CO7 Electrolyte Clinical Biochemistry & Body Water Balance

Question 1

electroneutrality is maintained in each compartment, ie intracellular and extracullular compartments. What ions are found in the cell vs in the blood vessels?

Answer 1

Cell = ICF:
K+ > major ICF cation
Mg++
PO4
Proteins
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Blood vessel = ECF:
Na+ > major ECF cation
Cl-
HCO3-

Question 2

how do we measure Electrolytes = Sodium, Potassium, Chloride?
- how can we get a messed up glucose measurement?

Answer 2

• Regular serum tubes – red top, lemon top, tiger top
  > Spin down serum from RBCs once clotted ~15-30 min
  > remember prolonged contact time with the clot reduces the glucose in the sample
• Heparinized plasma
  > Spin down serum / plasma
  > coagulation factors will still be in plasma, unlike in serum tubes (coagulation hasnt happened) , most importantly fibrinogen
• Method: ion-selective electrode Units: mmol/L

Question 3

how do electrolytes move? ie. in and out of the body, throughout the body

Answer 3

1. Intake – decreased or increased
2. Shifts between ECF and ICF
3. Increased retention (kidney)
4. Increased loss (GI, kidney, skin, 3rd spacing)

Question 4

Sodium & Chloride – Interpretation requires knowledge of what?

Answer 4

Requires knowledge of hydration status
* Total body water – euhydrated, dehydrated, over hydrated?
* If dehydrated
> Was water lost in excess of electrolytes?

Question 5

major reasons for Hyponatremia & Hypochloremia (together)

Answer 5

1. Excess loss of NaCl-rich fluids:
   * GIT
   * Renal
   * Cutaneous
   * 3rd space
2. Decreased intake

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3. increased total body water
   > interstitial space or body cavity with increased water > electrolytes follow
   > overhydration hypotonic fluids > dilutes out electrolytes in vasculature
   * Edematous states:
   * CHF
   * Cirrhosis
   * Nephrotic syndrome
   * Iatrogenic

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4. H2O Shifting ICF > ECF
   > water drawn into vasculature dilutes out sodium
   * Hyperglycemia
   * Mannitol

Question 6

how can we get hypochloremia alone?

Answer 6

Excess loss of HCl-rich fluids
* Vomiting / excess reflux removal
* Sequestration
> LDA, duodenal torsion, pyloric blockage, ileus

Question 7

common ways to get hypernatremia and hyperchloremia (together)

Answer 7

Dehydration:
1. Inadequate water intake
2. Excess pure water loss
> Dehydration due to pure water loss = hypertonic dehydration
* Panting / high fever/ heat stress
* Diabetes insipidus

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Less common, excess Na+ intake / retention:
* Ingestion – salt poisoning
* IV administration
* Increased aldosterone
> renal retention of Na+

Question 8

how to get hyperchloremia, alone
UNCOMMON AND PROB NOT ON EXAM

Answer 8

Less common – increased body chloride
> Selective loss of HCO3- (poop, pee) due to mechanism in intestine
> bicarb lost in excess effectively traps chloride in the body; theres a switch between chloride and bicarb in the small intestine
> if you don’t have bicarb, you can’t regulate the chloride, to get it out of the body through the GI tract, and so it backs up in blood
> or, renal tubular acidosis, where the body is not capable of bringing bicarb back into the body

Question 9

what does aldosterone do?

Answer 9

-encourages kidney to:
> retain sodium, excrete potassium

Question 10

what is the danger electrolyte?
are serum levels a reliable indicator of total body level?
what do low serum levels generally mean?

Answer 10

Potassium - can cause bradycardia and death if in excess
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* Serum K+ is not a reliable indicator of total body (TB) K+
> because of shifts that occur to maintain electroneutrality
> cell K+ can move into blood to replenish levels
* Low serum K+ almost always indicates TBK+ depletion
> no more to sequester from cells

Question 11

reasons for hyperkalemia
* ON EXAM *

Answer 11

1. Shift from ICF to ECF
   * acidemia; H+ in blood moves down concentration gradient into cell, K+ moves out of cell into circulation to replenish to maintain electroneutrality
   * muscle / tissue damage
   * in vitro hemolysis > pseudohyperkalemia, due to sample mishandling; certain animals have high K+ in RBC

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2. Increased TBK
   * Decreased excretion:
   * Acute renal failure
   * Ruptured bladder; urine high in garbage k+, moves down concentration gradient from petitoneal cavity into blood
   * Low aldosterone – Na:K ratio (eg. from hypoadrenocorticism)
   *Iatrogenic

Question 12

reasons for hypokalemia

Answer 12

1. Decreased intake
   * Anorexia
   * Poor diet
2. Shift from ECF to ICF
   * Alkalemia; too much bicarb in blood, hydrogen moves out of cells and into blood to titrate out bicarb to try to fix alkalemia > we’ve lost H+ from the cell so to maintain electroneutrality K+ moves in
3. Increased loss
   * GI – calf ETEC diarrhea
   * Renal
   * Burns, sweating (horses)
   * etc.

