Pathophysiology of Acid Base

Question 1

What is the biggest acid production mechanism?

Answer 1

Carbonic acid produced in cell respiration which is excreted by the lungs

Question 2

Where are the non-volatile acids excreted?

Answer 2

Kidneys

Question 3

What are the two chemicals which cause acidosis?

Answer 3

Increase in pCO2 (respiratory acidosis) or decrease in HCO3- (metabolic acidosis)

Question 4

How are respiratory acidosis and alkalosis compensated for?

Answer 4

Kidneys will either increase H+ excretion and retain HCO3- or increased loss of HCO3- (if alkalosis)

Question 5

What ion concentrations would you expect in metabolic acidosis and alkalosis?

Answer 5

• Low PH and low PaCO2 (due to respiratory compensation) for acidosis
• High PH and high PaCO2 fro alkalosis

Question 6

What ion concentrations would you expect in Respiratory acidosis and alkalosis?

Answer 6

• Low PH and high HCO3- (due to compensation) for acidosis

- High PH and low HCO3- for alkalosis

Question 7

What is the difference between chronic and acute respiratory alkalosis and acidosis?

Answer 7

chronic has greater change in the HCO3- for acidosis greater increase for alkalosis greater decrease

Question 8

What acid-base problem can result from asthma?

Answer 8

• Acute respiratory alkalosis
• due to mismate of ventilation/perfusion causing hypoxia and hypocapnia
• if asthma deteriorates can get hypoventilation which will result in respiratory acidosis which may need to be treated with assisted ventilation

Question 9

What acid-base problem can result from Hyperventilation usually due to anxiety?

Answer 9

• acute respiratory alkalosis
• hypercapnia
• with persistent hyperventilation can become chronic (treatment is calm patient and reassure them)

Question 10

What acid-base problem can result from COPD?

Answer 10

• chronic respiratory acidosis caused by hypoxia and hypercapnia
• if COPD exacerbated may need controlled O2 therapy (can give too high flow) and ventilation

Question 11

What acid-base problem can result from CKD?

Answer 11

• Metabolic acidosis
• Failure to excrete non-carbonic acids and failure to reabsorb bicarbonate
• failure to excrete potassium so cells retain potassium which causes displacement of H+ from cells
• Treat CKD but also can give bicarbonate to treat

Question 12

What acid-base problem can result from renal tubular acidosis and what are the types?

Answer 12

• Metabolic acidosis
  1) failure to secrete H+ (distal tubular defect)
  2) Failure to reabsorb bicarbonate (proximal tubular defect)
• Both treated with bicarbonate
• Can get hypokalaemia in both

Question 13

What acid-base problem can result from diarrhoea?

Answer 13

• metabolic acidosis
• loss of fluid, bicarbonate and potassium
• so get acidosis and hypokalaemia
• Treat by giving fluids and electrolytes

Question 14

What acid-base problem can result from Vomiting?

Answer 14

• Metabolic alkalosis
• loss of gastric acid
• get hypokalaemia increasing alkalosis
• also get hyperaldosteronism as compensation of low blood volume
• Hyperaldosteronism causes further metabolic alkalosis as kidneys will secrete more hydrogen ions
• aldosterone can also prevent kidney from excreting bicarbonate

Question 15

What acid-base problem can result from changes in aldosterone?

Answer 15

• Increased aldosterone = alkalosis

- Decreased aldosterone = acidosis

Question 16

What acid-base problem can result from Diabetic ketoacidosis?

Answer 16

• fat breakdown means more acid in form of acetone etc released
• metabolic acidosis
• get hyperkalaemia due to loss from cells and diuresis
• treat by giving insulin, bicarbonate and electrolytes

Question 17

What acid-base problem can result from hepatocellular dysfunction?

Answer 17

• Chronic respiratory alkalosis
• abnormal toxin and hormone levels stimulate respiratory centre
• Can also get metabolic acidosis due to abnormal level of amino acids or other acids

Question 18

What acid-base problem can result from Salicylate (aspirin)?

Answer 18

• metabolic acidosis
• too much non-carbonic acid ingested
• get hyperventilation which can then result in alkalosis
• treat with alkaline diuresis

Question 19

What acid-base problem can result from IV saline?

Answer 19

• metabolic acidosis
• Dilution of bicarbonate and increase in chlorine
• treat with citrate based infusion

Question 20

What are some of the causes of respiratory alkalosis?

Answer 20

• hyperventilation
• hypoxia
• liver disease
• heart failure (increase in ventilation)
• Intake of respiratory stimulants e.g. aspirin

Question 21

Causes of respiratory acidosis?

Answer 21

• Hypoventilation can be caused by asthma or COPD

- Intake of respiratory depresses e.g. morphine

Question 22

Causes of metabolic alkalosis?

Answer 22

• Vomiting
• Hyperaldosteronism
• Hypovolemia
• Alkali ingestion
• diuretics
• Cystic fibrosis
• Hypokalaemia

Question 23

Causes of metabolic acidosis?

Answer 23

Normal anion gap 
- Renal tubular acidosis 
- Chronic renal disease 
- diarrhoea 
- ingestion of ammonium chloride
Increased anion gap
- chronic renal disease 
- Lactic acidosis 
- Ketoacidosis
- Liver disease
- ingestion of acids e.g aspirin

Question 24

What is the normal PH ranges?

Answer 24

7.35-7.45

Question 25

What is the normal blood PaCO2 and venous blood PaCO2?

Answer 25

• 4.6-6.4 kPa

- 5.6-7.4 kPa

Question 26

Are veins or arteries carrying more acidic blood?

Answer 26

veins as more CO2, normal venous PH will be 7.45-7.55

Question 27

What is normal blood HCO3- and venous blood HCO3-?

Answer 27

• 22-30

- 23-31

Question 28

What is normal total CO2?

Answer 28

23-31

Question 29

What is normal anion gap?

Answer 29

<12 mmol/L