Clinical Chem 2 - Electrolytes PDF

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Summary

ELECTROLYTES    Ions capable of carrying an electric charge Classified as anions or cations o Anions- negative charge (-), moves toward anode (+) o Cations – positive charge (+), moves towards cathode (-) Essential component in numerous process including: Volume and osmotic regulatio n Myocardial...

Description

ELECTROL ELECTROLYTES YTES   

Ions capable of carrying an electric charge Classified as anions or cations o Anions Anions- negative charge (-), moves toward anode (+) Cations – positive charge (+), moves towards cathode (-) Essential component in numerous process including:

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DIFFUSIONS Pasasive movement o ions across a membrane Distribution of water in the various body fluid compartments is controlled by maintaining the concentration of electrolytes and proteins in the individual compartments

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 Volume and osmotic regulation

Myocardial rhythm and contractility

Cofactors in enzyme activa activation tion

Regulation of ednosine triphosphate ion pumps

Na+ ClK+

K+ Mg++ Ca+

Mg++ Ca++ Zn++

Mg+

OSMOLALIT OSMOLALITY Y   

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Acid Base Balance

Blood Coagulation

Neuromuscular excitability

HCO3K+ Cl-

Ca++ Mg

K+ Ca+ Mg+

Production and use of ATP from glucose Mg++ PO4-

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Water  

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Average water content of the human body : 40-75% of total body weight Solvent for all processes in the human body: o Transports nutrients to cells o Determines cell volume by way of urine o Acts as body’s coolant by way of sweating Located in the intracellular and extracellular compartments o Intracellular Fluid – fluid inside the cells; 2/3 of the total body water o

Extracellular Fluid -1/3 of total body water -NaNaNa-major cation in ECF  Intravascular extracellular fluid –  Plasma  Interstitial cell fluid  Fluid that surrounds the cells in the tissue

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Physical property of a solution that is based on the concentration of solute solutess per kilogram of solven solventt (w/w) Expressed as millimoles per kg of solvent Electrolytes such as: o Sodium (Na) Provide largest -largely determines the contribution of osmolality osmolality of serum value of serum o Chloride (Cl) o Bicarbonate (HCO3 ) Measured by: o Urine o Serum Related to freezing point depression and vapor pressure decrease [these are colligative properties ; these are the basis or the routine basis of osmolality in the laboratory] Inc blood osmolality [meaning inc of solute in blood] leads to secretion of arginine vvasopressin asopressin hormone (A (AVP) VP) / ADH [anti-diuretic hormone; { this increases watery absorption by the kidney}] and sensation of thirst[natural response of body: consume more fluid; inc water content in the ECF; Water will dilute the solute [electrolytes] causing decrease osmolality;same w/ ADH] Thirst sensation – major defense against hyperosmolality and hypernatremia Reference ranges for osmolality: 

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Serum = 275 -295mOsm/Kg Urine = 300-900mOsm/Kg

Colligative Properties (Freezing point depression vapor pressure dec dec) o

Basis for the routine measurement of osmolality in the lab

*ADH -Promotes H2O reabsorption in the CD -If H2O is reabsorb = DEC blood osmolality -INC H2O intake = INC water in extracellular fluid = Dec blood osmolality

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Normal plasma is about 93% of water with the remaining volume occupied by lipids 7% (Lipids & Proteins) – and proteins

REGULA REGULATION TION OF BLOOD VOLU VOLUME ME 

ACTIVE TRANSPOR TRANSPORT T 

Mechanism that requires energy to move ions across cellular membranes

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Regulation of both sodium and water is interrelated in controlling blood volume *If you control the blood volume you will also control the sodium levels in the body If there is decrease blood volume, there is also decrease blood pressure, decrease sodium levels this will signal your body to secrete RENIN. And with the presence of angiotensinogen this renin will become Angtiotensin I with

