Fluid and Electrolyte Balance

Question 1

Describe the amounts of normal water intake, excretion and turnover per day?

Answer 1

Intake: 2000ml
Turnover: 9000ml
Excretion: 100ml

Question 2

What junctions are found between enterocytes?

Answer 2

Tight junctions.

Question 3

How do amino acids, peptide, bile salts and vitamins move into the enterocyte?

Answer 3

Via a sodium co-transporter.

Question 4

How does chloride move into the enterocyte?

Answer 4

It is exchanged for bicarbonate via an antiporter.

Question 5

How does sodium move into the enterocyte?

Answer 5

The sodium potassium pump on the side next to the capillary moves sodium out the enterocyte and into the blood in exchange for potassium.

Sodium then moves from the intestine into the cell via a co-transporter with amino acids, vitamins, bile salts and peptides.
It is also exchanged for hydrogen ions.
It also moves quickly via ion channels.

Question 6

How does water move into the cell?

Answer 6

Follows sodium passively between enterocytes.

Question 7

How does glucose influence sodium chloride absorption?

Answer 7

In the presence of glucose, sodium chloride can be fully absorbed. This is due to the SGLT1 transporter which moves sodium and glucose into the cell.
For this reason, glucose is found in oral rehydration therapies.

Question 8

What is the role of the CFTR transporter?

Answer 8

CFTR is a chloride ion channel. It transports chloride out of the cell to the intestine and sodium follows.
Water follows sodium, and creates a layer of water close to the cells.
It worked by being phosphorylated by Protein Kinase A and is part of a cAMP pathway. Things that alter the cAMP pathway way affect this - e.g. E. coli and V cholerae. This can lead to sodium chlorde and water loss in cells.

This transporter is also found in the pancreas and airways.

Question 9

Name the 3 types of diarrhoea?

Answer 9

Secretory
Inflammatory
Osmotic (malabsorptive)

Question 10

Describe secretory diarrhoea?

Answer 10

e.g. in acute infection.
Involved decreased absorption and increased secretion to give high volume diarrhoea.
Secretes NA, K+, Cl, HCO3.

Question 11

Describe inflammatory diarrhoea?

Answer 11

E.g. chrons, IBS, chronic.
Increased secretion and propulsive activity of the bowel.
Low volume.

Question 12

Describe osmotic diarrhoea?

Answer 12

e.g. pancreatic insufficiency, inflammatory disease.
Decreased intestinal absorption.
High volume.

Question 13

How would diarrhoea be treated in children?

Answer 13

Fluid replacement (ORS).
Zinc supplements: Decrease severity and duration).
Continue feeding.
Increase fluids in general: Drink water.

Question 14

How can diarrhoea be prevented?

Answer 14

Vaccination: e.g. Rotavirus, measles. 
Early breast feeding and vitamin A supplements. 
Hand washing.
Improved water quality. 
Community sanitation programmes.

Question 15

What would high osmolality in the circulation cause?

Answer 15

Water to be drawn out of cells and into the circulation, so would cause cellular dehydration.

Question 16

What would low osmolality in the circulation cause?

Answer 16

Water would enter cells and then expand (could damage tissues e.g. brain).

Question 17

What does ‘reduced osmolality’ mean?

Answer 17

Less sodium and chloride.

Question 18

Why would reduced osmolality in oral rehydration solutions be beneficial?

Answer 18

Better recovery due to decreased stool output, less dehydration, less need for IV therapy.

Question 19

Name and describe the 2 types of IV solutions?

Answer 19

1. Colloids: Large molecular weight. Contains large proteins such as albumin (cant pass through capillaries and stay in vascular bed so increase blood volume).
2. Crystalloids: Water and electrolytes. E.g. saline, dextrose, Ringer-lactate, Hartmanns. Iso-osmotic solutions usually preffered.

Question 20

What percentage of saline solution stays in the vascular bed?

Answer 20

25% - Good ‘middle’ solution as some stays un vascular bed but can also rehydrate tissues.

Question 21

How much dextrose solution stays in the vascular bed?

Answer 21

10%.

As glucose is quickly metabolised.

Question 22

Describe the standard post-op regimen for IV fluids?

Answer 22

2:1 Saline to dextrose.

Question 23

Why would you use Ringer-lactate or Hartmanns solutions in patients with acidosis?

Answer 23

As they contain lactate. Lactate is metabolised and bicarbonate is produced.

Question 24

What factors affect the rate of fluid replacement?

Answer 24

Age
CV status
Renal function
Severity of dehydration and time it took to develop.

Question 25

How is the rate of IV fluids expressed?

Answer 25

500ml x running time.
e.g. Emergency - 2-hourly (6L)
Normal regimen - 6-hourly (2L)

Question 26

How much potassium is found in the cells and the plasma (%)?

Answer 26

95% in cells

5% in plasma

Question 27

How would you potassium supplement in IV fluids?

Answer 27

Must be diluted so added to other fluids.

Must cardiac monitor!