Question 13

How is Water Balance Regulated?

Answer 13

• we are either adding or getting rid of sodium to either expand or contract blood volume
• we are either adding or getting rid of water to either concentrate or dilute out sodium

Question 14

how does the body balance fluid volume?

Answer 14

• volume regulation controlled by changes in sodium *
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• Aldosterone; causes Na+ to be brought back in, which holds on to water in the vasculature
• atrial natriuretic peptide; if stretch receptors are activated, kidney gets rid of sodium

Question 15

how does the body balance osmolality?

Answer 15

• osmolality controlled by changes in water balance *
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• Antidiuretic hormone (ADH); brings water back in
• thirst centres

Question 16

How Does Water Move in the Body?

Answer 16

SLOW:
1. Hydrostatic forces
2. Oncotic forces – proteins (80% albumin)
3. Osmotic forces – osmolality
* Measurement of Na, Cl, K, urea, glucose

FAST:
4. Aquaporins
> kidney collecting duct; aquaporings are inserted by ADH, allowing water back into the body (a more concentrated urine is therefore produced)

Question 17

Major and minor osmotic determinants:

Answer 17

MAJOR: Na+, Cl-, HCO3-

MINOR: glucose, urea

Question 18

how does sodium function as a major osmotic determinant

Answer 18

• Na+ actively controlled & if Na+ moves, water follows
• ↑ Na+ leads to an increase in ECF volume
• ↓ Na+ leads to a decrease in ECF volume

Question 19

Blood Plasma =

Answer 19

Water + Dissolved Substances

Question 20

how do we measure and calculate (estimate) the osmolality of plasma?

Answer 20

Measured Osm(meas)
* Freezing point depression osmometer

Calculated (an estimate)
* Principal osmotically active solutes from biochemical profile
Osmcalc = 2 [Na+ + K+] + urea + glucose

Question 21

what is the osmol gap? what does a high gap mean? what is our threshold for detrmining if there is a problem?

Answer 21

Osm(meas) - Osm(calc) = osmol gap

↑ Osmol gap =
* Presence of an osmotically active molecule in blood
> That is not measured on the serum biochemical profile
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TOXINS!
* Ethylene glycol, ethanol, methanol, paraldehyde
* Mannitol or radiographic contrast medium
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normal osmole gap <10

Question 22

Hyperosmolality - 2 causes

Answer 22

1. Increased solutes:
   a) Hypernatremia, hyperglycemia, azotemia/uremia
   * Normal osmol gap
   b) Ethylene glycol toxicity, mannitol or radiographic contrast medium, methanol, paraldehyde
   * Increased osmole gap
2. Decreased ECF volume
   * Water loss > electrolyte loss

Question 23

Hyperosmolality may or may not cause clinical problems
- what does this depend on?

Answer 23

• generally depends on whether there are fluid shifts or not
• fluid shifts depend on whther we have an effective or inneffective osmol

Question 24

hyperosmolality without fluid shifts:
- do we see clinical signs? why?

Answer 24

without fluid shifts:
ICF osmo = ECF osmo
ie. ineffective osmol

eg. Uremia - contributes to osmolality but it is a small non-polar molecule that equilibriates between the two compartments
> it doesn’t draw water towards it

• No clinical signs attributable to increased osmolality

Question 25

hyperosmolality with fluid shifts:
- do we see clinical signs? why?
* PROB NOT ON TEST *

Answer 25

• we can have clinical signs (not always but we can)

With fluid shifts:
ICF osmo < ECF osmo

eg. Salt toxicity, diabetes mellitus, EG toxicity

• Neurological signs a_ributable to increased
  ECF osmolality
  > neurons become dehydrated

Question 26

Dehydration – Laboratory Evidence

Answer 26

• Increased plasma proteins
  > Increased albumin
• Highly concentrated USG (urine specific gravity)
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• Hemoconcentration (increased PCV)
• Clinically apparent skin tent
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• Dehydration can be hypertonic, isotonic, hypotonic
  > Correlates with the amount water versus electrolytes lost

Question 27

THERE IS ONLY ONE REASON FOR ALBUMIN TO BE INCREASED

Answer 27

dehydration

Question 28

how do I know if I have hypertonic dehydration? causes?

Answer 28

Dehydration - albumin, USG, PCV up

• Look at sodium and chloride
  > both elevated? > hypertonic dehydration

Water loss > NaCl loss

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Dehydration due to pure water loss as with evaporation from the respiratory tract from panting

Question 29

how do I know if I have isotonic dehydration? causes?

