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Question 1

What is the pH level indicating acidaemia?

Answer 1

<7.35

Question 2

What is the pH level indicating alkalosis?

Answer 2

> 7.45

Question 3

What is the respiratory acidosis caused by?

Answer 3

Processes that cause hypoventilation

Examples include CNS depression, respiratory depression, hypoventilation, respiratory failure, and airway obstruction.

Question 4

List some causes of respiratory acidosis.

Answer 4

• CNS depression (head injury, stroke, drugs)
• Respiratory depression (myopathy, spinal cord injury, drugs)
• Hypoventilation (pain, chest wall injury/deformity, raised intra-abdominal pressures)
• Respiratory failure (pneumonia, pneumothorax, edema, bronchial obstruction)
• Airway obstruction
• Chronic respiratory acidosis (COPD, restrictive lung disease)

Question 5

What is the formula for correcting the anion gap with albumin?

Answer 5

Add 2.5 to the anion gap for every 1 g/L that albumin is below normal.

Question 6

Define osmolar gap.

Answer 6

Difference between measured osmolality & calculated osmolality = 2x (Na+ + Urea + Glucose)

Question 7

What can cause an osmolar gap?

Answer 7

• Mannitol
• Glycine
• Methanol
• Ethylene glycol
• Ethanol
• Non-metabolised substances

Question 8

What is the formula for calculating the anion gap (AG)?

Answer 8

AG = [Na+] - ([Cl-] + [HCO3-])

Question 9

What does a high anion gap metabolic acidosis indicate?

Answer 9

Normal AGMA causes include ‘USED CRAP’.

Question 10

What does ‘CHAMPS’ stand for in the context of hyperventilation causes?

Answer 10

• CNS disease (stroke, hemorrhage, psychogenic)
• Hypoxia (pneumonia, PE, asthma, altitude)
• Mechanical or excessive ventilation
• Progesterone, pregnancy
• Salicylates and sepsis
• Small bowel fistula
• Diarrhea
• Carbonic anhydrase inhibitor
• Renal tubular acidosis
• Addison’s disease
• Pancreatic duodenal fistula

Question 11

What is the expected change in HCO3- for acute respiratory acidosis?

Answer 11

For every 10 mmHg CO2 rises above 40 mmHg, expect HCO3- to increase by 1 mmol/L.

Question 12

What is the expected change in HCO3- for chronic respiratory acidosis?

Answer 12

For every 10 mmHg CO2 rises above 40 mmHg, expect HCO3- to increase by 4 mmol/L.

Question 13

What is Winter’s formula for expected pCO2 in metabolic acidosis?

Answer 13

Expected pCO2 = (1.5 x [HCO3-]) + 8

Question 14

What is the delta ratio in metabolic acidosis?

Answer 14

Delta ratio = (AG - 12) / (24 - HCO3-)

Question 15

What are some causes of metabolic alkalosis?

Answer 15

• Contraction (volume contraction)
• Liquorice, laxative abuse
• Endocrine (Conn’s, Cushing’s)
• Vomiting, GI losses
• Excess alkali (antacids)
• Renal (Bartter’s)
• Post-hypercapnia
• Diuretics

Question 16

What is the expected change in HCO3- for acute respiratory alkalosis?

Answer 16

For every 10 mmHg CO2 gets below 40 mmHg, expect HCO3- to reduce by 2 mmol/L.

Question 17

What is the expected change in HCO3- for chronic respiratory alkalosis?

Answer 17

For every 10 mmHg CO2 gets below 40 mmHg, expect HCO3- to reduce by 5 mmol/L.

Question 18

What is the formula for expected compensation in metabolic alkalosis?

Answer 18

Expected pCO2 = (0.7 x HCO3-) + 20