WATER-ELECTROLYTE BALANCE

Serkan SAYINER, DVM PhD. Assist. Prof.Near East University, Faculty of Veterinary Medicine, Department of Biochemistry

serkan.sayiner@neu.edu.tr

Water

■ Water is an indispensable factor in

life.

■ There is a living thing that can

sustain a lightless or oxygen-free

existence, but there is no living

creature that can protect its life

without water.

■ In adult living organisms, 60-70% of

body weight differs by the amount of

water in individual organs and

tissues.

OrganWater

Ratio %

Total Body

Water Share %

Eye 98 0.1

Blood 79 5

Muscle 77 50

Skin 72 7

Skeleton 22 12

Fat 15 2

Teeth 10 < 0.1

Functional Distribution of Water

■ Intracellular Fluid (ICF)

■ Extracellular Fluid (ECF)

– Intercellular (Interstitial)

– Intravenous (Intravasal)

■ A horse of about 500 kg,

– 300 L water = 200 L ICF + 75 L intercellular + 25 L intravasal

■ Approximately 65-70% of total body weight in mammalians is

water.

Water Availability

■ Free Water (Unbound water)

– Blood, lymph, CSF (cerebrospinal fluid), body fluids.

■ Bound Water

– Hydrate Water

• Water bound to macromolecules like proteins,

carbohydrates by H bridges.

– Intermolecular Water

• It is found in fibers and membranes (connective tissue)

and lost its fluidity.

Biological importance and functions of water

1. It is the building block of macromolecules.

– Many complex compounds, such as polysaccharides, proteins and nucleic acids, have the ability to hold water regularly. The macromolecule and the water molecule are linked by hydrogen bonds.

2. A good building block for small molecules.

– It is a solvent in which many metabolism events occur in the water, where the substrates are transported, and metabolism events are the result of eliminating many residual products.

3. A substrate and co-substrate.

– Water participates in many reactions of metabolism. Hydrolaseand hydratase group enzymes require water as co-substrate; Oxidases, respiratory enzymes produce water as a reaction product (oxidation water).

Biological importance and functions of water

4. Regularly manages energy.

– Hydrogen bonds can change to covalent bonds when

hydrated, or vice versa.

5. It is a good body temperature regulator.

– The water has a high melting point and evaporation heat.

– The evaporation of a small amount of water in the organism

causes a lot of heat loss.

– This is the cooling effect of the body. The emergence of

water vapor through the skin and lungs constitutes an

important mechanism of body temperature regulation.

Biological importance and functions of water

■ Total amount of body water is fixed for every living

thing.

– There are regulatory mechanisms that provide protection

for this constant.

– There is an inverse relationship between water fluctuations

and the organizing grade of living being.

• The fluctuation is high in primitive life (procaryote), and low in

advanced life.

■ Body water and solute electrolytes resembles a

solution to form a functional unit.

– A change in one of these is often reflected in the other.

■ ECF;

– Primary cation is Na+

– Primaray anions are HCO3-

and Cl-

• Found as NaCl and NaHCO3

■ ICF;

– Primary cations are K+ and

Mg++

– Primary anions are proteinat

and H2PO4- ;HPO4

-

Electrolyte distribution

Water and Water intake

■ What is the organism's water requirement?

■ How are the water requirements met or what are the

water resources?

■ What losses can be compensated for?

Water Intake

■ Water intake and discharge are affected by a number of factors.– Age, nutrition, physiological status, body weight, climate and

activity etc.

■ For this reason it is quite difficult to determine the daily water requirement.

■ All data reported in this area should be considered as approximate values.

■ For example;– 7,6 L/day for Rams

– 49-59 L/day for Jersey cows

– 30-57 L/day for a 500 kg horse living in hot climate

– 50 mL/kg Live Animal Weight for dogs.

– Disease conditions change daily requirements.

Water Sources

■ EXOGENOUS WATER

– It is the water that is ingested with the foodstuff and drinks.

