Electrolytes - Shori.ppt PDF

Electrolytes Aims and objectives Review of body water Introduction to electrolytes Describe the role of the kidneys in maintaining balance of water and electrolytes  Water Steady State Amount Ingested = Amount Eliminated Pathological losses...

Electrolytes Aims and objectives Review of body water Introduction to electrolytes Describe the role of the kidneys in maintaining balance of water and electrolytes  Water Steady State Amount Ingested = Amount Eliminated Pathological losses vascular bleeding (H20, Na+) vomiting (H20, H+) diarrhoea (H20, HCO3-).  Body Fluids and Fluid compartments Individual variability (lean body mass) 55 - 60% of body weight in adult males 50 - 55% of body weight in adult female (5% extra adipose tissue) ~42 L For a 70 Kg man and ~ 38 L for a 70 kg woman Input RBC PLASMA WATER 5% 3L Semi-permeable membrane 20% CELL WATER INTERSTITIAL ECF = 14 L FLUID 40% COMPARTMENT 15% 10 L ICF = 28 L TRANSCELLULAR WATER Na+,Cl-, HCO3- K , Protein , PO + - 4 3- 1% 1L Body Fluids and Fluid compartments Intracellular fluid (ICF) – inside cells  major cation is potassium and major anion is phosphate Extracellular fluid (ECF) – outside cells Divided further into interstitial fluid (found between cells), plasma (found in the circulatory system) and the transcellular fluid (found within epithelial lined spaces and often not calculated as a fraction of the extracellular fluid)  major cation is sodium and major anion is chloride. Sodium is responsible for osmotic balance of ECF space. Body Fluids and Fluid compartments Exchange of water between body fluid compartments is facilitated by two forces hydrostatic pressure - (the back pressure exerted by water against the membrane) Osmotic pressure - (The pressure exerted by the flow of water through a semi-permeable membrane separating two solutions with different concentrations)  Osmolality The number of dissolved particles in the body water is measured by the osmolality (unit of measurement is osmoles)  Particles exist as individual molecules e.g glucose and proteins or as ions from electrolytes e.g sodium ions and chloride ions  Dissolved particles exert an osmotic pressure  Movement of water from low osmolality to one of high osmolality  Omostic pressure same on both sides of the membrane (i same osmolality)  Calculation of osmolality Osmoles is defined as the amount of solute that when dissolved in water gives the same osmotic pressure as that expected from one mole of an ideal non-ionised solute Osmolality is the number of osmoles dissolved in 1 kg of water In body fluid osmolality is measured in milliosmoles (mOsmol) Osmolality = [ sodium x 2 ] + urea + glucose Normal = 280 - 290 mOsm kg-1 The Importance of the Anion Gap Anion Gap = {[Na+]+[K+]} – {(Cl- ] + [HCO3-]} Normal range = 6-18 mmol/l  Anion Gap =  unmeasured anions in the sample Clinical significance: diseases relating to increased anions like lactate, acetoacetate, ß-hydroxybutyrate, phosphates, sulfates, etc. Not measured frequently as the ‘main’ electrolytes  Fluid imbalance in disease Fluid loss: GI: diarrhoea, vomiting, etc. renal: diuresis (urine) vascular: haemorrhage skin: burns, sweat Fluid gain: Heart / liver / kidney failure  Electrolytes Volume and osmotic regulation Maintaining Acid/Base balance (body pH) Acting as cofactors for enzyme reactions Conduction of nerve impulses (potassium important in nerve impulses) Maintain cardiac contractility and rhythm Plus many others…….  Electrolytes Composed of anions and cations depending on their charge Play an important role in metabolic processes and in the control of water balance  Electrolytes – ICF & ECF Electrolyte Symbol/Charge Terminology Reference range (serum) 3.7-5.2 milliequivalent/L Potassium K+ “-kalemia” 1 mEq/l=1millimole Magnesium Mg2+ “-magnesemia” 1.8-2.4 mg/dL ICF Phosphate PO4- “-phosphatemia” 4.5-6.0 mg/dL ( 11 yrs) 3.0-4.5 mg/dL ( 12 yrs) Sodium Na+ “-natremia” 136-145 mEq/L Chloride Cl- “-chloremia” 98-108 mEq/L ECF Bicarbonate HCO3- 22-32 mEq/L Calcium Ca2+ “-calcemia” 8.9-10.2 mg/L Adapted from Sara Duesterhoeft’s lecture, 2002.  