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the presence of ACE this Angiotensin I will become Angiotensin II. Angiotensin II can : o promote vasoconstriction o cause release of aldosterone (Promotes Na Reabsorption)  Increases the sodium count in your blood ADH will also secrete in the body  Inc water reabsorption in the kidney =INC the blood volume

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To prevent equilibrium from occurring ATPase ion pumps are present in all cells Na+, K+ - A ATPase TPase ion pumps move three Na+ ions out of the cell in exchange for two K+ ions moving into the cells as ATF is converted to ADp o Sodium and P Potassium otassium has an inverse relati relationship onship K – most abundant intracellular cation; Inversely proportional to sodium Na – most abundant extracellular cation

Reference ranges for sodium: 

Serum plasma: 136-145 mmol/l Urine (24hr) : 40-220 mmol/day, varies with diet

 Regulation of Sodium 

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The plasma sodium concentration depends greatly on the intake and excretion of water and to a somewhat lesser degree on renal regulation of sodium Three processes are of primary im importance portance portance: 1. Intake of water in response to thirst *what stimulates thirst sensation? Inc osmolality *what suppresses thirst sensation? Dec osmolality 2. The excretion of water 3. The blood volume status

***HYPONA ***HYPONATREMIA TREMIA 

Four other factors that affect blood volume: o Atrial Natriuretic peptide (ANP)  Antihypertensive agent secreted by cardiac atria  Causes natriuresis  Block aldosterone & renin secretion  Dec BP & DEC Blood volume  inhibits the action of angiotensin II & vasopressin o o

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Glomerular filtration rate (GFR) All other things equal, an increased plasma

sodium will increase urinary sodium excretion and vice versa Urine osmolality values may vary widely on water intake and the circumstances of collection o Decreased Decreased: diabetes insipidus & polydipsia(inc thrist) o Increased Increased: SIADH (Syndrome of inappropriate ADH secretion) and hypovolemia

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Defined as serum / plasma level less than 135mmol/L One of the most common electrolyte disorder in hospitalized and non hospitalized patients Most instances occur with decrease osmolality Hyponatremia w/ High Osmolality is associated with Hyperglycemia (Inc glucose) : o Inc the osmalility of) serum o Shift of water from the cells to the blood Levels below 130 mmol/L may be caused by: o Increased sodium loss  first cause of hyponatremia o Increased water retention o Water imbalance Classification of hyponatremia by plasma/serum osmolality o With low osmolality o With normal osmolality o

With high osmolality

Levels below 130 mmol/L may be caused by:

SODIUM   

Most abundant extr extracellular acellular cation in the ECF (represents 90% of all extracellular cations) Largely determines the osmolality of the plasma Sodium concentration in the EXF is much larger than inside the cells. Because small amount can diffuse through the cell membrane, two sides would reach equilibrium

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INCREASED SODIUM Increased sodium loss in the urine can occur with decreased aldosterone production (meaning less water is reabsorbed by kidney), certain diuretics, ketonuria or a salt losing nephropathy Potassium de deficiency ficiency also causes sodium loss because of the inverse relationship of the two ions in the renal tubules

(If serum potassium is low; kidney tubules will conserve more potassium so it won’t be excreted in the urine = sodium will be excreted in exchange or the potassium conserved; causing increase sodium loss) Prolonged vomiting or diarrhea or severe burns can result increase sodium loss (urine sodium levels are usually less than 20 mmol/day in these disorders). o

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INCREASED WA WATER TER RETENTION Increased water retention causes dilution of serum/plasma sodium as with acute or chronic renal failure In nephrotic syndrome and hepatic cirrhosis, plasma proteins are decreased, resulting to decrease colloid osmotic pressure in which intra intravascular vascular fluid migr migrates ates to the tissue.[ tissue.[results to edema- can happen if 3L of fluid retained in the tissue] [plasma volume decreases=secretion of renin leading to production of ADH causing water retention]. The low plasma volume causes AVP to be produced causing fluid retention and resulting to dilution of sodium. This retention and resulting to dilution of sodium. This compensatory mechanism can also be seen with congestive heart failure (CHF) as a result of increased venous pressure.  

