Acid base balance 2

Question 1

What is the normal range for plasma pH?

Answer 1

7.35-7.45

Question 2

What is the normal range for plasma bicarbonate?

Answer 2

23-27

Question 3

What is the normal range for arterial partial pressure of carbon dioxide

Answer 3

35-45

Question 4

What is the difference between compensation and correction?

Answer 4

Compensation - aims to get the body pH back within a normal range at the expense of bicarbonate and carbon dioxide levels
Correction - aims to get the body pH back within a normal range and simultaneously have normal buffer levels

Question 5

What happens immediately after a pH change? How quick is this response?

Answer 5

Buffering (dilution of acid or base) by blood (Hb, bicarbonate) or ECF (largely bicarbonate) buffers. Very quick

Question 6

To get a patients pH status what should be performed?

Answer 6

Blood gas analysis

Question 7

What is respiratory acidosis? Give examples

Answer 7

Carbon dioxide retention of respiratory origin

Anaesthesia (respiratory depression)
COPD
Airway restriction (asthma, tumour, etc)
Chest injuries

Question 8

How do respiratory disorders cause acidosis?

Answer 8

Carbon dioxide retention drives the buffer equation to the right causing a rise in hydrogen ions and bicarbonate. The hydrogen ion rise has more effect

Question 9

When would you diagnose uncompensated respiratory acidosis?

Answer 9

pH 45

Clinical picture fits

Question 10

How is respiratory acidosis compensated for?

Answer 10

No extracellular buffering as respiratory system is the cause so purely renal compensation.
Increased partial pressure of carbon dioxide drives hydrogen secretion within the kidney which causes reabsorption of filtered bicarbonate and secretion of acids hence “new” bicarbonate addition to the blood

Question 11

What does renal compensation for respiratory acidosis cause (biochemically speaking)?

Answer 11

Rise in blood bicarbonate. Rise in blood pH

Question 12

How does correction of respiratory acidosis occur?

Answer 12

The partial pressure of carbon dioxide must be lowered restoration of normal respiratory function

Question 13

What is respiratory alkalosis? Give some examples

Answer 13

Excess removal of carbon dioxide from the body by the respiratory system.

Hysterical overbreathing
Hyperventilation as a result of hypoxia at altitude (i.e altitude sickness)
Hyperventilation (fever, brainstem injury, etc)

Question 14

How do respiratory disorders cause alkalosis?

Answer 14

Excess removal of carbon dioxide drives the equilibrium of the buffer reaction to the left. Hydrogen and bicarbonate fall but it is the decreased hydrogen which causes the alkalosis

Question 15

When would you diagnose uncompensated respiratory alkalosis?

Answer 15

pH > 7.45

pCO2

Question 16

How is respiratory alkalosis compensated for by the kidney?

Answer 16

Fall in partial pressure of carbon dioxide decreases hydrogen secretion by the tubules meaning it cannot reabsorb all the bicarbonate and this thus increases excretion of bicarbonate (alkaline urine). No titratable acid is formed either.

Question 17

What does renal compensation of respiratory alkalosis cause (biochemically speaking)?

Answer 17

Fall in bicarbonate thus decrease in pH

Question 18

What is metabolic acidosis? Give examples

Answer 18

Excess hydrogen ions arising from sources other than carbon dioxide

• Ingestion of acid
• Excessive metabolic production (DKA, lactic acid from exercise)
• Excessive loss of base (diarrhoea)

Question 19

How would you diagnose uncompensated metabolic acidosis (biochemically speaking)? Why does this occur?

Answer 19

pH

Question 20

How is metabolic acidosis compensated for?

Answer 20

Respiratory compensation occurs when peripheral chemoreceptor sense the fall in pH and stimulate an increase in respiration. Increased respiration causes removal of carbon dioxide and thus the equilibrium of the buffer system shifts to the left. Hydrogen and bicarbonate levels both fall

Question 21

How is metabolic acidosis corrected?

Answer 21

Filtered bicarbonate is low and readily reabsorbed by the kidneys. Hydrogen ions being secreted form titratable acids which get excreted in the urine (acidic urine). These two mechanisms allow bicarbonate to return to normal

Question 22

What occurs after metabolic acidosis has been corrected?

Answer 22

Ventilation returns to normal

Question 23

How important is respiratory compensation in metabolic acidosis?

Answer 23

Very important as renal correction is delayed!

Question 24

Which is more common metabolic acidosis or metabolic alkalosis?

Answer 24

Metabolic acidosis

Question 25

What is metabolic alkalosis? Give examples

Answer 25

Excess loss of hydrogen from the body.

• Excessive vomiting (loss of HCL from stomach)
• Ingestion of alkali
• Aldosterone hyper secretion

Question 26

How does aldosterone hyper secretion cause metabolic alkalosis?

Answer 26

Increased activity of the hydrogen sodium exchanger at the apical membranes of tubular cells causes increased excretion of acid

Question 27

How would you diagnose metabolic alkalosis (biochemically speaking)? Why does this occur?

Answer 27

pH > 7.45
H2CO3 > 27
Clinical picture fits

Decreased hydrogen or addition of base causes bicarbonate rise

Question 28

How is metabolic alkalosis compensated for?

Answer 28

Rise in pH is detected by peripheral chemoreceptors and ventilation slows. This causes carbon dioxide retention (increase in partial pressure) and shifts equilibrium of the buffer equation to the right. Hydrogen and bicarbonate both rise

Question 29

How is metabolic alkalosis corrected?

Answer 29

Bicarbonate is so high that it cannot all be filtered and is mostly excrete in the urine (alkaline urine). No titratable acid is generated