Term
| What are the characteristics of metabolic acidosis? |
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Definition
1) primary reduction in HCO3
2) low extracellular pH
3) compensatory hyperventilation (-1.2mmHgPaCO2/-1.0mEq/L HCO3 |
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Term
| How is metabolic acidosis buffered against and compensated for? |
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Definition
1) bicarbonate buffering (conversion into CO2)
2) respiratory compensation (inc alveolar vent - (dec pH on medulla))
3) bicarbonate reabsorption w/ acid excretion by kidney |
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Term
How long after the acid load do the following events require to take place:
distribution and extracellular buffering
cell buffering
respiratory compensation
renal H excretion |
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Definition
1) 6hrs
2) 12hrs
3) 24hrs
4) 72hrs |
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Term
| What ist he cause of proximal renal tubular acidosis (type 2 RTA)? distal renal tubular acidosis (type 1 RTA)? |
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Definition
1) failure of the reabsorption of bicarbonate w/ carbonic anhydrase in PCT
2) failure of the excretion of acid in the distal nephron |
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Term
| What are the major basic mechanisms for metabolic acidosis? |
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Definition
1) increased acid production
2) decreased acid excretion
3) loss of bicarbonate |
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Term
| What are the two types of metabolic acidosis w/ increased acid production? What is the effect on the unmeasured anions for each? |
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Definition
1) organic acid addition (lactic acid, ketoacids) - increased concentration of unmeasured anions
2) mineral acid (HCl) - unchanged unmeasured anion concentration |
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Term
| What is the common cause of decreased acid secretion? How does it result in acidosis? |
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Definition
1) kidney failure
2) Stage III: decreased ability to adjust to higher acid load; total ammonium excretion falls, HCO3 falls, UA no change, followed by progressive increase in UA
3) Stage V: HCO3 stabilizes; buffering by bone w/ Ca release |
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Term
| Describe how distal renal tubular acidosis causes metabolic acidosis |
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Definition
1) decreased net acid excretion from inability to lower urine pH below 5.5-6.0
2) reduced efficiency of titratable acid buffering due to high pH
3) impairment of apical H-ATPase pump |
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Term
| What are two major mechanisms for loss of bicarbonate leading to metabolic acidosis? |
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Definition
1) diarrhea
2) renal tubular acidosis type II |
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Term
| Describe how diarrhea leads to metabolic acidosis |
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Definition
1) loww of fluids w/ high concentration of HCO3
2) decreased ECF, w/ inc. Na and Cl reabsorption w/ reduced ability of kidney to compensate
3) HCO3 falls w/ inc. Cl |
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Term
| Describe how proximal renal tubular acidosis (type II) causes metabolic acidosis |
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Definition
1) impaired proximal bicarbonate reabsorption
2) bicarbonate loss occurs until a lower reabsorptive capacity is reached |
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Term
| What are the clinical manifestations of metabolic acidosis wrt to the: respiratory system |
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Definition
| 1) increased alveolar ventilation |
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Term
| What are the clinical manifestations of metabolic acidosis wrt to the: cardiovascular system |
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Definition
1) depressed myocardial contractility (at pH<7.2)
2) ventricular arrhythmia
3) decreased vascular resistance (impaired response to catecholamines) |
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Term
| What are the clinical manifestations of metabolic acidosis wrt to the: gastrointestinal system |
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Definition
- nausea
-vomiting
- abdominal pain
- diarrhea |
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Term
| What are the clinical manifestations of metabolic acidosis wrt to the: electrolyte/metabolic disturbances |
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Definition
1) Potassium: leaves cell to maintain electropneutrality
2) Calcium: displaces from albumin and increases ionized calcium; loss from bone |
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Term
| What are the two categories of metabolic acidosis? Why is it important to differentiate? |