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WA WATER TER IMBALANCE Water imbalance can occur as a result of excess water intake, as with polydipsia (Inc thirst) SIADH causes an increase in water retention because of increased AVP production Pseudohyponatremia can occur when sodium is measured using indirect ion selective electrode in a patients who is hyperproteinemic or hyperlipidemic o Can be seen in In Vitro Hemolysis  Most common cause of false decrease levels of sodium

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SYMPTOM SYMPTOMS S OF HYPONA HYPONATERMIA TERMIA Between 125 and 130 mmol/L – gastrointestinal symptoms Below 125 mmol/L – nausea and vomiting, muscular weakness, headache, lethargy and ataxia. More severe symptoms include seizure, comma, respiratory depression. Below 120mmol/L for 48 hours or less – is considered as medical emergency TREA TREATMENT TMENT F HYPONA HYPONATREMIA TREMIA Treatment is directed at correction of the condition that caused either water loss or sodium loss in excess water loss Conventional treatment of hyponatremia involve involvess fluid restriction ((Water dilutes sodium)and providing hypertonic saline and/or other pharmacological agents that may take several days to reach desired effects and may have deleterious side effects Correcting severe hyponatremia o rapidly :cause cause cerebr cerebral al myelinosis o slowly :cerebral erebral edema ***HYPERNA ***HYPERNATREMIA TREMIA Results from excess loss of water relative to sodium loss, decreased water intake or increased sodium intake or retention It is less commonly seen in hospitalized patients than hyponatremia Loss of hypotonic fluid may occur either by the kidney or through profuse sweating, diarrhea or severe burns Hypernatremia may result from loss of water in diabetes insipidus either because the kidney cannot respond to AVP or because the AVP secretion is impaired 2 types of diabetes insipidus: o Nephrogenic Diabetes insipidus -kidney can not response to AVP; secretion is normal

Central Diabetes in insipidus sipidus -secretion of AVP Excess water loss may occur in renal tubular disease, such as acute tubular necrosis, in which the tubules become unable to fully concentrate the urine Water loss through the skin by breathing accounts for about 1L of water loss per day in adults ( in sensible loss) Commonly hypernatremia occurs in those persons who may be thirsty but who are unable to ask for obtain water, such as adults with altered mental status and infants Chronic hypernatremia aleart patient is indicative of hypothalamic disease Hypernatremia may be from excess ingestion of salts or administration of hypertonic solutions of sodium, such as sodium bicarbonate or hypertonic dialysis solutions o

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TREA TREATMENT TMENT OF HYPERNA HYPERNATREMIA TREMIA

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HYEREMATRUMIA – neonate are susceptible 

Treatment is directed at correction of the underlying condition that caused the water depletion or sodium rentention Hypernatremia must be corrected gradually because too rapid correction of serious hypernatremia can induce cerebral edema and death

DETERMINA DETERMINATION TION OF SODIUM 

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Specimen: o Serum o Plasma- Lithium Heparin, Ammonium, Lithium Heparin o Urine (24hr) Hemolysis do not cause signiicant change in serum or plasma values as a result of decreased levels o intracellular sodium (insensible loss) Marked hemolysis may result to decreased vaues due to dilutional effect Sweat is also suitable for analysis

METHODS OR DETERMINA DETERMINATION TION OF SODIUM SYMPTOM SYMPTOMS S OF HYPERNA HYPERNATREMIA TREMIA 

Symptoms most commonly involve the CNS as a results of hyperosmolar state

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Symptoms include altered mental status, lethargy, irritability, restless, seizures, mucle twitching, hyperreflexes, fever, nausea or comiting, difficult respiration and increase thirst Serum sodium concentration of more than 160 mmol/L is associated with mortality rate off 60% to 75%

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Chemcal methods Lame emission spectrophotometry Atomic absorption spectrophotomtry Ion selective (Glass aluminum silicate) – most ionized sused method....