Fluid replacement therapy Flashcards
Outline the distribution of body fluids in males
- 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
Outline the distribution of body fluids in females
- 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
What is the total body water of a newborn baby?
- 75%
- Makes them more vulnerable to dehydration
What is the total body water in the elderly?
-45%
Does ECF differ between the blood plasma and interstitial fluid?
- No
- Nothing prevents ions diffusing between the compartments
Why does the composition of ECF differ from the composition of ICF?
- Due to cell membranes
- Na+ is main cation of ECF
- K+ is main cation of ICF
Why might patients need IV fluids?
- Nil by mouth
- Malfunctioning gastrointestinal tract
- Dehydration
- Fluid losses
- Abnormal electrolytes
Which fluids should you give to a patient?
- Maintenance fluids
- Replace any additional fluid lost too
Why can’t we just give a patient pure water as an IV fluid?
- Water is too hypotonic compared to plasma
How do we give a patient a ‘drink of water’ through IV fluids?
- Prescribe 5% dextrose
- Osmolarity of 278 MOSM/Kg
- Isotonic to plasma so water distributes proportionately across body compartments and reduces their osmolarity
What happens to the glucose in 5% dextrose solution?
- Taken up by cells rapidly
- Used for metabolism
- If infusion rate is greater than uptake and metabolism, patient can become hyperglycaemic
Why is dextrose not suitable for a haemorrhaging patient?
- 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
Which IV fluids will only go into the ECF?
- 0.9% saline (contains Na+ and Cl-)
- Hartman’s
Why is Hartman’s solution ideal for fluid resus?
- Contains Na+, Cl-, K+, Ca2+, lactate
- Iso-osmotic to plasma
- Maintains osmolarity as well as volume
What is a combination bag?
- Contains dextrose solution and saline/Hartman’s
- Dextrose acts to reduce osmolarity of all compartments
- Saline remains in ECF only
Why do hospitalised patients’ fluid requirements differ from non-hospitalised people?
- Reduced free water excretion (hyponatraemia)
- Increased water and salt retention (volume overload)
What causes hospitalised patients to retain more water than healthy patients?
- 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
What are the NICE guidelines for maintenance fluids?
- 25-30 mL/kg/day of water
- 1 mmol/kg/day of K+, Na+ and Cl-
- 50-100g of glucose per day
What are the NICE guidelines for fluid resuscitation?
- 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
When would you give resuscitation fluids?
- 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
When would you prescribe maintenance fluids?
- 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
What is the electrolyte constitution of gastric juice?
- 14 mmol/L K+
- 20-60 mmol/L Na+
What is the electrolyte constitution of diarrhoea?
- 30-70 mmol/L K+
- 20-80 mmol/L HCO3-
What fluid would you prescribe to a patient suffering from dehydration?
- Saline 0.9%
- Increases ECF only
