Term
| What percentage of total body weight is made up by water? |
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Definition
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Term
| What compartments contribute to the extracellular fluid (ECF)? |
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Definition
| blood, interstitial fluid, 3rd space compartments (e.g. peritoneum, pleura, pericardium), gastrointestinal tract |
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Term
| What is the effective circulating volume? |
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Definition
| the portion of extracellular fluid that perfuses the tissues and stimulates volume receptors |
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Term
| What is the difference between osmolality and osmolarity? |
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Definition
Osmolality: number of solute particles/unit WEIGHT of solution
Osmolarity: number of solute particles/unit VOLUME of solution
**In ECF osmolality and osmolarity are about equal |
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Term
| What is the normal ECF osmolality (particles/kg) in health? |
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Definition
300 milliosmoles/kg
**changes in ECF osmolality will result in passive shifts of water between ICF and ECF to the region with higher osmolality |
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Term
| What are the major contributors to serum osmolality? |
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Definition
SODIUM and CHLORIDE
*and do a lesser extent, urea, glucose, bicarbonate, potassium + unmeasured anions and cations |
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Term
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Definition
| the EFFECTIVE osmolality (solutes/kg) of a solution i.e. the concentration of solutes that will induce a shift in water across a semipermeable membrane |
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Term
| Which of the serum osmoles is ineffective and why? |
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Definition
urea is an ineffective osmole
urea is a small molecule that freely diffuses across cell membranes so it does not contribute to tonicity (i.e. the concentration of solutes that can cause shifts of water across membranes) |
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Term
| Describe the two methods for measuring serum osmolarity (as a surrogate for ECF osmolarity)? Which is most precise? |
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Definition
freezing point depression (1mol/kg solution of a solute in water will have a freezing point 1.86C lower than that of pure water) **More common and more precise***
Vapor pressure depression (1mol/kg solution of a solute in water will have a vapor pressure 0.003 mmHg lower than that of pure water) |
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Term
| What formulas can be used to calculate serum osmolarity in a sample with normal glucose and bun? In a sample with either increased glucose or bun? |
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Definition
normal glucose/BUN:
mOsm/kg= 2[Na+K]
for high glucose or BUN:
mOsm/kg= 1.86[Na+K] + [glucose/18] + [BUN/2.8]
or 2[Na] + [glucose/20] + [BUN/3] |
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Term
| What is the osmolal gap? What does an increased osmolal gap indicate? |
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Definition
Numerical difference between measured osmolality (freezing point or vapor pressure depression) and calculated
Increased osmolal gap indicates that the presence of unmeasured anions (e.g. ethylene glycol, propylene glycol) |
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Term
| T/F all animals that are hypernatremic are also hyperosmolal? |
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Definition
True
**accumulation of other endogenous solutes (e.g. glucose, BUN) can also produce hyperosmolality |
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Term
| T/F all animals that are hypernatremic are also hyperosmolal? |
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Definition
True
**accumulation of other endogenous solutes (e.g. glucose, BUN) can also produce hyperosmolality |
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Term
| What is the effect of hypertonic serum (increased effective osmolality) on cell volume? |
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Definition
hypertonicity causes cell shrinkage
**that's why isotonic fluid therapy in animals with hypertonic serum (e.g. salt toxicity) needs to be slowly administered, to avoid cell swelling and injury |
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Term
| In what situation can urea be an effective osmole? |
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Definition
urea toxicity in cattle
urea cannot readily cross the thick epithelium of the rumen and acts to increase rumen tonicity producing rapid shifts of ECF into the rumen --> this results in secondary hypernatremic hypertonicity in the serum because of rapid decreased in vascular water without concurrent loss of sodium (cannot diffuse across cell membranes) |
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Term
| T/F hypo-osmolality is ALWAYS associated with hyponatremia but not all cases of hyponatermia are hypo-osmolal |
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Definition
True
a hyponetremic patient may also have concurrent hyperglycemia or increased BUN which could normalize the osmolality |
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Term
| What is the effect of hypo-osmolality on cellular volume? |
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Definition
hypo-osmolality produces hypotonicity --> shift of fluid from ECF to ICF --> cellular swelling*
*rapid development of hypo-osmolality can induce intravascular homeless and cerebral edema |
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Term
| What analytes are directly measured in blood gas analysis? |
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Definition
partial pressure of oxygen (PO2), partial pressure of carbon dioxide (PCO2), and hydrogen ion concentration (pH)
**HCO3 and BE are calculated values |
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Term
| What is the methodology of laboratory based blood gas instruments? |
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Definition
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Term
| What is the effect of sample type (arterial vs. venous) on blood gas analysis? |
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Definition
only arterial samples are appropriate for measuring pO2, either arterial or venous samples are fine for other analytes (e.g. PCO2, pH) but reference intervals are different compare to the same analytes measured from an arterial sample
**sample should be processed anaerobically and expediently to prevent diffusion of gasses out of or into the sample |
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Term
| How does patient body temp affect blood gas results? |
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Definition
Blood gas machines are set to measure samples at 37C
*partial pressure of PCO2 depends on temp (increased temp -> increased PCO2), there is not consensus as to the benefit of applying temperature correction factors to blood gas results however, and results at 37C should always be reported even if a correction is applied |
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Term
| What is the formula used to determine the amount of O2 dissolved in plasma using PO2? Why is this important? |
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Definition
PO2 x 0.01014 = O2 (mEq/L)
Most O2 in the blood exists bound to hemoglobin, so PO2 reflects only a small fractions of O2 in the blood but DOES influence the magnitude of hemoglobin oxygen saturation |
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Term
| What is the equation that illustrates the relationship between CO2 and H2CO3 in the blood? |
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Definition
