Lecture 24 - Hydration and Osmolality Flashcards
Osmolality = [solute] per ______ of ______ (mOsm/kg)
- Aqueous solution with an osmolality of 1.0:
1 osmole of solute is added to 1 __ (1__) of water
Osmolality = [solute] per kilogram of SOLVENT (mOsm/kg)
- Aqueous solution with an osmolality of 1.0:
1 osmole of solute is added to 1 kg (1 L) of water
Osmolarity = [solute] per _____ of ______ (mOsm/L)
Aqueous solution with an osmolarity of 1.0:
1 osmole of a solute is placed in a beaker, and H2O is added to make ?
Osmolarity = [solute] per liter of SOLUTION (mOsm/L)
Aqueous solution with an osmolarity of 1.0:
1 osmole of a solute is placed in a beaker, and H 2 O is added to make 1 L
Technically, osmolality ___osmolarity; biologically they are ___________. For clinical purposes, we use the term __________.
Technically, osmolality ≠ osmolarity; biologically they are interchangeable
For clinical purposes, we use the term OSMOLALITY
Osmolality is measured by ?
Osmolality is measured by freezing-point depression osmometry
Osmolality measures ____ the osmoles in ______.
Osmolality measures all the osmoles in plasma
Normal plasma osmolality:
Dog: ______-____ mOsm/kg
Cat: _____-_____ mOsm/kg
Horse & Cow: _____-____ mOsm/kg
Normal plasma osmolality:
Dog: 210 -310 mOsm/kg
Cat: 290 -300 mOsm/kg
Horse & Cow: 270 -300 mOsm/kg
Estimate the plasma osmolality using an equation
Diuresis occurs when urine flow is ______ than normal.
Dogs and Cats: > ___-___ mL/kg/h
Diuresis occurs when urine flow is greater than normal.
Dogs and Cats: >1-2 mL/kg/h
When does osmotic diuresis occur?
Osmotic diuresis occurs when there is __________ urine flow caused by _______ amounts of ________ solutes within the renal tubules ( Example: 3?)
Urine osmolality approaches ______ osmolality
Example: diabetes mellitus (_________)
Osmotic diuresis occurs when there is increased urine flow caused by excessive amounts of impermeant solutes within the renal tubules ( Example: Na, Glucose, mannitol) Urine osmolality approaches plasma osmolality
Example: diabetes mellitus (glucosuria)
When does water diuresis occur?
Water diuresis occurs when there is _______ urine flow caused by decreased ________ of _____ water.
Urine osmolality may drop ______ plasma osmolality
Example: diabetes _______
Water diuresis occurs when there is increased urine flow caused by decreased reabsorption of free water.
Urine osmolality may drop below plasma osmolality
Example: diabetes insipidus
What is specific gravity?
Specific Gravity is the ratio of weight of a volume of ____ to the weight of an equal volume of _________ ________.
Specific Gravity is the ratio of weight of a volume of liquid to the weight of an equal volume of distilled water.
Specific gravity is dependent upon?
Dependent upon:
1. The number of particles present
2. The molecular weight of those particles
Urine Specific Gravity is an estimate of _________; there is a _______ relationship between them
Urine Specific Gravity is an estimate of osmolality; there is a linear relationship between them
How is Blood Volume and Body Fluid Tonicity maintained?
- Both are maintained within a narrow range
- 2 methods:
1. Water balance … ADH/Vasopressin
2. Sodium (Na) regulation … Aldosterone - Water balance controls
- osmolality and Na concentration
- Extracellular Fluid Volume (ECF) is determined by Na content
What does water balance depend on?
- Depends on:
- Adequate _____
- _____ and ____ function
- Losses in ______ and ________
- ______ control
–> Requires a Functional Kidney
1. Adequate delivery of tubular ______
* Normal renal ______ flow
* Normal ________
* ________ resorption of ___ and ____ from the proximal tubules
2. Normal functioning ascending?
3. Collecting ducts remain ____________ to H2O
- Depends on:
- Adequate intake
- Renal and GI function
- Losses in sweat and respiration
- Neural control
–> Requires a Functional Kidney
1. Adequate delivery of tubular fluid
* Normal renal plasma flow
* Normal glomerular filtration rate
* Isoosmotic resorption of Na and H2O from the proximal tubules
2. Normal functioning ascending Loop of Henle
3. Collecting ducts remain impermeable to H2O
Physical sensors: Osmoreceptors in the ____________
Physical sensors: Osmoreceptors in the hypothalamus
Hyperosmolality —> they ___ —> stimulates ____ release –> This increases water __________ via the kidney, Stimulates ____ response (?)
