Electrolytes Study Guide PDF

Quiz 4 Study Guide Electrolytes 3  Chloride o Most abundant extracellular anion  More concentrated in ECF than inside the cell o Moves secondary to Na+ or HCO3- shifts  Reabsorbed along with Na+ in kidney to m...

Quiz 4 Study Guide Electrolytes 3  Chloride o Most abundant extracellular anion  More concentrated in ECF than inside the cell o Moves secondary to Na+ or HCO3- shifts  Reabsorbed along with Na+ in kidney to maintain electroneutrality  Moves into RBCs to balance HCO3- movement out of RBCs  Chloride Shift: o CO2 from cellular metabolism diffuses in to plasma and RBCs o In RBCs, combines with H2O to form H2CO3 which dissociates into H+ and HCO3- o HCO3- moves out of cell o To maintain electroneutrality, Cl- moves into cell o Functions – Helps to maintain electroneutrality o Regulation  Some filtered Cl- reabsorbed secondary to Na+ reabsorption  Excess Cl- is excreted in urine and sweat o Reference Range  Serum/Plasma Chloride: 98-107 mmol/L Critical Values: < 70 or > 120 mmol/L o Hypochloremia = low serum/plasma Cl- levels  Cl- < 98 mmol/L  Causes: Often a result of the same conditions causing decreased Na+ levels, Hypoaldosteronism, Diuretics, GI loss of Cl-, (among others), Metabolic Alkalosis o Hyperchloremia = high serum/plasma Cl- levels  Cl- > 107 mmol/L  Causes: Conditions causing increased Na+ levels, Excess Cl- Intake, Renal Tubular Acidosis, Metabolic Acidosis  o Specimen Requirements:  Type of sample: Serum, Plasma, Whole Blood or Urine  Lithium Heparin  NO Marked Hemolysis  Not affected by intracellular chloride but can have dilutional effect  Can also be run on Sweat  Cystic Fibrosis = autosomal recessive inherited disease affecting the exocrine glands, causing electrolyte and mucous secretion abnormalities  Can cause pneumonia and pancreatic insufficiency secondary to heavy mucous secretions  More common in Caucasian population o Methods:  Current Method: Ion-Selective Electrode – (see Sodium)  Electrode used for Cl- : Ag-Cl electrode  Sweat Chloride Analysis – used for Cystic Fibrosis diagnosis  Pilocarpine stimulates sweat glands  Sweat absorbed onto gauze pad via iontophoresis  Positive Test for CF: > 60 mmol/L – confirmed with a second test  Bicarbonate o 2nd most abundant extracellular anion  More concentrated in ECF than inside cell  Total CO2 = HCO3- + H2CO3 + pCO2 (patial/dissolved)  Bicarbonate (HCO3-) accounts for > 90% Total CO2  Total CO2 is used as a measurement of HCO3-  Bicarbonate cont. o Moves out of RBCs to maintain pH  Balanced by Cl- movement into RBCs  Bicarbonate Buffer System: o CO2 from cellular metabolism diffuses in to plasma and RBCs o In RBCs, CO2 combines with H2O to form H2CO3 (carbonic acid)  Helps prevent toxic CO2 from building up  Catalyzed in either direction by carbonic anhydrase o H2CO3 dissociates into H+ and HCO3- CA o CO2 + H2O   H2CO3  H+ + HCO3- o HCO3- moves out of cell  Can act as a buffer to combine with excess H+ in plasma o To maintain electroneutrality, Cl- moves into cell o HCO3- and H+ in plasma  H2O and CO2, which is eliminated via the lungs o Functions  Temporary storage form of CO2 until it can be eliminated  Helps to maintain pH (Buffer) o Regulation  Filtered as HCO3-, converts to H2O and CO2 in tubules  Reabsorbed as CO2, converts back to HCO3- in plasma o Reference Range  Serum/Plasma Total CO2: 22-33 mmol/L o Acidosis = low HCO3- levels compared to pCO2  Decreased HCO3-: < 22 o Alkalosis = high HCO3- levels compared to pCO2  Increased HCO3-: > 33 mmol/L  Bicarbonate cont. o Specimen Requirements:  Type of sample: Serum or Plasma and Whole Blood  Lithium Heparin  Separate plasma from cells immediately  