Fluid Mx

Question 1

Maintenance vs resuscitation fluid

Answer 1

• Maintenance fluid replaces insensible losses

* Resuscitation fluid replaces deficit and ongoing losses (blood, vomit, sweat)

Question 2

Tonicity vs osmolarity

Answer 2

• Tonicity = total concentration of solutes that exert an osmotic force across a membrane
○ Glucose and water do not exert osmotic force because they moves across membranes into cells very quickly.
• Osmolarity = number of osmoles of solute per litre of solution

Question 3

What is the rule about what fluid you should replace for the fluid that is lost?

Answer 3

‘replace like with like’ - For example, consider post-hip replacement bleeding. Blood is from the intravascular compartment, which is a part of the ECF. Therefore the fluid which is chosen should resemble ECF.

Question 4

What are the normal values of Na and K?

Answer 4

[Na] 135-145 mmol/l

[K] 3.5-5.0 mmol/l

Question 5

Give examples of isotonic and hypotonic solutions (of crystalloid fluids).

Answer 5

• Isotonic
	○ Plasmaplyte
	○ Saline 0.9% i.e. normal 
	○ Hartmann's solution
• Hypotonic 
	○ 4% dextrose 
	○ 5% dextrose

Question 6

In which fluid compartment do isotonic and hypotonic solutions distribute?

Answer 6

• Isotonic solutions - fluid largely stays in ECF

- Hypotonic solutions introduce a lot of free water, which then enters the intracellular space

Question 7

Which fluid is closest to physiological fluid?

Answer 7

Plasmalyte

Question 8

What can isotonic 0.9% saline cause in large volumes?

Answer 8

hyperchloraemic metabolic acidosis (high [Cl])

Question 9

What can Hartmann’s i.e. CSL cause in large volumes? When can you not use it?

Answer 9

• Hyponatraemia

- Lactic acidosis

Question 10

What is the traditional maintenance fluid mx?

Answer 10

4:2:1:
○ 4 mL/kg/hr for 0-10 kg
○ 2 mL/kg/hr for 10-20 kg
○ 1 mL/kg/hr for 20+ kg

• Maximum 100mL/hr

Question 11

What is wrong with the traditional maintenance fluid mx? Explain.

Answer 11

• May overestimate fluid requirements
• Stress response -> ADH Release -> water retention at kidneys -> water moves from ECF to ICF -> cellular swelling -> cerebral oedema
  
  • Causes:
    ○ Headache, Nausea, Vomiting
    ○ Drowsiness, Irritability, Seizures
    ○ Brainstem herniation
• Children also have a large brain so have distorted intra-cranial volume ratio i.e. ICP increases more with the same increase in volume

Question 12

What is now the ideal maintenance fluid mx?

Answer 12

• Consider 2/1/1 instead of 4/2/1 for sick patients(or 2/3 of 4/2/1) - unless dehydrated

Question 13

What is the standard maintenance fluid used at RCH?

Answer 13

Plasma-Lyte148 and 5% Glucose

Question 14

What are the benefits of dextrose in solution?

Answer 14

○ Dextrose gives osmolarity not tonicity - as soon as its in the patient, it disappears and is quickly metabolised
○ Dextrose prevents ketosis and hypoglycaemia
○ Dextrose also prevents hypotonic solutions from causing haemolysis - its brief presence in the intravascular space allows it to mix with blood

Question 15

What kind of short-term Mx must be done once maintenance fluids are administered?

Answer 15

○ Every 6-12 hoursreview
○ Weight
○ Electrolytes
○ Assessment of ongoing losses (urine, vomiting, NG loses)
○ Urine output
○ Consider urine osmolality, urine [Na+]
○ Daily electrolytes

Question 16

What are considered high risk groups for fluid mx?

Answer 16

• Neurological disease
• Craniofacial/neurosurgery patients, major surgery
• Neonates
• Any child requiring full maintenance fluids is at high risk

Question 17

What should you remember of hypotonic fluid use in paediatric care?

Answer 17

It is no longer recommended in children - associated with morbidity/mortality secondary to hyponatraemia