1 Sodium Disorders Flashcards

1
Q

What makes up the electrolyte panel?

A
Sodium (Na)
Potassium (K)
Chloride (Cl)
Bicarbonate (CO2)
Calcium
Magnesium*
Phosphate*

*Not usually part of BMP, will usually have to order them separately

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2
Q

Total body water = _____% of total body weight

A

60%

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3
Q

Of the total body water, how much is in the ICF and how much in the ECF?

A

2/3 ICF

1/3 ECF (interstitial fluid and plasma)

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4
Q

Percentage total body water in Newborns vs Adult Males vs Adult Females vs Elderly

A

Newborns = 80%
Adult Males = 60%
Adult Females = 50%
Elderly = 45%

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5
Q

Total body water of an obese person is …

A

Much lower than total body water in a lean person

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6
Q

What does “TIE 60,40,20” mean?

A

Total body water = 60%
Intracellular water = 40% (2/3 of 60)
Extracellular water = 20% (1/3 of 60)

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7
Q

In the ECF, how much is interstitial fluid and how much is plasma?

A

3/4 Interstitial fluid

1/4 plasma

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8
Q

Most important ECF cation?

A

Sodium

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9
Q

Most important ICF cation?

A

Potassium

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10
Q

Most important ECF anion?

A

Chloride

And some HCO3- (but mostly Cl-)

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11
Q

Most important ICF anion?

A

PO4 and organic anions

Oh and some protein

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12
Q

Total solute concentration in a fluid compartment

A

Osmolality

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13
Q

What are the main solutes that determine the calculated osmolality of the ECF?

A

Sodium
Glucose
Urea

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14
Q

Normal range of osmolality

A

280-295 mOsm/kg

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15
Q

How do we calculate Osmolality?

A

(2 x Na) + (Glucose/18) + (BUN/2.8)

SODIUM is the biggest factor

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16
Q

Symptoms occur if osmolality is > _____ or < ______.

A

> 320 mOsm/kg or <265 mOsm/kg

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17
Q

Other “osmotically active” substances that aren’t included in the calculated osmolality (because they aren’t supposed to be there)

A

Mannitol (given as a med for cerebral edema) and various proteins

Ethanol, methanol, and ethylene glycol

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18
Q

High amounts of osmotically active substances in the blood can lead to an elevated…

A

Osmolal Gap (Measured Osmolality - Calculated Osmolality)

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19
Q

What is the normal Osmolal Gap?

A

<10

If it’s greater than 10, it’s usually because of ethanol, methanol, or ethylene glycol

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20
Q

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

A

Tonicity

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21
Q

To increase ECF tonicity, a solute must be …

A

Confined to the ECF compartment (unable to cross from ECF to ICF

Examples: SODIUM, glucose, mannitol

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22
Q

______ easily crosses cell membranes and therefore distributes evenly throughout total body water (contributing to OSMOLALITY , but NOT TONICITY)

A

Urea

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23
Q

Why do we care about tonicity?

A

Because it affects the size of cells

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24
Q

Decreased Na+ —> decreased tonicity of the ECF —>

A

Shift of water from ECF to ICF —> cells (including brain cells) swell with extra water

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25
Q

What is the major determinant of the size of ECFV (extracellular fluid volume)

A

Total amount of Na+

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26
Q

Increased Na+ —>

A

Increased ECFV or HYPERVOLEMIA

Think edema

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27
Q

Decreased Na+ —>

A

Decreased ECFV or HYPOVOLEMIA

think dry patient

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28
Q

90-95% of the total body sodium is located in…

A

The ECF

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29
Q

Serum [Na+] (lab value) primarily refers to …

A

The amount of water relative to Na+ in the ECF (NOT the total body Na+ amount)

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30
Q

Abnormal serum Na+ is a sign of …

A

A disorder of water regulation

High Na+ = too little water relative to sodium

Low Na+ = too much water relative to sodium

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31
Q

The ECFV is determined by …

A

Overall volume status of the patient

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32
Q

An abnormality with the size of the ECFV is a marker of…

A

Abnormal sodium control (too much/too little total body sodium)

High ECFV = “too much sodium”
Low ECFV = “too little sodium”

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33
Q

How do we describe a patient’s volume status?