Analyze immediately once uncapped (to prevent CO2 loss) o Methods:  Common Methods:  Ion-Selective Electrode – (see Sodium)  Acid used to convert all forms of CO2 to gas (pCO2)  Electrode used for CO2 : pH electrode  Enzymatic Method  Alkalinized to convert all forms of CO2 to HCO3-  Enzymes used to catalyze the following reaction (simplified):  HCO3-  Oxaloacetate + NADH  Malate + NAD+   HCO3- =  NADH =  Absorbance at 340 nm Electrolytes 4  Calcium o Found in:  1. Bone (99 %) – acts as storage for Ca2+, Mg2+ and PO43-  2. ECF and ICF  More concentrated in ECF than inside cell o Forms:  1. Free ionized Ca2+ (45 %) – biologically active form  2. Protein-bound – mostly bound to albumin  3. Ion-bound  Ionized Ca2+ - closely maintained, critical for proper muscle contractility  Albumin changes do not affect ionized Ca2+  Total Ca2+ - can change with changes in albumin and bound-ions  Not a reliable measure of ionized Ca2+, especially in acutely ill individuals o Functions  Maintenance of muscle contractility  Bone and Teeth formation, Nerve Impulse transmission, Coagulation, Enzyme activation o Reference Range  Serum/Plasma Calcium: 8.5-10.5 mg/dL Serum Ionized Calcium: 4.6-5.3 mg/dL o Regulation  Non-protein bound Ca2+ enters the filtrate  1. Parathyroid Hormone (PTH)  Decrease in ionized Ca2+ stimulates secretion from parathyroid gland  Increases bone resorption, kidney reabsorption, kidney production of Vitamin D and absorption in intestine   2. Vitamin D  Decrease in ionized Ca2+ stimulates PTH secretion which stimulates renal production of Vitamin D  Increases absorption in intestine, kidney reabsorption, and enhances bone resorption  3. Calcitonin  Significant Increase in ionized Ca2+ stimulates release from thyroid gland  Blocks bone resorption, decreases intestinal absorption, and decreases kidney reabsorption o Hypocalcemia = low serum/plasma Ca2+ levels  Ca2+ < 8.5 mg/dL  Causes: Hypoparathyroidism, Vit D Deficiency, Hypoalbuminemia, Renal Disease  Hypoparathyroidism:  Calcium,  Phosphate,  PTH*  Vit D Deficiency:  Calcium*,  Phosphate*,  PTH  Symptoms: Neuromuscular, Cardiac Arrhythmia o Hypercalcemia = high serum/plasma Ca2+ levels  Ca2+ > 10.5 mg/dL  Causes: Hyperparathyroidism, Vit D Excess, Milk Alkali Syndrome, Malignancy  Hyperparathyroidism:  Calcium,  Phosphate,  PTH*  Vit D Excess:  Calcium*,  Phosphate*,  PTH  Symptoms: Neuromuscular, Renal calculi, GI o Specimen Requirements:  Total Calcium – type of sample: Serum, Plasma, Urine  Lithium Heparin (NO EDTA – chelates calcium causing false decrease)  Ionized Calcium – type of sample: Serum, Whole Blood  Heparin, collected anaerobically – CO2 loss to atmosphere can cause increased pH, will cause more Ca2+ binding to albumin, and falsely decrease ionized Ca2+  o Ionized Calcium is of greatest importance compared to Total Calcium  Especially important for patients in critical condition (e.g. ICU, Surgery) o Methods:  Reference Method: Atomic Absorption Spectrophotometry  Current Methods: Ion Selective Electrode  Used to measure ionized/free Ca2+  Also measures pH, used to correct calcium to a pH of 7.40 = “normalizing”  Current Methods: Dye-Binding Methods  Used to measure Total Ca2+  Sample is acidified to release any bound Ca2+  All calcium is now in “free” state, complexes with either: o Orthocresolphthalein Complexone (o-CPC) or Arsenazo III Dye   Calcium =  Dye Complex =  Absorbance  Magnesium o Second most abundant intracellular cation  More concentrated inside cell than ECF o Found in:  1. Bone – acts as storage for Ca2+, Mg2+ and PO43-  2. Tissue, 3. ECF and RBCs (little) o Forms:  Found in free ionized Mg2+ form, protein-bound form, and