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76 Cards in this Set
- Front
- Back
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What is volatile acid?
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carbonic acid produced by oxidative metabolism of carbs, protiens, and fats
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Upon what does volatilic acid production depend?
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caloric utilization and substrate mix
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How is volatilic acid excreted?
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through the lungs as CO2
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What is fixed acid?
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hydrogen ions produced through metabolic processes
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How do you create fixed acids?
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oxidation of sulfhydryl groups of cystine and methionine to form H2SO4
hydrolysis of phosophoproteins, phospholipids, nucleic acids to form H3PO4 incomplete metabolism of carbohydrates, fats, proteins |
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How much fixed acid do you produce?
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1 mmol/kg/day
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What are the extracellular buffers?
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bicarbonate and ammonia
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What are the intracellular buffers?
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proteins and phosphate
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What is the most important buffering system?
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bicarbonate
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How do you compensate for imbalances that cannot be corrected by the buffering system?
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changing the rate of ventilation, which alters the carbon dioxide concentration in the blood and alters the pH
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How does the body compensate if the pH drops too low?
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increases breathing, expels CO2, fewer free hydrogen ions
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What do teh kidneys do in response to acidosis?
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tubular cells absorb more bicarbonate fromt eh fluid, collecting duct cells secrete more hydrogen, generate more bicarbonate, ammoniagenesis and increased formation of NH3 buffer
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What does the kidney do for alkalosis?
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excretes more bicarbonate by decreasing hydrogen ion secretion, lowering rates of glutamine metabolism and ammonia excretion
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At what pH is the body acidemic?
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blood gas < 7.36
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At what pH is the body alkalemic?
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blood gas > 7.44
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What causes a metabolic disturbance?
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change in serum bicarbonate concentration
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What causes a respiratory disturbance?
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change in PCO2
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What is compensation?
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physiologic metabolic and respiratory change to return pH toward normal, does not return pH completely to normal
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How long does it take for buffering to happen?
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minutes to 6 hours
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How long does it take for respiratory compensation to happen?
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minutes to 12 hours
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How long does it take for metabolic compensation to happen?
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24-72 hours
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What is normal pH?
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7.35-7.45
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What is normal pCO2?
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35-45
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What is normal bicarbonate?
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22-26
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What characterizes a metabolic acidosis?
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low arterial pH, reduced plasma HCO3, compensatory alveolar hyperventilation, decreased PCO2
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What causes a metabolic acidosis?
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depletion of body bicarbonate buffers
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What is a hyperchloremic metabolic acidosis?
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serum bicarbonate concentration is reduced, chloride concentration increases, no net change in anion gap
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How do you calculate an anion gap metabolic acidosis?
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AG = [Na] - ([Cl] + [HCO3])
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What is the anion gap?
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unmeasured cations, unmeasured anions
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What is the normal anion gap?
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12 +/- 2
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What is a significantly elevated anion gap?
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> 20
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What happens if you have a significantly elevated anion gap?
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metabolic acidosis, regardless of pH or bicarb concentration
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What are the causes of a nonanion gap acidosis?
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GI bicarbonate loss, renal bicarbonate loss, hydrochloric acid administration
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What are the causes of GI bicarbonate loss?
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diarrhea, ureteral diversions
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What are the causes of renal bicarbonate loss?
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renal tubular acidosis, early renal failure, carbonic anhydrase inhibitors, aldosterone inhibitors
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What are the causes of anion gap acidosis?
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ketoacidosis, toxins, uremia, lactic acidosis
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What are the causes of ketoacidosis?
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diabetic, alcoholic
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What are the toxins that cause anion gap acidosis?
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methanol, ethylene glycol, paraldehyde, salicylates
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What do you use to assess hyperchloremic metabolic acidosis?
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urine anion gap
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How do you calculate urine anion gap?
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difference in measured cations in the urine (Na and K) and urine Cl
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What does the kidney do in non-renal causes of hyperchloremic acidosis?
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compensates by increasing net acid excretion, increase in urinary ammonium excretion
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How do you measure urinary ammonium excretion?
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UAG
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How do you interpret UAG?