A

Hypovolemic

Euvolemic

Hypervolemic

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34
Q

Common causes of hypovolemia

A

Anything that causes dehydration

GI losses (bleeding, NG suction, diarrhea, vomiting)

Renal losses
• Salt and water loss: diuretics
• Water loss: diabetes insipidus

Skin losses: sweat, burns

Sequestration without loss
• Intestinal obstruction
• Pancreatitis
• Rhabdomyolysis

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35
Q

Clinical features of hypovolemia

A

Increased thirst, decreased sweating
Decreased skin turgor & dry mucus 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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36
Q

Common causes of hypervolemia

A
Acute or chronic renal failure
Nephrotic syndrome
Primary aldosteronism
Cushing’s syndrome
Liver disease***
Heart failure***
Pregnancy
37
Q

Clinical features of hypervolemia

A
Edema
SOB
Orthopnea, paroxysmal nocturnal dyspnea 
Jugular venous distention 
Hepatojugular reflux
Crackles on pulmonary exam
38
Q

Water retention is influenced by:

A

Thirst

ADH aka vasopressin

39
Q

Salt retention is influenced by:

A

Renin-Angiotensin system***

Also:
ANP and catecholamines
Renal function
Renal blood flow

40
Q

ADH is produced in the _________, then transported to the ________, from which it is released into the blood stream

A

Hypothalamus —> Posterior Pituitary

41
Q

Aldosterone’s main actions are:

A

Increase renal sodium reabsorption (Na+ retention)

Increase renal potassium secretion (K+ excretion)

42
Q

What is the most common electrolyte abnormality in hospitalized patients?

A

Hyponatremia

A hypotonic disorder due to serum sodium <135

43
Q

What is a normal serum [Na+]?

A

135-145 (varies by lab)

44
Q

Mild Hyponatremia is a [Na+] of…

A

125-135

45
Q

Moderate hyponatremia is a serum [Na+] of ..

A

120-125

46
Q

Severe hyponatremia is a serum [Na+] of …

A

<120

Life threatening if [Na+] < 120 with SEIZURES

47
Q

The “danger zone” for [Na+] is …

A

Below 125 (patients not generally symptomatic until about 125)

48
Q

Hyponatremia can be acute or chronic, so always compare a low [Na+] to…

A

The patient’s BASELINE sodium

The faster the Na decreases —> the more severe the symptoms

49
Q

Hyponatremia is most common in what populations?

A

The very young and the very old

Can also be seen in association with pulmonary disease or CNS disorders

50
Q

Symptoms of hyponatremia depend upon …

A

Level of cerebral edema

Headache, dizziness
N/V
Lethargy, weakness
CONFUSION
Hypoventilation, respiratory arrest
SEIZURES
COMA
DEATH!!!
51
Q

Condition characterized by falsely low serum sodium

A

Pseudohyponatremia

Serum Na<135 but NORMAL osmolality (Isoosmolar)

This is a LABORATORY ARTIFACT - relative % of water reduced and FLAME photometry reports artificially low sodium

52
Q

Patients with what conditions can have pseudohyponatremia?

A

Hyperlipidemia and hyperproteinemia

Can also occur with obstructive jaundice and multiple myeloma

53
Q

What should you do if you suspect pseudohyponatremia?

A

Speak to your lab about more specialized tests to confirm true sodium level

54
Q

What is redistributive or hyperosmotic hyponatremia?

A

A hyperosmotic state (“relative hyponatremia”) caused by osmotically active solutes in ECF that draw H2O from cell, diluting serum sodium concentration

Increased glucose in ECF causes shift of water from ICF —> ECF, thus lowering serum Na

55
Q

What is the most common cause of redistributive or hyperosmolar hyponatremia?

A

Hyperglycemia!

Because it elevates osmolality and makes Na+ look super low

56
Q

How do you calculate corrected [Na+] in patients with redistributive or hyperosmolar hyponatremia?

A

Add 1.5mEq/L to sodium value for every 100mg/dL serum glucose > 100mg/dL

Ex: if labs show Na = 125 and Glucose = 400

400-100= 300 so 3x1.5 = 4.5

Corrected Na = 125 + 4.5 = 129.5

57
Q

Hypervolemic hyponatremia is commonly caused by…

A

Hepatic cirrhosis

CHF

Renal Failure

58
Q

Treatment for hypervolemic hyponatremia?

A

Diuretics, dialysis, fluid restriction

59
Q

What are some renal causes of hypovolemic hyponatremia?

A

Diuretics (esp thiazides)
Osmotic diuresis
Addison’s disease*** Primary adrenal insufficiency —> low cortisol (which controls ADH)

60
Q

What are some non-renal causes of hypovolemic hyponatremia?

A

External GI: vomiting, diarrhea, NG suction, fistula
Internal GI: pancreatitis, peritonitis
Burns

61
Q

Treatments for hypovolemic hyponatremia?

A

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

62
Q

What are some causes of euvolemic hyponatremia?

A

SIADH

Psychogenic polydipsia (drinking too much water)

Ecstasy intoxication (can cause psychogenic polydipsia)

Hypothyroidism

Adrenal insufficiency

63
Q

Treatment for Euvolemic hyponatremia?

A

Fluid restriction, treat underlying cause

64
Q

Hallmark findings in SIADH

A

Concentrated urine (>100mOsm/kg) with low serum osmolality and euvolemia (so long as kidneys working well)

65
Q

Causes of SIADH

A
CNS disease
Pulmonary disease (esp SMALL CELL LUNG CA****)
Meds
Major surgery
Stress
Psych
Pain
66
Q

Upwards of 35% of hospitalized patients can develop …

A

SIADH

67
Q

How is SIADH diagnosed?

