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X Clin Lab Med > Sodium Disorders > Flashcards

Sodium Disorders Flashcards

1
Q

What is total body water?

A 
60% of total body weight (2/3 is ICF and 1/3 is ECF)
TIE 60, 40, 20
Total body fluid is 60%
ICF is 40% body weight
ECF is 20% body weight
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2
Q

What gender has more percent of weight being water?

A

Males (by 10%)

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3
Q

What body type has more body water?

A

Lean (b/c fat will have no water in it)

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4
Q

Primary ions of ECF

A

Na (principle cation) and Cl

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5
Q

Primary ions of ICF

A

K and PO4/organic anions

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6
Q

What is osmolality?

A

Total solute concentration in a fluid compartment

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7
Q

What solutes determine calculated osmolality of ECF?

A

Sodium, glucose and urea

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8
Q

Normal osmolality range

A

280-295 mOSM/kg

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9
Q

How to calculate osmolality

A

(2xNa) + (glucose/18) + (BUN/2.8)

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10
Q

When do sxs occur regarding osmolality?

A

> 320mmOsm/kg or <265 mOSM/kg

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11
Q

What are other osmotically active substances that aren’t in the calculated osmolality?

A

Mannitol (and other proteins)
Ethanol, methanol and ethylene glycol
*will see an elevated osmolal gap over 10

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12
Q

What is tonicity?

A

Ability of the combined effect of all of the solutes to generate osmotic driving force that causes water movement from one compartment to another

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13
Q

How can a solute increase ECF tonicity?

A

That solute must be confined to the ECF (Na, glucose, mannitol)

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14
Q

Does urea contribute to osmolality or tonicity?

A

ONLY osmolality because it easily crosses cell membranes and can distribute evenly throughout total body water

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15
Q

What happens when there is decreased tonicity of the ECF due to decreased Na?

A

Shift of water from ECF to ICF and cells will swell with the extra water

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16
Q

What is the major determinant of the size of the extracellular fluid volume?

A

Total amount of Na in the ECF (so increase it and get hypervolemia)

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17
Q

What does serum [Na+] refer to?

A

Amount of water relative to Na in the ECF (NOT total body amt of Na)
High Na: too little water relative to sodium etc

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18
Q

What is a marker of abnormal sodium control?

A

Abnormality with the size of the ECFV

High ECFV: too much sodium etc

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19
Q

What is clinical volume status proportional to?

A

Size of the ECFV

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20
Q

Causes of hypovolemia

A 
GI losses (bleed, vomit, diarrhea)
Renal losses (diuretics, diabetes insipidus)
Skin losses (sweat, burns)
Sequestration without loss (intestinal obstruction, pancreatitis, rhabdo)
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21
Q

Presentation of hypovolemia

A

Increased thirst/ decreased sweating
Decreased skin turgor and dry mucous membranes
Oliguria with increased urine concentration
CNS depression
Weakness and muscle cramps
Decreased BP (postural hypotension/dizziness)
Increased pulse, postural pulse increase

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22
Q

Main causes of hypervolemia

A

Heart failure
Liver disease
Acute/chronic renal failure
(nephrotic syndrome, primary hyperaldosteronism, pregnancy)

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23
Q

Presentation of hypervolemia

A 
Edema
SOB
Orthopnea, PND
JVD
Hepatojugular reflux
Crackles on pulm exam
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24
Q

What is water retention influenced by?

A

Thirst and ADH

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25
Q

What is salt retention influenced by?

A

RAAS, ANP and catecholamines

GFR, RBF etc

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26
Q

Actions of aldosterone

A

Increase renal Na reabsorption

Increase renal K secretion

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27
Q

What is the most common electrolyte abnormality in hospitalized pts?

A

Hyponatremia

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28
Q

When is hyponatremia severe?

A

Serum sodium <120 (sometimes below 125 is when you see sxs)

*faster the decrease, the more severe the sxs

29
Q

What diseases are associated with hyponatremia?

A

Pulmonary or CNS disorders

30
Q

Manifestations of hyponatremia

A 
HA/dizzy
N/v
Lethargy
Weakness
Confusion
Hypoventilation/ respiratory arrest
Seizures (frequent when severe)
Coma, death
**sxs depend on level of cerebral edema
31
Q

Causes of hyponatremia

A

Pseudohyponatremia
Redistributive hyponatremia
Hypo/hyper/euvolemic hyponatremia (must determine their volume status)

32
Q

What is pseudohyponatremia?

A

Falsely low serum sodium (serum Na<135 but normal osmolality–isoosmolar)

33
Q

What does pseudohyponatremia occur with?

A

Hyperlipidemia and hyperproteinemia (also with obstructive jaundice and multiple myeloma)

34
Q

How is pseudohyponatremia classified?

A

As a laboratory artifact (relative % of water reduced and flame photometry reports artificially low sodium)
*if suspected then there are more specialized tests that can be done

35
Q

What causes redistributive or hyperosmolar hyponatremia?