Hyperosmolality —> they shrink —> stimulates ADH release
ADH increases water reabsorption via
the kidney Stimulates thirst response
(drink water)
Hypoosmolality —> osmoreceptors ______ —>
__________ ADH release ,Increases renal
water ________
Hypoosmolality —> osmoreceptors swell —>
inhibits ADH release Increases renal
water excretion
Low body water and/or high plasma osmolality leads to:
* ↑ _____
* ↑ renal water __________
Low body water and/or high plasma osmolality leads to:
* ↑ thirst
* ↑ renal water reabsorption
Excess body water and/or low plasma osmolality leads to:
* ↑ renal water ________
Excess body water and/or low plasma osmolality leads to:
* ↑ renal water excretion
Water regulation affects plasma _________
It also affects the ______ concentration
_________ water, decreases [_____]
________ water, increases [____]
Water regulation affects plasma osmolality
It also affects the sodium (Na) concentration
Increase water, decreases [Na]
Decrease water, increases [Na]
__________ is the primary regulator of blood volume
Sodium is the primary regulator of blood volume
Regulation of Blood Volume
* It is regulated by sensing of:
- Atrial stretch
- Renal perfusion pressure
Regulation of Blood Volume
Hormones involved:?
- Renin-angiotensin-aldosterone system
- Sympathetic nervous system
- Atrial natriuretic peptide (ANP)
What are the major outcomes of blood volume regulation?
urine Na retention or excretion
**
TBW is ~____% of body weight in healthy animals with a normal BCS
**
TBW is ~60% of body weight in healthy animals with a normal BCS
TBW divided into sub-compartments:
1. Intracellular fluid (ICF) (___)
2. Extracellular fluid (ECF) (____)
- Intravascular (“-volemia”) used to describe changes in blood _______ (____% of ECF)
- Intercellular fluid
- Transcellular/”Third spaces” – ________, ________, ________
- _____ tract
TBW divided into sub-compartments:
* Intracellular fluid (ICF) (2/3)
* Extracellular fluid (ECF) (1/3)
* Intravascular (“-volemia”) used to describe changes in blood volume (25% of ECF)
* Intercellular fluid
* Transcellular/”Third spaces” – pleural, peritoneal, pericardial
* GI tract
TBW volume determines hydration status
* Controlled by water _____ (____) and renal ______
TBW volume determines hydration status
* Controlled by water intake (thirst) and renal output
__________ are present in all intracellular and extracellular body fluids
Electrolytes are present in all intracellular and extracellular body fluids
Electrolytes are most commonly measured in _______
Electrolytes are most commonly measured in serum
_______ electrolyte concentrations may not completely reflect balance of electrolytes in the body (especially for _______ electrolytes).
Serum electrolyte concentrations may not completely reflect balance of electrolytes in the body (especially for intracellular electrolytes)
Maintaining appropriate concentrations of electrolytes within a ______ range is essential to maintain health and is achieved mainly by: ?
Maintaining appropriate concentrations of electrolytes within a narrow range is essential to maintain health and is achieved mainly by: GI tract & Kidneys
HIGHEST IN THE INTRACELLULAR FLUID (ICF)?
Paisley, Caroline, Meagan, and Parascandola
* Potassium
* Calcium
* Phosphorus
* Magnesium
HIGHEST IN THE EXTRACELLULAR
FLUID (ECF)
- Sodium
- Chloride
Sodium (Na+)
◦ Primary cation in the ECF
◦ Most important cation for renal conservation of water ◦ Acquired through the diet
◦ Excreted through feces, urine, and sweat
Chloride (Cl-)
◦ Primary anion in the ECF
◦ Important component of secretory fluids (gastric, sweat, and saliva)
◦ Typically moves in the same direction as sodium (electroneutrality) ◦ Typically moves in the opposite direction of bicarbonate
Potassium (K+)
Most is in the ICF
K+ can be exchanged between ECF and ICF in acid-base imbalances
Osmolality = concentration of osmotically active particles (solutes) per ___ of ______ (_____ or _____) (expressed in mOsm/kg)
* Solutes: electrolytes (mainly ____ and ___), _____, _____, ______
* Changes in ____ osmolality influence ______ water shifts between ECF and ICF
Osmolality = concentration of osmotically active particles (solutes) per kg
of solvent (plasma or serum) (expressed in mOsm/kg)
* Solutes: electrolytes (mainly Na+ and K+), proteins, glucose, urea
* Changes in ECF osmolality influence passive water shifts between ECF and ICF
How is osmolality of the ECF measured?