• Dry foods: 6-10%

• Semi-wet: 24-60%

• Wet: 68-84%

– Exogenous water was made isotonic in the digestive tract.

– Most of them are absorbed from the small intestine, the

remaining large intestine (colon).

– The water taken into the bloodstream is transported to the

tissues and stored in the interstitial fluid.

Water Sources

■ ENDOGENOUS WATER (Metabolic Water)

– It is the water obtained by metabolic events. It also called as Metabolic water.

– It is obtained from the oxidation of hydrogen in organic materials. The amount of water synthesized in this way depends on the nature of the foodstuffs. Number of hydrogen atoms are directly proportional with the amount water produced (more hydrogen, more water).

– I.e. Glucose = 0.6 mL/g ; Stearic acid = 1,14 mL/g

■ When sheep are fed with wet grasses, they can live without drinking water. Horses require an additional 40-50 liters of water per day, despite the water they receive and/or water produced in metabolism.

Water Losses

■ Insignificant Water Losses

– Ordinary, inevitable.

– I.e. In large breed dogs, 40 mL/kg

■ Significant Water Losses

– Can be regulated.

■ Water Losses related to a special condition

– Physiological and healthy

Insignificant Water Losses

■ Losses due to evaporation

– Skin loss

• Very little perspiration (salt water, air arrest weakens thermal

conductivity)

– Respiratory losses (pure water)

– Frequent breathing (+++ dog + cat)

■ Saliva losses

– Lots of eating (+/0 dog < +++ cat)

Significant Water Losses

■ Urinary Losses– Source; Renal Infiltration

– It can be regulated.

– Cat = 15-20 ml/kg/day

– Dog = 24-40 ml/kg/day

– Ability to concentrate the urine;

• Cat > Dog

• Density; Cat 1035-1060, Dog 1015-1045

– Amount of absorbet water

– Dissolved molecules

• I.e. 1 g NaCl need 30 ml water, 1 g urea need 100 ml water.

Nephrone

Filtrated volume

(>4xH2O total)

Vena

Coll

ecti

ng

Du

ct

TCP

Descending

Limb

Ascending

Limb

Loop of Henle

AA EA

Absorbtion

Significant Water Losses

■ Faecal Losses

– Mandatory but less.

– Sources

• Faecal humidity: 60-80% for normal life.

• Normal or pathological digestive secretions.

– Change factors

• The amount of salt, the level of nutrition

• Moisture level of food

• The nature and proportion of fibers (non-digestible residues and

fermentation products)

Water Losses related to a special condition

■ Lactation

– For example, in dogs there are 77.2 grams of water in 100

milliliters of milk and 81.5 grams of water in cats.

■ Diarrhea

– Functional: Motor malfunction, impairment of permeability

– Osmotic: Digestive insufficiency, dietary overload,

malnutrition

– Infectious or inflammatory.

Effective Forces on Water-Electrolyte Balance

1. Cell permeability

– Cell membranes have large

permeability to water and a large

number of dissolved nutrients

(glucose, amino acid, etc.).

2. Capillary permeability and isotonia

– Changes in the amount of electrolyte

in any sector will cause the osmotic

pressure to change and this will

cause inter-sectoral water movement.

– In regular;

• ICFosm. Pressure > ECFosm. pressure

Daily water balance of an adult human

■ Physiological water losses are about 50 mL/kg/day.

