Water Balance - Ex 5 Flashcards
Fluid Compartments - which do we measure?
ICF
Plasma - measure
ISF
Anion gap?
difference between measured cations (Na and K) and the measured anions (Cl and HCO3)
Two main solutes in Plasma
Na and Cl
Two main solutes in ISF
Na and Cl
Two main solutes in ICF
K and other anions (lots of albumin - mainly this forms anion gap)
What regulates osmolality
Water is lost (urine) or gained (intake) in order to regulate:
Osmolality
What regulates blood volume
Sodium is regulated in order to alter:
Blood volume
**Because water follows sodium!
Changes in osmolality are corrected by retention or excretion of
water
Changes in blood volume are corrected by retention or excretion of
sodium
Small changes may not be detected in a new patient - why?
Normal ranges are wide
3 reasons that cause the solute/particle content has been altered
- protein losing disease
- whole blood loss
- anemia for other reasons
What could the PCV look like if animal is anemic AND dehydrated?
PCV can be WNL
**After animal is re-hydrated the anemia could become evident
Caution - electrolytes
Electrolytes change quickly! and are not always reliable measure of water balance
Dehydration
Deficit in Total Body Water
Dehydration Status and CS
1-4%
Very mild
Non-detectable
Dehydration Status and CS
5-6%
Mild
Skin doughy Inelastic Slight loss of skin turgor Dry mm Conjunctiva injected
Dehydration Status and CS
7-9%
Moderate
Definite loss of skin turgor, with slow return
Enopthalmos
CRT 2-3sec
Dehydration Status and CS
10-12%
Severe
Pronounced loss of skin turgor with incomplete return
Peripheral vasoconstriction
Cold extremities
CRT >3 sec
Dehydration Status and CS
13-15%
Very severe
Vascular collapse
Renal shutdown
Death
Isotonic Dehydration
Loss of isotonic fluids –> electrolytes are NORMAL
Hypertonic Dehydration
Loss of hypotonic fluid –> electrolytes are INCREASED
Hypotonic Dehydration
Loss of hypertonic fluid –> electrolytes are DECREASED
Causes of hypertonic dehydration
Diabetes insipidus –> dilute urine, more water loss
Water loss from panting (dogs)
Sweat (cows)
What kind of dehydration occurs during heat stress (horses)
Hypotonic! Horses sweat is hypertonic –> too much sweat = hypotonic dehydration
Causes of hypotonic dehydration
Secretory diarrhea (calf scours)
Vomiting
“Third space” abnormalities (e.g. displaced abomasum)
Sweating (horses)
What is the most common cause of dehydration??
Hypertonic water loss (Animal is hypotonic)
What is osmolality influenced by?
Na, BUN, Glucose
Hyperosmotic
osmolality exceeds normal reference interval for plasma
Isosomotic
WNL
Hypoosmotic
lower than normal interval
