Electrolytes, Osmolality, Hydration (In progress)

What percent of total body water is intracellular fluid?

2/3

What percent of total body water is extracellular fluid?

1/3

What percent of extracellular fluid is in vasculature?

1/4

What percent of extracellular fluid is interstitial?

3/4

What is total body water/hydration status primarily controlled by?

Water intake and renal output

Is sodium concentration greater inside or outside the cell?

Outside

Is potassium concentration greater inside or outside the cell?

Inside

Is calcium concentration greater inside or outside the cell?

Inside

Is magnesium concentration greater inside or outside the cell?

Inside

Is chloride concentration greater inside or outside the cell?

Outsude

Is bicarb concentration greater inside or outside the cell?

Outside

Is hydrogen phosphate/dihydrogen phosphate concentration greater inside or outside the cell?

Inside

What is the ratio of cations to anions in all body fluids?

Equal

Under normal conditions, how is Na+, K+, Cl- obtained?

Via oral route

How is HCO3- generated?

By carbonic anhydrase reactions (lung, gastric mucosa, kidney, rbc)

Why are intracellular and extracellular electrolyte concentrations and pH regulated within a very narrow range?

-Maintenance of precise osmotic gradients

-Nerve function

-Muscle function

-Cellular enzyme systems (pH)

What is electrolyte balance maintained by?

Numerous systems:

-Renal

-Gastrointestinal

-Hormonal

-Neural

What is bicarbonate called on many chem panels?

TCO2

What is the major determinant of extracellular osmolality and is important in regulation of hydration?

Sodium

What causes abnormal electrolyte concentrations in plasma or serum?

1. Increased or decreased intake

2. Shifts between the ECF and ICF

3. Increased renal retention

4. Increased loss through: GI, renal, skin, airway

What is an essential component of electrolyte assessment?

Hydration status

What happens when one compartment loses or gains H2O or electrolytes?

It will alter volume and solute concentration of other compartments

What body compartment does plasma/serum values reflect?

ECF concentration

What does loss of hypertonic ECF result in?

Hypotonic ECF

What does loss of hypotonic ECF result in?

Hypertonic ECF

What does loss of isotonic fluid result in?

Loss of ECF volume

-Does not by itself cause osmotic shifts/electrolyte changes

-Compensatory H2O intake/renal H2O retention will dilute ECF

An increase in sodium is normally accompanied by what?

An increase in Chloride

An increase in chloride is normally accompanied by what?

A decrease of bicarb

What is dehydration?

Decreased total body water

What is the best way to determine dehydration?

Loss of weight

What are clinical signs of dehydration?

-Loss of skin elasticity, dry MM, retraction of eyes, prolonged CRT, increased HR, shock

-Specific lab values- Protein, Hct, UN, USG

-These values may be influenced by other conditions- they must be used in conjunction with physical examination

What does loss or sequestration of hypotonic fluid result in?

Hypertonic dehydration (increased Na+)

What does loss of isotonic fluids result in?

Isotonic dehydration (WRI Na+)

What does loss of hypertonic fluids result in?

Hypotonic dehydration (decreased Na+ and Cl-)

What is the result of pure water loss?

Hypernatremia

What are causes of hypertonic dehydration?

-No access to water with continued insensible loss (panting, hyperventilation, fever) or diabetes insipidus

How does ICF and ECF react to hypertonic dehydration?

They share burden of water loss

-ECF osmolality is greater than ICF, therefore water shifts to ECF

What would you see on clinical exam for a patient with isotonic dehydration?

Animal is dehydrated by skin-turgor tests, +/- hyperalbuminemia and relative erythrocytosis

How does ICF and ECF react to isotonic dehydration?

ICF osmolality = ECF so no fluid shifts

What are the causes of isotonic dehydration?

Vomiting or diarrhea

What are the causes of hypotonic dehydration?

Severe secretory diarrhea

How does ICF and ECF react to hypotonic dehydration?

ECF osmolality is less than ICF, therefore fluid shifts into ICF and makes hypovolemia worse

What is osmolality?

Number of solute particles per unit weight of solution

What is tonicity?

The effective osmolality of a solution

What are effective osmoles?

Osmoles that do not cross permeable membranes (electrolytes, glucose)

What are ineffective osmoles?

Osmoles that readily cross membranes (urea) and do not contribute to tonicity

What does an osmometer measure?

Measures ALL osmols in solution (both effective and ineffective)

How does an osmometer work?

-Vapor pressure (elevation) or freezing point (depression)

What is the freezing point principle?

Freezing point is related to osmotic concentration (if concentration is higher, it will lower the freezing point)

How much does potassium impact osmolality? (IMPORTANT)

Not very much

Calculated osmolality is typically ________mOsm less than the measured value in a healthy state

10 mOsm

What is the osmolar gap?

Measured Osm - calculated osmolarity

What does it mean if there is an increased amount in the osmolar gap?

There are increased numbers of osmotically active particles in blood NOT accounted for in the equation, such as lactate, ketones, alcohols, ethylene glycol, mannitol, oxalic acid, salicylic acid

What are two of the important functions of sodium?

-Blood pressure and volume

-Function of muscles and nerves

Plasma sodium is a balance between what?

What is consumed in food and drink and what is excreted in urine

A small amount of sodium is lost through what?

