6 Water- Balance-AND- Electrolytes PDF

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WATER BALANCE AND ELECTROLYTES Body Water • Bulk of body mass à water • Constitutes the medium by which solutes are dissolved and by which metabolic reactions take place • Two main compartments: – Intracellular Fluid – Extracellular Fluid Distribution • 40-75% - average water content of the human bo...

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WATER BALANCE AND ELECTROLYTES Body Water • Bulk of body mass à water • Constitutes the medium by which solutes are dissolved and by which metabolic reactions take place • Two main compartments: – Intracellular Fluid – Extracellular Fluid Distribution • 40-75% - average water content of the human body • ECF – 1/3 (16 L) – intravascular extracellular fluid (plasma) – interstitial cell fluid • ICF – 2/3 (24 L) • Normal plasma - 93% water and 7% solutes (glucose, lipids, NPN, amino acids and ions) Osmolality • Physical property of a solution that is based on the concentration of solutes (expressed as millimoles) per kilogram of solvent (w/w). • Parameter to which the hypothalamus responds. • Affects the Na+ concentration in plasma. Formula for Osmolality

Physiologic Response (Increased ECF Osmolality) • Antidiuretic Hormone (ADH) or Vasopressin release via hypothalamic chemoreceptors. • Stimulation of the hypothalamic thirst center. • Redistribution of water from the intracellular fluid compartment. Regulation of ECF Volume • Regulation of Renal Excretion of Sodium or Glomerular Filtration Rate à 70% of Na is reabsorbed by the earlier parts of the renal tubule. • Aldosterone via RAA System à JG of the kidneys release renin à converts angiotensinogen à angiotensin I à Angiotensin II à stimulates adrenal cortex to produce Aldosterone à promote retention of sodium and excretion of potassium. Disorders of Water Balance • Dehydration – Pure Water loss or deficit à Leads to increased ECF Osmolality • Compensates by recruiting water from the ICF. • Lowers total body water but total body sodium remains normal. – Water and Sodium Loss à hypovolemia readily takes place. • Overhydration à excessive intake of water or excessive reabsorption of water. What are Electrolytes? • Electrolytes are ions that carry an electric charge. (anions/cations) • Electroneutrality. • Dissociation of solutes into charged particles (ions) depends on the chemical composition of

the compound and on the concentration of • other charged particles in the medium.

For every 100 mg/dL increase in blood glucose, serum sodium decreases by 1.6 mmol/L .

Regulation of Electrolytes Regulation of Sodium • Active transport - mechanism that requires • Diet energy to move ions across cellular membranes. Kidney à renal threshold for sodium • Diffusion - passive movement of ions across •a membrane. (110-130 mmol/L); 70-80%à reabsorbed at the proximal tubule. • RAA à release of aldosterone • Atrial natriuretic factor (ANF) à produced by the atrial myocardium; promotes natriuresis and relaxation of the vascular smooth Functions muscle. • Volume and osmotic regulation • Myocardial rhythm and contractility Hyponatremia • Cofactors in enzyme regulation • Regulation of adenosine triphosphatase • is an electrolyte disturbance in which the (ATPase) ion pumps sodium concentration in the serum is • Acid-base balance lower than normal. • Blood coagulation • Hyponatremia is defined as a serum level • Neuromuscular excitability of less than 135 mEq/L and is considered • Production and use of ATP from glucose severe when the serum level is below 125 mEq/L. Anion Gap • Refers to the difference between the Symptoms sums of the concentration of the principal • Nausea + + cations (Na & K ) and of the principal anions (Cl • Vomiting • headache & HCO3- ) • AG = Na+ – (Cl- + HCO3- ) • Confusion – NV: 7-14 mmol/L • Fatigue • AG = (Na+ + K +) - (Cl- + HCO3- ) • Appetite loss – NV: 10-18 mmol/L • Restlessness • Irritability • Muscle weakness Increased Anion Gap • Uremia • Spasms • Ketoacidosis (Starvation or Diabetes) • Cramps • Methanol, Aspirin, or ethylene glycol poisoning • Seizures • Severe dehydration • Decreased consciousness or coma • Lactic Acidosis Causes of Hyponatremia • Use of diuretics Decreased Anion Gap • Multiple myeloma • Syndrome of Inappropriate ADH (SIADH) • Protein and instrument error secretion • Aldosterone deficit secondary to Addison's disease SODIUM • It is the major cation in the extracellular • Bartter's Syndrome - it is a rare condition fluid (ECF). wherein sodium chloride gradients • It plays a central role in maintaining the cannot form in the loop of Henle causing normal distribution of water and osmotic the retention of chloride ion that is not pressure in the ECF compartments. available for the countercurrent • Renal Regulation mechanism. • Principal osmotic particle outside the cell