■ Water Loss Ways

– Skin : 500 mL

– Lung : 400 mL

– Intestine : 100 mL

– Kidney : 500 mL

■ Water Intake Ways

– Metabolic Water : 400 mL

– Water taken with foods : 1100 mL

Regulation of Water-Electrolyte Balance

1. Effective circulating volume (ECV)

2. ADH (Vazopressin)

3. Renin-Angiotensin-Aldosteron System

(RAAS)

4. Atrial-Natriuretic Factor/Peptide

(ANF/ANP)

Renin-Angiotensin-Aldosteron System (RAAS)

* Hypovolemia

* Decrease in

efferent arteriole

pressure

* Increase of Na

value of tubular

urine in macula

densa

Filtrated

Volume

(> 4 x H2O

total)

3-100

0,5-5

URINE

99,5%

absorbed

33

20

100 515

0,5

40

Co

llec

ting D

uct

AA

AE Passive NaCl

Transport

Na+ change with

K+,H+,NH4+

Active Na+

transport(Cl-, HCO 2- follows)

3

Su

30

1020-30

K absorbtion+

K+

Passive ure

transport

100 100

100 10

50

Filtrated

Volume

(> 4 x H2O

total)

URINE

99,5%

geri emilir> 119 ml/dak

AA

EA

100

0,5%

< 1 ml/dak

Water

Active

Resorption

(ADH)

33

20

15

5

Water Filtration and Resorption

Co

llec

ting D

uct

Approx. 120

ml/dak

Sodium Filtration and Resorption

Filtrated

Volume

(> 4 x H2O

total)

3-500

URINE

AA

AENa+ change

with

K+,H+,NH4+

K absorption+

K+

100

20-30

10

Coll

ecti

ng

Du

ct

Urea Filtration and Resorption

Filtrated

Volume

(> 4 x H2O

total)

40

URINE

AA

EA Urea

Passive

transport

100

50

100

Co

llec

ting D

uct

Atrial-Natriuretic Factor/Peptide (ANF/ANP)

■ It is especially synthesized by heart and released

to circulation.

■ It extends the atrial wall. It is a given response to

increased venous blood pressure.

■ It reduces systemic blood pressure.

■ It triggers diuresis and natriuresis in kidneys

■ It blocks aldosterone release.

Water- Electrolyte Imbalances

■ DEHYDRATION

– Loss of fluid by 5-7% of body

weight causes the following

symptoms to appear:

– Skin wrinkles

– Migration in the eye pits

– Pulse increase

– Suspension Dryness in mucous

membranes

– Hyperthermia

– Weight loss Fatigue

– → 12-15% ends with SHOCK.

■ HYPERHYDRATION

– There is a total increase in total

liquid and it is accompanied by

water as well as Na.

– Main symptoms are

• Nausea,

• Vomiting

• Disgusting beverages

• (Water intoxication)

Water- Electrolyte Imbalances

Water loss, more than intake

Water and electrolyte inadequacy

DEHYDRATION

DehydrationIsotonic Hypertonic Hypotonic

• Water and salt loss together.

• Na+, Cl and osmolality..... Normal

• Hemoconcentration

• PCV and plasma proteins increase.

• Skin wrinkles, tiredness, ring

around eyes, no thirst, pulse weak

and fast, frequently kidney failure

• Water loss = Salt loss

• isonatremic dehydration• Diarrhea, renal diseases

• Isotonic salt and glucose solution

recommended.• (0.9% NaCl + 5% Dextrose)

• ECF water loss > Na+ loss

• Na+, Cl and osmolality..... High

• Hemoconcentration

• PCV and plasma proteins increase.

• Water loss from cells (get out)

• Severe thirst, dryness in tongue

and mucous membranes, fever,

general impairment and nervous

symptoms

• Water loss > Salt loss• Hypernatremic dehydration

• D. insipidus, Hypodipsia, diarrhea,

pulmonary losses due to hyperventilation

and temperature

• Hypotonic salt and glucose

solution is recommended.• (0.4% NaCl + 5% Dextrose)

• Serum Na is not dropped quickly.

• Edema in brain cells!!!

• ECF water loss < Na+ loss

• Na+, Cl and osmolalitye..... Low

• PCV and plasma proteins

increase.

• Water enters in the cells and

swells, nausea and vomiting, loss

of thirst sensation, disgust from

water, moist tongue, loss of

appetite and convulsions

• Salt loss > Water loss

• Hyponatremic dehydration• Secretary diarrhea, vomiting, 3rd spacing

losses

• Hypertonic salt and glucose

solution recommended• (4.5% NaCl + 30% Dextrose)

* PCV and plasma protein do not increase if there is simultaneous protein loss or anemia.