A

Check urine and serum osmolality - urine should be highly osmolar, but serum should be low osmolar

Determine underlying cause:
• CT/MRI of head to check for CNS disorder
• CXR to check for lung tumor/infection
• Review all patient meds

68
Q

How do you treat SIADH?

A

FLUID RESTRICTION (usually sufficient on its own)

Treatment of underlying pathology

For refractory cases:
• Hypertonic saline
• Democlycline
• Urea
• Lithium
• Vaptan
69
Q

What labs do you look at first in cases of hyponatremia?

A

First look at: UA(Na), UA (Osm), Serum Osm, CMP (serum Na)

Second: TSH, serum cortisol

70
Q

Treatment of hyponatremia depends upon…

A

The underlying cause

71
Q

When do you hospitalize a patient with hyponatremia?

A

If Na<125 OR symptomatic

Chronic hyponatremia must be managed with extreme care

72
Q

Why is slow, cautious correction of serum sodium important?

A

Rapid increase in serum sodium can lead to cerebral pontine myelinolysis (CPM) - aka osmotic demyelination syndrome - b/c of quick water shifts in and out of brain

73
Q

Traditional treatment of chronic hyponatremia is …

A

Demeclocycline (to induce nephrogenic DI)

“Vaptans” are a new class of treatment agents which are vasopressin receptor antagonists

74
Q

What should the rate of correction be in patients with severe symptomatic hyponatremia?

A

6-12 mEq/L in the first 24 hours and ≤18 mEq/L in 48 hours

If chronic hyponatremia, should try to keep it ≤8mEq/L in the first 24 hours

Check serum sodium q2h as you are replacing, to make sure you are not over correcting

75
Q

What is Central Pontine Myelinolysis

A

A poorly understood entity characterized by focal demyelination in the pons and extra-pontine areas

IT IS IRREVERSIBLE

Dysarthria, dysphagia, seizures, altered mental status, quadriparesis, hypotension, etc begin 1-3 days after overcorrection

76
Q

Clinical features of hypernatremia are due to …

A

Brain shrinkage secondary to increased ECF osmolality

77
Q

Causes of hypernatremia

A

GI losses: common in elderly and infants with diarrhea

Skin loss: sweating, fever, etc

Renal loss

Drug related: diuretics (thiazides usually cause hypo but other diuretics can cause hyper), lithium (b/c it can induce nephrogenic DI)

Osmotic diuresis from Hyperglycemia or increased mannitol

78
Q

In general, which is more common: Hypo- or Hypernatremia?

A

Hyponatremia

79
Q

Clinical features of hypernatremia?

A

Often asymptomatic

Thirst, signs of volume depletion

AMS, weakness

Neuromuscular irritability

Focal neurological deficits

Seizures or coma

80
Q

Symptoms of hypernatremia are related to…

A

Rate of onset

If it develops slowly, symptoms may be less dramatic

81
Q

What is our body’s normal response to hypernatremia

A

Create thirst and increase fluid intake

Maximally concentrate the urine to prevent further water loss

The vast majority of cases of hypernatremia are due to WATER LOSS, not sodium loss

82
Q

Nonosmotic urinary water loss in the setting of elevated serum sodium (urine is dilute when it should be concentrated

A

Diabetes Insipidus

The collecting ducts are impermeable to water so water is not reabsorbed

83
Q

Central DI is due to…

A

Impaired secretion of ADH

AKA neurogenic DI

84
Q

Central DI is typically treated with …

A

Desmopressin (often an inhaled DDAVP nasal spray or IV DDAVP)

85
Q

Nephrogenic DI is due to …

A

Lack of kidney response to ADH, causing continued water loss even though patient is low on water. Adequate ADH is present but useless

Desmopressin will NOT help in nephrogenic DI

86
Q

What causes Nephrogenic DI

A

Can be genetic or acquired

If acquired, typically from:
• Chronic renal insufficiency
• Tubulointerstitial renal disease
• Amyloidosis
• Lithium toxicity
87
Q

Treatment for Nephrogenic DI

A

Thiazides diuretic

Amiloride (potassium sparing diuretic)

Chlorpropamide (antidiabetic oral agent)

NSAIDs have been tried (including indomethacin)

88
Q

How do we treat hypernatremia in general?

A

Hospitalize if severe

STOP WATER LOSS

REPLACE WATER DEFICIT
• Orally, NG tube, or IV (hypotonic fluid)
• DO NOT replace too rapidly, esp if patient has been hypernatremic for days —> CPM

89
Q

How do you calculate a patient’s water deficit?

A

Water deficit = Normal TBW - current TBW

Normal TBW = 0.6 x body weight in kg

Current TBW = (Normal serum Na x Normal TBW)/(Measured serum Na)