Stool and sweat (in horses) in health

What osmole is the most abundant cation of plasma and therefore is the major determinant of extracellular tonicity?

Sodium

What is plasma Na+ controlled by?

Regulation of blood volume and Regulation of plasma osmolality/tonicity

How does the body correct hypovolemia?

Activation of RAAS --> Na+ resorption in the kidneys --> ADH release (hypothalamus) --> H2O resorption in the kidneys --> dilution of plasma (Na+)

How does the body correct hypervolemia?

Atrial stretch --> release of ANP --> renal Na+ wasting

How does the body correct hyperosmolality?

Stimulation of thirst centers (hypothalamus) --> Increased H2O intake --> dilution of plasma (Na+) --> ADH release --> Increased H2O absorption in the kidneys --> dilution of plasma

How does the body correct hypoosmolality?

Decreased thrist/water intake --> Decreased ADH release --> increased urinary water excretion --> increased plasma (Na+)

What is serum Na+ dependent on?

The ratio of total body Na+ to total body water

What are the two things that can cause hyponatremia? Which one is more common?

-H2O deficit group (most common)

-Na+ excess group

What are the 3 mechanisms that can cause H2O deficiency?

-Decreased H2O intake

-Pure water loss

-H2O loss > Na+ loss

What conditions can cause decreased H2O intake?

-H2O deprivation

-Defective thirst center (adipsia, seen in mini schnauzers and Staffordshire bull terriers)

What conditions can cause pure H2O loss?

-Panting, hyperventilation, fever

-Diabetes insipidus (ADH)

What conditions can cause H2O loss that is greater than Na+ loss?

-Osmotic diuresis (diabetes mellitus, mannitol)

-Osmotic diarrhea

What are the two mechanisms that can cause increased sodium?

-Excess Na+ intake

-Decreased renal Na+ excretion

What conditions cause excess salt intake?

-Salt poisoning

-Hypertonic saline infusion

What condition can cause decreased renal Na+ excretion?

Hyperaldosteronism (rare)

What categories can cause hyponatremia?

-Na+ deficit group

-H2O excess group

-Shifting of H2O from ICF to ECF

-Intravascular to extravascular Na+ shift

What mechanisms can cause Na+ deficit?

-Na+ loss > H2O loss

-Renal Na+ wasting

What specific condition causes Na+ loss > H2O loss?

-Alimentary loss (vomiting, diarrhea, third-space loss)

What specific condition causes renal Na+ wasting?

Hypoadrenocorticism, diuresis

What mechanisms cause H2O excess?

H2O retention > Na+ retention (with or without edema)

What specific condition causes H2O retention > Na+ retention?

Congestive heart failure, hepatic cirrhosis, nephrotic syndrome, inappropriate ADH secretion (rare), infusion of Na+ poor fluids

What mechanism causes shifting of H2O from ICF to ECF?

Osmotic shifting of H2O to ECF

What specific condition causes osmotic shifting of H2O to ECF?

Marked hyperglycemia, mannitol infusion

What mechanism causes intravascular to extravascular Na+ shift?

Shift of Na+ down concentration gradient

What specific condition causes shift of Na+ down a concentration gradient?

Uroperitoneum

Does normonatremia mean normal total body Na+?

No

What are the types of normonatremia?

-Hypervolemic/edematous

-Hypovolemic/dehydrated

What can cause hypervolemic/edematous normonatremia?

Heart failure, cirrhosis, nephrotic syndrome

What is normonatremia?

A normal ratio of sodium and H2O

What can cause hypovolemic/dehydrated normonatremia?

-Alimentary losses (vomiting, diarrhea, third-space shifts)

-Renal losses (most polyuric states other than diabetes insipidus, e.g. chronic renal failure)

What is serum potassium dependent on?

1. Shifting of potassium in and out of cells

2. tbK+

What causes shifting of K+ in and out of cells?

-Acid-base balance

-Insulin

What causes fluctuation of total body potassium?

-Intake

-Excretion/losses: kidneys, alimentary tract

What mediates potassium in the kidneys?

Aldosterone, tubular flow rate

What is the goal of K+ and acid-base balance?

Maintain electroneutrality

How does alkalosis affect potassium?

Causes hypokalemia

How does inorganic acidosis affect potassium?

Causes hyperkalemia

Does inorganic or organic acidosis cause hyperkalemia?

Inorganic only

Why does hyperkalemia not occur with organic acidosis?

The positively charged hydrogen ion enters the cell with a negatively charged organic anion, therefore electric neutrality is maintained and K+ does not have to leave

What are the categories that can cause hyperkalemia?

-Shifting from ICF to ECF

-Reduced ECF to ICF movement

-Increased tbK+

What mechanisms cause shifting of potassium from ICF to ECF?

-Shift in exchange for H+

-Cellular necrosis

-Pseudohyperkalemia

What specific conditions cause a shift in exchange for H+?

Metabolic acidosis

What mechanisms cause cellular necrosis?

Rhabdomyolysis, tumor lysis syndrome, intravascular hemolysis in dogs with high K+ -RBCs (Akita, shiba)

What specific conditions can cause pseudohyperkalemia?

-Marked thrombocytosis (serum) IMPORTANT

-In-vitro hemolysis in dogs with high K+ -RBCs (Akita, Shiba)