| PCO2 x 0.03 = H2Co3 (mmol/L) |
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Term
| How does [PCO2] correlate with alveolar ventilation? |
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Definition
increased alveolar ventilation --> decreased [PCO2]
decreased alveolar ventilation --> increased [PCO2) |
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Term
| What buffer systems in the blood function to maintain normal blood pH? Which of these buffer systems are measured for clinical evaluation of a patient? |
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Definition
protein, phosphate and bicarbonate buffer systems exist,
we only measure the bicarbonate buffer system clinically |
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Term
| How is bicarbonate calculated from blood gas measurements? |
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Definition
calculated from pH and PCO2 via henderson-hasselbalch equation:
pH= 6.1 + log[HCO3/ (0.03xPCO2)]
remember, 0.03XPCO2 = H2CO3; so, pH is determined by the ratio of bicarbonate to carbonic acid |
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Term
| What is the difference between the actual and standard HCO3 calculations reported by blood gas analyzers, and how are they used clinically? |
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Definition
Actual is calculated from henderson-hasselback equation (pH=6.1 + log[HCO3 /(0.03xPCO2)])
Standard is derived from the actual HCO3 and takes into consideration the normal PCO2 and [Hgb] in people, since this isn't universally applicable to veterinary species standard HCO3 isn't really useful for anything but humans |
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Term
| What analytes are used to calculated base excess? |
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Definition
Standard HCO3, measured Hgb, PCO2 and body temp
**doesn't provide any additional info beyond [HCO3-] and may be inaccurate in veterinary species |
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Term
| In general, how does base excess change with acidosis vs. alkalosis? |
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Definition
BE decreases with acidosis and increases with alkalosis
**however, not as good as HCO3 (actual) for assessing acid base status in veterinary species |
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Term
| What sampling considerations should be considered with performing total CO2 measurements (e.g. as part of routine chemistry panel)? |
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Definition
| The blood sample should completely fill the collection tube to prevent diffusion of CO2 out of the sample |
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Term
| What concurrent pathologic process can cause falsely elevated TCO2 in samples measured via enzymatic techniques? |
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Definition
extensive muscle damage
**if run with ion selective electrode techniques there is no effect with concurrent muscle damage |
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Term
| Although TCO2 consists predominantly of HCO3-, what else also contributes? |
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Definition
| dissolved H2CO3 and carbamino acids |
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Term
| What ratio of bicrabonate to carbonic acid maintains normal pH in most veterinary species? |
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Definition
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Term
| Which compensatory response to an acid base disturbance is faster, metabolic or respiratory? |
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Definition
| Respiratory compensation (of a metabolic derangement) occurs more quickly (within minutes), while metabolic compensation (of a respiratory derangement) takes more time (often several days) |
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Term
| How do small organic acids (e.g. lactate, ketones) contribute to maintenance of blood pH? |
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Definition
increased production of these molecules occurs rapidly in response to metabolic or respiratory alkalosis and conversely, acidosis leads to decreased production of these molecules
**however, the relative importance of this mechanism for pH control in disease states in animals is unknown |
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Term
| What pattern of pH, PCO2, HCO3 are expected with an uncompensated metabolic acidosis? |
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Definition
decreased pH and HCO3
normal PCO2 (UNCOMPENSATED) |
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Term
| What pattern of pH, PCO2, HCO3 are expected with a partially compensated respiratory acidosis? |
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Definition
decreased pH
Increased [PCO2], [HCO3] |
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Term
| What is the equation to calculate anion gap? |
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Definition
AG= ([Na+K] - [Cl+HCO3])*
AG= UC - UA
*can also calculate using TCO2 instead of HCO3, however, since TCO2 is always a little higher than HCO3 reference interval will be slightly different between calculations |
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Term
| What other substances contribute to the anionic portion of blood in health, but are not included in the anion gap equation (because they contribute such a small relative amount)? |
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Definition
Albumin*, phosphates, sulfates, and small organic acids
*this is why hypoalbuminemia can contribute to a low AG
AG =UA-UC |
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Term
| What other substances contribute to the cationic portion of blood in health, but are not included in the anion gap equation (because they contribute such a small relative amount)? |
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Definition
fCa, fMg, some gamma globulins
some antibiotics are cations and can contribute to unmeasured cations if present in large quantities (decreased AG) |
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Term
| What is the postprandial effect on blood pH in monogastric animals? |
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Definition
ingestion of food (in monogastrics) lease to a transient slight increased in blood pH with concomitant increase in urine pH (postprandial alkaline tide) due to increased production of HCO3 secondary to gastric secretion of HCL
**the magnitude of increased pH in blood/urine is greater in older dogs compared to young. Also normal bovine diets typically have a net alkalizing effect on blood/urine pH |
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Term
| What is the dietary cation anion difference equation and how is it used? |
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Definition
DCAD = Na + K - CL - SO4 (mEq/kg dry weight matter)
The DCAD allows one to determine the alkalinizing or acidifying effects of a diet, esp. used in dairy cattle to feed an acidifying diet just prior to partuition which increases fCa (minimizing incidence of milk fever) |
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Term
| What is the goal DCAD to acidify the blood in a cow prior to partuition (to reduce incidence of milk fever)? |
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Definition
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Term
| Which species have erythrocytes with high [K]? |
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Definition
horses, pigs, primates
**few dogs breeds (akita, shiba inu) also have high intra-erythrocyte [K] |
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Term
| What are some potential sources of pseudohyperkalemia in blood samples? |
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Definition
Marked thrombocytosis with release of K+ during platelet activation
leakage of K+ from hemolysis or prolonged contact with sample clot in species with high RBC [K] (primates, pigs, horses, japanese dogs) |
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