Hyponatremia & Hypernatremia Flashcards Preview

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Flashcards in Hyponatremia & Hypernatremia Deck (17)
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1
Q

Hypertonic Hyponatremia

A

sOsm > 300mOsm / kg

Hyponatremia is caused by a shift of water from cells to the interstitium in response to elevated serum osmolarity, usually hyperglycemia

2
Q

sOsm adjustment for hyperglycemia

A

For every 100 mg/dL excess (above normal = 100) in serum glucose, serum Na+ falls by 1.6mEq/L

3
Q

Isotonic Hyponatremia

A

sOsm = 280-300mOsm/kg

Due to a lab artifact caused by any condition that reduces plasma water (hyperlipidemia, hyperprotenemia); the machine “sees” less Na+ because more of the blood volume is occupied by other solutes than by plasma water

4
Q

Hypotonic Hyponatremia

A

sOsm < 280 mOsm/kg

True alteration of the ratio between ECF Na+ and ECF water; may be hypervolemic, euvolemic, or hypovolemic

5
Q

Hypervolemic hyponatremia

A

Total body water is elevated more than total body Na+

Associated with heart failure, cirrhosis, and nephrotic syndrome which decrease EABV, causing ADH-mediated retention of water and salt; UNa is usually low

6
Q

Hypovolemic Hyponatremia - 2 categories

A

Non-osmotic release of ADH in response to decreased volume dilutes total body Na+

Associated with salt and water loss, either renal (UNa > 20) or extra-renal (UNa < 20)

7
Q

Euvolemic Hyponatremia

A

Inappropriate release of ADH; caused by:

SIADH
Hypothyroidism
Cortisol deficiency
Potomania

8
Q

SIADH - Diagnostic criteria and etiologies

A

Hypoosmotic, euvolemic hyponatremia with less-than maximally dilute urine (Uosm > 100)

Caused by carcinomas, pulmonary diseases, CNS disorders, and medications

9
Q

Clinical presentation of hyponatremia

A

Anorexia
Nausea / vomiting
Seizures
Cerebral edema

10
Q

Treatment of hyponatremia

A
Water restriction 
Furosemide - increases free water excretion 
Hypertonic NaCl (3%) 

Avoid raising serum Na too quickly to avoid central pontine myelinolysis

11
Q

Central pontine myelinolysis

A

In order to prevent cerebral edema in the setting of hyponatremia, the brain loses some of its own osmoles; if you then overload the patient with hypertonic fluid, water will leave the brain to enter the ECF and cause brain shrinkage

12
Q

3 categorical causes of hypernatremia

A
  1. Decreased total body Na+ due to loss of hypotonic fluid (i.e. free water loss > Na+ loss); loss may be renal (UNa > 20) or extrarenal (UNa < 20)
  2. Increased total body Na+ due to administration of hypertonic fluids
  3. Normal total body Na+ due to ADH deficiency (Centrial Diabetes Insipidus) or ADH resistance (Nephrogenic Diabetes Insipidus)
13
Q

Central Diabetes Insipidus

A

i.e. ADH deficiency; caused by head trauma, surgery, neoplasm

Characterized by increased urine volume (2-15L / day) and dilute urine osmolality (<200mOsm/kg)

Kidneys respond to exogenous ADH (DDAVP)

14
Q

Nephrogenic Diabetes Insipidus

A

Renal collecting duct does not respond appropriately to ADH; may be congenital (rare, X-linked) or acquired (chronic renal failure, hypercalcemia, hypokalemia, ethanol)

Administration of DDAVP does not increase urine osmolality

15
Q

Treatment of hypernatremia & Risk

A

Fluids +/- sodium

Risk of cerebral edema with fluid push; the brain protects itself from dehydration by increasing its own osmolality with production of free AAs (“idiogenic osmoles”); water repletion must occur slowly in order to allow inactivation of these solutes and avoid cerebral edema

16
Q

Clinical presentation of hypernatremia

A

Cellular dehydration occurs as water shifts out of cells, causing:

Neuromuscular irritability - hyperreflexia, twitches
Seizures
Coma
Death

Mortality rate 60-75% and 2/3 of survivors will have peermanent neurological injury

17
Q

Water replacement formula for treatment of hypernatremia

A

Water needed (L) = 0.6 x body weight (kg) x [(actual Na/desired Na) - 1]