Lecture 7 Flashcards
(43 cards)
Describe the distribution of water in the body
60% body weight
40% intracellular
20% extracellular
15% interstitial
5% intravascular
How do you increase water
intake through water and food (GI)
Renal reabsorption
How do you decrease water
Excretion through urine, feces, saliva, and sweat
What is the difference between dehydration and hypovolemia
Dehydration describes whole body depletion of water while hypovolemia describes only intravascular fluid depletion
Dehydration might occur in a chronic renal failure patient while hypovolemia might occur with a hit by car
What are you measuring when you get a blood sample
Electrolytes in extracellular compartment
What is the major extracellular cation?
Major intracellular cation?
Sodium- extracellular
Potassium- intracellular
How is the movement of water in the body regulated?
Regulated by osmolality- primarily sodium
What is colloid osmotic pressure
Pressure caused by colloidal molecules
Holds fluid intravascularly
Due to plasma proteins
How is body water concentration regulated
Like movement, it’s measured by osmolality acting on the thirst center and ADH
I.e. high osmolality detected -> thirst increased and ADH released -> water retained
How is body water volume regulated
Through the RAAS system
Liver releases angiotensinogen and kidneys amd lungs converts it to angiotensin which acts on adrenal glands to produce aldosterone which increases sodium and decreases potassium
What tests are used for body fluid volume
Tests of hydration
Tests of perfusion
What tests are used for body fluid concentration
Osmolality
Osmolal gap
Colloid osmotic gap
What tests are used to measure electrolytes
Electrolyte concentrations
Sodium: potassium ratio
What physical and laboratory parameters are used to measure hydration
Skin turgor MM moisture Body weight PCV/TS USG
What physical exam and laboratory findings are used to test perfusion
MM color and CRT Heart rate and pulse quality Blood pressure Central venous pressure BUN/creatinine Lactate
When would you use the osmolality test
Cases of suspected ethylene glycol intoxication or pseudohyponatremia
What causes hyperosmolality
Increased solutes
Decreased water
What causes hypoosmolality
Hyponatremia
Clinical signs associated with changes in osmolality
Are due to cellular dehydration or overhydration
Depends on whether or not fluid shifts occur
Severity of change
Rate of development
How do cells compensate for hyperosmolality
By producing idiogenic osmoles
What is the osmolal gap
Difference between measured and calculated osmolality
Useful for ethylene glycol poisoning
What regulates colloid osmotic pressure
Liver synthesis of albumin
When measuring electrolytes, what blood samples should you use and hy
Red top tube with no anticoagulant; can use heparinized plasma with horses
Anticoagulants can contaminate sample
Functions of sodium
Major determinant of osmolality
Essential for control of hydration (RAAS)
