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24 Cards in this Set
- Front
- Back
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Condition in which both base excess and bicarbonate are less than normal.
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Metabolic Acidosis
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Condition in which both base excess and bicarbonate are both above normal.
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Metabolic Alkalosis
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Condition in which PaCO2 is above normal (hypoventilation).
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Respiratory Acidosis
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Condition in which PaCO2 is less than normal (hyperventilation).
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Respiratory Alkalosis
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What are the normal limits of blood pH?
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7.36 to 7.44
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What are the normal limits for PaCO2?
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34 to 46 mmHg
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What are the normal limits of bicarbonate?
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22 to 26 mEq/L
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What are the normal limits of base excess?
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+/- 2.5 mEq/L
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What are the normal limits for anion gap?
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10 +/- 3 mEq/L
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What are the normal limits for total CO2?
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22 to 32 mEq/L
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What equation defines the anion gap?
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Serum Na - (Serum Cl + Total CO2) = Anion Gap
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Describe what happens to create a normal anion gap (or hyperchloremic) metabolic acidosis.
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The body is losing bicarbonate, and in order to maintain electrical neutrality, the body retains chloride ions to compensate. The result is that the anion gap does not change.
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Describe what happens to create metabolic acidosis having an increased anion gap.
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Bicarbonate is being neutralized by acid, but electrical neutrality is maintained by the counter anion of the acid, so chloride stays the same. The sum of bicarbonate and chloride falls, therefore the anion gap increases.
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What are the three major causes of bicarbonate deficit (normal anion gap) metabolic acidosis?
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Diarrhea, Urinary Diversion Surgery, and Drugs (acetazolamide, topiramate, zonisamide, & lithium)
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What are the four causes of increased anion gap metabolic acidosis?
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1) Lactic Acidosis (exercise, shock, or ischemia), 2) Ketoacidosis (low insulin levels / lipolysis), 3) Severe renal failure (GFR < 10) (acids of metabolism), & 4) Toxins (e.g. salicylates, methanol, ethylene glycol)
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Describe the therapeutic approach for correcting a metabolic acidosis from bicarbonate deficiency.
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Replace the lost bicarbonate w/ non-chloride Na or K salts (either HCO3- or a "bicarbonate precursor," such as lactate, acetate, or citrate). Estimate the deficit as a number of mEq/L below zero BE or 24 mEq/L totCO2 and use a 0.5 L/kg volume of distribution to calculate the mEq needed.
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Describe the therapeutic approach to treating lactic acidosis.
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Shock is the most common cause, and in those cases, treatments for shock, such as fluids, that improve tissue perfusion will allow the lactic acid to be metabolized rather quickly to correct the imbalance.
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Describe the therapeutic approach to the treatment of metabolic acidosis caused by ketoacidosis.
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Insulin is given to suppress lipolysis, thereby preventing the formation of ketone bodies.
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Describe the therapeutic approach for treating metabolic acidosis caused by renal failure.
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Dialysis
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Describe the therapeutic approach to treating metabolic acidosis caused by toxins.
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Dialysis is used for severe intoxication. For methanol or ethylene glycol, inhibition of alcohol dehydrogenase with fomepizole can prevent the respective conversions to formic acid or glycolic, then oxalic, acid.
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Explain the hazard to intracellular pH associated with use of bicarbonate in treating metabolic acidosis due to elevated anion gap.
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Bicarbonate reacts with the acid excess to produce carbonic acid, which dissociates to produce carbon dioxide. Bicarbonate cannot cross the cell membrane readily, but carbon dioxide can. So the intracellular levels of carbon dioxide rise, actually decreasing the pH within the cell, making the acidosis worse intracellularly.
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What is the Mnemonic for causes of Metabolic Alkalosis?
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C (Chloride deficit; gastric losses) R (Renal perfusion reduced) A (Aldosterone increased or high dose steroid Rx) P (Potassium deficit)
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Describe the therapeutic approach to treating metabolic alkalosis.
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If renal function is okay, supplement w/ KCl, improve renal perfusion (i.e. fluids for dehydration), decrease gastric acid losses (Rx for N&V, H2RAs or PPIs), and decrease exogenous and endogenous mineralocorticoid activity (spironolactone; change steroid Rx). Acetazolamide can be given to decrease renal bicarbonate reabsorption. If the kidneys are not working, dialysis is used. And, in severe cases, ammonium chloride can be administered.
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Describe how ammonium chloride helps correct metabolic alkalosis and which patients SHOULD NOT receive it as a treatment for metabolic alkalosis.
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The liver converts the ammonia into urea, liberating HCl in the process. People who have liver failure should not receive ammonium chloride.
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