Answer 29

Look at sodium and chloride
* Both within the reference interval?
* Isotonic dehydration

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Causes:
* Renal disease
* Diarrhea

Question 30

how do I know if I have hypotonic dehydration? causes?

Answer 30

• Look at sodium and chloride
• Both BELOW the reference interval?
• Hypotonic dehydration

NaCl loss > water loss

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Causes:
* Secretory diarrhea
* Vomiting
> Chloride+/- sodium, potassium, HCO3-
* Heat stress & sweating in horses
> Often Cl- losses are greater than Na+ losses

Question 31

Hyponatremia and hypochloridemia happen because of (choose all that apply):
a) Vomiting
b) Diarrhea
c) Major skin abrasions
d) Movement into the thoracic or abdominal cavity
e) Decreased intake
f) Administration of hypotonic fluids

Answer 31

a) Vomiting
b) Diarrhea
c) Major skin abrasions
d) Movement into the thoracic or abdominal cavity
* Yes – all of these are correct because they involve movement of electrolytes out of blood and either out of the body or into a different body compartment
e) Decreased intake
* Yes – this contributes to mild decreases in sodium and chloride, and not eating makes it worse when the animal already is vomiting or has diarrhea
f) Administration of hypotonic fluids
* Also true! If we give more water than electrolytes, we will dilute out what is already in the vasculature. But I leave further discussions of this to anesthesia and emergency medicine!

Question 32

Sometimes we have disproportionately high chloride loss relative to sodium loss. Why does this happen? (choose all that apply):

a) Vomiting
b) Excessive removal of gastric content
c) Ileus (decreased/absent motility of the small intestine)
d) Left displaced abomasum
e) Pyloric blockage

Answer 32

a) Vomiting
b) Excessive removal of gastric content
* Yes, these two happen when there’s more loss of HCl from the stomach
> theres relatively little Na in stomach juice

c) Ileus (decreased/absent motility of the small intestine)
* Yes! This is one of the reasons why post-op ileus is a big deal (the other is pooping).There’s quite a lot of chloride that ends up in the small intestine, so if there’s decreased motility, there’s less uptake of the chloride and consequently, less chloride makes it into the blood stream.

d) Left displaced abomasum
e) Pyloric blockage
* Yes! Both of these lead to sequestration of chloride in the acid stomach (ileus is sequestration of chloride in the small intestine)

Question 33

Which of the following are ways that a patient can be “overhydrated”? (choose all that apply):

a) Congestive heart failure
b) Administration of hypotonic fluid
c) Diabetes insipidus
d) Mannitol injection

Answer 33

a) Congestive heart failure
* Yes! Failure of forward flow of the blood leads to an edematous state
* Same is true for patients with liver cirrhosis and nephrotic syndrome
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b) Administration of hypotonic fluid
* Yes! If we add more water than electrolytes to the system, then that causes increased total body water, and additionally, dilutes out blood sodium and chloride
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d) Mannitol injection
* Yes! This is an osmotic diuretic and it works by drawing water into the vasculature which then gets presented to the kidney and then the water goes out in urine.
* Just like hyperglycemia, mannitol also causes dilution of sodium and chloride because of that water moving into blood, so add this to the list of things that can cause hyponatremia and hypochloremia!
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Also hounorable mention to diabetes mellitus due to increased glucose in the blood > draws water into

Question 34

Question 4
(A) What are some of the consequences of iatrogenic overhydration and
(B) how are they recognized?

Answer 34

A:
* Peripheral edema
* Pulmonary edema
* Cavitary effusions

B:
* Increased body weight
* Increased respiratory rare and effort < how well do O2 and CO2 diffuse through water? (A: not well and this is a very serious problem)
* Edema in the bulbar conjunctiva and conjunctiva of the eyelid
* Changes in ultrasonographic and ECG findings (I’ll leave those to other courses!)

Question 35

Which of the following are naturally occurring osmols in blood?
a) Sodium
b) Chloride
c) Potassium
d) Urea
e) Glucose
f) Ketones
g) Mannitol
h) Ethylene glycol

Answer 35

a) Sodium
b) Chloride
c) Potassium
d) Urea
e) Glucose
?f) Ketones?

Question 36

An increase in which of the following analytes gives definitive proof of dehydration? (select all that apply)
a) Albumin
b) Globulin
c) Glucose
d) Urea
e) Creatinine

Answer 36

a) Albumin
* Yes! There is only one reason for increased albumin… dehydration!
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b) Globulin
* Globulin increases with dehydration but also increases with inflammation
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c) Glucose
* Glucose can be high from stress and diabetes mellitus, and does not give definitive proof of dehydration
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d) Urea
e) Creatinine
* Both urea and creatinine will increase secondary to decreased glomerular filtration rate. But decreased GFR happens with: heart disease, shock, kidney disease, and dehydration.
* Therefore, while urea and creatinine are often increased in dehydrated patients, it’s not pathognomonic for dehydration.

