Lecture 11: Acid-Base Balance (Bolsor)

Question 0

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

Answer 0

extracellular

Question 1

What are the major buffering systems?

Answer 1

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

Question 2

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

Answer 2

NO

Question 3

3 stage response to acid/base change:

Answer 3

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)

Question 4

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

Answer 4

H2CO3 doesn’t completely dissociate in the blood

Question 5

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

Answer 5

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)

Question 6

Respiratory acidemia and possible causes

Answer 6

failure of the lungs to excrete adequate amounts of CO2.

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

Question 7

How is respiratory acidemia compensated for?

Answer 7

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

Question 8

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

Answer 8

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

Question 9

What does an “isobar” represent?

Answer 9

constant CO2 level while pH and HCO3 concentrations change

Question 10

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

Answer 10

Must increase

Question 11

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

Answer 11

decreases

Question 12

metabolic acidemia and possible causes

Answer 12

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

Causes: diabetes, trauma, shock, diarrhea

Question 13

Most common type of acidosis

Answer 13

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

Question 14

How is metabolic acidemia compensated for?

Answer 14

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

Question 15

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

Answer 15

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)

Question 16

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

Answer 16

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

Question 17

Which two cations constitute the vast majority of extracellular cations?

Answer 17

Na and K (95% of extracellular cations)

Question 18

Which 2 anions constitute 85% of extracellular anions?

Answer 18

Cl and HCO3

Question 19

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

Answer 19

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

Question 20

Metabolic acidemia with elevated anion gap is assoc. with:

Answer 20

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

- increased H+

Question 21

Common cause of metabolic acidosis with elevated anion gap

Answer 21

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

Question 22

respiratory alkalemia and possible causes

Answer 22

hyperventilation with excessive loss of CO2

Causes: CNS lesions, anemia

Question 23

How is respiratory alkalemia compensated for?

Answer 23

increased renal excretion of bicarbonate and thus an alkaline urine

Question 24

metabolic alkalosis and possible causes

Answer 24

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)

Question 25

How is metabolic alkalosis compensated for?

Answer 25

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

Question 26

How does acid/base status alter plasma K concentration?

Answer 26

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

Question 27

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

Answer 27

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.

Question 28

Define 4 regions on HCO3 vs. pH Davenport diagrams

Answer 28

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

Question 29

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

Answer 29

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

Question 30

Low pH indicates

Answer 30

acidosis

Question 31

High pH indicates

Answer 31

alkalosis

Question 32

High PCO2 with low pH indicates

Answer 32

pH disturbance (acidosis) has a respiratory component

Question 33

Low pH, high PCO2, and low HCO3 indicates:

Answer 33

Acidosis with ONLY a respiratory component (no metabolic component)

Question 34

Low pH, low PCO2, and low HCO3 indicates:

Answer 34

no respiratory component to pH disturbance