ACIDBASE DISORDERS

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ACID-BASE DISORDERS

• Slides by Sherri Clewell D.O.
• 9/1/05

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Plasma Activity

• Normal value H 40meq/L
• PH 7.4
• Linear relationship H to pH
• Plasma H f(production, excretion, buffer)
• pKaphysiologic pH

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Plasma Acid Hemostasis

• H influenced by
• Rate of endogenous production
• Rate of excretion
• Buffering capacity of body
• Buffers effective at physiologic pH
• Hemoglobin
• Phosphate
• Protiens
• bicarbonate

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Henderson-Hasselbach Equation

• Demonstrates interrelationship between
• Carbonic acid
• Bicarbonate
• pH
• pH pK log HCO3- /H2CO3

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Kassirer-Bleich equation

• H 24 x PCO2/ HCO3-
• Can be used to calculate any component of buffer
  system provided other 2 components are known
• (how bicarb is calcuated on a blood gas)

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Acid production and Excretion

• Lung PCO2 action is immediate
• Liver uses HCO3- to make urea
• Prevents accumulation of ammonia and traps H in
  distal tubule
• Kidney lose or make HCO3-
• Proximal tubule reclaims 85 filtered HCO3-
• Distal tubule reclaims 15, and excretes H

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Fundamental acid base disorders

• Acidemia pos net H in blood
• Alkalemia neg net H in blood
• Normal or high pH does not exclude acidosis
• Normal or low pH does not exclude alkalosis

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Fundamental acid base disorders

• Respiratory Disorder first affect pco2
• Metabolic disorder first affect HCO3-

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Anion Gap

• AG Na (HCO3 Cl-)
• Normal anion gap is 7 /- 4
• Is the unmeasured anion concentration

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Metabolic Acidosis

• Caused by an decrease in bicarb this is replaced
  by unmeasured anion (elevated anion gap) or by
  chloride (no anion gap)
• Loss by GI-vomiting, enterocutaneous fistula
• Loss by kidney- RTA, carbonic anhydrase inhibitor
  therapy

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Metabolic Acidosis

• Unopposed metabolic acidosis results in decreased
  serum bicarb and increased H
• H stimulates respiratory center to increase
  minute ventilation to lower H by reduction in
  PCO2

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Metabolic Acidosis

• The compensatory mechanism calculation
• PCO2 (1.5 x HCO3- 8) /- 2
• With normal respiratory compensation the PCO2
  fallby by 1 mm Hg for every 1 meq/L fall in HCO3-
• If calculation PCO2 differs from pts PCO2 then
  concominant respiratory disorder

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Anion gap metabolic acidosis

• M methanol
• U uremia
• D DKA
• P paraldahyde, propylene glycol
• I Isoniazide, Iron
• L lactic acidosis
• E ethylene glycol, ethanol
• S salicylates, starvation ketoacidosis

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Non anion gap metabolic acidosis

• Bicarb loss in GI, urine
• Hypoaldosteronism, renal tubular acidosis,
  urinary tract obstruction
• Sometimes referred to as hyperchloremic metabolic
  acidosis

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Metabolic Acidosis

• Treatment is aimed at treating the underlying
  cause, restoring normal tissue perfusion
• Must know if underlying respiratory disorder
  because must treat respiratory first

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Buffer Therapy

• Must use bicarb judiciously
• Can cause paradoxical CNS acidosis
• Give if
• Bicarb lt4
• pH lt7.2 with signs of shock or myocardial
  irritability
• Severe hyperchloremic acidemia

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Metabolic alkalosis

• Chloride sensitive
• Causes vomiting, diarrhea, diuretic, CHF
• Treatment normal saline
• Chloride insensitive
• Cause excessive mineralcorticoid, no chloride
  loss
• Treatment treat underlying cause

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Respiratory acidosis

• Inadequate ventilation
• Diagnosed when PCO2 is greater then expected
  value

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Acute Respiratory Acidosis

• /\ H 0.8 (/\ PCO2)
• If the H is higher or lower than suggested by
  change in PCO2 a mixed disorder is present

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Chronic Respiratory Acidosis

• /\H 0.3 (/\ PCO2)

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Respiratory Alkalosis

• Acute
• /\H 0.4 (/\PCO2)
• Chronic
• /\H 0.75(/\PCO2)

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Questions

• 1.Causes of anion gap acidosis include all of the
  following except
• A. salicylate poisoning
• B. isopropyl alcohol ingestion
• C. uremia
• D. seizures

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QUESTIONS

• 2. An elevation anion gap and an elevation of the
  osmolar gap may be seen in all of the following
  except
• A. uremia
• B. ethanol intoxication
• C. methanol poisoning
• Diabetic ketoacidosis

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Questions

• 3. The pulmonary excretion of CO2
• A. Raises the serum H concentration
• B. Raises the serum pH
• C. Decreases the renal excretion of bicarbonate
• D. Raises the serum concentration of bicarbonate

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Questions

• 4. Physiologic compensation for metabolic
  acidosis occurs through all of the following
  mechanisms except
• A. Persistent vomiting
• B. Pulmonary excretion of CO2
• C. Increased renal H excretion
• D. Increased renal bicarbonate losses

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ANSWERS

• 1. B
• 2. B
• 3. B
• 4. D