs in chronic Hypernatremia
9. Assess the need to treat diabetes insipidus

Question 24

What are the IV therapy guidelines for hypernatremia?

Answer 24

• Mild volume depletion – use D5W but watch glucose to avoid hyperglycemia/glucosuria to prevent further renal water loss
• Moderate volume depletion – use 0.45%NS. The saline component will restore the ECF, the free water component repletes body water
• Severe volume depletion – use 0.9% NS initially then follow with 0.45% NS when hemodynamically stable