ChemPath: Acid-Base Handling ✔️

Question 1

What is the normal range for H+ concentration?

Answer 1

35-45 mmol/L in ECF

Question 2

What equation links H+ concentration to pH?

Answer 2

pH = log1/[H+] OR pH = -log[H+]

Question 3

What are the three main physiological buffers?

Answer 3

• Bicarbonate (H+ + HCO3- –> H2CO3) in kidneys
• Haemoglobin (H+ + Hb –> HHb) in RBCs
• Phosphate (H+ + HPO4- –> H2PO4)

NOTE: also protein and bone

Question 4

What is the rate of production of H+ ions per day?

Answer 4

50 - 100 mmol/day

Question 5

How is bicarbonate regenerated?

Answer 5

Bicarbonate used up as it buffers H+ forming CO2+H2O
As bicarb must be regenerated, it then forms carbonic acid (H2CO3)
From the carbonic acid, H+ is excreted in the kidneys
Bicarbonate is reabsorbed in proximal convoluted tubule (AKA leads to regeneration of bicarbonate)

Question 6

Describe how H+ ions pass through the renal epithelial membrane.

Answer 6

H+ ions cannot pass through the membrane itself so a transport system is necessary (Na+/H+ exchange)

Question 7

What is the rate of production of carbon dioxide per day?

Answer 7

20,000-25,000 mmol/day

Question 8

The 4 types of acid-base abnormalities:

Answer 8

1. Metabolic acidosis
2. Respiratory acidosis
3. Metabolic alkalosis
4. Respiratory alkalosis

Question 9

1. What is the primary abnormality in metabolic acidosis? List three causes with examples.

Answer 9

Primary abnormality = increased H+ (with decreased bicarbonate)

Caused by:

• Increased H+ production (e.g. DKA, lactic acidosis)
• Decreased H+ excretion (e.g. renal tubular acidosis)
• Bicarbonate loss (e.g. intestinal fistula)

Question 10

1.1. How is metabolic acidosis compensated?

Answer 10

Stimulates respiratory centre –> decreased PCO2
H+ returns towards normal

Question 11

Click to look at arterial [H+] against arterial pCO2 (kPa) plotted on a graph:

Answer 11

Question 12

2. What is the primary abnormality in respiratory acidosis? List three causes with examples.

Answer 12

Primary abnormality = increased CO2 (therefore, increased H+) and a slight increase in bicarbonate

Caused by:

• Decreased ventilation
• Poor lung perfusion
• Impaired gas exchange

NOTE: metabolic compensation is slower than respiratory compensation

Question 13

2.1. How is respiratory acidosis compensated?

Answer 13

Over few days, increased renal excretion of H+ and generation of bicarbonate
H+ returns to normal but pCO2 and bicarbonate remain elevated

Question 14

3. What is the primary abnormality in metabolic alkalosis? List three causes.

Answer 14

Primary abnormality = decreased H+ (with increased bicarbonate)

Caused by:

• H+ loss (e.g. pyloric stenosis)
• Hypokalaemia (e.g. diuretics)
• Ingestion of bicarbonate

Question 15

3.1. How is metabolic alkalosis compensated?

Answer 15

Inhibit respiratory centre to increase pCO2 = increase [H+]

Question 16

4. What is the primary abnormality in respiratory alkalosis? List three causes.

Answer 16

Primary abnormality = reduced CO2 via lungs

Can be caused by hyperventilation due to:

• Voluntary (e.g. anxiety hyperventilation)
• Artificial ventilation
• Stimulation of the respiratory centre

Question 17

4.1. What is the metabolic compensation for prolonged respiratory alkalosis?

Answer 17

If prolonged, this can lead to reduced renal H+ excretion and reduced bicarbonate generation
H+ returns to normal but PCO2 and bicarb remain low

Question 18

Describe the respiratory control over carbon dioxide.

Answer 18

• Respiratory is controlled by chemoreceptors in the hypothalamic respiratory centre
• An increase in CO2 will stimulate an increase in ventilation which then brings down CO2 concentration

Question 19

What information is provided by ABGs?

Answer 19

• pO2
• pCO2
• pH

Question 20

Steps to read ABG to assess acid-base status?

Answer 20

1. H+/pH –> to determine whether acidosis or alkalosis
2. pCO2 –> determine respiratory disturbance (primary or secondary)
3. Bicarbonate –> determine compensatory mechanisms etc.

Question 21

What derangement of acid-base balance would be caused by pyloric stenosis?

Answer 21

Metabolic alkalosis due to loss of H+ from profuse vomiting

Question 22

Which condition classically causes a mixed respiratory alkalosis and metabolic acidosis?

Answer 22

• Aspirin overdose
• Aspirin stimulates ventilation and reduces renal excretion of H+