Electrolytes Flashcards
What are three sites that calcium is regulated?
- GI
- Bone
- Renal
How is calcium regulated in the kidney?
PTH increases reabsorption (tubular)
PTH increases vitamin D production
Calcitonin decreases reabsorption (tubular)
What three things influence general interpretation of total blood calcium?
- Calcium fractions (ionized, protein blound, complexed) - total calcium on biochem is assumed to represent ionized
- Protein influence
- pH influence
What does the biochemistry calcium measure? What is the term for this?
50% ionized
40% protein bound
10% complexed (citrates, phosphates)
Calcium fractions
What calcium fraction is biologically active?
Ionized calcium
T/F
Calcium is heavily regulated, tight to its reference range
True
What is the #1 cause for hypocalcemia? Does this alter the ionized Ca levels?
Hypoalbuminemia
No - not to worry!
What is the correction formula for albumin influence?
Total Ca - albumin + 3.5
How does pH influence calcium?
Calcium and hydrogen compete for binding sites on albumin. Increase or decrease hydrogen can have an affect on calcium
With acidemia, what will the calcium look like? Alkalemia?
acidemia – Hypercalcemia
alkalemia – Hypocalcemia
What would cause the masking of a pathologic change in Ca? When is this clinically most important
Protein value
Blood pH
with alkalemia
Could alkalemia alone cause clinical signs of hypoclacemia?
No
What is the most common cause for hypercalcemia?
Humoral Hypercalcemia of malignancy
What are causes for high hypercalcemia values?
HHM
Primary hyperparathyroidism
Vitamin D toxicity
Addison’s disease
What are causes for lesser elevations in calcium?
Very high value disease (early stage)
Renal failure
Various bony lesions (HOD, fungal)
+/- alkalemia (increase protein bound fraction)
What are causes for hypocalcemia?
- may show symptoms to hypocalcemia (severe)
1. Hypoproteinemia
2. Equine colic (anorexia, decreased absorption)
3. Renal failure
4. Acute Pancreatitis (calcification)
5. Hypomagnesemic (“Grass”) tetany
6. Mercury toxicity
7. *Milk Fever, eclampsia
8. *Ethylene glycol toxicity
9. *Hypoparathyroidism
10. *Blister beetle toxicity
What are two HHM causes? Most common to least
Lymphosarcoma»_space; anal sac adenocarcinoma
What is the mechanism for HHM?
stimulation of osteoclastic activity (PrPTH)
What is the most common change in calcium during primary renal azotemia? Mechanism?
Normocalcemia or mild hypocalcemia
Hypocalcemia secondary to effects of increased P and decreased vitamin D production
How do horse’s calcium values present during primary renal azotemia? Why?
Hypercalcemia
High Calcium diets
GI poorly regulates Calcium (normally kidney gets rid of excess Ca)
Renal azotemia –> decrease excretion of Ca –> horse continues to eat –> hypercalcemia
What is a common sign of persistant hypercalcemia?
PU/PD (hyperCa interferes with ADH activity on tubules), secondary to renal tubular damage
What does moderate-severe hypercalcemia with laboratory evidence of renal failure probably indicate?
Secondary renal involvement!!
Hypercalcemia INDUCED renal azotemia
What is a severe hypercalcemia value?
> 13-14
What does hypercalcemia with metastatic calcification result in?
Tubular degeneration
Mineralization of BM’s
Interstitial fibrosis
Primary renal azotemia
What are 5 causes for hyperphosphatemia?
- Renal (decrease GFR)
- Vitamin D toxicity
- Hypoparathyroidism (decreased PTH)
- Young animal (active BM 6 month - 1 year)
- Osteolytic bone lesions
What does PTH do to Phosphorus at the level of the kidney?
PTH reduces phosphorus reabsorption
What are causes for hypophosphatemia?
- HHM (renal azotemia may influence the P to elevate - depends)
- Hyperparathyroidism
- Anorexia, inadequate diet
- Diabetes mellitus (osmotic diuresis)
- Insulin therapy (drives P into cells)
- Bovine post-parturient hemoglobulinuria (uncommon, dairy cow on P deficient soil)
What are the major mechanism categories for phosphorus shifts?
