Fluid Management

Question 1

Roughly how much water is in a 70kg adult?

Answer 1

42 litres (60%)

Question 2

How is water distributed in the body?

Answer 2

2/3 intracellular (28 litres)
1/3 extracellular
- interstitial fluid (10.5 litres)
- plasma (3.5 litres)

Question 3

Which component of water should be most carefully considered and why?

Answer 3

Plasma –> carries blood (oxygen) to the tissues

Question 4

How does interstitial fluid support plasma?

Answer 4

Interstitial fluid is a reservoir for plasma –> can move quickly into vessels if blood is lost

Question 5

Which 3 things must be considered when planning fluid management?

Answer 5

Basal requirements
Existing deficit
Predicted losses

Question 6

What is the basal requirement of water for a 70kg adult?

Answer 6

30-40ml/kg —> 2100-2800ml

Question 7

What is the basal requirement of sodium + potassium?

Answer 7

1-2mg/kg of each per day

Question 8

What might be seen on examination of a dehydrated patient?

Answer 8

Dry mouth
Loss of skin elasticity
Cold peripheries

Increased HR + decreased BP tend to be late signs

Question 9

Which investigations are helpful in a patient who may be dehydrated?

Answer 9

Fluid balance chart (records input + output)
Urine output
Urea + creatinine (if increased may indicate dehydration or pre-renal failure due to hypovolaemia)

Question 10

What is the minimum acceptable urine output?

Answer 10

0. 5ml/kg/hour

- -> about 30ml/hour

Question 11

What are the different types of fluid available?

Answer 11

Cystalloids
Colloids
5% glucose

Question 12

What do crystalloids contain and give two examples?

Answer 12

Contain water + electrolytes –> isotonic with extracellular fluid

• Sodium chloride (0.9% saline)
• Hartmann’s solution (Ringer’s lactate)

Question 13

How does 0.9% saline compare to plasma and what effect does this have?

Answer 13

Slightly more sodium and much more chloride than plasma

–> high chloride means that H+ comes out of cells so risk of patient becoming acidotic

Question 14

What are the advantages of 0.9% saline?

Answer 14

Cheap and widely available

Good for both resuscitation and maintenance

Question 15

What are the risks if going large quantities of 0.9% saline?

Answer 15

Hypernatraemia

Metabolic acidosis

Question 16

How is Hartmann’s different to saline?

Answer 16

Much closer to plasma in terms of ion concentrations

Question 17

What happens when 5% glucose is given IV?

Answer 17

Effectively like giving free water as all of the glucose is metabolised by the liver
Water goes into all the compartments, mainly intracellularly

Question 18

What are the clinical uses of 5% glucose?

Answer 18

Good for pure hydration (replacement of water) and maintenance fluids
Useless for resuscitation (as doesn’t stay in plasma)

Question 19

What do colloids contain?

Answer 19

Big molecules exerting oncotic pressure (fluid follows them)

0.9% saline (so causes same problems with acidosis)

Question 20

Theoretically, why would colloids be better than crystalloids?

Answer 20

Big molecules stay in intravascular space, attracting water due to oncotic pressure –> volume expanders

Question 21

What are the disadvantages of colloids?

Answer 21

No proven benefit over crystalloids in resuscitation
More expensive
May interfere with clotting
Small risk of anaphylaxis

Question 22

What are the general principles of fluid maintenance for a patient who will be nil by mouth for 24 hours?

Answer 22

3 bags of fluid (1 salty, 2 sweet) equally daily required volume of water –> 1x 0.9% saline, 2x 5% glucose
Add 20mg potassium to each bag
–> give over 24 hours

Question 23

Why does potassium need to be added to bags of maintenance fluid?

Answer 23

Crystalloids do not contain enough potassium for maintenance

Question 24

What are the signs of fluid overload?

Answer 24

Raised JVP

Peripheral, sacral or pulmonary oedema

Question 25

Which group of patients are most at risk of fluid overload?

Answer 25

Elderly –> compensation mechanisms less efficient

Question 26

How is response to a fluid challenge monitored?

Answer 26

Increasing BP and slowing HR

Central venous pressure (CVP) monitoring (in more complex patients)

Question 27

If CVP remains unchanged or rises then falls after a fluid challenge, what does this indicate?

Answer 27

Patient is dry

Question 28

If CVP rises and stays up following a fluid challenge, what does this indicate?

Answer 28

Patient is adequately filled

Question 29

If CVP rises by >4cmH2O following a fluid challenge, what does this indicate?

Answer 29

The patient is overfilled or has heart failure