Fluid and electrolyte balance

Question 1

What percentage of lean body mass is water?

Answer 1

60%

Equates to 42L of total body water in a 70kg man

Question 2

How is the fluid divided up in the body?

Answer 2

Intracellular fluid = 66% (approx 28L)
Extracellular fluid = 33% (approx 14L)
Intersitium = 75% (approx 11L)
Intra-vascular = 25% (approx 3L)

Question 3

How do the fluid compartments fluctuate daily?

Answer 3

The extracellular fluid fluctuates by approx 2500ml/day

Input = 2500ml (fluid 1300ml, food 800ml, metabolic water 800ml)

Output = 2500ml ( Sensible losses: Urine 1500ml, faeces 100ml. Insensible losses: skin 500ml, lung 400ml)

Question 4

What are the normal salt requirements/ day?

Answer 4

Sodium = 1mmol/kg/day 
Potassium = 1mmol/kg/day 
Chloride = 1.5mmol/ kg/day

Question 5

What must be achieved when prescribing fluids?

Answer 5

1. correction of pre-existing deficits
2. fulfilment of daily requirements
3. replacement of ongoing losses

Question 6

How can maintenance fluids be calculated for 24hrs?

Answer 6

100ml/kg for 1st 10kg
50ml/kg for 2nd 10kg
20ml/kg for every kg after that

eg for 70kg man:
(100 x 10) + (50 x 10) + (20 x 50) = 2500ml

Question 7

Describe the amount of electrolytes in saline and hartmanns

Answer 7

Saline: 150mmol Na, 150 mmol Cl
Hartmanns: 131 mmol Na, 111mmol Cl, 5 mmol K, 29 mmol HCO3

Question 8

What is acceptable urine output?

Answer 8

30ml/hr = maintenance
50ml/hr = trauma

Question 9

What are the causes of hyperkalaemia?

Answer 9

HI POTASSIUM

Hypoaldosteroniam (addison's)
Iatrogenic (excess infusion)
Potassium sparing diuretics 
Oliguria
Tissue destruction (burns, rhabdo)
Acidosis 
Spurious (lab error)
Suxamethonium 
Ingestion (potassium iodide, bananas, citrus)
Massive blood transfusion

Question 10

Symptoms of hyperkalaemia

Answer 10

Cardiac arhythmias, sudden death.

Tall, tented t waves on ECG

Question 11

When do you treat hyperkalaemia?

Answer 11

K > 6.5mmol/L + ECG changes (rule out spurious value)

Question 12

How do you treat hyperkalaemia?

Answer 12

Treat underlying cause
10ml of 10% of calcium resonium
20U insulin with 50ml 50% glucose
Calcium resonium enema

Question 13

What are the causes of hypokalaemia?

Answer 13

CRAMPING

Cushings and Conn's syndrome 
Renal tubular failure
Alkalosis 
Mucus per rectum (villous adenoma)
Pyloric stenosis 
Intestinal fistula
NG aspiration 
GI upset

Question 14

What are the symptoms of hypokalaemia?

Answer 14

Muscle cramping and weakness.

Cardiac arrhythmias - small or inverted T and U waves on ECG

Question 15

How do you treat hypokalaemia?

Answer 15

Treat underlying cause.
if > 2.5mmol use oral supplementation
if <2.5mmol use slow IV infusion

Question 16

What are the causes of hypernatraemia?

Answer 16

SALTED

Sweating
Addison's disease
Lack of fluids 
TPN
Emesis (vomiting)
Diabetes insipidus

Question 17

How does hypernatraemia present?

Answer 17

Thirst, confusion, coma, seizures.

Look for sunken eyes, dry mucous membranes, skin tenting and mottling.

Question 18

How do you treat hypernatraemia?

Answer 18

Oral water or normal saline

Question 19

Describe the different types of hyponatraemia

Answer 19

Hypovolaemic:
both sodium and water are lost resulting in low blood volume
normal osmolarity
caused by burns, pancreatitis, excessive diuretics, NG suction
treat with normal saline

Euvolaemic
only sodium is lost, blood volume remains constant
hypo-osmolarity
caused by SIADH, and CNS abnormalities
in SIADH treat with normal saline and frueosmide, followed by fluid restriction

Hypervolaemic
blood volume is increased, sodium remains constant
dilutional hypo-osmolarity
caused by renal failure, cardiac failure, liver failure, IV fluid excess
treated by fluid restriction and diuretics