Fluid replacement therapy

Question 1

Outline the distribution of body fluids in males

Answer 1

• 40% total body mass solids
• 60% total body mass fluids
• 2/3 ICF
• 1/3 ECF
• 75% ECF is interstitial fluid
• 25 % ECF is plasma

Question 2

Outline the distribution of body fluids in females

Answer 2

• 45% total body mass solids
• 55% total body mass fluids
• 2/3 ICF
• 1/3 ECF
• 75% ECF is interstitial fluid
• 25 % ECF is plasma

Question 3

What is the total body water of a newborn baby?

Answer 3

• 75%
• Makes them more vulnerable to dehydration

Question 4

What is the total body water in the elderly?

Answer 4

-45%

Question 5

Does ECF differ between the blood plasma and interstitial fluid?

Answer 5

• No
• Nothing prevents ions diffusing between the compartments

Question 6

Why does the composition of ECF differ from the composition of ICF?

Answer 6

• Due to cell membranes
• Na+ is main cation of ECF
• K+ is main cation of ICF

Question 7

Why might patients need IV fluids?

Answer 7

• Nil by mouth
• Malfunctioning gastrointestinal tract
• Dehydration
• Fluid losses
• Abnormal electrolytes

Question 8

Which fluids should you give to a patient?

Answer 8

• Maintenance fluids
• Replace any additional fluid lost too

Question 9

Why can’t we just give a patient pure water as an IV fluid?

Answer 9

• Water is too hypotonic compared to plasma

Question 10

How do we give a patient a ‘drink of water’ through IV fluids?

Answer 10

• Prescribe 5% dextrose
• Osmolarity of 278 MOSM/Kg
• Isotonic to plasma so water distributes proportionately across body compartments and reduces their osmolarity

Question 11

What happens to the glucose in 5% dextrose solution?

Answer 11

• Taken up by cells rapidly
• Used for metabolism
• If infusion rate is greater than uptake and metabolism, patient can become hyperglycaemic

Question 12

Why is dextrose not suitable for a haemorrhaging patient?

Answer 12

• Not enough water makes it into the intravascular compartment
• This is because water distributes proportionately across all body compartments
• Only 1/12 of total infusion volume will make it into intravascular compartment

Question 13

Which IV fluids will only go into the ECF?

Answer 13

• 0.9% saline (contains Na+ and Cl-)
• Hartman’s

Question 14

Why is Hartman’s solution ideal for fluid resus?

Answer 14

• Contains Na+, Cl-, K+, Ca2+, lactate
• Iso-osmotic to plasma
• Maintains osmolarity as well as volume

Question 15

What is a combination bag?

Answer 15

• Contains dextrose solution and saline/Hartman’s
• Dextrose acts to reduce osmolarity of all compartments
• Saline remains in ECF only

Question 16

Why do hospitalised patients’ fluid requirements differ from non-hospitalised people?

Answer 16

• Reduced free water excretion (hyponatraemia)
• Increased water and salt retention (volume overload)

Question 17

What causes hospitalised patients to retain more water than healthy patients?

Answer 17

• Vasopressin due to non osmotic stimuli e.g. drugs (morphine), pain, nausea
• No excessive sweating
• RAAS and catecholamines due to stress response
• Reduced caloric expenditure

Question 18

What are the NICE guidelines for maintenance fluids?

Answer 18

• 25-30 mL/kg/day of water
• 1 mmol/kg/day of K+, Na+ and Cl-
• 50-100g of glucose per day

Question 19

What are the NICE guidelines for fluid resuscitation?

Answer 19

• Fluid bolus of 500ml of crystalloids (saline or Hartman’s) is given
• Expert help required for patients given >2000ml of crystalloids but still needing fluid resus

Question 20

When would you give resuscitation fluids?

Answer 20

• Systolic BP <100 mmHg
• HR >90 bpm
• Capillary refill time >2 seconds or cold peripheries
• Resp rate >20 breaths per minute
• NEWS score >5
• Passive leg raises suggest fluid responsiveness

Question 21

When would you prescribe maintenance fluids?

Answer 21

• Patient is haemodynamically stable but unable to meet daily fluid requirements via oral or enteral routes
• Fluids should be administered during daytime hours to minimise disturbance to sleep

Question 22

What is the electrolyte constitution of gastric juice?

Answer 22

• 14 mmol/L K+
• 20-60 mmol/L Na+

Question 23

What is the electrolyte constitution of diarrhoea?

Answer 23

• 30-70 mmol/L K+
• 20-80 mmol/L HCO3-

Question 24

What fluid would you prescribe to a patient suffering from dehydration?

Answer 24

• Saline 0.9%
• Increases ECF only

Question 25

What would you happen to the fluid compartments of a patient who has not urinated for several hours?

Answer 25

- ECF would expand and its osmolarity would decrease - Water would move to ICF to balance osmolality of ECF - ICF osmolality also decreases until a new equilibrium is reached

Question 26

What would you happen to the fluid compartments of a patient who is haemorrhaging?

Answer 26

- ECF loses volume but its osmolality does not change - Water does not move out of ICF to compensate

Question 27

What would you happen to the fluid compartments of a patient who has diarrhoea and vomiting?

Answer 27

- ECF loses volume and its osmolality increases (pt can't drink enough to replace water lost) - Water moves from ICF to ECF to balance change in osmolality - Osmolality of both compartments increases - New equilibrium is reached - Want to give dextrose and Hartman's/saline

Question 28

If you're prescribing dextrose and saline, what should the ratios be?

Answer 28

- 2 dextrose : 1 saline/Hartman's