Sodium Disorders

Question 1

Which electrolytes are present intracellularly?

Answer 1

-Potassium (K): 3.5 - 5 meq/L

-Magnesium (Mg): 1.5 - 2 meq/L

-Phosphorus (P): 2.5 - 4.5 mg/dl

Question 2

Which electrolytes are present extracellularly?

Answer 2

-Sodium (Na): 135 - 145 meq/L

-Chloride (Cl)

-Bicarbonate (HCO3-)

Question 3

Normal range of sodium (Na)

Answer 3

135 - 145 meq/L

Question 4

Hyponatremia VS Hypernatremia

Answer 4

Hyponatremia: Na < 135 mEq/L

Hypernatremia: Na > 145 mEq/L

Question 5

Most common electrolyte disorder

Answer 5

Hyponatremia
-low serum sodium

Question 6

Categorization of Hyponatremia

Answer 6

-Hypotonic Hyponatremia: low serum Osm
(< 275mOsm/kg)

-Hypertonic Hyponatremia: high serum Osm
(>290 mOsm/kg)

Question 7

Symptoms and Signs of Hyponatremia

Answer 7

-generally asymptomatic
-symptoms if Na < 120 mEq/L:
N/V, headache, confusion, fatigue, muscle weakness, seizure, coma

Question 8

Factors that determine the treatment of Hyponatremia

Answer 8

-Cause of hyponatremia
-Presence or absence of symptoms
-chronicity of hyponatremia (how long has the patient been hyponatremic)

Question 9

Meaning and most common cause of HYPERTONIC Hyponatremia

Answer 9

-Meaning: excess of solutes

-most common cause: Hyperglycemia, patient admitted with diabetic ketoacidosis (DKA)

-Calculation of corrected Na (it might actually not be hyponatremic after accounting for the glucose)

Question 10

Equation for corrected Na value
NOT on the EXAM
NAPLEX

Answer 10

Na(corrected) =
Na measured + [(BGmeasured - 100) / 100] *1.6

Question 11

Treatment of Hypertonic Hyponatremia

Answer 11

-treat the underlying disease state: often diabetes -> treat the blood sugar

-don’t give sodium or fluids due to low Na levels
What would happen?

Question 12

Types of HYPOTONIC Hyponatremia

Answer 12

-Hypovolemic: low volume of water + greater deficit in sodium

-Euvolemic: slight excess in body water, normal body sodium,

-Hypervolemic: significant excess of body water, slight excess in body sodium

Question 13

Causes of HYPOTONIC HYPOVOLEMIC Hyponatremia

Answer 13

(great sodium deficit, low body volume)
Renal or Extra-renal

S/sx: dehydration, dry mouth, low UOP

-> Use urine Na U(Na) to differentiate between renal and extra-renal

Question 14

How to differentiate between Renal or Extra-renal causes of HYPOTONIC HYPOVOLEMIC Hyponatremia

Answer 14

-Use urine Na U(Na) to differentiate between renal and extra-renal

Question 15

How to treat HYPOTONIC HYPOVOLEMIC Hyponatremia

Answer 15

Fluids

outpatient: electrolyte replacement solution: Gatorade, Powerade, Pedialyte

inpatient: IV Fluids containing sodium salt

Question 16

What are the urine sodium levels in a HYPOTONIC HYPOVOLEMIC Hyponatremic patient -> with a renal cause?

Answer 16

Renal cause: high U(Na): > 20 mEq/L

-the kidney is not able to keep the sodium

-> due to drugs: diuretics
-> due to disease: renal tubular acidosis, osmotic diuresis, cerebral salt wasting

-electrolyte replacement solution + HOLD diuretics

Question 17

What are the urine sodium levels in a HYPOTONIC HYPOVOLEMIC Hyponatremic patient -> with Extra renal cause?

Answer 17

Extra-renal: low U(Na): <20 mEq/L

low volume, low sodium
but here the kidney is able to retain the sodium -> U(Na) is low -> so the problem would be somewhere else -> probably GI related

-N/V, third spacing (fluid collection in a third space - abdomen f.e.), burns (drainage from burned tissue)

Question 18

Calculate Na deficit

Answer 18

1. Subtract current sodium from desired sodium
2. multiply by 0.6 * wt (kg) = … mEq needed to replace

Question 19

Causes of Hypotonic Euvolemic Hyponatremia

Answer 19

-no sodium deficit, slight excess in body water (dilutional effect)

-Causes:
SIADH (most common)
small cell lung cancer, pancreatic cancer
head trauma
Meds: Carbamezapin (CBZ), SSRis
Glucocorticoid deficiency (when you get off steroids abruptly?)
Beer protomania

