Diabetes cases

Question 1

A 16 year old is unconscious. Has been acutely unwell for a few days, with vomiting and breathlessness

pH: 6.85

PCO2 = 2.3 kPa (normal is 4-5)

PO2 = 15 kPa

Na = 145, K = 5, U = 10, glucose = 25, Cl = 96, bicarb = 4

1. What is the acid base abnormality?
2. Why is he unconscious?
3. What is the osmolality in this case?
4. What is the anion gap?
5. What is the likely cause of the high anion gap?

Answer 1

1. Metabolic acidosis - low pH = acidosis and low CO2 = low bicarbonate
2. He is unconscious because brain enzymes cannot function at a very acid pH

Osmolality = charged molecules + uncharged molecules which can reduce down to

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

3. 2(145+5) + 10 +25 = 335

Anion gap = Na+K-Cl-bicarb - (normal anion gap is 18mM)

4. Anion gap = 145 + 5 -96 -4 = 50
5. Which is high, and suggests extra anions - ketones! - Diabetic ketoacidosis

Question 2

1. How do you calculate osmolality?
2. How do you calculate the anion gap?

Answer 2

1. Osmolality = charged molecules + uncharged molecules which can reduce down to

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

2. Anion gap = Na+K-Cl-bicarb - (normal anion gap is 18mM)

Question 3

Case

A 19 year old known to have type 1 diabetes for several years presents unconscious

Results:

• pH = 7.65
• PCO2 = 2.8kPa
• Bicarb = 24mM (normal)
• PO2 = 15kPa

Na = 140, K =4 , bicarb = 24, Cl = 100, glucose = 1.3mM

1. What is the acid base abnormality?
2. What is the anion gap?
3. What is the diagnosis?

Answer 3

1. High pH = alkalosis, low CO2 = respiratory so respiratory alkalosis
2. Anion gap = 140 + 4 - 100 - 24 = 20 = normal
3. Anxiety caused by hypoglycemia

Question 4

Case

60 year old man presents unconscious to casualty, with a history of polyuria and polydipsia

Results:

• Na = 160
• K = 6
• U = 50
• pH = 7.3
• Glucose = 60

1. What is the osmolality?
2. Why is he unconscious?

Answer 4

1. 2(160+6) + 50 + 60 = 442mosm/kg
2. He is unconscious because the brain is very dehydrated

Question 5

Case

59 year old man known to have type 2 diabetes, on a good diet and metformin presents to casualty unconscious. Urine is negative for ketones

• Na = 140
• K = 4
• U = 4
• pH = 7.10
• Glucose = 4
• PCO2 = 1.3kPa
• Cl = 90
• Bicarb = 4mM

1. What is the osmolality?
2. What is the anion gap?
3. What is the acid base disturbance?
4. What is causing the excess amount of anions?
5. Why is he unconscious?

Answer 5

1. Osmolality = 2(140+4) + 4.0 + 4.0 = 296mosm/kg
2. Anion gap = 140+4-90-4 = 50 (high)
3. Metabolic acidosis
4. The anion gap is 50, which is high, but it is not ketones. It has to be something else. In this case, metformin is overdose can cause a lactic acidosis and the lactate is 10mM while normal is less than 2mM. Metformin inhibits the conversion of lactate in the liver to the glucose, part of the Cori cycle
5. He is unconscious as the brain cannot function at such an acidic pH

Question 6

What are the definitions for Type 2 diabetes for the following

1. Fasting glucose
2. Glucose tolerance test and Plasma glucose

Answer 6

1. Fasting glucose > 7mM
2. Glucose tolerance test

• Plasma glucose > 11.1mM at 2 hours
• 7.8-11.1 at 2 hours = impaired glucose tolerance