Clinical pathology: clinical chemsitry-(ii)Fluids and acid-base metabolism Flashcards
Describe each of the different status of dehydration ranging from mild dehydration to very severe dehydration.(5)
INTRO: Total body water is about 60% of body weight; about half is extracellular and half is extracellular.
(i) Very mild dehydration occurs with water loss of 1-4% of body weight. Clinical signs are not detectable.
(ii) Mild dehydration occurs with water loss of 5-6% of body weight. Clinical signs include dry mucous membranes, slight loss of skin turgor, infected conjunctiva and inelasticity of skin.
(iii) Moderate dehydration occurs with water loss of 7-9% of body weight. Clinical signs include loss of skin turgor with slow return, prolonged capillary refill time(2-3 seconds), enophthalmos
(iv) Severe dehydration occurs with water loss of 10-12% of body weight. clinical signs include extreme loss of skin turgor, peripheral vasoconstriction, cold extremities and prolonged capillary refill time(>3 seconds)
(v) Very severe dehydration occurs with water loss of 13-15% of body weight; clinical signs include vascular collapse, renal failure and death.
What is isotonic dehydration and are the level of sodium and chloride concentrations affected? What happens to the packed cell volume and plasma proteins level?
Give examples of when isotonic dehydration can occur.
Isotonic dehydration occurs with equal losses of water and solute. sodium and chloride concentrations are not affected. Increased packed cell volume(PCV) with increased plasma proteins. It occurs in some cases of diarrhea and renal disease.
What is hypertonic dehydration and are the level of sodium and chloride concentrations affected? What happens to the packed cell volume and plasma proteins level?
Give examples of when isotonic dehydration can occur.
Hypertonic dehydration occurs when more water than solute is lost.
1/Concentration of sodium and chloride increases.
2/PCV increases, with increased plasma proteins.
3/Occurs most commonly in diabetes insipidus.
NOTE: Species that produce hypotonic sweat(cattle) or little sweat(dogs, cats) develop hypertonic dehydration with heat stress.
What is hypotonic dehydration and are the level of sodium and chloride concentrations affected? What happens to the packed cell volume and plasma proteins level?
Give examples of when isotonic dehydration can occur.
Hypotonic dehydration occurs when more solute than water is lost.
- Concentrations of sodium and chloride decrease.
- This results in a contraction of the extracellular fluid volume with expansion of intracellular fluid volume to restore osmotic equilibrium.
- Most common type of dehydration, where the solute loss induces a secondary loss of water.
- Hypotonic dehydration from heat stress occurs in species that produce hypertonic sweat(horses)
What is the Henderson-Hasselbach equation?(3)
- pH= pKa + log[A-]/[HA]
- The carbonic acid-bicarbonate system is usually used: pH= pKa + log[HCO3-]/[H2CO3]
- pH= 6.1 + log[HCO3-]/0.03(PCO2)
How can we characterise acid-base disorders if HCO3 measurement is not available?
If HCO3 measurement is unavailable, total CO2 from a chemistry profile can be used as an estimate. Total CO2 is about 1 to 2 mmol/L greater than the HCO3 concentration.
Which changes trigger metabolic disorders? How is compensation provided?
Metabolic disorders characterised by changes in HCO3. Compensation is via rapid changes in ventilation to alter pCO2.
CHECK FLASHCARD PICTURE 4
What changes trigger respiratory disorders? How is this compensated?
Respiratory disorders characterised by changes in pCO2. Compensation is via a change in urinary acidification to alter HCO3. This process is slower than compensation in ventilation.
What is the difference between simple, combined and compensated acid-base disorders?
- Simple acid-base disorders occur when there is a primary change, but no compensation has taken place.
- Compensated acid-base disorders occur when primary changes are present along with evidence of a compensatory change in the complementary system. the pH rarely returns to normal with compensation.
- Combined acid-base disorders occur when there are changes in the same direction in both systems .
What is the primary change and accompanying compensatory change in the following acid-base disorders:
(i) metabolic acidosis
(ii) metabolic alkalosis
(iii) respiratory acidosis
(iv) respiratory alkalosis
(i)Metabolic acidosis Primary change is decreased HCO3 pCO2 will decrease in compensation (ii)Metabolic alkalosis Primary change is increased HCO3 pCO2 will increase in compensation (iii)Respiratory acidosis Primary change is increased pCO2 HCO3 will increase in compensation There is a larger compensation in chronic respiratory acidosis compared with an acute event. (iv)Respiratory alkalosis Primary change is decreased pCO2 HCO3 will decrease in compensation There is a larger compensation in chronic respiratory alkalosis compared with an acute event
How are base excess and base deficit calculated? What do increased and decreased values indicate?
Base deficit and base excess are calculated from blood gas parameters by the blood gas analyser. This calculation is based on human relationships and is probably valid for dogs and cats. this calculation might not be valid for other species.
- Increased values reflect a base excess corresponding to metabolic alkalosis.
- Decreased values reflect a base deficit, corresponding to netabolic acidosis
What is the anion gap equation and what is the objective of using this?
Give examples of unmeasured anions and cations. What happens to the anion gap when the level of unmeasured:
(i) anions and
(ii)cations increase
Anion gap= (Na + K) - (Cl + HCO3); the objective is to estimate changes in the unmeasured anions and cations without having to measure them.
Unmeasured anions include sulfate, lactate, phosphate, pyruvate, albumin, and ketoacids
Unmeasured cations include primarily calcium and magnesium.
If the anion gap increases, then unmeasured anions have have increased. If the anion gap decreases, then unmeasured cations have increased.
What is osmolality?
Osmolality is the concentration or number of osmotically active particles in an aqueous solution.
What is osmolal gap?
Osmolal gap is the difference between the actual measured serum osmolarity and the calculated estimate of osmolality.
What is the equation of calculated osmolality?
Calculated osmolality(mOsm/L) = 1.86[Na(mmol/l)] + [glucose(mg/dL)/18] + [BUN(mg/dL)/2.8] + 9
NOTE: The osmolal gap increases when there is an increase in any osmotically active particles that are not included in the calculated equation.
The osmolal gap will increase whenever the anion gap is increased.
