Electrolyte abnormalities

Question 1

Overview of causes of electrolyte imbalances

Answer 1

1. Renal
2. Endocrine
3. Gastrointestinal
4. Skin

Question 2

Treatment priority

Answer 2

1. pH
2. Potassium
3. Calcium
4. Magnesium
5. Sodium
6. Chloride

Question 3

Etiology of hypernatremia

Answer 3

\++Sodium
1. Conn's syndrome
Hypokalemia, alkalosis,hypertensive
\++loss of sodium:water
1. Fluid loss without water replacement
Diarrhea
Vomiting
Burns
2. Incorrect IV replacement
3. Diabetes insipidus
4. Osmotic diuresis -> DKA

Question 4

Management of hypernatremia

Answer 4

1. Oral fluid replacement - water if possible
2. If not, IV 5% dextrose, guide by urine
3. Do not decrease sodium by >0.5mmol/L / h or 10mmol/L / 24h
4. If hypovolemic->may use NS
5. Avoid hypertonic solutions

Question 5

Calculating decrease in serum sodium/ L 5% glucose

Answer 5

][Serum sodium]/ TBW + 1

TBW= 0.6 in men, 0.4 in women

Question 6

Etiology of hyponatremia

Answer 6

Check plasma osmolality
1. Factitious
->N osmolality= +lipids, proteins (MM)
->+Plasma osm= osmotic solutes drawing in= glucose, urea (hypertonic)
->Pseudohyponatremia
2. Hypoosmolar
a. Euvolemic
R: Drugs (lots of them….like NSAIDS, TCA’s, Carbamazepine)
E: ↓ Thyroid
G: H2O Intoxication (psychogenic polydipsia)
S: S.I.A.D.H. ( Nothing to do with skin this time)
b. Hypervolemic (+Na, +H20)
R: ARF, Nephrotic syndrome
E: ↑ Aldo (eg. CCF)
G: Cirrhosis (low albumin/protein)
S: I.V. Fluids (too much hypotonic stuff eg 5% Dextrose)
c. Hypovolemic (low sodium, low water)
R: diuretics, RTA, ARF, nephritis
E: Addisons, low aldosterone, osmotic diuresis
G: DV, fistula, NGT, pancreatitis
(3rd space occupation,)
S: sweat, burns

Question 7

Clinical features

Answer 7

1. Anorexia, nausea, malaise initially
2. HA, irritability, confusion
3. Weak, -ve GCS, seizures
4. Determine if deH or not
5. Edema?

Question 8

Iatrogenic hyponatremia

Answer 8

1. Infusion of 5% dextrose
2. Metabolised->hypotonic fluid
3. Hyponatremia
4. +Risk for those on diuretics, elderly, physiologic stress

Question 9

Management of hyponatremia

Answer 9

1. Correct the underlying cause
2. If mild, chronic->fluid restriction
3. If severe seek expert help
   IV 3% saline, target not >120 initially
4. Moderate
   Fluid restriction 500ml-1L/24 h
   Monitor serum/electrolytes/urine output daily
   May consider demeclocycline (ADH antagonist)
5. Volume depletion
   NS w/ potassium
6. If hypervolemic
   Can consider vaptans->excretion of electrolyte free fluids

Question 10

What is the concern with rapid correction of hypernatremia, risks, how to avoid

Answer 10

1. Permanent central nervous system injury due to osmotic demyelination
2. Those w. chronic +
   10mmol (/L in first 24 hour
   X +>18mmol/L in first 48 hours
   Goal therapy +4-8mmol/L

Question 11

When could more rapid correction in hypernatremia occur

Answer 11

1. Seizures or coma
2. Self induced acute water intoxication
3. Known hyponatremia for

Question 12

Pathogenesis of CNS damage with rapid sodium correction

Answer 12

1. Cerebral shrinkage endothelial- +BBB permeable,
   cytokines enter brain
2. Cell water shrinks, potassium and cations enter cells

Question 13

Calculation infusion rate of NaCl 3%- use a 60kg woman, with serum sodium 110, want to be 118

Answer 13

1. calculate desired increase
   in 24 hours. Say current = 110, want to
   be 118 in 24 hours= 8mmol/L increase over 24 hours
2. Increase in Na/L of infused 3%= 513- Na serum mmol/L/
   TBW + 1 (TBW= wt X 0.5 (female), 0.6 (male), elderly 0.45, 0.5
3. 13mmol/L of 3% increase over 24 hours
   so 8/13 X 100= 615ml of 3% to +by 8mmol. 25ml/hour of solution If already given boluses need to deduct from total infusion amount

Question 14

Etiology of hyperkalemia

Answer 14

1. Pseudo
Hemolysed
From IV arm
\+WCC
2. Shift
Acidosis: decrease in Na/K pump= -ve IC K and +ECF K->low conc in tubular cell = reduced diffusion in tuular lumen = accumulation of K in body.
Exercise
Low insulin
Digoxin toxicity
Hyperkalemic periodic paralysis
3. Load= +external K
Supplements
Blood transfusion
Rhabdomyolysis
Hemolysis
Suxamethonium
4. Loss
Renal failure, burns
K sparing diuretics, ACEi
-ve aldosterone->Addisons

Question 15

ECG changes in hyperkalemia

Answer 15

1. +K in ECF= MP less -ve, closer to threshold= +excitability but -ve Na channels open= -ve automaticity
2. Short QT interval
3. Tall T waves
4. Arrythmias
5. Wide QRS
6. P waves disappear
7. QRS sine wave and asystole/VFib

Question 16

Management of hyperkalmeia (emergency)

Answer 16

1. Confirm diagnosis with secondary testing
2. Assess Acid base and fluid status/kidney function
3. ECG
4. IV access
5. Calcium gluconate
6. IVF replacement
7. Glucose + insulin (renal failure)-> 10u insulin + glucose 50% 50ml IV over 5 minutes
8. Nebulised salbutamol
9. Polyestyrene sulfonate resin orally
10. Consider bicarbonate if acidosis
11. Measure acid base, electrolytes, renal failure, fluid balance, glucose regularly
12. Dialysis
13. If due to adrenal insufficiency->hydrocortisone, avoid glucose

Question 17

Most common 2 causes of hyperkalemia

Answer 17

1. Chronic renal failure

2. Loss of fluid

Question 18

Etiology of hypokalemia

Answer 18

1. Shift
Alkalosis
\+Insulin
Catecholamine infusion
2. Loss
Renal: liquorice, renal tubular acidosis
Endorcine: +Aldosteone (primary), secondary due to CCF, cirrhosis, ascites
Cushings/steroids/ACTH
Low magnesium
Phaeochromocytoma
3. Drugs
Diuretics
Penicillin
Lithium
Antiparkinsons
4. Other
Bartter's syndrome
Acute myeloid leukemia
Rectal villous adenoma
Pyloric stenosis
Poor nutrition

Question 19

Clinical features of hypokalemia

Answer 19

1. Muscle weakness
2. Hypotonia
3. Hyporeflexia
4. Cramps
5. Tetany, palpitation

Question 20

ECG changes in hypokalemia

Answer 20

1. Small, inverted T waves
2. Prominent U waves
3. Long PR
4. Depressed ST segments

Question 21

When to suspect Conns

Answer 21

1. Hypertensive
2. Hypokalemic
3. Alkalosis
4. Not taking diuretics

Question 22

Management of hypokalemia

Answer 22

1. Confirm
2. ECG
3. Assess kidney and fluid status, acid base
4. Potassium chloride SR
5. Consider IV if Xoral, severe