Term
| How much body fluid is in each compartment? |
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Definition
- intracellular fluid - 2/3 TBW
- Extracellular fluid - 1/3 TBW
- Interstitial fluid - 3/4 of extracellular fluid
- Plasma - 1/4 of extracellular fluid |
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Term
| Example: If a 40 year old man is 70 kg, how much fluid in a blood draw does he have? |
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Definition
A 40 year old man has 60% of his weight in water --> 0.6 * 70 = 42L
1/3 of total water is ECF --> 0.33 * 42 = 14 L --> 1/4 of ECF is blood --> 0.25 * 14 = 3.5 L |
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Term
| How is osmolality calculated and what is the normal value? |
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Definition
- (2 * Na) + (Glucose/18) + (BUN/2.8)
- Normal - 275 - 290 |
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Term
| What are the different types of tonicities? |
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Definition
- Hypertonic - a high osmolality (more solutes) outside of the cell causes water to rush out, cells shrink
- Hypotonic - A low osmolality (less solutes) outside of the cell causes water to move into the cells, cells burst
- Isotonic - water neither moves in nor out. |
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Term
| What is the osmolal gap, and what does it indicate? |
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Definition
- OSM gap = measured osmolality - calculated osmolality
- If more than 10, an exogenous substance (mannitol, alcohol, sorbitol) is in the blood. |
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Term
| What crystalloids (fluids containing electrolytes) exist? |
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Definition
- 3% saline - high osmolality, moves fluid into ECF, only use in emergency
- 0.9% saline - used for rehydration
- Lactated ringer - used for rehydration, lower osmolality
- 0.45% saline - 2/3 ECF, 1/3 ICF
- D5W - contains dextrose, acts like free water, moving mostly into cells creating a hypotonic scenario. Not used in dehydration
- Colloids extremely rehydrating, very expensive |
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Term
| How is a patient's water requirement determined? |
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Definition
All adult patients need 1500 mL for the first 20 kg,
Then 20 mL for each remaining kG --> add up. |
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Term
| Example: Estimate the fluid requirements in a women weighing 80 kg? |
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Definition
First 20 kg - 1500 mL
60kg * 20mL = 1200 mL
1200 + 1500 = 2700 mL |
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Term
| How is sodium related to water? |
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Definition
Serum sodium is indicative of water:
Low serum sodium = more water than sodium
High serum sodium = more sodium than water |
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Term
| How does sodium relate to ECFV? |
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Definition
Sodium is the major determinant of ECFV
Increased sodium = volume overload
Decreased sodium = volume depletion
Kidneys respond to changes to try to CORRECT balance
- Hypertonic - high serum sodium/water - decreased excretion to correct balance
- Hypotonic - Less solutes, increased excretion |
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Term
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Definition
In response to increased tonicity, ADH released and Na/Water retained
-SIADH - inappropriate release of ADH, tricyclics and SSRIs most common cause
- Central diabetes insipidus - absence of ADH leads to excessive Na/water loss
- Nephrogenic diabetes insipidus - caused by lithium, renal tubes unresponsive to ADH |
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Term
| What is the lab value for Hyponatremia and what are types of hyponatremia? |
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Definition
- Na < 135
Mild 124 - 135
Moderate 115 - 125
Severe < 115
Can be isotonic, hypertonic, or hypotonic |
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Term
| What types of hyponatremia are pseudo-hyponatremia? |
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Definition
Isotonic hyponatremia - problem with measured values, no Tx necessary
- Hypertonic hyponatremia - Decreased Na and increased water in ECF. Why? Elevated blood glucose shifts water out of cells |
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Term
In hypertonic hyponatremia, Na conc. decreases 1.7 mEq/L for every 100 mg/dL increase in serum blood glucose above 100.