Source: Wiki

Hypertonic Dehydration

ECF

350 mEq

ICF

350 mEq

ICF

310 mEqECF

600 mEq

Hypotonic

losses

1 2 3

Hypotonic Dehydration

ECF

310 mEq

ICF

310 mEq ECF

280 mEq

ICF

280 mEqICF

310 mEqECF

200 mEq

Hypertonic

losses

1 2 3

Isotonic Dehydration

ECF

310 mEq

ICF

310 mEqICF

310 mEqECF

310 mEq

Isotonic

losses

1 2

1. Normal 2. Change due to dehydration 3. Compensation

ECF

310 mEq

ICF

310 mEq

Degree of water loss and clinical symptoms

Mild

3-5%

Moderate

6-9%

Severe

>10%

General

symptoms

Pulse

Blood pressure

Urine

Thirst,

Restless,

Decline in food

intake

Plump

Normal

Oliguria

Thirst, Incoordination,

Respiratory Strength,

Hemoconcentration

Fast

Normal-low

Oliguria

Sweating, Comatose,

Nervous disorders

Weak

Can notmeasured

Anuria

Hyperhydrations

Isotonic Hypertonic Hypotonic

• Na+ and osmolality..... Normal

• Water and Na+ retention

• GFR decreases

• Weight gain, edema, pleuro-

peritoneal transudates

• Causes

• Hypovolaemia

• Hypoproteinemia

• Malnutrition

• Cirrhosis

• Renin-angiotensin- Aldosterone

system (RAAS) is activated.

• Water > Na+ retention

• Na+ and osmolality... Low

• Nausea, vomiting

• Causes

• Therapeutic failure (Liquid

support in an oligo-anuric

patient)

• Increase in ADH release

(contrast to diabetes

insipidus)

• The blood dilution system is

activated.

• Na+ Cl - and osmolalitye... High

• Apart from intracellular

dehydration, an extracellular

hyperhydration develops, but

hyperosmolarity is dominant in

both sectors

• Severe thirst

• Causes

• Hypertonic NaCl

administration

• Low NaCl diet and plenty of

water intake are recommended.

Hypertonic Hyperhydration

1. Normal 2. Change due to hyperhydration

Isotonic HyperhydrationSaline

ECF

420 mEq

ICF

310 mEq

ECF

342 mEqICF

342 mEq

1 2

Hypertonic NaCl solution

Hypotonic Hyperhydration

ECF

236 mEq

ICF

310 mEq

1 2

Water

ECF

310 mEq

ICF

310 mEq

ECF

287 mEq

ICF

287 mEq

Clinical Evaluation

■ What is the degree of fluid loss?

■ Is there osmolar imbalance?

■ Is there acid-base disturbances?

■ How is potassium metabolism?

■ How are kidney functions?

Clinical Laboratory Examination■ History and Clinical Observation

– General status of animal

– Skin turgor (distensiton-rigidity)

– Color of mucous membranes

– Capillary refill time

– Pulse and heart rhythm

– Respiratory frequency

– Urinary flow

■ Hematological and Biochemical Assessments– Hematocrit (PCV)

– Plasma total protein

– Blood urea (or BUN-Blood Urea Nitrogen)

– Blood glucose

– Ionogram and osmolality (pH, Na,K,Cl,HCO3-)

– Urinanalysis

Sodium (Na)

■ Sodium has many important functions, including maintaining normal blood pressure and volume and maintaining normal function of muscles and nerves.

■ These functions are dependent on keeping plasma sodium concentrations within a narrow range.

■ The concentration of sodium in the blood is predominantly a balance between what is consumed in food and drink and what is excreted in urine.