ion-bound form just like Ca2+ o Functions  Cofactor for many enzymes  Affects Cardiovascular, Metabolic and Neuromuscular functions o Reference Range  Serum/Plasma Magnesium: 1.7-2.4 mg/dL  o Regulation  Non-protein bound Mg2+ enters the filtrate  1. Parathyroid Hormone (PTH)  Increases kidney reabsorption, and intestinal absorption o Hypomagnesemia = low serum/plasma Mg2+ levels  Mg2+ < 1.7 mg/dL  Symptoms: Neuromuscular, Cardiac Arrhythmia, Psychiatric o Hypermagnesemia = high serum/plasma Mg2+ levels  Mg2+ > 2.4 mg/dL  Symptoms: Neuromuscular, Cardiac (Bradycardia), GI, Skin (Flushing) o Specimen Requirements:  Total Magnesium – type of sample: Serum, Plasma, Urine  Lithium Heparin  NO Hemolysis, Remove serum or plasma from cells ASAP  Affected by intracellular Mg2+ o Methods:  Reference Method: Atomic Absorption Spectrophotometry  Current Methods:  Mg2+ + Calmagite, Formazan Dye, or Methylthymol Blue  colored complex Increased Absorbance   Mg2+ =  colored complex =  Absorbance  Phosphate o Most abundant intracellular anion  More concentrated inside cell than ECF o Found in:  1. Bone – acts as storage for Ca2+, Mg2+ and PO43-  2. Tissue, 3. ECF and RBCs (little) o Forms:  1. Inorganic PO43- (25 %) – includes free and bound  2. Organic PO43- – found as constituents in organic molecules o Functions  Component of organic molecules such as DNA and RNA, Coenzymes, ATP, 2,3-BPG, etc.  Bone and Teeth formation, Buffer o Reference Range  Serum/Plasma Phosphate: 2.5-4.5 mg/dL o Regulation  Inorganic, non-protein bound PO43- enters the filtrate  1. Parathyroid Hormone (PTH)  Decreases kidney reabsorption (increases excretion)  2. Vitamin D  Increases intestinal absorption and kidney reabsorption  3. Calcitonin  Decreases kidney reabsorption (increases excretion) o Hypophosphatemia = low serum/plasma PO43- levels  PO43- < 2.5 mg/dL  Causes: Hyperparathyroidism, Vitamin D Deficiency, Malabsorption  Hyperparathyroidism:  Calcium,  Phosphate,  PTH*  Vit D Deficiency:  Calcium*,  Phosphate*,  PTH o Hyperphosphatemia = high serum/plasma PO43- levels  PO43- > 4.5 mg/dL  Causes: Hypoparathyroidism, Vitamin D Excess  Hypoparathyroidism:  Calcium,  Phosphate,  PTH*  Vit D Excess:  Calcium*,  Phosphate*,  PTH o Specimen Requirements:  Total Phosphate – type of sample: Serum, Plasma, Urine  Lithium Heparin  NO Hemolysis, Remove serum or plasma from cells ASAP  Affected by intracellular PO43- o Methods: Fiske and Subbarow Method (at AcidicpH)  PO43-  Phosphomolybdate + Reducing Agent  Molybdenum blue  Can read Phosphomolybdate OR can read further reduced Molybdenum blue  Both Phosphomolybdate and Molybdenum blue have an Increased Absorbance (Electrolytes 1)  Anion Gap o Electrolyte panel measures: Na+, K+, Cl-, HCO3- (TCO2) o Anion Gap = the difference between measured anions and cations due to unmeasured anions and/or cations (Due to electroneutrality, the charge balance between anions and cations will always = 0; By accounting for measured anions and cations in the calculation, and charge imbalances will be a result of the influence of unmeasured anions and or cations) o Unmeasured anions and cations include:  PO4-, Ca2+, Mg2+, lactic acid, methanol, ethanol, ethylene glycol, salicylates, possibly K+ o 2 equations for Anion Gap:  Without Potassium: Na – Cl – CO2 (add cations, subtract anions)  With Potassium: Na + K – Cl – CO2 o Reference Range  AG without Potassium: 7-16 mmol/L AG with Potassium: 10-20 mmol/L o Some Causes of Increased Anion Gap:  Uremia / Renal Failure, Ketoacidosis, Methanol, Ethanol or Ethylene Glycol Poisoning, Salicylate Poisoning, Lactic Acidosis o Some Causes of Decreased Anion Gap:  Hypoalbuminemia