Body Water, Osmolality, Anion Gap, and the Monovalent Electrolytes

Complete the following with the appropriate percentage of total body water that is present in each compartment:

Intracellular fluid (ICF): ______

Extracellular fluid (ECF): ______

______ = Blood / plasma

______ = Interstitial fluid

ICF: ~ 66%

ECF: ~ 33%

Blood/plasma: ~ 25%

Interstitial: ~ 75%

What are the two processing by which we obtain water?

- ingestion

- oxidative metabolism

What are three ways/methods we lose water?

- Urinary tract

- GI tract

- Respiratory tract (panting)

- Integument (evaporation)

How is input/thirst and output/urine of total body water regulated - i.e. what are two regulators of these things?

antidiuretic hormone (ADH) (thirst, renal)

aldosterone (sodium regulation)

ADH primarily regulates _______ water volume. (ICF/ECF)

ICF

Aldosterone primarily regulates _______ water volume by regulating ___________ (ICF/ECF, electrolyte)

ECF

sodium

How is TBW estimated?

using hydration status

What are some clinical parameters that help us assess hydration status?

skin elasticity

mucous membranes

retraction of the eyes

body weight*

What clinical parameter is the most objective assessment of hydration status?

serial body weight measurements

What are some laboratory parameters that help us assess hydration status?

hematocrit 9PCV)

protein (total protein, albumin)

urea nitrogen and creatinine

urine specific gravity

In most disease states, loss of fluids occurs initially from the _______ (ICF/ECF)

ECF

Hypovolemia: volume depletion

Decreases in TBW -

_________ fluid intake

_________ water losses

Decreased

Increased

What are some things that can cause increased water loss and lead to hypovolemia?

diarrhea

vomiting

polyuria

severe sweating

polypnea

What is the clinical manifestation of hypovolemia?

dehydration

The following are clinical manifestations of what?

tacky mucous membranes

low blood pressure

weak

low body temperature

rapid heart rate

can lead to multi-organ failure and death if not corrected immediately

hypovolemic shock

Hypervolemia - volume retention

Increases in TBW:

___________ fluid intake (animal drinking excessively)

___________ (overzealous fluid therapy)

Syndrome of inappropriate _______ release.

Increased

Iatrogenic

ADH (SIADH)

Syndrome of inappropriate ADH release (SIADH): Causes retention of water in absence

of __________/__________. Patients are __________ with increased urine osmolality.

hypernatremia/ hyperosmolality

hyponatremic

What are clinical manifestations of hypervolemia?

increased body weight*

edema (peripheral, pulmonary)

effusions (ascites, hydrothorax)

What is "third-spacing"?

It is a redistribution of total body water

What are the four main factors/substances that are key to maintaining fluid balance?

Fluid volume

pressure

sodium concentration

albumin concentration

If redistribution of TBW is severe, especially in the transcellular spaces (body cavities), this can lead to reduced cardiac output, hypotension, and ___________ ______

hypovolemic shock

Maintenance of ICF occurs in part by regulation of plasma ____________

osmolality

Maintenance of ECF is closely related to the regulation of __________ balance

sodium

Sodium and chloride concentrations are higher in the _______, and potassium concentration is higher in the _______

ECF

ICF

Which electrolyte(s) primarily regulate(s) ECF volume?

Sodium and chloride

Which electrolyte(s) primarily regulate(s) ICF volume?

potassium

___________ is the measure of the number of particles in solution.

Osmolality

___________ refers to the number of particles that cannot diffuse readily across cell membranes, but are able to generate or establish an osmotic gradient.

Tonicity

What are the four main substances that determine serum osmolality in health?

Sodium

Potassium

Urea

Glucose

What is the main substance that determines the osmolality in health?

Sodium

What is calculated osmolality - what values are included in its calculation?

(we do not need to know this formula)

Calculated osmolality is estimated using a formula

involves [Na+], [K+], glucose, and BUN

What is measured osmolality?

Osmolality can be measured based on freezing point depression (preferred method) or vapor pressure using an osmometer.

What is the osmol gap?

A gap above ~10 mOsmol/kg indicates what?

it is the difference between measured osmolality and calculated osmolality

An increased osmol gap suggests the presence of high concentrations of exogenous small molecular weight substances such as ethylene glycol, methanol, ketones, or lactic acid.

___________ is volume depletion. What can cause it?

Hypovolemia

decrease in fluid intake or increased water losses

____________ is volume retention. What general things might cause this?

Increased fluid intake (animal drinking excessively)Iatrogenic (overzealous fluid therapy)Syndrome of inappropriate ADH release (SIADH):

What is redistribution of total body water?

If there is a problem with one or more of these components, fluid shifts occur, typically from the intravascular space into extracellular space

What is hyperosmolality?