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Definition
1) high vs. normal aanion gap
2) different causes and require different treatment strategies |
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Term
| What are the major unmeasured cations? Unmeasured anions? |
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Definition
1) Ca, K, Mg
2) HPO4, SO4, albumin, organic acids |
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Term
| What is the equation for the anion gap? What is a normal value? What contributes the largest amount to the UA? |
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Definition
1) [UA] - [UC] = [Na] - ([Cl] + [HCO3])
2) 8-12mEq/L
3) albumin: -2.5mEq/L of AG per -1.0 gm/dL albumin |
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Term
| What is the effect of organic metabolic acidosis on the Anion gap? mineral metabolic acidosis? |
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Definition
1) extracellular bicarbonate is replaced by unmeasured anion from organic acid, leading to an elevation in AG
2) mEq-for-mEq replacement of extracellular bicarbonate by Cl, w/ unchanged AG |
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Term
| What is the effect of chronic kidney disease (CKD) on the anion gap with mid-CDK (stage III)? late CKD (stage IV, V)? |
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Definition
1) normal AG metabolic acidosis
2) high metabolic acidosis |
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Term
| What are major clinical syndromes associated with bicarbonate loss induced metabolic acidosis |
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Definition
1) GI losses: biarrhea, pancreatic drainage, biliary drainage
2) kidney losses: CA inhibition; RTA-II
3) dilutional acidosis |
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Term
| What are the clinical syndromes associated with increased acid load induced metabolic acidosis? |
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Definition
1) organic load: lactic acid, diabetic ketoacidosis, ethylene glycol intoxication, methanol intoxication, salicylate intoxication
2) mineral acid: HCl administration, NH4Cl administration, cationic amino acid administration |
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Term
| What are the clinical syndromes associated with impaired acid excretion induced metabolic acidosis |
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Definition
1) kidney failure
2) RTA-I
3) adrenal insufficiency |
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Term
| Describe metabolic acidosis from increased acid load of lactic acid |
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Definition
1) hydrogen ion to bicarbonate: decreased bicarbonate level and increased anion gap seen in lactic acidosis
2) metabolized back to bicarbonate, CO2, and H2O once O2 delivery returns
3) 4 major mechanisms for lactate accumulation
4) caused by shock
5) Tx: underlying d/o; bicarb only w/ arterial pH<7.15
6) marked mixed venous acidemia |
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Term
| What are the 4 major mechanisms underlying the accumulation of lactate? |
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Definition
1) enhanced pyruvate production
2) reduced pyruvate conversion to carbon dioxide
3) altered redox state in which pyruvate is preferentially converted to lactate (suboptimal tissue O2 delivery
4) decreased lactate utilization |
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Term
| What is the underlying cause of most cases of lactic acidosis? |
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Definition
| 1) shock (cardiac arrest/sepsis) |
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Term
| What are the problems with bicarbonat etherapy for lactic acidosis? |
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Definition
1) transient elevation in plasma bicarbonate
2) possible worsening of intracellular acidosis
3) reversal of cause, will allow lactate to convert to bicarb, resulting in huge increase in plasma bicarb |
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Term
| Describe diabetic ketoacidosis as a cause of metabolic acidosis |
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Definition
- hepatic synthesis of ketoacids due to inc. delivery of FFA's and high glucagon to alter metabolism
- potassium wasting by potassium shift
- morbidity due to: hyperosmolality, ECF depletion, electrolyte imbalance, impaired kidney fxn due to dec GFR
- TX: insulin, volume replacement, potassium repletion, bicarb IFF art pH<7.2 or plasma HCO3 < 10mEq/L |
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Term
| Given metabolic acidosis w/ PaCO2 drop of <1.2mmHg/1mEq/L HCO3 dec, what is the cause? What about w/ PaCO2 drop of >1.2mmHg/1mEq/L HCO3 dec |
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Definition
1) mixed acid-base d/o w/ an accompanying respiratory acidosis
2) mixed acid-base d/o w/ an accompanying respiratory alkalosis |
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