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Clin Lab Med Unit 2 > 1 Sodium Disorders > Flashcards

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
What is the major determinant of the size of ECFV (extracellular fluid volume)
Total amount of Na+
26
Increased Na+ —>
Increased ECFV or HYPERVOLEMIA Think edema
27
Decreased Na+ —>
Decreased ECFV or HYPOVOLEMIA | think dry patient
28
90-95% of the total body sodium is located in...
The ECF
29
Serum [Na+] (lab value) primarily refers to ...
The amount of water relative to Na+ in the ECF (NOT the total body Na+ amount)
30
Abnormal serum Na+ is a sign of ...
A disorder of water regulation High Na+ = too little water relative to sodium Low Na+ = too much water relative to sodium
31
The ECFV is determined by ...
Overall volume status of the patient
32
An abnormality with the size of the ECFV is a marker of...
Abnormal sodium control (too much/too little total body sodium) High ECFV = “too much sodium” Low ECFV = “too little sodium”
33
How do we describe a patient’s volume status?
Hypovolemic Euvolemic Hypervolemic
34
Common causes of hypovolemia
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
35
Clinical features of hypovolemia
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
36
Common causes of hypervolemia
``` Acute or chronic renal failure Nephrotic syndrome Primary aldosteronism Cushing’s syndrome Liver disease*** Heart failure*** Pregnancy ```
37
Clinical features of hypervolemia
``` Edema SOB Orthopnea, paroxysmal nocturnal dyspnea Jugular venous distention Hepatojugular reflux Crackles on pulmonary exam ```
38
Water retention is influenced by:
Thirst ADH aka vasopressin
39
Salt retention is influenced by:
Renin-Angiotensin system*** Also: ANP and catecholamines Renal function Renal blood flow
40
ADH is produced in the _________, then transported to the ________, from which it is released into the blood stream
Hypothalamus —> Posterior Pituitary
41
Aldosterone’s main actions are:
Increase renal sodium reabsorption (Na+ retention) Increase renal potassium secretion (K+ excretion)
42
What is the most common electrolyte abnormality in hospitalized patients?
Hyponatremia A hypotonic disorder due to serum sodium <135
43
What is a normal serum [Na+]?
135-145 (varies by lab)
44
Mild Hyponatremia is a [Na+] of...
125-135
45
Moderate hyponatremia is a serum [Na+] of ..
120-125
46
Severe hyponatremia is a serum [Na+] of ...
<120 Life threatening if [Na+] < 120 with SEIZURES
47
The “danger zone” for [Na+] is ...
Below 125 (patients not generally symptomatic until about 125)
48
Hyponatremia can be acute or chronic, so always compare a low [Na+] to...
The patient’s BASELINE sodium The faster the Na decreases —> the more severe the symptoms
49
Hyponatremia is most common in what populations?
The very young and the very old Can also be seen in association with pulmonary disease or CNS disorders
50
Symptoms of hyponatremia depend upon ...
Level of cerebral edema ``` Headache, dizziness N/V Lethargy, weakness CONFUSION Hypoventilation, respiratory arrest SEIZURES COMA DEATH!!! ```
51
Condition characterized by falsely low serum sodium
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
Patients with what conditions can have pseudohyponatremia?
Hyperlipidemia and hyperproteinemia Can also occur with obstructive jaundice and multiple myeloma
53
What should you do if you suspect pseudohyponatremia?
Speak to your lab about more specialized tests to confirm true sodium level
54
What is redistributive or hyperosmotic hyponatremia?
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
What is the most common cause of redistributive or hyperosmolar hyponatremia?
Hyperglycemia! Because it elevates osmolality and makes Na+ look super low
56
How do you calculate corrected [Na+] in patients with redistributive or hyperosmolar hyponatremia?
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
Hypervolemic hyponatremia is commonly caused by...
Hepatic cirrhosis CHF Renal Failure
58
Treatment for hypervolemic hyponatremia?