Diabetic hyperosmolar state - it causes Hyperkalemia efflux of cellular water with consequent • It is a serum potassium concentration osmotic dilution of serum sodium. above the upper limit of the reference interval. • Congestive Heart Failure • Hyperkalemia is seen in the following • Azotemia conditions: • Burns – Dehydration • Vomiting – Diabetes insipidus – Hypoadrenalism Pseudohyponatremia – Acidosis – Hemolysis • Occurs when Na+ is measured using indirect ion-selective electrodes (ISEs) in Hypokalemia a patient who is hyperproteinemic or hyperlipidemic. • It is a serum potassium concentration below the lower limit of the reference interval • It is seen in the following conditions: ◦ Infusion of insulin to diabetics ◦ Alkalosis Hypernatremia ◦ Vomiting • It is a serum sodium concentration above ◦ Over hydration the upper limit of the reference interval. ◦ Use of Loop diuretics ◦ Syndrome of Inappropriate ADH (SIADH) Causes of Hypernatremia secretion • Diabetes insipidus ◦ Bartter's syndrome (it is a condition • Hyperaldosteronism whose primary cause is the excess • Hyperadrenocorticism excretion of potassium) ◦ acute myelogenous leukemia Methods of Determination ◦ acute myelomonocytic leukemia • Ion-specific Electrodes ◦ acute lymphocytic leukemia • Atomic Absorption Spectrophotometry (AAS) Analytical Methods • Flame Emission Spectrophotometry (FES) • Ion Selective Electrode (ISE) is the method of / Emission Flame Photometry (FEP) choice • Colorimetric Method – Albanese Lein • Atomic Absorption Spectrophotometry (AAS) – Combining sodium with zinc • Flame Emission Spectrophotometry (FES) uranyl acetate à sodium uranyl acetate precipitate à addition of water Reference Interval produces yellow solution. Serum: 3.5 – 5.1 mmol/l •

Reference Interval • 135-145 mmol/L serum • 40-220 mmol/L urine • 138-150 mmol/L csf POTASSIUM • It is the major intracellular cation • Its functions include regulation of:  Neuromuscular excitability  Contraction of the heart  Intracellular fluid volume  Hydrogen ion concentration

Plasma Male: 3.5 – 4.5 mmol/l Female: 3.4 – 4.4 mmol/l Urine (24 h) 25 – 125 mmol/day CHLORIDE • It is the major extracellular anion. • Together with sodium, they represent the majority of the osmotically active constituent of the plasma. • Maintaining electrical neutrality • Regulate fluid content on the body and its influence in the kidney Hyperchloremia • It can be seen in the following conditions:  Dehydration

 Renal tubular acidosis Clinical Significance  Acute renal failure Increased calcium levels are seen in:  Metabolic acidosis associated with •  Periods of rapid growth in prolonged diarrhea children  Pregnancy Hypochloremia  Lactation • It is seen in:  Prolonged vomiting • Decreased calcium level is seen in:  Profuse sweating  Old age  Increased gastric juice secretion Factors Influencing Calcium Levels  Salt-losing nephritis • Increased calcium absorption  Addison’s disease ◦ Vitamin D (major stimulus of calcium absorption) Analytical Methods ◦ Growth hormone • Ion-selective electrode ◦ Increased dietary protein • Mercurimetric Titration (Schales-Schales • Decreased calcium absorption method) ◦ Formation of insoluble salts with  Colorimetric method uses phosphorus mercuric thiocyanate and ferric ◦ Phytic acid nitrate to form a reddish-colored ◦ Dietary oxalate complex with a peak at 480 nm. ◦ Fatty acids  Coulometric-Amperometric Titration ◦ Cortisol (Cotlove Chloridometer) • Increased urinary calcium excretion ◦ Hypercalcemia Reference Interval • Normal serum concentration ◦ Phosphate deprivation 98 – 106 mmol/L ◦ Acidosis • Daily urinary output ◦ Glucocorticoid 110 – 250 mmol/L • Diminished urinary calcium excretion ◦ PTH CALCIUM ◦ Certain diuretics • It is the fifth most common element and ◦ Vitamin D the most prevalent cation in the human body. Hypercalcemia Functions • It is a condition characterized by an • It is important in skeletal mineralization increased serum calcium level. • It plays a vital role in: • It is associated with anorexia, nausea, ◦ Blood coagulation vomiting, constipation, hypotonia, ◦ Neural transmission depression & coma. ◦ Enzyme activity ◦ Maintenance of normal tone Causes ◦ Excitability of skeletal and • The most common causes are: cardiac muscle  Primary hyperthyroidism • It is involved in glandular synthesis and  Multiple endocrine neoplasia regulation of exocrine and endocrine glands  Familial hypocalciuria • It preserves the cell membrane's hypercalcemia integrity and permeability particularly in terms of  Vitamin D intoxication sodium and potassium exchange.  Thyrotoxicosis  Hypoadrenalism Distribution  Multiple myeloma • Free or ionized form (50%) • Bound to plasma protein (40%) Hypocalcemia • Complex form (10%)

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It is a condition characterized by a low serum calcium level. Severe hypocalcemia will eventually lead to tetany.