Question 20

SIADH Pathophysiology

Answer 20

the patient produces too much ADH -> causing water to be transported into the blood via aquaporins

-Euvolemic Hyponatremia

Question 21

Treatment of Hypotonic Euvolemic Hyponatremia

Answer 21

-DC offending agent
-water restriction (restrict from water intake)
-diureses +/- hypertonic saline
-Vasopressin antagonists (aquaretics)
-Demeclocycline

Question 22

Vasopressin Antagonists

Answer 22

-Conivaptan (Vaprisol)
-Tolvaptan (Samsca) - oral, avoid in liver impairment
-Demeclocycline works the same way

-selective water diuresis (aquaresis): no change in sodium or potassium excretion
-short-term fix
-not seen often, costly

Question 23

MOA of Vasopressin Antagonists

Answer 23

Blockage of V2 receptors on the convolute tube -> water diuresis (elimination of free water)

Question 24

Hypotonic Hypervolemic Hyponatremia

Answer 24

-low serum Osm, excess in body water + slight excess of body sodium

Question 25

Causes of Hypotonic Hypervolemic Hyponatremia

Answer 25

-HFrEF
-Cirrhosis
-CDK

Question 26

Treatment of Hypotonic Hypervolemic Hyponatremia

Answer 26

-fluid restriction
-diuresis
-treatment of underlying conditions (CKD, cirrhosis, HFrEF)

-treatment based on diuresis, not sodium replacement (unless symptomatic)

Question 27

When to treat patients with saline in Hypotonic Hypervolemic Hyponatremia?

Answer 27

-Hypertonic saline (3% (common), 7%, 23.4%)
-when symptomatic: seizure, coma, evidence of cerebral edema) Na: <120 mEq/L

Question 28

How to approach sodium correction

Answer 28

-treat with saline treatment, but not aggressively

-maximum sodium correction in asymptomatic patients is 6-8 mEq/L per 24h, complete correction in 48-69h

-rapid correction (>12 mEq/L in 24h) can cause central pontine myelinolysis/ osmotic demyelination syndrome
-paralysis, dysphagia, loss of consciousness
-irreversible brain damage

Question 29

Central pontine myelinolysis/ osmotic demyelination syndrome

Answer 29

rapid rise of serum sodium can cause a quick efflux of water out of the brain
-> dehydration of the myelin sheath (myelin layer)

-correction should not be more than 6-8 mEq/L in 24h

Question 30

Causes of Hypernatremia

Answer 30

-often due water loss - less commonly due to sodium gain

-Causes:
diabetes insipidus (central or nephrogenic)
insensible losses
GI losses (diarrhea)
Iatrogenic (Na-rich IV fluids)

Question 31

Symptoms and signs of Hypernatremia

Answer 31

-generally asymptomatic
-confusion, coma

Question 32

Hypovolemic, Euvolemic, Hypervolemic Hypernatremia

Answer 32

Hypovolemic: Water losses
Euvolemic: Diabetes insipidus
Hypervolemic: Exogenous sodium

Question 33

Which lab values are expected in Hypovolemic Hypernatermia?

Answer 33

low volume, high osmolality, concentrated urine: >6: UOsm: >600 mOsm/kg (highly concentrated)
U(Na): < 20 mEq/L

-water replacement (PO or IV (with D5W))

Question 34

Treatment of Euvolemic Hypernatremia

Answer 34

-Treat the disease

-Cause: Diabetes Insipidus
if central: pituitary injury or disease
if nephrogenic: drugs (lithium), genetic disorders

Labs: UOsm: <300 mOsm/kg

Question 35

Pathophysiology of Diabetes Insipidus

Answer 35

Normally: The pituitary gland produces ADH -> Aquaporins in the convoluted tube
-> increase in plasma volume and concentrated urine

-diabetes insipidus: loss of the ability to concentrate the urine
urine volume goes up (diluted urine), plasma volume goes down

Question 36

Treatment of Diabetes Insipidus

Answer 36

-Central: related to the pituitary gland (could be a timer) -> ADH (Vasopressin) deficiency -> treat with Desmopressin (DDAVP)

-Nephrogenic: renal ADH deficiency;
treat with NSAID/diuretic combo

Question 37

Treatment of Hypervolemic Hypernatremia

Answer 37

-high volume, high sodium
-due to aggressive administration of Na IV fluids

-DC fluids or medications causing it

Question 38

How to correct sodium levels in Hypervolemic Hypernatremia

Answer 38

-similar to Hypotonic Hypovolemic Hyponatremia

-do not lower sodium by more than 6-8 mEq/L over 24 h
-it may cause rapid efflux into the brain, resulting in cerebral edema