Chem path 13 - Diabetes CPC

Question 1

What are the units for Hba1c and what is the cut off for diabetes?

Answer 1

mmol/mol, for a diagnosis of diabetes the Hba1c needs to be above 48mmol/mol (6.5%)

Question 2

What is the normal value for Hba1c (non-diabetics)?

Answer 2

<42mmol/mol

Question 3

WHat is the cut off for WHOLE fasted-blood in diabetics?

Answer 3

> /=6.1mmol/L

Question 4

o 48yo unconscious, presented February 2002
o Acutely unwell a few days, vomiting, polyuria, polydipsia, SOB and dehydrated
o PMHx: appendicectomy, osteoporosis, poorly controlled HTN
o DHx: amlodipine 10mg, atenolol 100mg
o O/E: obese, dehydrated, BP 80/40

What is the cause of this woman’s unconsciousness and what investigation would you do next?

Answer 4

Hypotension

ABG

Question 5

What are some causes of metabolic alkalosis?

Answer 5

H+ loss (i.e. vomiting)
Hypokalaemia (hypokalaemic alkalosis is a thing)
Ingestion of bicarbonate (i.e. lots of rennie in peptic uclers)

Question 6

What will a high HCO3- do to CO2 levels?

Answer 6

It will slightly raise them due to a shift in the equilibrium and NOT as a form of compensation

Question 7

What effect does metabolic alkalosis have on ventilation and why is the extent of respiratory compensation limited in metabolic alkalosis?

Answer 7

Metabolic alkalosis will inhibit ventilation so this will drive CO2 up further however the extent of compensation is limited because ventilation needs to remain sufficient to maintain good O2 levels so there is relatively little resp compensation for met alk.

Question 8

How do you calculate osmolality?

Answer 8

2(Na+K) + U + G

Question 9

How do you calculate the anion gap?

Answer 9

Na + K - Cl - HCO3-

Question 10

How can the anion gap help you distinguish whether the cause is DKA or not?

Answer 10

DKA fuels a high anion gap through excess ketones

Question 11

What is the link between hypokalaemia and alkalosis?

Answer 11

Hypokalaemia causes alkalosis and alkalosis causes hypokalaemia, need to figure out which came first

Question 12

How does a low ECF K+ cause alkalosis?

Answer 12

Causes a drive of H+ in to cells (instead of K+)

Question 13

How does an alkalosis cause hypokalaemia?

Answer 13

Causes a drive of K+ in to cells (instead of H+)

Question 14

What are the 4 main causes of hypokalaemia?

Answer 14

GI loss, renal loss, redistribution in to cells and rare causes (GRRR)

Question 15

Name some causes of renal losses of K+

Answer 15

Mineralocorticoid excess e.g. hyperaldosteronism/Conn’s, Cushing’s

Increased Na+ delivered to DCT

Osmotic diuresis

Question 16

Name some causes of redistribution of potassium in to cells

Answer 16

Insulin/insulinomas
Beta agonists
Alkalosis

Question 17

What are some rare causes of hypokalaemia?

Answer 17

Renal tubular acidosis types 1 and 2
Hypomagnesaemia - low magnesium means you will be unable to bring back up a low K+ so you have to correct the mg2+ before you can correct the K+

Question 18

Explain the mechanism of renal potassium losses when excess Na+ reaches the DCT

Answer 18

Triple or co-transporter is blocked –> less Na+ is reabsorbed in the ascending LOH –> more reaches DCT.
More Na+ is absorbed in the DCT –> electronegative nephron which results in a loss of K+ down the electrochemical gradient through ROMK channels

Question 19

Which drug class blocks the triple and co-transporter (Na+/Cl-), respectively?

Answer 19

Triple transporter: Loop diuretics

Co-transporter: Thiazides

Question 20

Summarise the pathophysiology of hypokalaemia and alkalosis

Answer 20

Lack of extracellular K+ for exchange with Na+ –> Increased H+ entering cells and an extracellular alkalosis.
Lack of intracellular K+ –> increased excretion of H+ in exchange for sodium and the production of an acidic urine and generation of bicarbonate

Question 21

Name 3 endogenous causes of CUshing’s syndrome

Answer 21

Pituitary adenoma
Adrenal tumour
Ectopic ACTH

Question 22

What test is now done to assess for pituitary or ectopic cause of cushing’s instead of high dose dexamethasone suppression test?

Answer 22

IPSS (a high dose suppression test would have suppressed cortisol if pituitary cause but not ectopic, if adrenal cause then the ACTh would have been suppressed anyway)

Question 23

How does ectopic ACTH cause hypokalaemia?

Answer 23

Such high doses of cortisol overpowers MR receptors which has an aldosterone-like effect and causes K+ loss

Question 24

What are causes of ectopic ACTH?

Answer 24

Lung cancer (SCLC)
Other cancers

Question 25

Why do you do a repeat CXR in patients with pneumonia?

Answer 25

To ensure there isn’t an endobronchial lesion remaining

Question 26

This patient, who initially presented with hypotension and has Cuhsing’s, should be hypertensive but why are they not?

Answer 26

she was severely dehydrated (presented with glycosuria)

Question 27

How would you manage this severely dehydrated and hypokalaemic patient?

Answer 27

Rehydrate cautiously to prevent central pontine myelinolysis
And replace K+ cautiously as too much K+ at once can result in asystole

Question 28

This same patient comes back anuric with an elevated creatinine, given her PMH, what are the two possible causes of this presentaiton?

Answer 28

ATN (Dehydration) or chronic renal failure (diabetes)

Question 29

If you are anuric, at what rate will your creatinine rise?

Answer 29

It will rise by ~100/day

Question 30

What is the most effective investigation to differentiate between the two possible differentials?

Answer 30

Renal biopsy

Question 31

How would you manage if ATN and if diabetic glomerular kidney disease?

Answer 31

ATN: 3 weeks of dialysis then they will recover
Diabetic: life long dialysis

Question 32

What will be seen on renal biopsy of pt with ATN?

Answer 32

Tubules necrosed but glomeruli intact

Question 33

UMN vs LMN lesion signs

Answer 33

UMN

• Spastic paresis- increased tone
• Hyperreflexia
• Babinski +ve
• No atrophy
• No fasciculations
• Reduced power

LMN

• Flaccid paresis - HYPOTONIA
• Severe atrophy
• Hyporeflexia
• Babinski -ve
• Fasciculations
• Reduced power