Diuretics, dialysis, fluid restriction
59
What are some renal causes of hypovolemic hyponatremia?
Diuretics (esp thiazides) Osmotic diuresis Addison’s disease*** Primary adrenal insufficiency —> low cortisol (which controls ADH)
60
What are some non-renal causes of hypovolemic hyponatremia?
External GI: vomiting, diarrhea, NG suction, fistula Internal GI: pancreatitis, peritonitis Burns
61
Treatments for hypovolemic hyponatremia?
Replace fluid losses with isotonic fluid (ie NS) and treat underlying cause
62
What are some causes of euvolemic hyponatremia?
SIADH Psychogenic polydipsia (drinking too much water) Ecstasy intoxication (can cause psychogenic polydipsia) Hypothyroidism Adrenal insufficiency
63
Treatment for Euvolemic hyponatremia?
Fluid restriction, treat underlying cause
64
Hallmark findings in SIADH
Concentrated urine (>100mOsm/kg) with low serum osmolality and euvolemia (so long as kidneys working well)
65
Causes of SIADH
``` CNS disease Pulmonary disease (esp SMALL CELL LUNG CA****) Meds Major surgery Stress Psych Pain ```
66
Upwards of 35% of hospitalized patients can develop ...
SIADH
67
How is SIADH diagnosed?
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
How do you treat SIADH?
FLUID RESTRICTION (usually sufficient on its own) Treatment of underlying pathology ``` For refractory cases: • Hypertonic saline • Democlycline • Urea • Lithium • Vaptan ```
69
What labs do you look at first in cases of hyponatremia?
First look at: UA(Na), UA (Osm), Serum Osm, CMP (serum Na) Second: TSH, serum cortisol
70
Treatment of hyponatremia depends upon...
The underlying cause
71
When do you hospitalize a patient with hyponatremia?
If Na<125 OR symptomatic Chronic hyponatremia must be managed with extreme care
72
Why is slow, cautious correction of serum sodium important?
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
Traditional treatment of chronic hyponatremia is ...
Demeclocycline (to induce nephrogenic DI) “Vaptans” are a new class of treatment agents which are vasopressin receptor antagonists
74
What should the rate of correction be in patients with severe symptomatic hyponatremia?
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
What is Central Pontine Myelinolysis
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
Clinical features of hypernatremia are due to ...
Brain shrinkage secondary to increased ECF osmolality
77
Causes of hypernatremia
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
In general, which is more common: Hypo- or Hypernatremia?
Hyponatremia
79
Clinical features of hypernatremia?
Often asymptomatic Thirst, signs of volume depletion AMS, weakness Neuromuscular irritability Focal neurological deficits Seizures or coma
80
Symptoms of hypernatremia are related to...
Rate of onset If it develops slowly, symptoms may be less dramatic
81
What is our body’s normal response to hypernatremia
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
Nonosmotic urinary water loss in the setting of elevated serum sodium (urine is dilute when it should be concentrated
Diabetes Insipidus The collecting ducts are impermeable to water so water is not reabsorbed
83
Central DI is due to...
Impaired secretion of ADH AKA neurogenic DI
84
Central DI is typically treated with ...
Desmopressin (often an inhaled DDAVP nasal spray or IV DDAVP)
85
Nephrogenic DI is due to ...
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
What causes Nephrogenic DI
Can be genetic or acquired ``` If acquired, typically from: • Chronic renal insufficiency • Tubulointerstitial renal disease • Amyloidosis • Lithium toxicity ```
87
Treatment for Nephrogenic DI
Thiazides diuretic Amiloride (potassium sparing diuretic) Chlorpropamide (antidiabetic oral agent) NSAIDs have been tried (including indomethacin)
88
How do we treat hypernatremia in general?
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
How do you calculate a patient’s water deficit?
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)

Clin Lab Med Unit 2 (4 decks)

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