Lecture 11: Acid-Base Balance (Bolsor) Flashcards Preview

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Flashcards in Lecture 11: Acid-Base Balance (Bolsor) Deck (35)
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0
Q

Which buffering system (intracellular or extracellular) is sensitive to regulation and can respond more rapidly to changes in acid/base balance?

A

extracellular

1
Q

What are the major buffering systems?

A

intracellular (primarily protein and phosphates) and extracellular (primarily CO2/HCO3 system)

2
Q

Can the intracellular buffer system remove excess acid or base from the body?

A

NO

3
Q

3 stage response to acid/base change:

A

1) chemical buffering (rapid)
2) respiratory system (rapid; +/- alveolar ventilation of CO2 in response to changes in extracellular pH)
3) kidneys (delayed response; responds to chronic acidemia/alkalemia by controlling excretion/production of HCO3)

4
Q

Why is the amount of free H2CO3 in the body not equal to the amount of H+ ions?

A

H2CO3 doesn’t completely dissociate in the blood

5
Q

Equation for acid/base balance. What drives this equation left or right?

A

CO2 + H2O H2CO3 HCO3 + H

  • Equation shifts to the right when HCO3 is lost (tries to replace HCO3 that was lost)
  • Equation shifts to the left when HCO3 gained (tries to get rid of excess HCO3)
6
Q

Respiratory acidemia and possible causes

A

failure of the lungs to excrete adequate amounts of CO2.

Causes: alveolar hypoventilation due to pulmonary disease or central respiratory depression

7
Q

How is respiratory acidemia compensated for?

A

Metabolic compensation: increased renal reabsorption of bicarbonate and excretion of acidic urine

8
Q

How can you gauge how much H+ is released into circulation?

A

How much HCO3 lvls decreased in order to buffer the H+. Greater decrease in HCO3 = more H+ present

9
Q

What does an “isobar” represent?

A

constant CO2 level while pH and HCO3 concentrations change

10
Q

If pCO2 is increased and pH remains the same, what must happen to HCO3?

A

Must increase

11
Q

If pCO2 is constant and pH decreases, what happens to HCO3?

A

decreases

12
Q

metabolic acidemia and possible causes

A

abnormal retention of fixed (i.e. non-CO2) acids.

Causes: diabetes, trauma, shock, diarrhea

13
Q

Most common type of acidosis

A

metabolic acidemia. It is also the most common acid/base imbalance seen in animals with kidney failure

14
Q

How is metabolic acidemia compensated for?

A
  • hyperventilation to eliminate CO2
  • increased reabsorption and synthesis of HCO3 by kidneys
  • excretion of an acidic urine
15
Q

What is anion gap, what is it used for, and how is it calculated?

A

Measures the excess of unmeasured anions over unmeasured cations and is an index of whether or not the metabolic acidemia is due to loss of HCO3 or addition of H (determines what TYPE of metabolic acidosis is occuring). Calculated by subtracting concentrations of total chloride + bicarbonate from concentration of anions (primarily Na and K)

16
Q

Inadequate O2 delivery to tissues triggers switch to what kind of metabolism?

A

anaerobic metabolism. Produces a by-product of lactic acid which stimulates hyperventilation

17
Q

Which two cations constitute the vast majority of extracellular cations?

A

Na and K (95% of extracellular cations)

18
Q

Which 2 anions constitute 85% of extracellular anions?

A

Cl and HCO3

19
Q

Metabolic acidemia with normal anion gap is usually assoc. with:

A
  • loss of bicarbonate with no increase in unmeasured anions
  • hyperchloremia (kidney absorbs more Cl in response to low HCO3)
  • often caused by chronic diarrhea
20
Q

Metabolic acidemia with elevated anion gap is assoc. with:

A
  • increase in non-HCO3 and non-Cl anions (i.e. lactic acid)

- increased H+

21
Q

Common cause of metabolic acidosis with elevated anion gap

A

shock due to increased lactic acid. Lactic acid effectively replaces the HCO3 in circulation

22
Q

respiratory alkalemia and possible causes

A

hyperventilation with excessive loss of CO2

Causes: CNS lesions, anemia

23
Q

How is respiratory alkalemia compensated for?

A

increased renal excretion of bicarbonate and thus an alkaline urine

24
Q

metabolic alkalosis and possible causes

A

Excessive loss of H ions or excessive intake or retention of base

Causes: vomiting (loss of HCl), hypokalemia (H moves into cells to exchange for K ions that move into the extracellular fluid to replace lost K)

25
Q

How is metabolic alkalosis compensated for?

A

hypoventilation (increased CO2 retention), increased renal excretion of HCO3 and alkaline urine

26
Q

How does acid/base status alter plasma K concentration?

A

During acidemia, H+ moves into cells to be buffered. However, K+ moves out of the cell to counterbalance this change and result = hyperkalemia

During alkalemia, H+ moves out of cell to compensate, and K+ moves into cell to counteract it. Result = hypokalemia

BOTTOM LINE: acidemia or alkalemia can also elicit disturbances in K balance

27
Q

If VOMITING (loss of HCl) is the cause of metabolic alkalosis, how is kidney’s ability to compensate for the alkalosis compromised?

A

Loss of HCl results in hypochloremia (low Cl), which inhibits kidney’s ability to properly excrete HCO3. In severe cases, aldosterone secretion responding to low extracellular volume results in even more K excretion and exacerbates the situation.

28
Q

Define 4 regions on HCO3 vs. pH Davenport diagrams

A
Upper left (low pH, high HCO3): respiratory acidosis
Bottom left (low pH, low HCO3): metabolic acidosis
Upper right (High pH, high HCO3): metabolic alkalosis
Bottom right (high pH, low HCO3): respiratory alkalosis
29
Q

what do you look at first when reading a blood gas measurement? Second? Third? What do these values tell you?

A

1st: pH (tells you if disturbance is acidosis or alkalosis)
2nd: PCO2 (tells you if disturbance is respiratory or metabolic in origin)

30
Q

Low pH indicates

A

acidosis

31
Q

High pH indicates

A

alkalosis

32
Q

High PCO2 with low pH indicates

A

pH disturbance (acidosis) has a respiratory component

33
Q

Low pH, high PCO2, and low HCO3 indicates:

A

Acidosis with ONLY a respiratory component (no metabolic component)

34
Q

Low pH, low PCO2, and low HCO3 indicates:

A

no respiratory component to pH disturbance

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