Increased Na

When the accumulation of solutes ("effective osmols") increases tonicity, water shifts from ICF to ECF.

What occurs if hyperosmolality occurs acutely?

- If it is acute, cell shrinkage can occur (water shifting from ICF to ECF): especially neurons

- The animal can present as being depressed, stuporous, or even die because of the hyperosmolar state.

What occurs if hyperosmolality occurs slowly?

If this occurs slowly, there is intracellular production of organic molecules referred to as idiogenic osmoles (taurine, glycine, glutamine, sorbitol, inositol) that will diminish the osmotic gradient causing less water to leave the cells. The animal may not show obvious clinical (neurologic) signs.

However, if hypotonic fluids are given to reduce the osmolality, a rapid influx of water into cells can result in what two things?

♦Rapid return of hyperosmolal ECF to isotonicity can cause cellular edema.

♦Cerebral cellular edema can produce convulsions.

What is hypoosmolality? When does it typically occur

Hypoosmolaltiy is almost always associated with hyponatremia, but not all cases of hyponatremia are associated with hypoosmolality.

● Shift of water from ECF to ICF results in cellular swelling.

Other than hyponatremia, in what other instance might a patient have hypoosmolality?

Low Na+ concurrent with hyperglycemia - seen in diabetes mellitus

What are the clinical consequences if hypoosmolality occurs quickly?

Water shifts from ECF to ICF --> cell swelling

Rapid development of hypoosmolality can cause intravascular hemolysis and neurologic disorders.

If a patient is severely dehydrated and is in a hyposmolality state - what are the consequences?

loss of ECF volume is amplified by movement of water into the ICF.

This can lead to circulatory collapse and shock.

What four monoelectrolytes are measured in a chemistry profile and can be used to determine the anion gap?

sodium (Na+)+

potassium (K )

chloride (Cl−)

total CO2 (TCO2) (bicarbonate)

When obtaining a sample for measuring electrolytes, _________ can be obtained from a red top tube that contains no anticoagulant and ____________ can be obtained from a green top tube that contains lithium heparin.

serum

plasma

What tubes are not suitable for electrolyte analysis?

sodium heparin,

EDTA or citrate are NOT suitable.

____________: sodium below reference range

Hyponatremia

_____________: sodium above reference range

Hypernatremia

____________: sodium within reference range

Normonatremia

____________: potassium below reference range

Hypokalemia

_____________: potassium above reference range

Hyperkalemia

_____________: potassium within reference range

Normokalemia

______________: chloride below reference range

Hypochloridemia

_____________: chloride above reference range

Hyperchloridemia

_____________: chloride within reference range

Normochloridemia

_____________: osmolality below reference range

Hypoosmolality

_____________: osmolality above reference range

Hyperosmolality

____________: pertains to the volume of circulating fluid (plasma)

Volemia

____________: decreased circulating fluid volume (ex. dehydration)

Hypovolemia

_______________: increased circulating fluid volume (ex. edema)

Hypervolemia

___________ is the main ECF cation and that is it largely responsible for maintaining ECF.

Sodium

_________ Na+ reflects total body Na+

Serum

"_________ follows sodium"

water

Increases in [Na+] results in ______ expansion, which is ______volemia.

ECF

hyper

What are some clinical manifestations of an increase in Na+?

This results in hypervolemia

Clinical manifestations include peripheral edema, pulmonary edema, effusions.

Decreases in [Na+] results in ECF ___________, which is ______volemia.

depletion

hypo

What are some clinical manifestations of a decrease in Na+?

This results in hypovolemia

Clinical manifestations include loss of skin elasticity, dry mucous membranes, retraction of eyes back into the sockets, slow capillary refill time, or signs of shock.

The balance between what two things maintains ECF?

The balance between Na+ intake and renal excretion determines the amount of Na+ in the ECF, hence the size of the ECF.

What four things help maintain the balance between Na+ intake and renal excretion determines the amount of Na+ in the ECF?

1. Receptors in renal juxtaglomerular cells

2. Volume receptors

3. Pressure receptors

4. secretion of ADH

How do receptors in renal juxtaglomerular cells help maintain the balance between Na+ intake and renal excretion determines the amount of Na+ in the ECF?

These sense changes in renal perfusion and respond by activating the renin angiotensin-aldosterone system.

How does RAAS respond when the renal juxtaglomerular cells detect a decrease in renal perfusion (i.e. a low ECF volume/low Na+)?

In response to decreased renal perfusion (implies a low ECF):

♦ release of renin

♦ renin convert angiotensinogen to angiotensin I

♦ angiotensin I is converted to angiotensin II by angiotensin-converting enzyme

♦ angiotensin II ▬ directly promotes renal Na+ retention & causes release of aldosterone from the adrenal cortex

♦ aldosterone promotes Na+ retention in the distal nephron

___________ promotes Na+ retention in the distal nephron

aldosterone

How do volume receptors help maintain the balance between Na+ intake and renal excretion?

