Electrolytes

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Electrolytes
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Chloride

• Major Extracellular anion (103 mEq/L)
• Maintains hydration, osmotic pressure, ionic
  balance
• Changes parallel changes in Na
• ISE Silver Chloride/silver sulfide sensing
  element
• Also colorimetric and coulometric-amperometric
  (Ag Cl- ? AgCl)
• Sweat Chloride Cystic Fibrosis

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Chloride Clinical Significance

• Normal Range (98-109 mmol/L)
• Increased Hyperparathyroidism, renal tubular
  disease, diarrhea, dehydration, CHF
• Decreased Salt losing renal disease,
  overhydration, prolonged vomiting, burns

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Chloride Clinical Significance

• Obtained from the diet and completely absorbed
• Excreted through the GI tract, skin, urine
• Reabsorbed by the proximal tubule and the loop of
  Henle

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Sweat Chloride

• 17th Century Saying
• Woe to that child who when kissed on the
  forehead taste salty. He/She is bewitched and
  soon must die
• Pilocarpine nitrate A stimulant which causes
  localized sweating so that sweat may be collected
  and analyzed

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Sweat Chloride for Cystic Fibrosis

• Gauze soaked in pilocarpine nitrate and potassium
  sulfate reagents
• Gauze is placed on the arm and connected to the
  electrodes
• Sweat is then analyzed for chloride
• Ranges
• Normal 0 35 mmol/L
• Ambiguous 35-60 mmol/L
• Cystic Fibrosis gt60 mmol/L

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CO2

• Primarily bicarbonate
• Keep sample capped to prevent loss of CO2
• Dissolved CO2 escapes rapidly once the sample is
  opened

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CO2 Specimen

• Serum or heparinized plasma (venous blood)

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CO2 Measurement

• Sample must be acidified or alkalinized
• Acidification converts various forms of CO2 to
  CO2
• Alkalinizing converts all CO2 to HCO3-
• Measurements involve electrode-based or enzymatic
  methods
• Electrodes use PCO2 electrode
• Enzymatic convert to bicarbonate, react with
  phosphoenolpyruvate, measure a decrease in
  absorbance at 340nm (NAHDH H ? NAD)

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CO2 Clinical Significance

• Normal Range (23-30 mmol/L)
• Increased Metabolic Alkalosis, Compensated
  respiratory acidosis, Emphysema
• Decreased Metabolic Acidosis, Compensated
  respiratory alkalosis, Hyperventilation

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Sodium

• Major extracellular cation (serum/plasma
  concentration 135-148 mEq/L, urine concentration
  40-217 mEq/24hr)
• Functions in maintaining osmotic pressure in the
  ECF
• Highly regulated by the kidneys
• 70-80 reabsorbed in the proximal tubules
• 20-25 reabsorbed in the loop of Henle

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Sodium Specimen

• Serum or heparinized plasma (no sodium-containing
  anticoagulants)
• Must be centrifuged in lt30 min from collection
• Serum/plasma may be stored at 2-4C
• Urine collected unpreserved
• Hemolysis DOES NOT cause significant errors
• Lipemic samples should be if measured by direct
  ion-selective electrode
• Avoid IV line draws (draw below IV)

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Sodium Measurement

• Atomic Absorption Spectra (AAS)
• Flame Emission Spectra (FES)
• Ion-selective Electrode (IES)
• Sodium electrode with a glass membrane
• Potentiometric method
• Indirect sample is diluted with a high ionic
  strength buffer
• Direct no dilution
• Subject to error by lack of selectivity, protein
  coating, and salt-bridge competition with the
  selected ion

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Clinical Significance Sodium

• Hypernatremia
• Water deficiency
• Excessive sweating
• Fever
• Burns
• Hyperventilation
• Diabetes insipidus
• Diarrhea and vomiting

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Clinical Significance Sodium

• Hyponatremia
• Water excess (dilutional hyponatermia)
• Heart failure, liver disease, nephrotic syndrome,
  renal failure
• Inappropriate ADH
• Sodium deficit gt water deficit vomiting
  diarrhea, GI obstruction, burns, diuretics,
  hypoaldosterone
• ECF to ICF
• Psuedohyponatremia hyperglycemia,
  hyperlipidemia, hyperglobulinemia

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Potassium

• Major intracellular cation (serum/plasma
  concentration of 3.5-5.3 mEq/L, urine
  concentration 30-90 mEq/24hr)
• Highly reabsorbed in the proximal tubules
• Secreted by the distal tubules for Na exchange
  when influenced by aldosterone
• Potassium is required for muscle irritability,
  respiration, and myocardial function

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Potassium Specimen

• MUST avoid hemolysis
• Levels in plasma and whole blood are 0.1-0.7
  mEq/L lower than serum (due to platelet release
  of K in serum)
• CANNOT refrigerate whole blood sample
• Falsely increased due to poor K-ATPase pump
  regulation leaking
• CANNOT store unseparated at room temp
• Glycolysis occurs and shifts K to ICF

Therefore, collect the sample between 25-37 C,
and centrifuge within 30 min.
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Potassium Measurement

• Atomic Absorption Spectra (AAS)
• Flame Emission Spectra (FES)
• Ion-selective Electrode (IES)
• Potassium electrode with liquid ion-exchange
  membranes which incorporate valinomycin
• Potentiometric method
• Indirect sample is diluted with a high ionic
  strength buffer
• Direct no dilution
• Subject to error by lack of selectivity, protein
  coating, and salt-bridge competition with the
  selected ion

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Clinical Significance Potassium

• Hyperkalemia (Addisons, Acidosis, Cardiac
  Arrest)
• Pseudohyperkalemia hemolysis, leukocytosis
• High intake/Decreased excretion renal failure,
  hyperalsodteronism, diuretics
• SYMPTOMS changes in EKG, arrhythmia, muscle
  weakness, paresthesias, cardiac arrest

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Clinical Significance Potassium

• Hypokalemia (Cushings, Alkalosis, Arrhythmias)
• ECF to ICF due to alkalosis, increased insulin
• Decreased intake
• Increased GI loss vomiting, diarrhea,
  malabsorption, laxatives
• Increased urinary loss increased aldosterone,
  renal disease, tubular acidosis, Fanconi syndrome
• SYMPTOMS nausea, vomiting, abdominal distension,
  muscle cramps, EKG changes, lethargy, confusion

No renal threshold for potassium!
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Electrolyte Exclusion Principle

• The exclusion of electrolytes from the fraction
  of plasma which is occupied by solids
• Solids occupy 7 of plasma (93 is water)
• Therefore, 145 x (100/93) 156 mEq/L
• Becomes a problem during hyperlipidemia or
  hyperproteinemia

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Anion GAP

• (Na K) (Cl CO2) (10 -20)
• Or
• Na (Cl CO2) (8-16)
• Difference between unmeasured anions and
  unmeasured cations
• Increased Renal failure, diabetic acidosis,
  lactic acidosis, drugs or toxins or lab error
• Decreased QC Check Cant be a negative number
• Analytical error, such as false elevated Cl or
  low Na
• Lipemia

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Correlations