W7 - Diabetes cases

Question 1

• 16 year old unconscious
• acutely unwell a few days
• vomiting
• breathless
• ABG: pH 6.85, PCO2 2.3 kPa, PO2 15kPa
• U&Es: Na 145, K 5.0, U 10
• Glucose 25

What is the acid/base abnormality?
Why is he unconscious?

Answer 1

Metabolic acidosis

Because brain enzymes cannot function at a very acid pH

Question 2

What is the formula for osmolality?

Answer 2

Osmolality = 2(Na + K) + U + G

Question 3

Measure osmolality:

• U&Es: Na 145, K 5.0, U 10
• Glucose 25

Answer 3

Osmolality = 2(145 + 5) + 10 + 25
= 2(150) + 10 + 25 = 335

Question 4

what is the anion gap?

Give examples of anions part of anion gap.

Give formula for measuring anion gap

Answer 4

We assume cations (Na/K) are equal to anions (Cl, bicarb, others)

The others is known as the anion gap and they are not taken into consideration when measuring osmolality. They include PO4, SO4, etc.

Anion gap = Na + K - Cl - HCO3

Question 5

Measure anion gap:
- U&Es: Na 145, K 5.0, U 10, G 25, Cl 96.0, HCO3 4.0

What does this suggest? Give top cause of this

Answer 5

Anion gap = 145 + 5 - 96 - 4 = 50.0

Suggests there are extra anions

The top cause of high anion gap is ketone presence, from newly diagnosed type I diabetes

Question 6

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

pH 7.65
PCO2 = 2.8 kPa
Bicarb = 24 mM (normal)
PO2 = 15 kPa
Na = 140, K=4.0, bicarb=24, Cl=100
Glucose 1.3 mM

1. What is the acid-base abnormality ?
2. What is the cause of this abnormality in this patient? Explain how this becomes a vicious cycle?
3. Explain management
4. Diagnosis

Answer 6

1. Respiratory alkalosis
2. Primary hyperventilation

Albumin becomes sticky => holds onto ca2+ => tetany-like => the patient becomes even more anxious.

3. Calm them down + give a paper bag for them to breathe through (increase CO2)
4. Anxiety caused by hypoglycaemia

Question 7

pH 7.65
PCO2 = 2.8 kPa
Bicarb = 24 mM (normal)
PO2 = 15 kPa
Na = 140, K=4.0, bicarb=24, Cl=100
Glucose 1.3 mM

Calculate anion gap

Answer 7

anion gap = 140 + 4 - 24 - 100
= 20 (normal)

Question 8

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

Na: 160, K: 6.0, U 50, pH 7.30, Glucose 60.

What is the osmolality?

Why is he unconscious? What is the likely diagnosis?

Answer 8

Osmolality = 2(160+6) + 50 + 60
= 320+ 12 + 110 = 442 mOsm/kg

because the brain is VERY dehydrated.

Undiagnosed T2DM leading to HHS (hyperosmolar hyperglycaemic state)

Question 9

What is a normal osmolality range?

Answer 9

285-295 mOsm/kg H2O

Question 10

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: 4.0, U 4.0, pH 7.10, Glucose 4.0
PCO2=1.3 kPa. Cl = 90. Bicarb = 4.0 mM
What is the osmolality:
What is the anion gap:
What is the acid-base disturbance:
Why is he unconscious:
What is the cause of his presentation:

Answer 10

Osmolality = 2(140 + 4) + 4 + 4 = 296 mOsm/kg

Anion gap = 140 + 4 - 90 - 4 = 50 (HIGH)

metabolic acidosis

b/c the brain cannot function in highly acidotic pH

Metformin in overdose can cause a lactic acidosis (given that he has no excess of ketones)

Question 11

How does metformin overdose cause lactic acidosis?

Answer 11

Metformin inhibits lactate conversion to glucose in the liver

If you have a huge overdose of metformin => lactate builds up => risk of lactic acidosis

Question 12

Definition of T2DM

Answer 12

Fasting plasma (not whole blood) glucose >7.0 mM

Glucose tolerance test (75g glucose given at time 0) => plasma glucose > 11.1 mM at 2hr

hbA1c > 48 mmol/mol (6.5%)

Question 13

Explain interpretation of glucose tolerance test results

Answer 13

plasma glucose > 11.1 mM at 2hr => T2DM

plasma glucose 7.8 - 11.1 mM at 2hr => impaired glucose tolerance

Question 14

Explain interpretation of HbA1c test results

Answer 14

>48 mmol/mol (6.5%) => T2DM

42-47 mmol/mol (6.0-6.4%) => prediabetic