– Only a small amount is normally lost through stool and sweat, but these routes can become more important in certain disease or physiological states, depending on species.

Sodium (Na)

■ The regulation of sodium cannot be discussed without also discussing water balance since these substances are intricately tied together.

■ Water balance between different compartments is dependent on osmotic pressures. As the most abundant cation of plasma, sodium, along with its associated anions, is the major determinant of extracellular osmolality.

■ Water and sodium regulation is associated with maintaining normal blood volume and osmolality.

■ Sensors of osmolality and vascular pressure result in changes of sodium and/ or water handling by the kidney.

Sodium (Na)

■ As little as a 1–2% increase in plasma osmolality will be

detected by osmoreceptors in the hypothalamus, resulting

in vasopressin (antidiuretic hormone) secretion from the

posterior pituitary.

– Alternatively, a perceived deficit in blood volume of 10% will result

in vasopressin release regardless of osmolality.

■ Vasopressin enhances water reabsorption in the renal

collecting duct to replenish vascular water. Osmoreceptor

cells are also involved in the sensation of thirst.

■ If arterial and atrial baroreceptors sense elevated blood

pressure or blood volume, impulses are sent to the

hypothalamus to inhibit vasopressin release.

Sodium (Na)

■ They also act to decrease sodium reabsorption in the distal nephron.

■ The juxtaglomerular cells of the kidney are baroreceptors that detect low blood pressure. These cells activate the renin- angiotensin-aldosterone system (RAAS) by secreting renin. – Angiotensinogen II causes the release of aldosterone from the

adrenal glands, increases secretion of vasopressin, and stimulates thirst centers.

– Aldosterone acts on the renal cortical collecting tubules to reabsorb sodium.

– The reabsorption of sodium is coupled with either the secretion of potassium (another very important function of aldosterone) or the absorption of chloride to maintain electroneutrality.

Sodium (Na)

■ When evaluating serum sodium concentration, the

animal’s total body water must be taken into

consideration.

■ Is there clinical or biochemical evidence of low body

water (dehydration) or does it appear normal or,

possibly, increased?

– An increase in serum sodium concentration can be due to

more sodium, less water, or a combination of causes.

– A decrease in serum sodium concentration can be due to

less sodium, more water, or a combination of causes.

Excess salt?

Did the

animal get

into

something

salty?

Was the

animal given

hypertonic

fluids I.V.?

Hyperaldosteronism

(Rare)

Water deficit

Decreased intake Water loss > Na

Frozen

or Spilled

Water

sourceMonitor water

intake

(Neurological

Deficit,

Weakness)

Renal GI

Fever

Panting

Hyperventilation

Serum Na+

(Hypernatremia)

EndogenousShifts

Sodium Deficit(Na Loss > Water)

Serum Na+

(Hyponatremia)

Excess Water?(Water Retention > Na)

lnappropriate

Secretion of

ADH

(Rare)

Excess

Sodium-

Poor Fluids

l.V.?

Hypovolemia/Edema

-Congestive Heart Failure

-Hepatic Fibrosis

-Nephrotic Syndrome

Plasma

Hyperosmolality

from Substance

Other Than Na

(Water shifts from

lCF to ECF)

Renal

Loss

Third-

Spacing of

Body Fluids

Sweating in

horses

GI

Loss

Chloride (Cl)■ Chloride is the major anion in the ECF and, similar to sodium,

chloride is important in the transport of electrolytes and water. Chloride also serves as a conjugate anion in acid base metabolism.

■ To maintain electroneutrality chloride either moves in the same direction of the positively charged sodium or exchanges with the negatively charged bicarbonate ions.

■ When evaluating an abnormality in serum chloride concentration, it is important to compare chloride levels with sodium levels and to the animal’s acid base status.– If abnormalities in chloride concentration appear to be in pro- portion

to abnormalities in sodium concentration, differentials to consider are similar to those given for hyponatremia or hypernatremia above. If the change in chloride concentration appears greater than a change in sodium concentration, bicarbonate concentration shouldbe evaluated and a blood gas analysis may be indicated.

