ACIDBASEDISORDERS.ppt
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Transcript of ACIDBASEDISORDERS.ppt
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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)• pKa~physiologic 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 <4– pH <7.2 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