Lecture 19: Clinical Problems: Electrolytes

Question 1

Question to ask before giving IVF

Answer 1

• is my patient, euvolaemic, hypovolaemic (dehydrated) or hypervolaemic (fluid overload)
• Does my patient need IVF
• How much?
• What type do they need?

Question 2

Types of Fluid

Answer 2

Hypotonic Fluid: (fluid→ cells, cells swell)

Hypertonic Fluid: (Fluid → out of cells, cells shrink)

Isotonic Fluid: Keep everything the same

Question 3

How do you assess volume status (fluid overload or dehydrated)

Answer 3

Fluid Overload:

• Weight gain
• Swollen ankles
• High BP

Dehydration:

• Weight loss
• Dry mouth
• Low BP
• Dizziness

Question 4

When DOESN’T the patient need IV fluids

Answer 4

Drinking enough, on enteral feed, already fluid overloaded

Question 5

What are the IV fluids for?

Answer 5

1. Maintenence: to maintain normal fluid balance (in patients not drinking/eating etc)
2. Replacement of losses: replace lost body fluids + electrolytes (vomiting, poops etc)
3. Rescuscitation: hypotensive, very very sick and need heaps of fluid to get system up.

Question 6

How much is maintenence fluid?

Answer 6

~2-3L

To counteract loss from pee, poo, sweat and breathing

Question 7

What is the 4:2:1 rule for paediatric IVF

Answer 7

Babies don’t need the same amount of fluid as adults (1L bag over 8hrs = 3L/day)

Question 8

Replacement Fluid: What might you be replacing? How do you know what to replace

Answer 8

Vomiting, post-surgery drainage, poops!

Replacing loss + continue maintenence fluid!

• Careful assessment of fluid status (weight and JVP helpful)
• Patient record of losses (fluid balance charts)

Question 9

What do we need to do if a patient is SHOCKED

Answer 9

Rescuscitation: give them a lot of fluid really quickly to bring the BP up

Question 10

When do you give Isotonic fluid?

Answer 10

Generally give this (safest). Unless your giving maintanence fluid and your overloaded (give hypotonic), or have a high serum Sodium (give hypotonic)

Plasmalyte (mimics plasma) or saline (0.9% NaCl)

Question 11

When do you give hypotonic fluid?

Answer 11

Rarely, when the patient needs maintenence fluid but already overloaded or with a high serum Na⁺.

Use 5% dextrose: start as isotonic but metabolised bu cells to → free water

Question 12

When do you give Hypertonic Fluid?

Answer 12

For very low serum Na⁺

Question 13

What is Hyponatraemia (low serum sodium)?

Answer 13

due to water excess (not low Na+).

Question 14

Where is the IV fluids going?

Answer 14

Extracellularly

Question 15

Na+ loss is from?

Answer 15

• GI loss (vomiting, diarrhoea)
• Hypo-aldosterone (less Na+ reabsorbed)
• Sweat
• Diuretics

Question 16

What is Pseudohyponatremia??

Answer 16

When lab tests say you have low Na+ but you don’t!!

Very high triglycerides or protein

Question 17

When do you get water excess?

Answer 17

Syndromes with water overload:

• Cirrhosis
• Heart Failure
• Nephrotic Syndrom

SIADH

Polydipsia

Question 18

Whats the serum osmolality like in hyponatremia?

Answer 18

Low! (most of osmo from Na+)

Question 19

Water Excess with euvolaemia

Answer 19

No signs of dehydration, oedema, JVP not elevated.

No evidence of fluid overload, so it’s probably
-SIADH
-Polydipsia
-Overhydration with low Na IVF
Diuretics

Question 20

How do you know the hyponatraemia is due to Polydipsia?

Answer 20

The patient will have a unusually low urine osmolality

(usually hyponatraemic patients have high urine osmolarity)

Question 21

SIADH

Answer 21

Usually in response to low BP or dehydration (sensed via baroreceptors and osmoreceptors)

ADH release despite neither of these occuring

Causes: tumors, CNS, drugs, lung disease

Question 22

Diuretics

Answer 22

Commonest tohave low Na+ with Thiazides

• can lead to an increased ADH
• cause decreased Na+ through decreasing NA+ reab.

Like SIADH but due to a drug

Question 23

Correction of Hyponatraemia

Answer 23

• Saline* for a dehydrated patient with sodium loss
• Fluid restriction* for patients with water excess