- Measured osmolality finds all the ______ in the blood.
- Calculated osmolality only represents osmoles reported in the __________ _____.
- Serum osmolality can be estimated based on the most numerous osmoles: ___________, ________, and ________.
Can be measured or calculated
* Measured on an osmometer based on vapor pressure or freezing point depression
* Calculated:
Na + and K + units = mmol/L
Glucose units = mg/dL
BUN units = mg/dL
- Measured osmolality finds all the osmoles in the blood.
- Calculated osmolality only represents osmoles reported in the chemistry panel.
- Serum osmolality can be es8mated based on the most numerous osmoles: electrolytes, glucose, and urea.
Normal serum osmolality ~ _______-______ mOsm/kg
300-310
Changes in plasma osmolality causes water shifts between ____ and ____ compartments
Changes in plasma osmolality causes water shifts between ICF and ECF compartments
Changes in plasma osmolality are usually associated with?
- Hypernatremia
- Hyperglycemia
- Ketoacidosis
- Uremia
- Presence of exogenous toxins (ie, ethylene glycol)
Plasma osmolality
* Clinical signs depend on weather or not?
fluid shifts occur
Plasma hyperosmolality without fluid shifts
* Increased plasma concentration of __________ solutes: intracellular osmolality ____ extracellular osmolality
* Example: ______
* ____ clinical signs
Urea is______ diffusible across cell membranes. Osmotic effects are __________
Plasma hyperosmolality without fluid shifts
* Increased plasma concentration of ineffective solutes:
intracellular osmolality = extracellular osmolality
* Example: Uremia
* No clinical signs
Urea is freely diffusible across cell membranes Osmotic effects are negligible
Plasma hyperosmolality with fluid shifts
* Increased plasma concentration of _______ solutes: intracellular osmolality is _____ than extracellular osmolality
* Examples: ?
* Leads to cellular _______
* Clinical signs: are those manifested of ______ cellular volume
* _______ changes secondary to cellular ______
* Depression –> stupor –> Coma
* Other neurologic changes: CNS deficits, Seizures
Plasma hyperosmolality with fluid shifts
* Increased plasma concentration of effective solutes: intracellular osmolality is less than extracellular osmolality
* Examples: Hypernatremia, Severe hyperglycemia (diabetes)
* Leads to cellular dehydration
* Clinical signs: are those manifested of cerebral cellular volume
* Neurologic changes secondary to cellular dehydration
* Depressionà stupor à Coma
* Other neurologic changes: CNS deficits, Seizures
Plasma HYPO-osmolality with fluid shifts
* Increased plasma concentration of _____ solutes: intracellular osmolality ___ extracellular osmolality
* Examples: _________
* Leads to cellular _____: Cerebral ____ & Cell ___
* Clinical Manifestations of Cerebral Edema & Cell Lysis:
* _______ changes secondary to cellular _______: Lethargy, weakness, Altered mentation, obtundation, seizures, death
Plasma HYPO-osmolality with fluid shifts
* Increased plasma concentration of effective solutes: intracellular osmolality > extracellular osmolality
* Examples: Hyponatremia
* Leads to cellular swelling: Cerebral Edema & Cell Lysis
* Clinical Manifestations of Cerebral Edema & Cell Lysis
* Neurologic changes secondary to cellular dehydration: Lethargy, weakness,
Altered mentation, obtundation, seizures, death
IMPORTANT: How do you calculate the Osmolar gap?
Osmolar substances NOT included in osmolality calculation?
Osmolar gap = measured osmolality – calculated osmolality
these are usually TOXINS or (some) therapeutics
Normal osmolar gap ~ ___ mOsm/kg
10
Osmolar gap is typically calculated to?
Typically calculated to differentiate between causes of increased
serum osmolality
If the osmolar gap is >10 mOsm/kg, indicates the presence of osmolar substances _____
included in osmolality calculation: ?
If the osmolar gap is >10 mOsm/kg, indicates the presence of osmolar substances NOT
included in osmolality calculation:
* Ethylene glycol
* Mannitol
* Ethanol and methanol
* Radiographic contrast media
Hydration: estimates?
