Lecture 2 Conditions of Sodium Imbalance

Question 1

What is the average daily Na+ intake, and how does Na+ homeostasis work?

Answer 1

1-1.5 g (adequate intake) - about 1/2 teaspoon of table salt

primary driver of osmolality in ECF - serum = (2 x [Na+]) + ([glucose]) + [blood urea nitrogen]) ⇒ normal is 280-300 mOsm/kg

actively transported out of cells via Na+K+ ATPase

kidneys responsible for Na+ excretion, responsive to changes in serum [Na+] to maintain osmolality, will conserve if needed

Question 2

Sodium Concentration Levels (Normal, Low, High)

Answer 2

Normal: 135-145 mmol/L (mEq/L) or around 280 mOsm/L

Low: hyponatremia <135 mmol/L or <280 mOsm/L, most common electrolyte abnormality encountered clinically

High: hypernatremia >145 mmol/L or >280 mOsm/L, always associated with hypertonicity and can cause reduction in ICF

Question 3

S&S of Hyponatremia (Mild/Chronic ⇒ Moderate/Severe)

Answer 3

Mild/Chronic (125-134 mmol/L) - asymptomatic, impaired attention, gait changes, postural changes, fall risk increased

Moderate/Severe (<124 mmol/L) - nausea, vomiting, H/A, lethargy, altered mental, seizures, respiratory arrest, risk of death increased

Question 4

Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)

Answer 4

Disease Induced: tumors (lung, pancreas), CNS disorders (head trauma, stroke, meningitis, pituitary surgery), pulmonary disease (TB, pneumonia)

Drug Induced: tricyclic antidepressants, phenothiazines, opioids, nicotine, carboplatin, cisplatin, bromocriptine, NSAIDs, acetaminophen

Question 5

Acute or Severely Symptomatic Hypotonic Hyponatremia Tx

Answer 5

IV solution until severe sx resolve - 3% NaCl, 0.9% NaCl

sx will usually resolve with small increase in [Na+] - ex. 5% increase or reaching 120 mmol/L

to minimize risk of osmotic demyelination syndrome the [Na+] should be corrected at rate that doesn’t exceed 6-12 mmol/L during first 24 hours

Question 6

Hypovolemic Hyponatremia Tx

Answer 6

treat underlying cause of fluid loss - GI, diuretics (reassess, dosage adjust)

reduce the elevated vasopressin release by restoring the IV volume - use solutions that remain in ECF, serum [Na+] will increase because replacement solution stays in ECF not from the Na+ content of solution

oral replacement: water, WHO-ORS, water+salt, sports drinks

NaCl infusion (ex. 0.9% NaCl)

Question 7

Hypervolemic Hyponatremia Tx

Answer 7

treat underlying cause of fluid retention - HF, nephrosis, cirrhosis

fluid restriction (1-1.2 L/day) 0 creates negative water balance, Na+ restriction (1-2 g/day)

vasopressin antagonists (tolvaptan, conivaptan) - V2 receptor: located on distal nephron; blockade of vasopressin binding decreases water reabsorption from collecting duct ⇒ large volume of water excretion, decrease in urine osmolality, increase in serum [Na+]

Question 8

Euvolemic Hyponatremia Tx

Answer 8

correct underlying cause if possible - ex. stop the drug that causes SIADH

fluid restriction (1-1.2 L/day) - create negative water balance

chronic SIADH may require solute (NaCl) tablet intake +/- loop diuretic

vasopressin receptor antagonists

Question 9

S&S of Hypernatremia

Answer 9

thirst mech (activated by vasopressin release) usually sufficient to resolve transient episodes - impairment by elders, children, disabled

mild to moderate: weakness, lethargy, restlessness, irritability, twitching, confusion

severe: seizures, coma, increased risk of death

Question 10

Classes of Hypernatremia

Answer 10

Hypovolemic: water loss faster than Na+ loss - sweating, diarrhea, vomit, high temps, usually thirst will fix this

Hypervolemic: Na+ overload (ex. overcorrect hyponatremia with 3% NaCl, etc)

Euvolemic: water loss with little or no loss of Na+ - diabetes insipidus most common cause

Question 11

What are some causes of diabetes insipidus?

Answer 11

daily urine volume > 3L

Central (low levels of vasopressin) - polyuria develops suddenly, unreplaced water loss from skin and lung, med conditions: hypodipsia, TB, head trauma, CNS malignancy, other: ethanol ingestion

Nephrogenic (renal tubules don’t respond to vasopressin) - polyuria develops gradually, med conditions: hypokalemia, hypercalcemia, kidney disease

drug induced: lithium, demeclocycline, amphotericin B

Question 12

Hypovolemic Hypernatremia Tx

Answer 12

hemodynamically stable: BP normal - oral solutions should be sufficient to correct

hemodynamically unstable: BP is low - 0.9% NaCl until hemodynamically stable ⇒ Adults: 200-300 mL/h, Children 10-20 mL/kg/h

once pt hemodynamically stable switch to 0.45% NaCl, D5W or other hypotonic solution

Question 13

Diabetes Insipidus Tx

Answer 13

Central: replace vasopressin - desmopressin acetate intranasally every 12-24 h

Nephrogenic: correct underlying (ex. hypercalcemia), if drug-induced stop or decrease dose (ex. Li+), limit Na+ intake and add thiazide diuretic - creates mild deficit in ECF which can lower urine output by increasing water reabsorption in renal tubule

Question 14

Sodium Overload Tx

Answer 14

administer D5W and loop diuretic (ex. furosemide) to facilitate Na+ elimination - measure [Na+] every 2-4 hours until <148 mmol/L and sx of hypertonicity have resolved

Question 15

How is chlorine involved in hypo and hypernatremia?

Answer 15

major ECF anion that follows Na+, normal conc is 96-106 mmol/L

Hypochloremia (<96 mmol/L) - associated with hyponatremia as well as loss of large volumes of stomach acid (ex. vomiting), diuretics may also cause, metabolic alkalosis,, Hyperchloremia (>106 mmol/L) - associated with metabolic acidosis and hypernatremia