Use of IV fluids

Question 1

Total body water and distribution

Answer 1

Question 2

Definition of osmosis

Answer 2

Water moves from a dilute solution (high water concentration) to a concentrated solution when separated by a permeable membrane

Question 3

How do you stop water from moving by osmosis?

Answer 3

By applying pressure to the concentrated solution (low water content) to prevent osmosis - this is called osmotic pressure.

Question 4

What is the most important factor affecting the rate of osmosis?

Answer 4

Number of particles - the more particles in solution, the higher the rate of osmosis and therefore the higher the osmotic pressure

Question 5

Osmolality vs osmolarity

Answer 5

• Osmolality
  
  • Number of osmoles of solute/kg
• Osmolarity
  
  • Number of osmoles of solute/Litre

Question 6

What is the normal plasma osmolarity range?

Answer 6

The plasma osmolarity is maintained within a narrow range, 280–300 mOsm/L.

Question 7

What is tonicity?

Answer 7

Tonicity is the total concentration of non-penetrating solutes/molecules. Symptoms of tonicity changes are largely neurological.

• Hypotonicicty - if a cell is in a hypotonic solution then water moves into the cell to balance this out - the cell swells and can burst.
  
  • Common in raised ICP and herniation
• Hypertonicity - if a cell is in a hypertonic solution then water moves out the cell - cellular dehydration
  
  • Common in Intracerebral hemorrhage, venous sinus thrombosis

Question 8

Theoretical distribution of IV fluids on infusion

Answer 8

Question 9

Sensible and insensible losses

Answer 9

Sensible losses

• Bleeding
• Urine
• Faeces
• Wounds
• Gastric drainage
• Vomiting

Insensible losses

• Sweat
• Respiration

Question 10

How can you assess fluid volume?

Answer 10

• ABCDE approach to assess whether patient is hypovolaemic and needs fluid resuscitation
• History - previous limited intake, thirst, abnormal losses, comorbidities
• Clinical examination - pulse, BP, cap refill, JVP, Oedema (peripheral/pulmonary), postural hypotension
• Clinical monitoring - NEWS, fluid balance charts, weight
• Lab assessments - FBC, urea, creatinine and electrolytes

Question 11

If you decide the patient needs maintenance fluids what will you give them?

Answer 11

Plasmalyte

e.g 0.18% NACL / 4% glucose / 0.3% KCl

This provides the daily requirements of water, Na, K and glucose

Question 12

Fluid replacement

Answer 12

• Add up all the losses in the last 24 hours e.g bleeding, D&V, drain output, fistulae etc
• Give this volume back - don’t give excess fluid as that is placing not replacing
• Give plasmalyte, colloid or blood