Chloride (Cl)

■ Hyperchloremia

– Hyperchloremia is usually associated with a water deficit.

– Alternatively, hyperchloremia can be related to

hypobicarbonatemia.

– Loss of bicarbonate can occur from the GI tract with

diarrhea, loss of saliva in cattle which contains a high

bicarbonate concentration, or vomiting intestinal contents

as can occur with intestinal obstruction.

– Renal loss of bicarbonate occurs with proximal or distal

tubular acidosis. In response to a respiratory alkalosis,

there is decreased renal conservation of bicarbonate,

resulting in retention of chloride.

Chloride (Cl)

■ Hypochloremia

– If chloride is decreased to a greater degree than sodium, differentials related to metabolic alkalosis must be considered.

– In the process of secreting HCl into the stomach, serum chloride is decreased and serum bicarbonate is increased. These changes are normally reversed when hydrogen and chloride ions and water are reabsorbed in the intestines.

– If gastric fluid is lost due to vomiting or sequestered due to a displaced abomasum, pyloric obstruction, or functional obstruction, serum chloride will remain low and bicarbonate will remain elevated.

– Serum chloride levels decrease when bicarbonate concentrations increase in the compensatory response to chronic respiratory acidosis.

Potassium (K)

Thrall ve ark. 2012

■ Potassium is a major intracellular cation that plays an

important role in resting cell membrane potential.

■ Clinical signs associated with abnormal serum

potassium concentrations manifest as cardiac and

skeletal muscle dysfunction and hyperkalemia can

have life-threatening effects on cardiac conduction.

Therefore, it is important to maintain serum potassium

concentrations within narrow limits.

Potassium (K)

■ Total body potassium is a balance between what is

ingested (100%) and what is excreted from the kidneys

(normally ∼90–95%) and colon (normally ∼5–10%).

■ The concentration of ECF (serum) potassium is also

reliant on the translocation of potassium between the

ECF and ICF.

■ Less than 5% of total body potassium is present in the

ECF; therefore serum potassium concentration is an

unpredictable representation of total body potassium

content.

Increased K+ Load

Serum K+

(Hyperkalemia)

Decreased Renal Excretion

Translocationbetween ICF & ECF

• Metabolic Acidosis

• Insulin Deficiency

• Severe Tissue Injury

Hypoadrenocorticism

Oliguric/Anuric Renal Failure

Urethral Obstruction

Ruptured Urinary Bladder

Decreased Renal Tubular

Flow from Hypovolemia

• Gastrointestinal Disease

• Body Cavity Effusions

In vitro artifacts

• Hemolysis

• Thrombocytosis

• Delayed Serum Removal

• EDTA Contamination

Serum K+

(Hypokalemia)

Decreased Intakeor

K-Poor Fluids I.V.?

• Gastric Vomiting

• Small Intestinal Diarrhea

• Chronic Renal Failure

• Distal Renal Tubular Acidosis

• Post-Obstruction Diuresis

• Diabetic Ketoacidosis

• Diuretics

• Hyperinsulinism

• AlkalosisLoss

Translocationbetween ICF & ECF

Renal Gastrointestinal

Sodium:Potassium Ratio (Na:K)

■ Hypoadrenocortisism

■ Na:K < 27:1 ??

– Na:K ratios <15 are more commonly associated withhypoadrenocorticism in dogs.

■ Absolute or relative K increase or Na decrease or combination.

– Increased K is the most common reason.

■ It is important in differential diagnosis.

– It may decrease in renal/urinary tract disorders, GI diseases, parasites (dogs), body cavity effusions, D. insipidus, pancreatitis, pyometra, ocular diseases.

Anion Gap

■ We measure several anions and cations in the blood,

but there are many others that are not routinely

measured.

■ Thepredominant cations of ECF are sodium,

potassium, calcium, and magnesium and the

predominant anions are chloride, bicarbonate, plasma

proteins, organic acid ions, phosphate, and sulfate.

