ChemPath: Diabetes Cases

Question 1

What does compensation mean with regards to acid-base balance?

Answer 1

You are improving pH by making something else worse

usually with

eg. DKA - metabolic acidosis (breathe off CO2)

COPD - Resp acidosis (CO2 getting worse)

Question 2

Why do acidotic patients become unconscious?

Answer 2

Brain enzymes cannot function at acidic pH

Question 3

State the equation for osmolality.

Answer 3

Osmolality = 2(Na + K) + urea + glucose

Question 4

What is the anion gap?

Answer 4

Na + K - Cl - Bicarb

There should always be a small gap between anions and cations due to the contribution of anions that are not measured

Normal ~18mM

Question 5

List some causes of high anion gap.

Answer 5

• Ketosis
• Lactic acidosis
• Methanol
• Ethylene glycol poisoning

Question 6

How does an increase in plasma pH affect serum calcium levels?

Answer 6

As pH increases, plasma proteins start to stick to calcium more than usual. Total plasma calcium levels will remain normal but there will be less free ionised calcium (active form). This leads to tetany (which can make patients hyperventilate even more).

Question 7

Why do patients with hyperosmolar hyperglycaemic state become unconscious?

Answer 7

It causes dehydration of the brain

Question 8

1. What is the danger of giving lots of fluids to someone with HHS?
2. What fluids should be prescribed and over what time period?

Answer 8

1. It can cause cerebral oedema
2. 0.9% saline over 1-4 hours should be used to achieve a slower reduction in plasma sodium

Question 9

What is a major consequence of metformin overdose?

Answer 9

Lactic acidosis

Question 10

Describe the Cori cycle. How does metformin affect this?

Answer 10

• Lactate is produced by anaerobic glycolysis in the muscles.
• This goes to the liver and is converted back to glucose which will then return to the muscle
• Metformin inhibits hepatic gluconeogenesis (the conversion of lactic acid to glucose in the liver) thereby resulting in lactic acidosis

NOTE: excess lactic acid is normally excreted by the kidneys, but in renal failure the kidneys cannot handle the excess lactic acid

Question 11

What is biochemical definition of diabetes mellitus?

Answer 11

Fasting blood glucose >7.00 mmol/L

Question 12

How are the results of an oral glucose tolerance test (75g glucose) interpreted?

Answer 12

Impaired glucose tolerance = 7.8 - 11.1 mM at 2 hours

Diabetes = > 11.1 mM at 2 hours

Question 13

What is the difference between pink puffers and blue bloaters in COPD?

Answer 13

• Pink puffers = very breathless, because they are still sensitive to CO₂ which rises due to poor lung function in COPD
• Blue bloaters = the brain stops responding to rising CO₂ so you are not breathless and the CO₂ will continue to rise