Basics

Question 1

What will happen if there is a rapid rise / drop of tonicity in Na correction?

Answer 1

Rise: central pontine myelinolysis
Drop: cerebral oedema

Question 2

DDx of hypoNa

Answer 2

0. Spurious (drip arm, dead space)
1. Hyperosmolar (hyperglycaemia, mannitol)
2. Isoosmolar (hyperproteinaemia, hyperlipidaemia)
3. Hypoosmolar
   a. Hypovolemic:
   i. extra-renal Na loss: GI, skin, abdominal sequestration
   ii. renal Na loss: diuretics, diuresis, Na+ wasting disease, mineralocorticoid deficiency
   b. Hypervolemic
   i. non-renal: CHF, cirrhosis, nephrotic syndrome
   ii. renal: AKI (oliguric phase), CKD
   c. Euvolemic
   i. normal ADH: ↑ water intake
   ii. ↑ ADH: hypothyroidism, hypocortisolism, SIADH

Question 3

What is pseudohyponatraemia and pseudohypernatraemia?

Answer 3

hypoNa caused by hyperglycaemia or mannitol electrolyte exclusion effect

hyperNa caused by severe hypoproteinaemia

Question 4

Mechanism that causes effective hypoNa

Answer 4

(hypervolemic hypoNa, non renal causes)
water shifts from ECF to ICF –> ↓ effective circulating volume –> activate RAAS and ADH to ↑ Na reabsorption –> ↑ hypervolaemia

Question 5

DDx of hyperNa

Answer 5

0. Spurious hyperNa
1. Isoosmolar: severe hypoproteinaemia
2. Hyperosmolar:
   a. hypovolemic:
   i. [Uosmo > 600] dehydration
   ii. [Uosmo: 300~600] osmotic diuresis, diuretics, partial DI
   iii. [Uosmo <300] complete DI
   b. hypervolemic: excess Na load

Question 6

Signs for abnormal hydration status

Answer 6

Hypervolemic: ↑ JVP, oedema, ascites…
Hypovolemic: ↓ capillary refill, ↓ skin turgor, mucousal dryness…

Question 7

Dx of SIADH (6)

Answer 7

• hypoosmolar hypoNa with inappropriately concentrated urine (Uosmo > Sosmo)
• clinically euvolemic
• UNa >40
• ⨉ renal, cardiac or endocrine causes
• ⨉ diuretics
• improvement after fluid restriction

Question 8

DDx of hyperK

Answer 8

0. PseudohyperK (blood taking contamination, IV contamination, ex vivo release from cells)
1. ↑ intake
2. Transcellular shift
   a. mineral acidosis, hypertonicity
   b. ↓ insulin, ↓ sympathetic, drugs
   c. exercise
   d. tumour lysis syndrome, rhabdomyolysis, trauma
3. ↓ excretion
   a. CKD, AKI (oliguric)
   b. Mineralocorticoid deficiency

Question 9

DDx of hypoK

Answer 9

0. PseudohypoK (drip arm, leukocytosis)
1. ↓ intake
2. Transcellular shift
   a. alkalosis
   b. ↑ insulin, ↑ sympathetic
3. ↑ excretion
   a. non renal loss (sweating, GI)
   b. renal loss (metabolic acidosis, metabolic alkalosis, hypoMg)

Question 10

Presentations of tumour lysis syndrome

Answer 10

1. hyperK –> arrhythmia
2. hyperP –> hypoCa –> seizures
3. hyperuricaemia –> gout, acute kidney injury

Question 11

What is TTKG?

Answer 11

trans-tubular potassium gradient
= U[K] / P[K] ➗ U[osm] / P[osm]
RR: 6~8

Question 12

Acute management of hyperK (3)

Answer 12

calcium gluconate
dextrose-insulin drip
resonium C

Question 13

Typical presentation of hypoK periodic paralysis

Answer 13

cannot stand up after a big meal / heavy exercise

Question 14

Why is there hypoMg and what are its effects?

Answer 14

cisplatin
↑ K excretion –> hypoK
↓ secretion & action of PTH –> hypoCa

Question 15

How to treat hypoK?

Answer 15

treat underlying causes
correct dehydration
replace K (PO / IV)

Question 16

DDx of hyperCa

Answer 16

hyperPTH
malignancy (local osteolysis, HHM)
TB (↑ calcitriol by activated macrophages)

Question 17

Examples of cancers with HHM (what is HHM?) (5)

Answer 17

humoral hyperCa of malignancy
- CA lung
- RCC
- ATLL
- CA breast
- CA oesophagus

Question 18

Presentations of hyperCa

Answer 18

bone pain, stones, abdominal groans (ileus, peptic ulcer, panceratitis), psychic moans (lethargy, depression)

Question 19

Chovostek’s sign

Answer 19

tapping –> twitching of facial muscles
==> hypoCa

Question 20

Trousseau sign

Answer 20

pressurise the arm by a sphygmomanometer –> muscle contraction of wrist & fingers
==> hypoCa

Question 21

Typical example of metabolic acidosis + respiratory alkalosis

Answer 21

aspirin overdose

Question 22

Typical example of metabolic alkalosis + respiratory acidosis

Answer 22

COPD on diuretics

Question 23

Common unmeasured osmoles that lead to ↑ osmolar gap

Answer 23

ethanol, methanol, isopropyl alcohol, mannitol

Question 24

DDx of high anion gap metabolic acidosis

Answer 24

Glycols
Oxoproline (paracetamol)
L-lactate
D-lactate
Methanol
Aspirin
Renal disease
Ketones

Question 25

L-lactic acidosis DDx

Answer 25

(a) Type A: tissue hypoperfusion
(b) Type B
- DM (↑ anaerobic glycolysis in muscles)
- Ethanol / methanol toxicity (↑ NADH –> ↓ metabolism of lactate)
- Metformin
… (liver failure, malignancy, IEM)

Question 26

Pathophysiology of D-lactic acidosis

Answer 26

short bowel syndrome: ↓ carbohydrate absorption –> ↑ metabolism into D-lactate by gut bacteria

Question 27

Ketones (which is the one detected by dipstick?)

Answer 27

acetoacetate (this), β-hydroxybutyrate

Question 28

DDx of ketoacidosis (4)

Answer 28

DKA (↓ insulin –> ↑ lipolysis & FA oxidation)
Ethanol toxicity (↑ NADH –> inhibit gluconeogenesis –> ↑ FA oxidation)
Starvation
IEM

Question 29

DDx of normal anion gap metabolic acidosis (4)

Answer 29

GI loss (diarrhoea)
Renal loss
Ingestion of HCl / NH4Cl
Urine diversion

Question 30

urine anion gap

Answer 30

Na+ + K+ - Cl-
RR: 20~90
Positive indicates high H+ in urine, like RTA 1,4, CKD

Question 31

Saline responsive metabolic alkalosis DDx (3)

Answer 31

hypovolaemia
vomiting, nasogastric suction
previous chronic use of diuretics

Question 32

Saline resistant metabolic alkalosis DDx (4)

Answer 32

Mineralocorticoid excess
Glucocorticoid excess
Base excess
severe hypoK (transcellular shift)

Question 33

Symptoms for hypoNa and hyperNa (4+4)

Answer 33

hypoNa: malaise, nausea, headache, confusion
hyperNa: thirst, lethargy, weakness, seizures