5 electrolytes kbm

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CLINICAL CHEMISTRY ELECTROLYTES Introduction – This chapter is largely about the water and electrolytes ( salts )in your plasma and how the body manages to keep you from drying up and blowing away even if you are in the hot Texas sun and without liquid drink Chapter KEY TERMS • • • • • • • • • • • • • Anion Anion Gap Cation Active transport Diffusion Electrolyte Osmolality Osmolality Polydipsia Tetany ADH Hypothalamus Gland Renin - Angiotensin Aldosterone System • • • • Hyper / Hypo … natremia , kalemia, calcemia Parathyroid Hormone ( PTH ) Acidosis / Alkalosis Calcitonin Ion Selective Electrode • • • • • • • Na K Cl CO2 Ca Mg PO4 • = Sodium = Potassium = Chloride = Carbon Dioxide = Calcium = Magnesium = Phosphate • Define the key terms General Objectives • Discuss the factors that regulate each of the electrolytes • Discuss the physiological functions and clinical significance of each of the electrolytes • Discuss ISE and Osmometers Electrolytes • Electrolytes – Substances whose molecules dissociate into ions when they are placed in water – CATIONS (+) ANIONS (-) • Medically significant / routinely ordered electrolytes include: – sodium (Na) – potassium (K) – chloride (Cl) – and CO2 (in its ion form = HCO3- ) Electrolyte Functions • • • • • • • • Volume and osmotic regulation Myocardial rhythm and contractility Cofactors in enzyme activation Regulation of ATPase ion pumps Acid-base balance Blood coagulation Neuromuscular excitability Production of ATP from glucose Electrolytes • General dietary requirements – Most need to be consumed only in small amounts as utilized – Excessive intake leads to increased excretion via kidneys – Excessive loss may result in need for corrective therapy • loss due to vomiting / diarrhea; therapy required - IV replacement, Pedilyte, etc Electrolytes • Water (the diluent for all electrolytes) constitutes 4070% of total body and is distributed: – Intracellular – inside cells • 2/3 of body water (ICW) – Extracellular – outside cells 1/3 of body water – Intravascular – plasma 93% water » Intrastitial -surrounds the cells in tissue (ISF) • Electrolytes Electrolytes • Ions exist in all of these fluids, but the concentration varies depending on individual ion and compartment • The body uses active and passive transport principles to keep water and ion concentration in place 10 bicarbonate ion (HCO3- ) • Carbon dioxide/bicarbonate – – * the major anion of intracellular fluid – 2nd most important anion (2nd to Cl) • Note: most abundant intra-cellular anion • 2nd most abundant extra-cellular anion 63 bicarbonate ion (HCO3- ) • Total plasma CO2 = HCO3- + H2CO3- + CO2 – HCO3- (carbonate ion) accounts for 90% of total plasma CO2 – H2CO3- carbonic acid (bicarbonate) 64 bicarbonate ion (HCO3- ) • Regulation: – Bicarbonate is regulated by secretion / reabsorption of the renal tubules ↓ renal excretion – Acidosis : ↑ renal excretion – Alkalosis : 65 bicarbonate ion (HCO3- ) • Kidney regulation requires the enzyme carbonic anhydrase - which is present in renal tubular cells & RBCs carbonic anhydrase carbonic anhydrase Reaction: CO2 + H2O ⇋ H2CO3 → H+ + HCO–3 66 bicarbonate ion (HCO3- ) CO2 Transport forms – 8% dissolved in plasma • dissolved CO2 – 27% carbamino compounds • C02 bound to hemoglobin – 65% bicarbonate ion • HCO3- - carbonate ion 67 bicarbonate ion (HCO3- ) • Normal values – Total Carbon dioxide (venous) – @ 2230 mmol/L • includes bicarb, dissolved & undissociated H2CO3 - carbonic acid (bicarbonate) – Bicarbonate ion (HCO3–) – 22-26 mEq/L 68 bicarbonate ion (HCO3- ) • Function – – CO2 is a waste product – continuously produced as a result of cell metabolism, – the ability of the bicarbonate ion to accept a hydrogen ion makes it an efficient and effective means of buffering body pH – dominant buffering system of plasma – makes up @ 95% of the buffering capacity of plasma 69 bicarbonate ion (HCO3- ) • Significance – The bicarbonate ion (HCO–3) is the body's major base substance – Determining its concentration provides information concerning metabolic acid/base 70 bicarbonate ion (HCO3- ) • CO2 /bicarb Determination – Specimen can be heparinized plasma, arterial whole blood or fresh serum Anaerobic collection preferred methods • • • • • Ion selective electrodes Colorimetric Calculated from pH and PCO2 values Measurement of liberated gas 71 Electrolyte balance • Anion gap – an estimate of the unmeasured anion concentrations such as sulfate, phosphate, and various organic acids 72 Electrolyte balance • Calculations – Na - (Cl + CO2 or HCO3-) = – NV 8-12 mEq/L – Or – (Na + K) - (Cl + CO2 or HCO3-) NV 7-14 mEq/L • which one to use may depend on whether K value is available Some authors feel that K value is so small and usually varies little, that it is not worth including into the formula 73 Electrolyte balance • Causes in normal patients – what causes the anion gap? – 2/3 plasma proteins & 1/3 phosphate& sulfate ions, along with organic acids • Increased AG – – uncontrolled diabetes (due to lactic & keto acids) – severe renal disorders • Decreased AG – a decrease AG is rare, more often it occurs when one test/instrument error 74 Normal Ranges SODIUM POTASSIUM CHLORIDE CO2 135 – 145 3.5 – 5.0 100 – 110 20 – 30 ANION GAP 10 - 20 PLASMA