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 (Co2, bicarb)

Question 2

Why do acidotic patients become unconscious?

Answer 2

Brain enzymes cannot function at acidic pH

Question 3

State the equation for osmolality and the normal values

Answer 3

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

Normal is 275-295 mOsmol/kg

Question 4

How do you calculate the anion gap, and what is a normal AG?

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 ~14-18mM

Question 5

List some causes of high anion gap.

Answer 5

• Ketosis
• Lactic acidosis
• Ethylene glycol poisoning
• Aspirin OD

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

What is the danger of giving lots of fluids to someone with HHS?

Answer 7

It can cause cerebral oedema, so 0.9% saline should be used to achieve a slower reduction in plasma sodium

Question 8

What can cause lactic acidosis?

Answer 8

Metformin OD
Ethanol
Methanol

Question 9

Describe the Cori cycle. How does metformin affect this?

Answer 9

• 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 10

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

Answer 10

• 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

Question 11

What is a normal osmolality?

Answer 11

275-295 mOsmol/kg

Question 12

What do you need to confirm a dx of T2DM?

Answer 12

Symptoms + 1 diabetes test result
Or
No symptoms + 2 results

Question 13

What would be expected on
1. Fasting glucose
2. Random glucose
3. OGTT
4. HbA1c
in a patient with diabetes?

Answer 13

1. Fasting glucose >7 mmol/l
2. Random glucose >11.1mmol/l
3. OGTT >11.1
4. HbA1c >48mmol/mol or 6.5%

Question 14

How is an OGTT performed

Answer 14

75g glucose given at 0h
Plasma glucose measured at 2h

Question 15

Define glucose values for
1. Impaired glucose tolerance
2. Impaired fasting glucose

Answer 15

1. Impaired glucose tolerance - 7.8 to 11.1
2. Impaired fasting glucose - 6.1 to 7

Question 16

Outline management for HHS

Answer 16

1. Fluids 0.9% saline (3-6L in 12 hours) as level of dehydration can be massive in HHS
   - Don’t give too quick - cerebral oedema & death
2. Monitoring (avoid rapid correction Na+, neurological status)
3. Insulin (0.05U/kg/hr) once BMs stop dropping OR ketones start to rise
   - Do not give insulin immediately, as insulin will push gluc into cells -> water follows -> even more dehydration

Question 17

Diagnosis for HHS (3)?

Answer 17

pH >7.3 (not acidotic)
Osmolarity >320mOsm
BM >30 mmol/L

Question 18

Diagnosis of DKA (3)?

Answer 18

D: BM > 11mmol/l
K: Ketones >3
A: Acidosis pH <7.3

Question 19

Management of DKA?

Answer 19

1. Fluids: 1L 0.9% NaCl over 1 hour, with KCl added to second litre
2. IV FRIII insulin after fluids (drives K into cells)
   - use 0.1 units/kg/hr
3. Avoid hypoglyc: Dextrose (125ml/h 10% dex) if glucose falls <15

Question 20

What is a marker of glucose control over the last 3 months?

Answer 20

HbA1c

Question 21

What is a marker of glucose control over the last 3 weeks?

Answer 21

Fructosamine (glycated protein)