Causes • The most common causes are:  Hypoparathyroidism  Pseudohypoparathyroidism  Deficiency in Vitamin D or its metabolite  Chronic renal failure  Hypomagnesemia  Acute pancreatitis

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It is essential for the function of cellular enzymes and energy metabolism. It has an important role in membrane stabilization, nerve conduction, and ion transport and calcium channel activity. It also plays an important role in maintenance of intracellular K* concentration.

Hypermagnasemia  It is a condition with high level of serum magnesium.  Increased magnesium level in the blood is rare and usually iatrogenic.  Elderly and patients with bowel disorder and renal insufficiency are the most at risk.  Clinical manifestations include hypotension, bradycardia, respiratory depression, depressed mental status and electrocardiographic (ECG) abnormalities.

Hypomagnasemia • It is a condition with low serum Analytical Methods magnesium level. • Total Calcium • The most common causes of  Spectrophotometric hypomagnesemia are: analysis with the metallochromic  Loss of magnesium in indicators. (Orthocresolphthalein the GI tract as in chronic complexone & Arsenazo III are most diarrhea and malabsorption widely used indicators) steatorrhea  Titration of fluorescent  Diabetes mellitus calcium complex with ethylene diamine secondary to glycosuria and tetra acetic acid (EDTA) or ethylene glycol osmotic diuresis tetra acetic acid (EGTA).  Alcohol  Atomic Absorption  Stress Spectrophotometry (AAS)  Clark and Collip Method Analytical Methods (Redox Titration Method) • Total Magnesium • Ionized Calcium ◦ Atomic Absorption  Ion-Selective Electrode Spectrophotometry (AAS) is the (ISE) for Calcium reference method but it is not routinely done in the clinical Reference Interval laboratory. Plama/Serum ◦ Photometric methods on • 8.8-10.3 mg/dL (2.20-2.58 mmol/L) total automated analyzers - These Calcium in adults methods employ metallochromic • 4.6-5.3 mg/dL (1.16-1.32 mmol/L) indicators or dyes such as ionized Calcium in adults calmagite, formazan dye, magon, Urine and titan yellow dye. • 300 mg/day (7.9 mmol/day) in normal • Ionized (Free) Magnesium adults • Ion-Selective Electrode for magnesium MAGNESIUM ◦ Intracellular Magnesium

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Fluorescence measurement using furapta (magnesium binder) Nuclear magnetic resonance spectroscopy Ion selective microelectrode Electroprobe microanalysis Reference Interval • I.6-2.6 mg/dL • 0.66-1.07 mmol/L

Induced by a shift of phosphorus from extracellular fluid into cells.  Increased urinary excretion, secondary to hyperparathyroidism, renal tubular defects and diuretic therapy.  Decreased intestinal absorption is observed in malabsorption.  Vitamin D deficiency and steatorrhea

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PHOSPHORUS • It is an important constituent in nucleic acid, phospholipid and phosphoproteins,Analytical Methods • It forms high energy compounds such as • Reaction of phosphate with ammonium ATP and cofactor (NADP) and is involved molybdate (FISKE SUBBAROW) in intermediary metabolism and various • Reduction of phosphomolybdate to enzyme systems. molybdenum blue which can be measured at • It is essential for muscle contractility, 600-700 nm spectrophotometrically. neurologic function, and electrolyte • Enzymatic method transport and oxygen-carrying by hemoglobin. Reference Interval • Adult: 2.8-4.5 mg/dL (0.89-1.44mmol/L) • Children: 4.0-7.0mg/dL (1.292.26mmol/L) Hyperphosphatemia • It is a condition characterized by a serum phosphorus concentration above the upper limit of the reference interval. • The usual causes are:  Decrease renal excretion in acute and chronic renal failure  Increase intake with excessive oral, rectal, intravenous administration.  Increase extracellular load due to transcellular shift in acidosis  Secondary to over medication with Vitamin D and production of Vitamin by granulomatous tissue. Hypophosphatemia • It is a condition characterized by a serum phosphorus concentration below the lower limit of the reference interval • It can be seen in:  Alcohol abuse  Intestinal loss due to vomiting, diarrhea, and use of phosphate binding antacids...