■ The number of unmeasured anions is greater than the

number of unmeasured cations, and the difference

between these is called the anion gap.

•Definition: Anion gap is the difference between UA and UC.

•Calculation: Anion gap is the difference between Na&K and Cl&HC03.

Anion Gap

■ An indirect method is used to calculate the anion gap.

The calculation is based on the law of electroneutrality

(The number of positive charges need to equal the

number of negative charges in the body).

■ Anion Gap = {[Na+] + [K+]} - {[Cl-] + [HCO3-]}

■ The anion and cation concentrations measured in the

serum to calculate anion gap. Ions are measured in

mEq/L or mmol/L.

■ Reference value = 10-25 mEq/L – 8-25 mmol/L

– It may vary depending on species, methods and

equipments.

Anion Gap

■ The greatest change in the anion gap is when an elevation occurs due to an increase of organic acids in the circulation. The anion gap, therefore, is important in determination of the acid-base status of an animal. – The anion gap is essentially used to determine the cause of

decreased blood bicarbonate concentrations (metabolic acidosis) or to detect metabolic acidosis during a mixed acid-base disorder in which bicarbonate may be normal or increased.

■ Since cations rarely change enough to affect the anion gap, a decrease in bicarbonate has to be accompanied by either an increase in unmeasured anions or a decrease in chloride to keep the equation equal and to maintain electroneutrality.

Anion Gap

■ Unmeasured anions that have the most affect on anion

gap are the endogenous products lactate, ketones, and

uremic acids, as well as the exogenous substances

salicylate and the metabolites of ethylene glycol toxicity.

– Lactic acidosis is produced during hypoxia and anaerobic

metabolism.

– Keto acids are produced when there is a negative energy

balance and metabolism switches from primarily glycolysis

to lipolysis.

– Uremic acids are phosphates, sulfates, and organic acids

that are no longer adequately filtered because of decreased

glomerular filtration rate (GFR).

Calcium (Ca)

■ Alterations in blood calcium concentrations can result in severe clinical problems, including death. Another reason is that recognizing and pursuing the cause of calcium abnormalities often aids in diagnosing the underlying disease process.

■ When measuring serum concentrations of calcium, it is important to understand the difference between the measurement of total calcium and free, ionized calcium.

– Free (unbound) ionized calcium (iCa) is the biologically active, hormonally regulated fraction that comprises approximately 50% of total calcium.

Predominant Hormone Actions on Serum Calcium and Phosphorus

Calcium Fractions

Calcium (Ca)

■ Hypercalcemia differentials (Total calcium)

– Granulomatous inflammation

– Osteolytic lesions

– Spurious results

– Hyperparathyroidism (primary)

– Dvitamin toxicity

– Addison’s disease

– Renal disease (chronic)

– Neoplasia

– Idiopathic

– Transient

Calcium (Ca)

■ Hypocalcemia differentials (Total calcium)

– Magnesium deficiency

– Injury to tissues (severe)

– Lactation/pregnancy

– D vitamin deficiency

– Pancreatitis

– Renal disease

– Albumin deficiency

– Intake from GI decreased

– Sepsis

– Ethylene glycol

Phosphorus (P)

■ Phosphorus is required for energy metabolism, nucleic acid synthesis, and cell signaling.

■ It is an important buffer in blood and urine and an important component in structural plasma membrane phospholipids and phosphoproteins and in bone.

■ Abnormalities in serum phosphorus concentrations can be due to abnormalities in hormonal balance, intestinal absorption, renal excretion, or tissue or cell distribution. Serum concentrations of phosphorus may not reflect total body levels.– If there is a concurrent abnormality in serum calcium, pursuing

and determining the cause of the calcium abnormality will often provide explanation for an abnormality in phosphorus. Examining the pattern of change between calcium and phosphorus can provide important clues.

