Diabetes CPC Flashcards
In someone with HHS, what is the CAUSE of coma?
it’s hypotension- as the brain is not being perfused
pH: 7.65 alkalosis
PCO2: 6.1kPa (N: 4.7-6.0) high
PO2= 15kPa
What is the metabolic abnormality?
metabolic alkalosis
causes of metabolic alkalosis
- vomiting: H+ loss
- hypokalaemia-Conn’s syndrome/refeeding syndrome
- ingestion of bicarbonate
what is compensation?
making the pH better but co2 worse
calculation of osmoality
2(Na+K) + urea + glucose
i.e. cations + anions + uncharged molecules
formula for anion gap
cations - anions
i.e.
Na + K - Cl - bicarb
what electrolyte abnormality is associated with alkalosis?
HYPOKALAEMIA!!!
hypokalaemia causes increase in HCO3-
causes of longstanding hypokalaemia
thiazide diuretics
explain the link between hypokalaemia and alkalosis
both can cause each other
if you did high dose dx suppression test (nB not done anymore but hypothetically) which cause of cushing’s syndrome would fail to suppress vs ssuppress?
- cushing’s disease: some suppression with high dose dex
- ectopic acth: no suppression
disease causes suppression
how does cushing’s syndrome cause hypokalaemia?
excess cortisol starts to behave like mineralocorticoid
therefore hypernatraemia and hypokalaemia
- Because VERY high levels of cortisol bind to the aldosterone receptor (MR)
- GCs are promiscuous for MRs, so it causes a longstanding hypokalaemic effect
- Ectopic ACTH causes hypokalaemia more often than other causes of Cushing’s
what is the only way to distinguish between acuute renal failure and chronic renal issues?
which is a “better” outcome?
renal biopsy
(acute- dehydration, chronic- diabetes)
ATN is a better outcome because this is reversible with dialysis
(diabetic chronic kidney disease is treated with LIFE LONG DIALYSIS- chronic and irreversible
***conclusion:
woman had lung cancer producing ectopic acth –> cushing’s syndrome with longstanding hypolkalaemia
a) HHS (acute presentation) + ATN –> treated with fluids–>resolved
b) diabetes–>MI–>treated
c) eventually the lung cancer metastasised to the brain –> focal neurological signs
d) eventually died from acute coronary ischaemia
diff between death from acute coronary ischaemia vs arrythmia
sometimes before the heart muscle has time to die, the patient can get VF and die due to arrythmia
in this case you wouldn’t see any necrosis of tissue in the post-mortem
*if you saw death of tissue+scarring –> cause of death is ischaemia not arrythmia*
How can anion gap assist in diagnosis of DKA?
Ketones are anions
Therefore, in DKA anion gap will be large
How can pituitary-dependent Cushing’s and ectopic ACTH be distinguished?
Pituitary petrosal sinus sampling
What metabolic imbalance is caused by metformin?
Lactic acidosis
overdose of metformin (or metofrmin in those with kidney failure) will impair heptatic gluconeogenesis so lactate accumualtes wihtout being coverted to glucose >> lactic acidosis
(These are anions so will cause high anion gap, but urine will be negative for ketones)
How can hypoglycaemia lead to a respiratory alkalosis?
Can cause significant anxiety –> hyperventilation
What are the 3 biochemical definitions of diabetes?
Fasting PLASMA glucose >7.0mM (nb. this value does not apply to fingerprick whole blood test)
HbA1c > 6.5% (equivalent >48mmol/mol)
2 hour plasma glucose in Glucose Tolerance Test of >11.1mM
What HbA1c values count as ‘impaired glucose tolerance’?
42-48mmol/mol
how does Hypokalaemia Leads to Alkalosis (Cells)
- The K+ swaps for Na+
- This results in a local hypokalaemia which leads to a shift of H+ into the cell
- This leads to an alkalosis and low K+
- In the kidneys, H+ ions are lost into the urine
- K+ is taken up into the cell
causes of Hypokalaemia/ Hypokalaemic Alkalosis
- decreased intake (Rare)
- intestinal loss - diarrhoea, vomiting, fistulae
- renal loss-
- Hyperaldosteronism, excess cortisol
- Increased sodium delivery into the distal nephron
- Osmotic diuresis
-
redistribution into cells
- insulin - drives potassium into cells so plasma K+ is low
Insulin, b-agonists, alkalosis
RARE CASES: Renal tubular acidosis type 1 + 2, hypomagnesaemia
NOTE: Treatment for HyperK+
- Insulin
- Salbutamol
- Can use HCO3 too
What are the Possible Causes of cushing’s
- Pituitary
- Ectopic ACTH
- Adrenal tumour
- ACTH: 250 = very high
- Cortisol: 3210nM = very high
- Dexamethasone FAILED to suppress
- Low dose dex: Cortisol- 3100nM
- High dose dex: Cortisol – 2990nM (totally failed to suppress)
what is the diagnosis
ectopic release of ACTH
if it was an adrenal source, the ACTH would be low. Pituitary Cushing’s may cause a suppression on high dose dexamethasone test.
Note high dose not used in practice anymore
causes of ectopic ACTH + what tests should be done
- Lung cancer- small cell lung cancer
- Other cancers
Respiratory examination
IV K+ can cause what problem
IV K+ can cause asystole so it needs to be given very slowly