If Serum BG = 360 and Na = 120, what is corrected Na? |
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Definition
- Elevated BG - Normal / 100 --> 360 - 100 / 100 = 2.6
- 2.6 * 1.7 (constant) = 4.4 mEq/L
- 120 + 4.4 = 124.4 mEq/L |
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Term
| What is true hyponatremia? |
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Definition
Hyponatremia with hypotonicity - a problem with water excretion. Must assess fluid status, can be hypo-, hyper-, or euvolemic
- Will have osmolality<275 and Na<135
- Physical exam assesses fluid status
- Hypovolemic - caused by sickness or diuretics
- Hypervolemic - CHF, cirrhosis
- Euvolemic - SIADH, renal failure, low solute intake |
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Term
| What is the goal of treatment in hypovolemic hypotonic hyponatremia? |
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Definition
- Avoid a 12mEq increase in Na in 24h
- For non-emergency - 0.9% NaCl infusion, do not exceed mEq limits. Monitor Na, signs of hypovolemia, volume overload |
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Term
Example: How to correct hyponatremia
In a 70 y.o. male 56 k.g. patient: what is their deficit |
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Definition
Deficit = ECFnormal - ECFcurrent
Normal weight = 15% * current weight! --> 0.15 * 56 = 64 kg
ECFnormal --> 0.5 (for 70 y.o. male) * 64 kg = 32 L * 1/3 = 10.7
ECFcurrent --> 0.5 * 56 * 1/3 = 9.3
10.7 - 9.3 = 1.4 L |
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Term
| How is euvolemic hypotonic hyponatremia corrected? |
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Definition
- water restriction to ~1 L/day
- Goal serum Na > 125 mEq - corrected w/ loop diurectics or NaCl tabs over a few weeks unless acutely symptomatic
- Vasopressin antagonists: Conivaptan/Tolvaptan |
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Term
| How is hypervolemic hypotonic hyponatremia treated? |
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Definition
ADHF patients, fluid overloaded, dilutes out sodium.
Restrict water and Na intake
Loop diuretics or vasopressin |
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Term
| How are symptomatic hyponatremic patients acutely managed? |
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Definition
Regardless of fluid status, 3% NaCl w/ goal of Na > 120, no more than 12 mEq/day increase in 24H
Must calculate change in serum Na to make sure goal is not exceeded |
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Term
| Example: If 1 Liter of 3% NaCl is given to a 55 y.o. 80 kg male w/ a current serum sodium of 110 and a goal of 120, is the goal of 12 mEq/day exceeded? |
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Definition
MEq in 3% NaCl = 513, 0.9% = 154
--> using formula - (513 - 110) / (0.6*80) + 1) --> 8.2 mEq change |
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Term
| How is hypernatremia diagnosed and controlled? |
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Definition
Na > 145 mEq/L, always more Na than water (hypertonic)
Stimulus for thirst, weakness, leads to seizures, coma, and death
- Assess fluid status - Hyper-,Hypo-, or Euvolemic |
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Term
| What is hypovolemic hypernatremia and how is it treated? |
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Definition
- Hypovolemic - Water > Na loss, high glucose, see signs of water loss
- If postural hypotension, give 0.9% NaCl until stable then D5W
- If no hypotension, give D5W
- Do not lower Na more than 10 mEq/L per day |
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Term
| Example: If a 78 y.o. man with hypernatremia weighing 55 kg and a SNa of 160 presents, how do you treat? |
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Definition
TBW = 0.5 * 55 = 27.5
Deficit = 27.5 / (160/140 - 1) = 3.9 L
140 is the goal Na --> 160 - 140 = 20Meq --> give 2 L each day of D5W |
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Term
| What is Hypervolemic Hypernatremia and how is it treated? |
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Definition
| Sodium excess - get rid of through loop diuretics. May replace free water with D5W |
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Term
| What causes Isovolemic Hypernatremia? |
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Definition
-Trauma and CNS malignancy
- Lithium and Demeclocycline cause Diabetes insipidus
- Check response to desmopressin. If +, continue Tx (central DI). If not, treat w/ thiazides (Nephrogenic). Use Amiloride for Lithium induced, Indomethacin helps. |
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