Electrolytes Some of the most important electrolytes measured in a clinical lab include: Na+, K+, Cl-, HCO3-, Mg2+, and Ca2+ Changes in electrolyte concentration Increase/Decrease in amount of electrolyte Increase/Decrease in amount of water Electrolytes can give many clues to the causes of patient illness  Electrolyte losses Renal excretion Stool losses Sweating Abnormal routes: e.g.. vomit and diarrhoea  Measuring Electrolytes in Human Samples Flame Spectrophotometry (often called Photometry)  Sample introduced into a flame  Each metal shows a characteristic colour Ion-Selective Electrodes (ISE) One is a reference electrode, in contact with the liquid to be measured. External reference The other, selective electrode ISE Internal reference electrode, is separated electrode from the test liquid by a special membrane that Internal electrode only allows one ion to get solution through. LaF3 membrane Other: colorimetric  Sodium Functions: Plasma osmolality Water balance (attracts water into the ECF) Nerve impulses Muscle contraction Regulation: Thirst Kidney Na+/K+ ATPase pumps Na+/H+ pumps Blood volume status  ADH (saves water) when  blood volume or plasma osmolality  renin when  arteriolar pressure or  Na+  aldosterone (saves salt) when  Na+ ( renin)  Hyponatremia Deficiency of sodium loss of sodium in Intake of water in excess of water and/or excess of the kidney’s ability to excrete it Symptoms Possible causes nausea/vomiting excessive renal loss of salt generalized weakness (aldosterone deficiency, kidney mental confusion disease, diuretics) headache excessive ADH secretion lethargy (syndrome of (inappropriate possible coma if too low antidiuresis (SIADH)) Hypotension water overload (congestive heart failure, cirrhosis, renal disease)  Hypernatremia Excess of sodium Sodium and/or Water deficit Symptoms Possible causes dehydration extrarenal loss Increased thirst (diarrhea, skin losses) fever renal losses tremors (diuretics therapy and  water intake) altered mental status impaired secretion or ability to lethargy respond to ADH (diabetes insipidus) seizures excessive water loss coma hyperaldosteronism Hypertension  Potassium Functions: Regulate cardiac contraction and rhythm, muscle contraction Attracts water into the ICF Nerve impulses Regulation: Kidneys Na+/K+ -ATPase pump Acid/Base balance (i.e., K+/H+ pumps)  Aldosterone results in  K+ excretion and shift extracellular to intracellular  Hypokalemia Deficiency of potassium Potassium and/or Water Symptoms Possible Causes weakness extra -> intracellular shifts fatigue (alkalosis, diuretics) anorexia extrarenal losses nausea (excessive diarrhea, vomiting) arrhythmia renal losses possible cardiac arrest (renal disease, polyuria) hyperaldosteronism  Hyperkalemia Excess of potassium Potassium and/or Water Symptoms Possible Causes muscular weakness intra -> extracellular shifts tingling (acidosis) numbness renal failure confusion cardiac arrhythmias (K+ secretion deficiency) possible cardiac arrest adrenal failure (hypoaldosteronism) leukemia pseudohyperkalemia (hemolysis of sample, leukocytosis)  Calcium Functions: Primarily resides in bone Muscular contraction Neurotransmission Membrane transport Enzymes and blood coagulation Regulation: Kidney (reabsorbed in the proximal tubules) Parathyroid hormone (PTH) Vitamin D – active form controls homeostasis Calcitonin – exact mechanism not known Disorders include: Hypocalcemia – hypoparathyroidism, malabsorption of calcium or Vit. D, renal failure Hypercalcemia – hyperparathyroidism, excess Vit. D, tumors  Magnesium Functions: Enzyme cofactor Calcium and bone homeostasis Regulation: Kidney  PTH,  serum Mg2+ aldosterone Disorders include: hypomagnesemia – decreased intake malabsorption, malnutrition), increased loss (renal disease, hyperaldosteronism, hyperparathyroidism) hypermagnesemia – usually increased intake of magnesium or renal disease  Chloride Functions: Maintains osmolality Blood volume Electric neutrality Regulation: kidneys (reabsorbed /w Na+ in the proximal tubules), aldosterone Disorders include: Hypochloremia – similar causes as hyponatremia, prolonged vomiting, high [bicarbonate] associated metabolic alkalosis Hyperchloremia – similar causes as hypernatremia, dehydration, low [bicarbonate] associated with prolonged diarrhea or metabolic acidosis  Bicarbonate Functions: determines pH (along with H+) buffering the blood and maintaining acid/base equilibrium Regulation: kidneys (reabsorption in the tubules) lungs Disorders include: Acid/Base disorders  Signs and Symptoms of Renal Failure Symptoms of Uraemia (nausea, vomiting, lethargy) Disorders of Micturation (frequency, nocturia, retention) Disorders of Urine volume (polyuria, oliguria, anuria) Alterations in urine composition (haematuria, proteinuria) Oedema (salt and water retention)  Diagnostic Tests Urinalysis Urine Osmolality Spot urine for Na+ and K+ Serum osmolality Creatinine Creatinine clearance Serum electrolytes 3.7-5.2 milliequivalent/L 1 mEq/l=1millimole