Question 37

Why does hypernatremia not cause an increased osmol gap? (Write down your answer)

Answer 37

because Na is accounted for in both measured and calculated osmols, so the difference will be zero
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Because it is included in the equation and in the measured osmolality. Since
it’s accounted for in both, it cannot cause an increased osmol gap.
* Only exogenous substances like ethylene glycol, mannitol, radiographic contrast agent, ethanol, etc. can cause an increased osmol gap.

Question 38

Which of the following cause increased total body potassium?
a) In vitro hemolysis in certain breeds of animal
b) Hypoaldosteronemia (hypoadrenocorticism)
c) Acute kidney injury
d) Ruptured bladder
e) Rhabdomyolysis
f) Acidemia

Answer 38

b) Hypoaldosteronemia (hypoadrenocorticism)
> Yes, this is a cause of increased total body potassium because renal potassium excretion is inhibited due to a lack of aldosterone

c) Acute kidney injury
> Yes, this is a cause of increased total body potassium from the kidney not functioning, so the waste product / danger electrolyte, potassium, backs up into the ECF

d) Ruptured bladder
> Yes, this is a cause of increased total body potassium because the bladder is ruptured, and potassium accumulates in peritoneal fluid and moves down its concentration gradient into blood (aka ECF)

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a) In vitro hemolysis in certain breeds of animal
> No, in vitro hemolysis does not result in increased total body potassium, just a shi9 of K+ from ICF to ECF

e) Rhabdomyolysis
> No, massive muscle damage does not result in increased total body potassium, just a shift of K+ from ICF to ECF

f) Acidemia
No, increased H+ in blood does not result in increased total body potassium, just a shift of K+ from ICF to ECF

Question 39

Which of the following cause hypokalemia?
a) Anorexia
b) Hypoaldosteronemia (hypoadrenocorticism)
c) Sweating in horses
d) Diarrhea
e) Alkalemia
f) Acidemia

Answer 39

a) Anorexia
> Yes, animals that are unwell, and particularly cats with kidney disease, may not take enough potassium in resulting in hypokalemia

c) Sweating in horses
> Yes, cutaneous losses of potassium can be significant in sweating horses and result in total body depletion of potassium (i.e., depletion from the ICF and ECF)

d) Diarrhea
> Yes, particularly calves with ETEC diarrhea lose a lot of potassium (and water) and result in marked total body depletion of potassium (as ICF potassium is drawn out into the ECF and then is lost in the diarrhea)

e) Alkalemia
> Yes, recall that when there is a decrease in H+ in the ECF, H+ is “dragged” out of cells into the ECF to titrate with the HCO3-. However, this removes a + charge from the ICF, and K+ moves into the cell to satisfy the need of ICF electroneutrality. This movement results in hypokalemia

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b) Hypoaldosteronemia (hypoadrenocorticism)
> No, this is a cause of hyperkalemia because potassium excretion is inhibited because of low aldosterone

f) Acidemia
No, recall the H+ K+ switch when there are too many H+ in blood, they move down their concentration gradient into cells, but then the cell has to maintain electroneutrality and has too many single + charges, so K+ gets bumped out of the ICF into the ECF leading to hyperkalemia

Question 40

Which of the following directly causes sodium movement in the body? Select all that apply.
a) Aldosterone
b) Atrial natriuretic peptide
c) Antidiuretic hormone
d) Thirst centres

Answer 40

a) Aldosterone
b) Atrial natriuretic peptide

Question 41

Which of the following causes an increased osmol gap?
a) Hypernatremia
b) Hyperglycemia
c) High urea
d) Ethylene glycol
e) Ethanol
f) Mannitol

Answer 41

d) Ethylene glycol
e) Ethanol
f) Mannitol

Question 42

You note that an animal has high albumin but decreased sodium and chloride on the biochemical profile.
What does increased albumin indicate?
a) Dehydration
b) Euhydration
c) Don’t know
d) Animals normally have high albumin

Answer 42

a) Dehydration

Question 43

You note that an animal has high albumin but decreased sodium and chloride on the biochemical profile.
What type of dehydration is it when sodium and chloride are decreased in a dehydrated animal?

a) Hypervolemic dehydration
b) Hypovolemic dehydration
c) Isotonic dehydration
d) Hypertonic dehydration
e) Hypotonic dehydration

Answer 43

e) Hypotonic dehydration

Question 44

Which analyte will be decreased by prolonged contact with the clot? Select all that apply.
a) Sodium
b) Potassium
c) Chloride
d) Glucose
e) Urea
f) AST

Answer 44

d) Glucose
> Yes, glucose decreases by ~10% / hour of serum contact time with the clot, as the RBC and WBC are still using glucose to produce ATP. This is why samples should be spun down and the serum separated and sent to the lab