Lecture 9 - Fluid Replacement Therapy

Question 1

In a standard 70kg male, what % of total body water is distributed into each compartment?

Answer 1

• 60% water (42L)
• 2/3 in ICF (28L)
• 1/3 in ECF (14L) split into interstitial fluid (10.5L) and plasma (3.5L)

Question 2

What is the total body water % of a newborn baby, a female and an elderly person and why is this the case?

Answer 2

Babies = 73% because they have a high SA:body ratio and a very high metabolic rate

Elderly = 45% because muscle holds more water than fat and muscle mass decreases with age.

Female = 50% because they have less muscle and more fat

Question 3

What occurs to the cells during hypernatraemia and hyponatreamia?

Answer 3

Hypernatraemia = Increased Na+ in plasma (osmolality increases) so water moves out of cells causing cell shrinkage, confusion & seizures

Hyponatreamia = Decreased Na+ in plasma (osmolality decreases) so water moves out of blood into cells causing cell swelling, cerebral oedema, headaches & seizures

Question 4

How does a bag of 1L 5% dextrose (50g glucose) distribute across compartments?

Answer 4

• 1L of water distributes evenly across compartments (2/3 to ICF, 1/3 to ECF)
• Glucose is taken up into cells and goes entirely into ICF
• Hyperglycaemia will occur if infusion rate fast than uptake and metabolism of glucose

Question 5

How does 1L 0.9& saline (NaCl) and 1L Hartmann’s distribute across fluid compartments?

Answer 5

• Na+ remains entirely within ECF compartment (3/4 in IF, 1/4 in plasma)
• Hartmann’s similar, almost entirely stays within ECF

Question 6

How will a bag of 1L of 4% dextrose and 0.18% saline distribute across fluid compartments

Answer 6

• 800mL of H2O will distribute evenly across fluid compartments (2/3 ICF, 1/3 ECF)
• 200mL of 0.9% saline will remain in the ECF only

Question 7

What patients require administration of I.V fluids?

Answer 7

• Nil by mouth patients (having surgery)
• Malfunctioning G.I.T (had a stoke/cant swallow)
• Dehydration
• Fluid losses
• Abnormal electrolytes

Question 8

What patients require administration of I.V fluids?

Answer 8

• Nil by mouth patients (having surgery)
• Malfunctioning G.I.T (had a stoke/cant swallow)
• Dehydration
• Fluid losses
• Abnormal electrolytes

Question 9

What hormonal changes do hospitalised patients normally undergo?

Answer 9

• Metabolically stressed so activate RAAS, aldosterone causes secretion of ADH
• This causes reduced water excretion leading to hyponatremia and increased water retention leading to volume overload.

Question 10

How is an individuals maintenance daily requirements (for fluids and electrolytes) calculated?

Answer 10

1) 25-30mL/kg/day water
2) 1mmol/kg/day of Na, K and Cl-
3) 50-100g glucose per day

Question 11

What is the protocol for giving fluid resuscitation to a hypovolaemic patient

Answer 11

1) Find cause of fluid deficit
2) Give 500mL bolus of crystalloids (either Hartmann’s or saline)
3) Replace fluids that are lost (check electrolyte crib sheet) and ongoing maintenance

Question 12

The electrolyte constitution of different body fluids are different, why is this important?

Answer 12

• The reason for fluid loss will determine what type of fluids are used to replace. E.g.: vomiting will result in different loss of electrolytes than diarrhoea.
• I believe this table below needs to be learned?