Water, Lytes, Acid/Base Ch5 D&P Flashcards
Total body water is approximately what percentage of body weight?
60%
How is total body water divided up in the body?
Intracellular fluid Extracellular fluid (Blood, intercellular fluid, transcellular fluid like third space peritoneaum etc, and GI tract like in ruminants).
What are the factors that influence effective circulating blood volume?
BLood volume AS WELL AS arterial blood pressure, arterial resistance and delivery of blood to volume receptors.
What are the 4 laboratory abnormalities associated with dehydration?
Increased hemtocrit
Increasted protein
INcreased BUN /; Crea
High urine SG
Increased total body water is best measured how and where does this accumulate?
Increased body weight.
It accumulates in the extracellular fluid or third spaces. (edema, ascites etc)
How can you have hypovolemia and increased total body water at the same time?
yes when water accumulates in third spaces or the GI tract like in ruminants where fluid is trapped in the rumen.
What is osmolality definition?
The number of solute particles/unit weight of a solution. (osmolarity is the number of solute particles per unit volume of a solution - usually in ECF they are about the same). THESE MAINTAIN FLUID INSIDE CELLS, DONT CONFUSE WITH COLLOID OSMOTIC PRESSURE WHICH MAINTAINS FLUID INSIDE A VESSEL (IE GLUCOSE AND PROTEIN)
What is the average ECF osmolality and what are the main contributors to osmolality?
Usually around 300milliosmoles per kilogram.
Electrolytes and small molecules like glucose and urea .
Larger stuff like proteins doesn’t contribute much to osmolality but does contribute to colloid osmotic pressure to keep fluid in vessels.
What is tonicity and ineffective osmoles versus effective?
The effective osmolality of a solution, ie the concentration of solutes that can cause shifts in water across a semipermeable membrane. Remember only solultes that DO NOT cross the membrane are effective osmoles and contribute to tonicity.
Urea freely passes between the ECF and ICF so it is an ineffective osmole and doesn’t contribute to tonicity.
What is the osmolar gap?
The numerical difference between measured osmolality and estimated osmolality. It usually ranges from -5 to 15 mOsm/L depending on the formula used to estimate and method used to measure.
What does an increase in osmolal gap mean?
The presence of unmeasured non polar, low molecular weight (ie small, not like protein which is large) substances such as ethylene glycol, propylene glycole, etc).
What can cause hyperosmolality?
Hypernatremia (all animals hypernatremic are also hyperosmolal).
Accumulation of other endogenous solutes like BUN or glucose.
What is hypertonicity and what may cause it?
Increase in effective osmoles like Na, Glc, ethylene glycol etc taht causes water to shift from ICF to ECF causing cell shrinkage.
What results from a rapid return to isotonicity from hypertonicity in the ECF?
Cellular edema as fluid flows back into cells > dire consequences. (ie as in cerebral cellular edema causing brain damage and death.)
Does hyperosmolality always mean you have hypertonicity in the ECF?
NO, not if the osmole is ineffective, ie BUT concentration does not increase tonicity or cause ICF or ECF water shifts b/c it is freely moveable across membranes (but it can produce changes in pH! - ie acidosis)
What can cause hypoosmolality?
Its always always associated with hyponatremia, BUT not all cases of hyponatremia are associated with hypoosmolality (ie like when you have hyperglycemia) which is also an effective osmole, and this is why you use D5W when you want to give an animal straight water IV without sodium in it so its isoosmolality with respect to serum/ECF.
What are the consequences of hypoosmolality?
Hypotonicity, fluid shifts ECF > ICF and cell swelling.
Intravascular hemolysis as fluid rushes into RBCs
Neurologic disorders
What happens if you have deydration and hypoosmolality?
Loss of ECF volume is even faster due to movement into cells / ICF so you can get circulatory collapse, shock etc.
With blood gas analysis, what values are measured and whats calculated from the measured values?
Measured: PO2, PCO2, pH (hydrogen ion conc).
Calculated: Blood bicard / HCO3 and standard bicarb and base excess values are calculated from the measured values.
When can you use venous versus arterial samples for blood gas measurement?
Arterial ONLY FOR PO2
Arterial or venous for pH, HCO3 and PCO2.
What does PO2 reflect?
Not the total O2 in the blood because most of it is bound to hemoglobin so it doesn’t contribute to PO2 but it does influence the percent saturation of Hgb with oxygen.
When does high and low PO2 occur?
High can only occur if the animal is on oxygen and low occurs in respirator disorders or with derangement of the respiratory control mechs.
What does PCO2 tell you?
Its proportional to dissolved CO2 in the plasma. Dissolved CO2 is in equilibrium with carbonic acid.
Its a measure of alveolar ventilation, if ventilation decreases, it increases and visa versa.
How is the blood bicarbonate level / ion determined HCO3-? How is the bicarb concentration maintained in health?
Calcuated from pH and PCO2 using Henderson Hasselbalch.
Its maintained in health by conservation and production of NaHCO3 by the renal tubules.