Acid-Base Balance II

Question 1

When would a person be considered to be of normal acid-base balance?

Answer 1

Plasma pH close to 7.4 (range 7.35-7.45)
[HCO3-]p close to 25 mmol/l (range 23-27)
Arterial PCO2 close to 40mmHg (range 35-45)

Question 2

What is compensation?

Answer 2

Restoration of pH irrespective of what happens to [HCO3-]p and PCO2

Question 3

What is correction?

Answer 3

Restoration of pH, [HCO3-]p and PCO2 to normal

Question 4

What is the first priority if normal acid-base balance is disturbed?

Answer 4

To restore pH

Question 5

What acid-base disturbances cause plasma pH to fall?

Answer 5

Respiratory acidosis and metabolic acidosis

Question 6

What acid-base disturbances cause plasma pH to rise?

Answer 6

Respiratory alkalosis and metabolic alkalosis

Question 7

What occurs in immediate buffering of pH change?

Answer 7

Immediate dilution of the acid or the base in ECF

Question 8

What carries out the immediate buffering of pH change?

Answer 8

Blood buffers or buffers in the ECF

Question 9

What is the issue with immediate buffering of pH change?

Answer 9

Response is very quick but the buffer stores are quickly depleted = kidney must rectify stores

Question 10

How is blood-gas analysis carried out?

Answer 10

A blood gas analyser can measure pH and PCO2

[HCO3-]p can then be calculated

Question 11

What is used to plot the results of blood-gas analysis?

Answer 11

A Davenport diagram

Question 12

What is respiratory acidosis?

Answer 12

Retention of CO2 by the body

Question 13

What are some causes of respiratory acidosis?

Answer 13

Chronic bronchitis, chronic emphysema, airway restriction, chest injuries, respiratory depression

Question 14

What does CO2 retention due to respiratory acidosis do to the equilibrium?

Answer 14

Drives it to the right = both [H+]p and [HCO3-] rise

Increased [H+] results in acidosis

Question 15

What is uncompensated respiratory acidosis?

Answer 15

pH < 7.35 AND PCO2 > 45 mmHg

Question 16

How are respiratory disorders compensated for?

Answer 16

Virtually no extracellular buffering in respiratory disorders so renal system must compensate

Question 17

What drives H+ secretion by the kidney?

Answer 17

PCO2 = CO2 retention stimulates H+ secretion into the filtrate

Question 18

How does the renal compensate in respiratory acidosis?

Answer 18

H+ secretion stimulated
All filtered HCO3- reabsorbed
H+ continues to be secreted and generates titratable acid and NH4+
Acid secreted and new HCO3- is added to blood

Question 19

What causes [HCO3-] to rise in respiratory acidosis?

Answer 19

Both the disorder and the renal compensation

Question 20

What does correction of respiratory acidosis and alkalosis require?

Answer 20

Restoration of normal ventilation

Question 21

What is respiratory alkalosis?

Answer 21

Excessive removal of CO2 by the body

Question 22

What are some causes of respiratory alkalosis?

Answer 22

Low inspired PO2 at altitude, hyperventilation, hysterical overbreathing

Question 23

What does respiratory alkalosis do to the equilibrium?

Answer 23

Drives it to the left = [H+]p and [HCO3-]p fall

Decreased [H+]p results in alkalosis

Question 24

What is uncompensated respiratory alkalosis?

Answer 24

pH > 7.45 AND PCO2 < 35 mmHg

Question 25

What effect does respiratory alkalosis have on the kidney?

Answer 25

Excessive removal of CO2 reduces H+ secretion into the tubule

Question 26

Why does respiratory alkalosis cause alkaline urine?

Answer 26

H+ secretion insufficient to reabsorb filtered HCO3- = HCO3- excreted in urine

Question 27

How does the renal system compensate for respiratory alkalosis?

Answer 27

HCO3- excreted in urine | No titratable acid or NH4+ produced so there is no new HCO3- generated

Question 28

What is metabolic acidosis?

Answer 28

Excess H+ from any source other than CO2

Question 29

What are some cause of metabolic acidosis?

Answer 29

Ingestion of acid/acid producing foods Excessive metabolic production of H+ (e.g DKA) Excessive loss of base (e.g diarrhoea)

Question 30

What cause [HCO3-] depletion in metabolic acidosis?

Answer 30

Buffering excess H+ or loss of HCO3- from the body

Question 31

What is uncompensated metabolic acidosis?

Answer 31

pH < 7.35, [HCO3-]p is low

Question 32

What stimulates the respiratory system in metabolic acidosis and alkalosis?

Answer 32

Peripheral chemoreceptors = decrease/increase in plasma pH respectively

Question 33

How does the respiratory system compensate for metabolic acidosis?

Answer 33

Ventilation is quickly increased and more CO2 is blown off, [H+]p is lowered raising the pH towards normal, [HCO3-]p is also lowered

Question 34

Why is respiratory compensation essential in correcting metabolic acidosis?

Answer 34

Acid load cannot be excreted immediately

Question 35

When does ventilation return to normal in metabolic acidosis?

Answer 35

Once acid load is excreted (acidic urine) and [HCO3-]p is restored

Question 36

How is metabolic acidosis corrected?

Answer 36

Filtered HCO3- is very low and very readily reabsorbed H+ secretion continues and produces titratable acid and NH4+ to generate more new HCO3- Acid excreted in urine

Question 37

What is metabolic alkalosis?

Answer 37

Excessive loss of H+ from body = less common than metabolic acidosis

Question 38

What are some causes of metabolic alkalosis?

Answer 38

Loss of HCl from stomach (e.g vomiting), ingestion of alkali/alkali-producing foods, hypersecretion of aldosterone

Question 39

What causes the rise in [HCO3-]p in metabolic alkalosis?

Answer 39

H+ loss or addition of base

Question 40

What is uncompensated metabolic alkalosis?

Answer 40

pH > 7.4, [HCO3-]p is high

Question 41

How does the respiratory system compensate for metabolic alkalosis?

Answer 41

Increased pH slows ventilation = CO2 retained, PCO2 rises | [H+]p rises which lowers pH and [HCO3-] rises further

Question 42

Why can't all of the filtered HCO3- be reabsorbed in metabolic alkalosis?

Answer 42

Filtered HCO3- load is so large compared to normal that there is too much to completely reabsorb

Question 43

How is metabolic alkalosis corrected?

Answer 43

No titratable acid or NH4+ generated so no new HCO3- produced, HCO3- is excreted in urine (alkaline urine), [HCO3-]p falls back towards normal