Renal excretion
Dietary intake
Hormonal influence
Transcellular shifts (insulin, possibly acid/base)
What is the number one cause for shifts in phosphorus?
Renal excretion (decrease GFR)
How does the glomerulus handle phosphorus? Tubules?
Freely filtered Tubular reabsorption (PTH decreases reabsorption)
What is renal secondary hyperparathyroidism?
Hyperphosphatemia induced hypocalcemia
What amount of the body’s magnesium is in the blood?
1%
the rest is in soft tissue and bone @ 50:50
T/F
Mg is tightly regulated
False
Mg is slowly corrected – equilibrium b/w pools is reached slowly
What primarily controls serum levels of Mg?
renal excretion
How can Mg affect calcium levels?
Mg is needed for PTH release!
What can cause hypomagnesemia?
- Milk tetany - all milk diet, low in Mg
- Grass tetany - adults, lush pastures, possibly after poor winter diet
High K interferes with Mg absorption
What is an important differential dx with sudden death syndrome?
Grass tetany
What could cause Mg to falsely elevate from low levels back to normal?
Muscle activity (Collect samples early!)
What is a good post mortem dx for hypomagnesemia?
urine concentration of Mg
Common causes of hypernatremia related to dehydration.
- Insensible water loss: fever, panting, restricted access
- GI loss: most vomiting, some diarrhea
- Renal failure (dependent on dehydration state)
- Diabetes insipidus (central or renal): mainly if water is restricted
Common mechanisms for hyponatremia
- Loss: GI, Renal
2. Redistribution: Third space disease, intravascular dilution (osmotic)
What are some causes for hyponatremia?
GI loss
- Diarrhea
- Saliva (horse)
Renal loss
- Renal failure (severe losses in bovine)
- Hypoadrenocorticism (Addison’s)
- . Osmotic diuresis (DM)
Redistribution
- Ascites/edema
- GI obstruction/sequestration
- Hyperglycemia (DM)
What is the Na value when we get concerned about medullary washout?
Na < 120
What would be normal to see in bovine renal failure and sodium?
severe hyponatremia – they have greater Na loss
What are 3 main mechanisms for potassium changes?
- Excretion (renal)
- Intake (GI)
- Internal shifts - redistribution (pH, insulin)
How is potassium handled by the glomerulus? Tubules?
Glomerulus - freely filtered
Tubules
- 100% reabsorbed by PCT
- secretion of K at distal tubuels for urinary losses
How does anuria, oliguria, and obstructive disease lead to marked hyperkalemia?
Decreased GFR
Decreased secretion
Associated acidemia
How does hypoaldosteronism lead to hyperkalemia?
Aldosterone normally retains sodium and excretes potassium. Now potassium remains and sodium is excreted.
When is chronic hyperkalemia associated with animals, especially cats?
Polyuric conditions
High output diseases like DM can cause this –> increase flow rate –> increase K losses (less time to reabsorb)
What dietary situations can cause hypokalemia?
- Anorexia (expecially herbivores and cats)
2. GI disease (gastric vomiting) - probably from loss through kidney while trying to regain H+
What are 3 major mechanisms for potassium changes?
- Renal
- GI/intake
- Internal shifts
What are some internal shifts that would cause change in potassium change?
- Acidemia
- Alkalemia
- Insulin
- Hemolysis
What is the difference b/w potassium levels in carnivores vs. herbivores? What species?
Herbivores > carnivores
- Horse, cow (mixed)
What happens to muscles with severe hypokalemia? What is this called?
Leads to muscular weakness and eventually rhabdomyolysis (myoglobinuria and increased CK)
Hypokalemic polymyopathy
What is a specific syndrome seen in older cats associated with renal disease/CRF? What are contributing factors?
Hypokalemic polymyopathy
- Increased renal loss (polyuria)
- Decreased overall food intake
- +/- Marginal dietary K content (food companies have mostly resolved this)
What do cats with hypokalemic polymyopathy commonly present as?
present with weakness –> +/- cervical ventroflexion
What genetic condition in Quarter Horses is related to an electrolyte disturbance? What is seen?
Hyperkalemic Periodic Paralysis
Skeletal muscle sodium channel gene
Transiently high K –> bradycardia