Sense changes in venous and atrial filling

Increases in atrial filling causes release of atrial natriuretic factor(ANF)

ANF promotes renal sodium excretion

How do pressure receptors help maintain the balance between Na+ intake and renal excretion?

- Decreased ECF volume stimulates receptors activating the sympathetic nervous system

- Leads to renal retention of sodium

How does ADH help maintain the balance between Na+ intake and renal excretion?

In response to hypertonicity in the ECF, ADH is secreted.

ADH acts on the kidney (inserts aquaporins) and causes it to retain water,

thereby decreasing the tonicity of the ECF.

Sodium concentration must be interpreted along with knowledge of your patient's ____________ status.

hydration

What are two basic mechanisms behind hyponatremia?

1) Na+ loss in excess of water loss +

2) Water intake or retention in excess of Na intake or retention

The following are all common causes of _______natremia.

●vomiting, diarrhea (especially severe)

● renal failure, especially in cattle

● diabetes mellitus: osmotic diuresis secondary to hyperglycemia

● ruptured or obstructed urinary tract: third space loss/sequestration

● hypoadrenocorticism (Addison's disease): lack of mineralocorticoids (ex. aldosterone)

● treatment with diuretics (thiazides, furosemide):

hypo

vomiting, diarrhea (especially severe) can lead to _______natremia

hypo

(can lead to hypernatremia if the animal stops drinking or has no access to water in these scenarios)

renal failure, especially in cattle, can lead to _______natremia

hypo

(can lead to hypernatremia if the animal stops drinking or has no access to water in these scenarios)

diabetes mellitus: osmotic diuresis secondary to hyperglycemia can lead to ________natremia.

hypo

(can lead to hypernatremia if the animal stops drinking or has no access to water in these scenarios)

ruptured or obstructed urinary tract: third space loss/sequestration can lead to ______natremia.

hypo

hypoadrenocorticism (Addison's disease): lack of mineralocorticoids (ex. aldosterone) can lead to _______natremia.

hypo

treatment with diuretics (thiazides, furosemide) can lead to _______natremia.

hypo

Na+ concentration within reference range can still indicate an abnormal state- in what instances?

if body water is abnormally high or low.

Animals that are dehydrated with ______________ have proportional deficits in body water and

Na+. Conditions where this is seen include renal failure, vomiting, diarrhea.

normonatremia

What are two basic mechanisms behind hypernatremia?

Water loss in excess of Na loss

Na+ intake in excess of water intake

Na+ concentration within reference range can still indicate an abnormal state if body ________ is

abnormally high or low

water

Animals that are dehydrated with normonatremia have proportional deficits in body water and Na+ - in what instances might this occur?

renal failure, vomiting, diarrhea.

What are three examples that explain a hypernatremic state?

● volume depletion with dehydration associated with vomiting, diarrhea, diabetes mellitus, renal failure and animal stops drinking or has no access to water.

● pure water loss

● increased salt intake without adequate water intake

Volume depletion with dehydration associated with vomiting, diarrhea, diabetes mellitus, and renal failure, and where the animal stops drinking or has no access to water can lead to ______natremia.

hyper

What are two examples of pure water loss that can lead to a hypernatremic state?

♦pituitary diabetes insipidus (lack of ADH or a failed response to ADH)

♦insensible water loss without replacement: heat stroke, high environmental temperature,

fever with concurrent lack of access to water

What are two examples of increased salt intake without adequate water intake that can lead to a hypernatremic state?

♦iatrogenic administration of hypertonic saline, excessive Na+ bicarbonate

♦salt poisoning in food animals that ingest high salt rations when water delivery systems fail

_____________ is the main intracellular cation.

Potassium

What three things regulate the movement of K+ via renal excretion and via movement from ECF o ICF?

- Aldosterone enhances renal excretion of K+

- Insulin drives K+ from ECF to ICF

- pH: acidosis causes movement of K+ from ICF to ECF, and the opposite with alkalosis

_______________ enhances renal excretion of K+.

_______________ drives K+ from the ECF to the ICF.

Aldosterone

Insulin

What is the effect of a low pH (acidity) on K+ movement?

Acidosis, not due to increased organic

acids, causes K+ to move from ICF to ECF (out of cells).

What is the effect of a high pH (alkaline) on K+ movement?

Causes K+ to move from ECF to ICF (into cells)

What can cause a pseudohyperkalemia? (5/6 general things)

● leakage of red cell K+ into the serum

● red cells not separated promptly from serum

● hemolysis

● extremely high leukocyte (> 100,000 / μl) or platelet counts (> 1,000,000 / μl)

● use of EDTA blood tube