Water Balance & Electrolytes

Intracellular fluid (ICF, about 2/3 of total body water)

Where is a majority of the water in the body?

1. Plasma (~25%)

2. Interstitial fluid (~75%)

(Transcellular and gastrointestinal fluids)

Extracellular fluid is split into what two categories?

Plasma

When we measure electrolytes what fraction of water are we measuring from?

1. Sodium

2. Potassium

3. Chloride

4. Bicarbonate

What are the electrolytes?

Bicarbonate

Total CO2 gives an estimate of serum what?

Decreased

If you have damage to the cellular membrane you would expect a ____________ sodium in the ECF

Osmolality

The concentration of all solute particles in a fluid compartment

1. Sodium

2. Potassium

3. Chloride

4. Bicarbonate

5. Glucose

6. Urea

In serum, what constitutes as the osmolality?

Sodium

What is the most abundant cation in the ECF?

Tonicity

The ability of solutes to generate an osmotic pull that causes water to move from one compartment to another

B

T or F: All particles in plasma contribute to tonicity

1

To contribute to tonicity a solute must be confined to ________ compartment

Effective osmole

Exerts an osmotic force and cannot permeate the cell membrane

Glucose and sodium

What are the effective osmoles?

Cell shrinkage

Addition of sodium into ECF results in what?

Ineffective osmole

A particle that diffuses readily across cell membranes and does not exert an osmotic force

Urea (also BUN)

What is the ineffective osmole?

Urea diffuses too quickly so cannot use it as an indicator of urine in abdomen

If you are wanting to check for a uroabdomen, why would you measure creatine over urea?

1. Amount of solute

2. Permeability across the membrane

Osmotic activity (tonicity) depends on what?

Osmolal gap

Difference between the measured osmolality and the calculate osmolality

Increased

An ___________ osmolal gap indicates accumulation of osmotically active particles other than those in the formula used for calculation

Ethylene glycol intoxication

What is one of the most common examples that would cause an increase in osmolal gap?

Colloid osmotic pressure

The part of the total osmotic pressure in plasma contributed by colloids

Albumin

The protein that makes the biggest contribution to colloid osmotic pressure

Edema

Hypoalbuminemia can cause what?

Dehydration

Loss of fluid from the body in one or multiple ways

A

T or F: Dehydration is not detectable on physical exam until ≥ 5%

Hypertonic fluid loss

Loss of solutes in excess of water

Hypotonic

Hypertonic fluid loss leads to ______________ dehydration

Isotonic fluid loss

Loss of equal amounts of water and electrolytes

Isotonic

Isotonic fluid loss leads to _____________ dehydration

Hypotonic fluid loss

Loss of water in excess of solutes

Hypertonic

Hypotonic fluid loss leads to _____________ dehydration

Extracellular fluid

In most disease states, fluid and solutes are initially lost from what?

160

Hypernatremia is defined as sodium > ________ mmol/L

Hypernatremia

Develops when water loss is greater than loss of sodium

1. Pure water deficit

2. Hypotonic fluid loss

3. Sodium overload/retention of sodium

What are the three general causes of hypernatremia?

1. Fever

2. High environmental temperature

3. Diabetes insipidus

4. Inadequate water intake

What can cause a pure water deficient leading to hypernatremia?

A. GI (vomiting/diarrhea), third space (body cavity effusion), and cutaneous burns

B. Osmotic diuresis (DM, mannitol), chronic/polyuric acute renal failure, loss of renal concentrating ability

What are causes of (A) extrarenal and (B) renal hypotonic fluid loss leading to hypernatremia?

1. Salt poisoning

2. Iatrogenic (hypertonic saline, sodium bicarbonate)

3. Primary hyperaldosteronism

What can cause sodium overload/retention of sodium leading to hypernatremia?

Neurologic signs (lethargy, weakness, muscle fasciculation, disorientation, behavioral changes, ataxia, seizures, stupor, coma)

What clinical signs are associated with hypernatremia?

A

T or F: Because water moves from the intracellular to extracellular compartment with hypernatremia, skin turgor may be adequate

1. Sodium deficient group

2. Water excess group

3. Shift of water from intracellular to extracellular space

4. Shift of Na from extracellular to intracellular

5. Shift of Na from intravascular to extravascular space

What are general causes for hyponatremia?

Pseudohyponatremia

Lipemia or severe hyperproteinemia lead to a decrease in measured sodium (depending on methodology for measurement)

Ion selective electrode (uses direct potentiometry)

Which type of analyzer would not have an issue with pseudohyponatremia?

Hyponatremia (increased renal loss of sodium and water) and hyperkalemia

Hypoadrenocorticism leads to a lack of aldosterone resulting in what?

Urethral obstruction

What is a classic example of a cause for increased total body K+?

Hypoadrenocorticism

Very low values (<20) for the Na:K ratio are strongly suggestive of what?

1. Massive tissue necrosis

2. Acidosis

3. Intravascular hemolysis

4. Pseudohyperkalemia

What leads to hyperkalemia without an increase in total body K+?

1. Horses

2. Pigs

3. Most cattle

4. Most sheep

5. Japanese Akita

6. Japanese Shiba Inu

7. Korean Jindo

Which animals and dog breeds have high [K] in their RBCs?

Pseudohyperkalemia

Marked thrombocytosis (>800,000 ul) leads to what?

Life threatening bradyarrhythmias

>7.0 hyperkalemia may cause what?

Changes in cell membrane excitability

Hyperkalemia clinical signs reflect what?

A. Weakness due to decreased excitability

B. Decreased excitability, increased refractory period, slowed conduction

What does hyperkalemia do to (A) skeletal muscle and (B) cardiac muscle?

1. Metabolic alkalosis

2. Insulin

What can lead to hypokalemia with no change in total body K+?

Muscle weakness

What is the most common clinical sign for hypokalemia?

Hypernatremia

Hyperchloremia has similar causes as what?

Hydration problems (dehydration or overhydration)

If Na+ and Cl- change in the same direction and are proportional this is indicative of what?

Acid base abnormalities

If Na+ and Cl- change in opposite directions or are not proportional this is indicative of what?

Decrease

Metabolic alkalosis is a(n) ___________ in Cl-

Increase

Metabolic acidosis is a(n) ____________ in Cl-

SID = Na - Cl

Strong ion difference is defined as what?

1. Low Cl- and metabolic alkalosis

2. Loss or sequestration of Cl- is occurring independent of Na+

3. Vomiting of gastric contents, abomasal atony or reflux from the abomasum into the rumen

An SID of >38 is indicate of what?