A

Osmotically active solutes in extracellular space that draw H2O from cell diluting serum sodium concentration (increased glucose in ECF causes shift of water from ICF to ECF thus lowering serum Na)

36
Q

Common metabolic cause of hyperosmolar hyponatremia

A

Hyperglycemia

37
Q

Causes of hypervolemia hyponatremia

A

Hepatic cirrhosis
CHF
Renal failure

38
Q

Tx of hypervolemia hyponatremia

A

Diuretics, dialysis, fluid restriction

39
Q

Causes of hypovolemia hyponatremia

A 
Renal losses (diuretics, osmotic diuresis, Addisons)
Non renal losses (external GI like vomiting or diarrhea, internal GI like pancreatitis or peritonitis, burns)
40
Q

Tx for hypovolemic hyponatremia

A

Replace fluid losses (with isotonic fluid) and treat underlying cause

41
Q

Causes of euvolemic hyponatremia

A

SIADH
Psychogenic polydipsia (urine maximally dilute)
Hypothyroidism
Adrenal insufficiency

42
Q

Tx for euvolemic hyponatremia

A

Fluid restriction, treat underlying cause

43
Q

What is SIADH?

A

High levels of ADH that impairs free water excretion but sodium continues to be excreted normally

44
Q

Hallmark lab findings of SIADH

A

Concentrated urine (>100mOsm/kg) with low serum osmolality and euvolemia

45
Q

Causes of SIADH

A 
CNS disease-MRI/CT r/o
Pulmonary disease (small cell lung CA)-CXR
Meds
Major surgery
Stress
Psych
Pain
Good amount of hospitalized pts get it
46
Q

Tx for SIADH

A 
Fluid restriction
Treat underlying pathology
Refractory cases (hypertonic saline, democlycline, urea, lithium, vaptan)
47
Q

Labs for nyponatremia

A

First look: UAna, UAosm, serum osm, CMP

Second look: TSH, serum cortisol

48
Q

When should you hospitalize a pt with hyponatremia?

A

Na<125 or symptomatic

49
Q

What can a rapid increase in serum sodium lead to?

A

Cerebral pontine myelinolysis (osmotic demyelination syndrome)

50
Q

When do you use hypertonic solutions for hyponatremic pts?

A

Severe symptomatic cases

51
Q

Traditional tx of chronic hyponatremia

A

Demeclocycline to induce nephrogenic DI

vaptans are newer and are vasopression receptor antagonists

52
Q

What is the rate of correction for pts with severe symptomatic hyponatremia vs chronic hyponatremia?

A

Severe: 6-12 mEq/L in first 24 hrs and <18mEq/L in 48 hrs
Chronic: <8 mEq/L in first 24 hrs–don’t overcorrect
*check serum Na q2h

53
Q

What is central pontine myelinolysis?

A

Poorly understood but characterized by focal demyelination in pons and extra pontine areas (irreversible!)

54
Q

Presentation of central pontine myelinolysis

A

Dysarthria, dysphagia, seizures, altered mental status, quadriparesis, hypotension etc– usually 1-3 days after over correction

55
Q

What is hypernatremia?

A

Hypertonic disorder due to serum sodium>145mEq/L
“too little water relative to salt”
Due to brain shrinkage secondary to increased ECF osmolality

56
Q

Causes of hypernatremia

A

Too little dietary water
Too much dietary salt
Excessive water loss from body
-GI losses, skin loss, renal loss, drug related, osmotic diuresis (hyperglycemia, increased mannitol)

57
Q

Presentation of hypernatremia

A 
Often asymptomatic
Thirst, signs of volume depletion
AMS, weakness
Neuromuscular irritability
Focal neurologic deficits
Seizures or coma
*sxs related to rate of onset
58
Q

What is bodys normal response to hypernatremia?

A

Create thirst and increase fluid intake

Maximally concentrate urine to prevent further water loss (vast majority are due to water loss)

59
Q

One of most common causes of hypernatremia

A

Diabetes insipidus

60
Q

What is diabetes insipidus?

A

Nonosmotic urinary water loss in setting of elevated serum sodium (urine is dilute when it should be concentrated–collecting ducts are impermeable to water and it is not reabsorbed)

61
Q

What is central DI?

A

Due to impaired secretion of ADH (neurogenic DI)

Typically treated with desmopression (inhaled dDAVP nasal spray or IV)–ADH analog

62
Q

What is nephrogenic DI?

A

Lack of kidney response to ADH, causing continued water loss even though pt is low on water
*adequate ADH present

63
Q

Cause of nephrogeneic DI

A

Can be genetic or acquired (from chronic renal insufficiency, tubulointerstitial renal disease, amyloidosis, lithium toxicity)

64
Q

Tx for nephrogenic DI

A

Thiazide diuretic
Amiloride (K sparing diuretic)
Chlorpropamide (antidiabetic oral agent)
NSAIDs have been tried (indomethacin)

65
Q

Tx of hypernatremia

A

Hospitalize if severe
Stop water loss
Replace water deficit (oral, NG tube or IV hypotonic fluid)

66
Q

Why should you not replace fluids too rapidly in hypernatremia?

A

*especially if it has been there for several days

Can cause seizures, brain damage and CPM (if acute then can correct rapidly)

67
Q

What is the importance of water deficit?

A

Must be calculated in order to replace free water in hypernatremia
-how much pt will need to drink etc to correct

68
Q

How to calculate water deficit

A

Water deficit=normal TBW-current TBW
Normal=.6 X body weight in kg
Current=(normal serum Na x normal TBW)/measured serum Na

X Clin Lab Med (4 decks)

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