Magnesium (Mg)

■ Magnesium is primarily an intracellular ion and is a cofactor of many enzymatic reactions, including all reactions involving the formation and utilization of ATP and many mitochondrial reactions.

■ It is also required for protein and nucleic acid synthesis. Vitamin D and PTH influence, but do not regulate magnesium metabolism.

■ Homeostasis is primarily a balance between intestinal absorption and renal excretion.

■ Magnesium has a similar charge as calcium and, as does calcium, exists in free ionized, protein-bound (approximately 30%), and complexed forms in serum. – Serum magnesium contains only approximately 1% of total body

magnesium and therefore is not necessarily an accurate representation of total body magnesium.

Magnesium (Mg)

■ Hypomagnesemia is more commonly associated with morbidity than hypermagnesemia. – Neuromuscular signs occur with hypomagnesemia, including

hyperexcitability, muscle tremors, spasms, and fasciculations, and ataxia.

– Other complications associated with hypomagnesemia include the development of hypokalemia or hypocalcemia. These deficiencies may not be able to be corrected unless hypomagnesemia is corrected first.

– Hypomagnesemia is typically associated with either increased loss or decreased intake.

– Losses, the most common cause of hypomagnesemia in small animals, are through the renal or gastrointestinal systems. • Renal loss occurs with diuresis and renal disease. Renal reabsorption

can also be inhibited by hypercalcemia. Malabsorption and diarrhea are causes of gastrointestinal magnesium loss.

Magnesium (Mg)

– Decreased intake is a common cause of hypomagnesemia

in ruminants. Grass tetany is a disease that is associated

with ruminants eating lush green pastures that are high in

potassium and low in magnesium content.

• Elevated potassium ingestion blocks normal magnesium

absorption in the rumen.

– Prolonged intravenous fluids or parenteral nutrition can

also lead to hypomagnesemia if magnesium

supplementation is not included.

– Other causes of hypomagnesemia include redistribution

and hypoalbuminemia (if total magnesium is measured

instead of free, ionized magnesium).

Magnesium (Mg)

■ Hypermagnesemia is typically a less significant

clinical problem, unless it develops acutely.

– It can result in cardiac or neurological problems and cause

nausea and vomiting.

– Hypermagnesemia can occur iatrogenically or due to

decreased renal excretion, primarily associated with acute

renal failure or urethral obstruction.

■ W% = (TPH - TPS) x 100/TPH

– W%: Fluid loss in blood plasma as a percentage

– TPH: Patient total protein (g/dL)

– TPS: Total protein of healthy animal (g/dL)

■ ECF Loss (L)= (W% x LW x 0,4)/100

– LW: Live Animal Weight

Calculation of Fluid Losses in Blood Plasma

Dehydrations and HyperhydrationsSyndromes Osmolality ECF ICF Causes

Hypertonic Dehydration

(Fluid depletion)Increase Decrease Decrease Water loss > Salt loss

Hypotonic Dehydration Decrease Decrease Increase Water loss < Salt loss

Isotonic Dehydration Normal Decrease Water loss = Salt loss

Hypertonic Hyperhydration Increase Increase Decrease Water retention < Salt retention

Hypotonic Hyperhydration

(water intoxication)Decrease Increase Increase Water retention > Salt retention

Izotonic Hyperhydration Normal Increase Water retention = Salt retention

Your Questions?Send to serkan.sayiner@neu.edu.tr

References

■ Karagül H, Altıntaş A, Fidancı UR, Sel T, 2000. Klinik Biyokimya. Medisan,

Ankara.

■ Prof. Dr. Arif ALTINTAŞ, Ders notları.

■ Sink CA, Weinstein NM, 2012. Practical Veterinary Urinanalysis, 1st ed.

Wiley-Blackwell.

■ Thrall MA, Weiser G, Allison RW, Campbell TW, 2012. Veterinary

Hematology and Clinical Biochemistry, 2nd edi. Wiley-Blackwell.

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