TBW status
DEHYDRATION = _________ TBW
1. ________ body weight
2. Physical exam findings:
* ________ skin tent
* __________ capillary refill time
* ______ mucous membranes
* _________ eyes
3. Clinicopathologic parameters:
* _________
* ___________ (?)
* ____________
* _____________
* +/- ?
DEHYDRATION = DECREASED TBW
1. Decreased body weight
2. Physical exam findings:
* Increased skin tent
* Increased capillary refill time
* Tacky mucous membranes
* Retracted eyes
3. Clinicopathologic parameters:
* Erythrocytosis
* Azotemia (pre-renal)
* Hyperproteinemia
* Hypersthenuria
* +/- Electrolyte abnormalities
OVERHYDRATION = ___________ TBW
* __________ body weight
* Accumulated fluid in _______ or _______ spaces
* PatIents can be ________ with _______ TBW:
* _______ or in ____ tract (rumen)
OVERHYDRATION = INCREASED TBW
* Increased body weight
* Accumulated fluid in extracellular or third spaces
* PaIents can be hypovolemic with increased TBW:
* Effusions or in GI tract (rumen)
Classification of dehydration
1. Type of fluid ______ from the body
2. Remaining ________ of body fluids
- Type of fluid loss from the body
- Remaining tonicity of body fluids
A. Hypertonic dehydration:
water loss ____Na loss
Na is _________
water loss > Na loss
Na is increased
Isotonic dehydration:
water loss __ Na loss
Na is ________
water loss = Na loss
Na is normal
Hypotonic dehydration:
water loss ___ Na loss
Na is ________
water loss < Na loss
Na is decreased
Hypertonic dehydration: Plasma [Na] is _____
Plasma [Na] is INCreased
Water loss in excess of electrolyte loss
* Differentials ?
Water shifts from ___ to ____ to maintain ____ volume
Water loss in excess of electrolyte loss
* Differentials:
* Diabetes insipidus
* Diabetes mellitus
* Osmotic diuresis
* Osmotic diarrhea
* Water Deprivation
Water shifts from ICF to ECF to maintain ECF volume
Isotonic dehydration:
Plasma [Na] is _______
Normal
In Isotonic dehydration:
Proportional loss of ?
◦ No change in _____ osmolality
◦ ____ and ___ concentrations do not change*
Differentials:
* _____ disease
* ________
◦ Water does not shift between ___ and _____ –> ___ volume decreases
In Isotonic dehydration:
Proportional loss of Na+, Cl-, and water
◦ No change in ECF osmolality
◦ Na+ and Cl- concentrations do not change*
Differentials:
* Renal disease
* Diarrhea
◦ Water does not shift between ICF and ECF –> ECF volume decreases
Hypotonic dehydration
Plasma [Na] is ________
DECreased
In a case of Hypotonic dehydration:
NaCl loss ____ water loss
◦ ECF osmolality _________ (________)
◦ Na+ and Cl- ________
◦ Water shifts from ___ to ___ –> volume _______
–> Differentials:?
In a case of Hypotonic dehydration:
NaCl loss > water loss
◦ ECF osmolality decreases (hypotonic)
◦ Na+ and Cl- decrease
◦ Water shifts from ECF to ICF –> volume depletion
–> Differentials:
* Secretory diarrhea
* Vomiting
* 3rd space loss
* Heat stress & sweating in horses: Often Cl- losses are greater than Na+ losses
Hypotonic dehydration Problems
1. Fluid shifts from _________ into cells
* Vascular volume _______ further, and cells _____
* Cerebral ______:
* Occurs when Na+ < _____-_____ mEq/L
* Especially with _______ change
2. Osmoreceptors _____ stimulated, ____ not released
3. May or may not have renal medullary _______
- Fluid shifts from vasculature into cells
- Vascular volume decreases further, and cells swell
- Cerebral edema:
- Occurs when Na+ < 115-120 mEq/L
- Especially with rapid change
- Osmoreceptors not stimulated, ADH not released
- May or may not have renal medullary washout
**Overhydration
* For example: Iatrogenic fluid overload
* IV fluid administration with __________ elimination
* Heart _______, _______ obstruction, _____/____ (RF)
* May cause:
* __________ overload
* Pulmonary _______
* Generalized ______
**Overhydration
* For example: Iatrogenic fluid overload
* IV fluid administration with inappropriate elimination
* Heart failure, renal obstruction, oliguria/anuria (RF)
* May cause:
* Cardiovascular overload
* Pulmonary edema
* Generalized edema