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negative when ammonium is present and balanced by negatively charged urinary chloride, if little ammonium present, UAG will be zero or positive
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What causes a low urine chloride level?
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GI hydrogen loss, past diuretic use, posthypercapnia
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What causes high or normal urine chloride?
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excess alkali administration, current/recent diuretic use, excess mineralocorticoid activity
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What causes GI hydrogen loss?
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vomiting, NG suction, chloride diarrhea
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What causes excess mineralocorticoids?
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Cushings/Conn's, Bartter's syndrome, exogenous steroids, licorice
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What is the most common cause of metabolic alkalosis?
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reduction in ECV, leads to reduction in GFR, increase in Na and HCO3 reabsorption
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What is the other factor that maintains metabolic alkalosis?
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hypokalemia
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What is the respiratory compensation for metabolic alkalosis?
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hypoventilation, not as predictable as hyperventilatory response to metabolic alkalosis
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What is saline responsive metabolic alkalosis?
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metabolic alkalosis that is associated with a reduction in volume, responds to normal saline
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What is saline unresponsive metabolic alkalosis?
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mineralocorticoid or hypokalemia induced alkalosis that does not respond to volume
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How do you treat patients with metabolic alkalosis due to excessive mineralocorticoid production?
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inhibition of mineralocorticoid action by aldosterone antagonist, can also do surgical or chemical ablation of adrenals
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What is respiratory acidosis?
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arterial pH < 7.35, elevated PCO2, compensatory increase in plasma HCO3 concentration
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How does the lung handle increased PCO2 due to increased CO2 production?
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increased alveolar ventilation, increases in PCO2 are always due to hypoventilation, not due to increased CO2 production
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What are the causes of respiratory acidosis?
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CNS depression, neuromuscular disorders, acute airway obstruction, severe pneumonia/pulmonary edema, impaired lung motion, thoracic cage injury, ventilator dysfunction
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How do the kidneys compensate for respiratory acidosis?
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too slow for acute acidosis, in chronic, kindeys increase serum bicarbonate concentration and renal acid excretion
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How much does the bicarbonate level rise in chronic respiratory acidosis?
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3.5 - 5.0 for each 10 torr increase in PCO2, rarely greater than 35-40
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How long does it take for the kidneys to compensate for respiratory acidosis?
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48 hours
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What is the stimulus for ventilation with chronic hypercapnia?
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hypoxia
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What are the symptoms of acute hypercapnia?
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headache, confusion, lethargy, obtundation
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How do you treat respiratory acidosis?
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treat the underlying problem
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What is respiratory alkalosis?
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arterial pH > 7.45, hyperventilation resulting in low PCO2, compensatory increase in plasma HCO3 concentration
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What are the causes of respiratory alkalosis?
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anxiety, hypoxia, lung disease with/without hypoxia, CNS disease, drug use, pregnancy, sepsis, hepatic encephalopathy, mechanical ventilation
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What drugs can cause respiratory alkalosis?
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salicylates, progesterone, catecholamines
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How do the kidneys compensate for respiratory alkalosis?
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renal bicarbonate excretion is increased and serum bicarbonate falls by 5 mmol/L for each 10 torr fall in PCO2
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What are the symptoms of respiratory alkalosis?
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lightheadedness, paresthesias, cramps, carpopedal spasm, seizures
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What is the primary process of a metabolic acidosis?
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decreased HCO3
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How do you compensate for a metabolic acidosis?
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decreased PCO3, winter's formula
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What is the primary process of a metabolic alkalosis?
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increased HCO3
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What is the primary process of a respiratory acidosis?
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increased PCO2
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How do you compensate for a respiratory acidosis?
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increased HCO3 by 5 for 10 increase in PCO2
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What is the primary process in a respiratory alkalosis?
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decreased PCO2
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What is the compensation for a respiratory alkalosis?
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decreased HCO3 by 5 for 10 decrease in PCO2
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How do you determine what is wrong?
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calculate anion gap, determine compensation, calculate excess anion gap (minus 12) and add to bicarbonate
if less than normal bicarbonate, nonanion gap metabolic acidosis, if greater than normal, underlying metabolic alkalosis |
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What is Winter's formula?
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1.5 (HCO3) + 8 +/-2
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