Electrolytes AcidBase Balance

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ElectrolytesAcid-Base Balance
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Electrolytes

• Sodium
• Potassium
• Chloride
• Bicarbonate

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Sodium

• Major extracellular cation
• Determines extracellular fluid volume
• Filtered in glomerulus, reabsorbed in proximal
  (70) and distal convoluted tubule (70) under
  influence of aldosterone
• N135-145 mEq/L

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Hypernatremia

• Water loss (sweating, vomiting, etc.)
• Severe dehydration due to insufficient water
  intake
• Hyperadrenalism (Cushings syndrome)
• Comatose diabetics following insulin treatment

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Hyponatremia

• Fluid replacement following dehydration
• Diabetic ketoacidosis
• Salt-losing nephritis
• Addisons disease, an adrenal corticol
  insufficiency

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Potassium

• Major intracellular cation- 30x more in
  intracellular fluid than extracellular
• Kidneys cannot reduce excretion of K to zero, as
  it does for Na
• Increase- inhibits muscle irritability
• Decrease- increases muscle irritability
• N3.5-5.5 mEq/L

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Hyperkalemia

• Whenever potassium leaves cells at a greater rate
  than can be excreted by kidneys
• Decreased urinary output
• Cell damage
• Addisons disease

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Hypokalemia

• Low intake over time
• Increased loss (vomiting, diarrhea, diuretics)
• Cushings syndrome

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Chloride

• Highest extracellular anion
• Absorbed in intestine, excreted in urine/sweat
• Main usefulness in calculation of anion gap
• Decrease-suspect error
• Increase-increase in organic acids

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Hyperchloridemia

• Dehydration
• Renal tubular acidosis
• Respiratory alkalosis

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Hypochloridemia

• Metabolic acidosis
• Vomiting, diarrhea
• burns

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Acid-Base Balance

• Metabolic processes produce CO2
• CO2 can
• Enter red blood cell to be buffered by hemoglobin
• Form carbamino compounds with plasma proteins
• Remain dissolved in plasma

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Fate of CO2 in RBC

• CO2 H2O ? H2CO3 ?? H HCO3-
• This reaction proceeds very slowly in plasma.
• In RBC, reaction is sped up by action of enzyme,
  carbonic anhydrase
• H buffered by hemoglobin, HCO3- diffuses into
  plasma chloride into RBC to maintain ionic
  balance (chloride shift)

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Bicarbonate/Carbonic Acid Buffer System

• Primary buffer system in plasma
• Henderson-Hasselbalch equation
• pHpKa log bicarb/H2CO3 or
• 7.46.1 1.3 Thus, bicarb/H2CO320

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• Acid-base balance consists of metabolic component
  (HCO3-) and respiratory component (H2CO3)
• Metabolic acidosis decrease HCO3-
• Metabolic alkalosis increase HCO3-
• Respiratory alkalosis decrease H2CO3
• Respiratory acidosis increase H2CO3

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Arterial Blood Gases

• pH N7.35-7.45
• pCO2 (.03 X pCO2 H2CO3)
• N35-45 mm Hg
• HCO3- N22-28 mEq/L

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Compensation of pH imbalances

• Respiratory metabolic compensation
• Metabolic respiratory compensation
• Resp. acidosis comp. by HCO3- retention
• Resp. alkalosis comp. by HCO3- excretion
• Met. acidosis comp. by hyperventilation
• Met. Alkalosis comp. By hypoventilation

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Aids in Analysis of Acid/Base

• Metabolic elevator
• Respiratory seesaw
• Interpretation
• Even if pH normal, acid-base balance only normal
  if pCO2 and bicarbonate normal
• If pCO2 normal, no respiratory dysfunction if
  respiratory, seesaw
• If bicarb normal, no metabolic dysfunction if
  metabolic, elevator

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• Metabolic acidosis
• Renal failure
• Diabetes
• Respiratory alkalosis
• Anxiety
• Drugs-CNS stimulants

• Metabolic alkalosis
• Vomiting
• Steroids
• Sodium bicarbonate
• Respiratory acidosis
• pneumonia

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Other useful hints

• Hypokalemia - metabolic alkalosis
• Normal pH with abnormal pCO2 and bicarb - fully
  compensated disorder
• Hyperchloridemia - metabolic acidosis or met.
  comp. for respiratory alkalosis
• Increased Anion Gap suggests metabolic acidosis