OSMOALITY CALCIUM IONIZED Ca MAGNESIUM PHOSPHATE LACTATE mEq/L mEq/L mEq/L mEq/L meq / L 275 - 295 8.5 – 10.0 4.5 – 5.5 1.2 – 2.1 2.5 – 4.5 0.5 – 17.0 mOsmol / kg mg/dL mg/dL mEq/L mg/dL mgl/dl 75 ELECTROYTE TOP 10 ∀ ↑ Osmolality is detected by the Hypothalamus Gland Thirst sensation and secretion of ADH by Posterior Pituitary Gland ADH increases renal reabsorption of water ∀ ↓ Blood Volume stimulates Renin - Angiotensin - Aldosterone system Aldosterone secretion by the Adrenal Cortex stimulates increased renal absorption of sodium • • • • • Sodium is the main extracellular cation and contributor to plasma osmolality Potassium is the main intracellular cation Plasma “CO2” = Dissolved CO2 + H2 CO3 + HCO3Chloride is usually a passive follower of Sodium to maintain electrical charge Sodium and Potassium usually move opposite each other • Parathyroid Hormone ( PTH ) secretion increases plasma calcium , increases plasma magnesium and decreases phosphate • Acidosis is associated with ↑ Potassium ( Alkalosis with ↓ Potassium ) 76 Electrolyte Links http://www.nlm.nih.gov/medlineplus/ency/article/002350.htm http://www.thirdage.com/health/adam/ency/article/002350.htm 77 [...]... Unconscious patients – Elderly 20 Electrolytes • Decreased osmolality – Diabetes insipidus • ADH deficiency • Because they have little / no water reabsorption, produce 10 – 20 liters of urine per day 21 Electrolytes • Osmolality normal values – – – – Serum – 2 75- 2 95 mOsm/Kgm 24 hour urine – 300-900 mOsm/Kgm urine/serum ratio – 1.0-3.0 Osmolal gap < 10- 15 mOsm (depending on author) 22 Electrolytes • Classifications... H2PO-4 – when body pH is normal, HPO-24 is the usual form (@ 80 % of time) 25 Electrolyte Summary • cations (+) • • • • • Na 142 K 5 Ca 5 Mg 2 154 mEq/L • anions (-) • • • • • • Cl 1 05 HCO324 HPO4-2 2 SO4-2 1 organic acids 6 proteins 16 » 154 mEq/L 26 Routinely measured electrolytes • Sodium – – the major cation of extracellular fluid outside cells – Most abundant (90 %) extracellular cation – Functions... samples, must centrifuge 18 Electrolytes • Calculated osmolality – uses glucose, BUN, & Na values – (Plasma Sodium accounts for 90 % of plasma osmolality) • Formula: – 1.86 (Na) + glucose∕18 + BUN∕2.8 = calculated osmolality • Osmolal gap = difference between calculated and determined osmolatity – Should be less than 10- 15 units difference • (measured – calculated = 10 to 15) 19 Electrolytes • Increase... Posterior pituitary secrets ADH • ( ADH increases H2O re-absorption by renal collection ducts ) • In both cases, plasma water increases 15 Electrolytes • Osmolality – concentration of solute / kg – reported as mOsm / kg • another term: – Osmolarity - mOsm / L - not often used 16 Electrolytes • Determination – 2 methods or principles to determine osmolality • Freezing point depression – (the preferred method)... intracellular cation 23 Electrolytes – Anions – have a negative charge - move toward the anode • Cl– (1st) most abundant extracellular anion • HCO–3 – (bicarbonate) second most abundant extracellular anion 24 Electrolytes • Phosphate is sometimes discussed as an electrolyte, sometimes as a mineral – HPO-24 / H2PO-4 – when body pH is normal, HPO-24 is the usual form (@ 80 % of time) 25 Electrolyte Summary... changing electrolyte balance 12 Electrolytes • Laboratory assessment of body hydration is often by determination of osmolality and specific gravity of urine 13 Electrolytes Osmolality • Physical property of a solution based on solute concentration – Water concentration is regulated by thirst and urine output – Thirst and urine production are regulated by plasma osmolality 14 Electrolytes Osmolality ∀ ↑.. .Electrolytes • Sodium has a pulling effect on water – Na affects extracellular fluids (plasma & interstitial) equally – However, because there is considerably more Na outside cells than inside, the water is pulled out of cells into the extracellular fluid – Na determines osmotic pressure of extracellular fluid 11 Electrolytes • Proteins (especially albumin)... Sodium (Na) • Sodium normal values – Serum – 1 35- 148 mEq/L – Urine (24 hour collection) – 40-220 mEq/L 31 Sodium (Na) • Urine testing & calculation: – 1st Because levels are often increased, a dilution of the urine specimen is usually required – Then the result from the instrument (mEq/L or mmol/L) X # L in 24 hr 32 Clinical Features: Sodium • Hyponatremia: < 1 35 mmol/L – Increased Na+ loss • Aldosterone... activity - sodium determines osmotic activity (Main contributor to plasma osmolality) • Neuromuscular excitability - extremes in concentration can result in neuromuscular symptoms 27 Routinely measured electrolytes • Diet - sodium is easily absorbed • Na-K ATP-ase Pump – pumps Na out and K into cells • Without this active transport pump, the cells would fill with Na and subsequent osmotic pressure would... resulting in dehydration (relative increase) – Sweating – Diarrhea – Burns – Dehydration from inadequate water intake, including thirst mechanism problems – Diabetes insipidus • (ADH deficiency …↑ H2O loss ) 35 Hypernatremia • Excessive IV therapy • comatose diabetics following treatment with insulin Some Na in the cells is kicked out as it is replaced with potassium – Cushing's syndrome - opposite of Addison’s
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