Fluid & Electrolytes

Question 1

Fluid requirements

Answer 1

• Maintenance (unable to take oral fluids)
  
  • Pre or post surgery
  • GI disease
  • Impaired consciousness
• Replacement (losses)
  
  • Previous
  • Ongoing

Question 2

Maintenance requirements

Answer 2

• <10kg = 100ml/kg/day (4ml/kg/hr)
• 10-20kg = 50ml/kg/day (2ml/kg/hr)
• >20kg = 25ml/kg/day (1ml/kg/hr)
• Caim for 100kcal/kg/day - if unable to achieve >60kcal/kg/day enterally for 3 days use TPN

Question 3

Mineral and trace element requirements

Answer 3

• Na⁺ - 2-4mmol/kg/day
• Cl^- - 2-4mmol/kg/day
• K⁺ - 1-2mmol/kg/day
• Ca²⁺ - 0.6-1mmol/kg/day
• PO^4- - 1-2mmol/kg/day
• Mg²⁺ - 0.3-0.5mmol/kg/day

Trace elements - Cu, Zn, Se, Mn, I, Cr

Question 4

Sodium content of crystalloid solutions

Answer 4

• 0.9% saline - 154mmol Na⁺/l
• 0.45% saline/5% dextrose - 75mmol Na⁺/l
• 0.18% saline/10% dextrose - 30mmol Na⁺/l
• Hartmann’s solution - 130mmol Na⁺/l
• 30% saline - 5mmol Na⁺/l
• Plasma-Lyte 148 - 140mmol Na⁺/l

Question 5

Ongoing losses

Answer 5

• Insensible
  
  • Lungs
  • Transdermal
  • Sweat
  • Faeces
• Urine
• Other

Question 6

Replacement

Answer 6

• Abnormal losses
  
  • Vomiting/NG
  • Diarrhoea
  • High urine output
  • Bleeding
  • 3rd spacing
  • Increased insensible (phototherapy/high ambient temperature)
• Pre-existing (estimate)
• Ongoing (measure)
• Gastric
  
  • Na content = 20-80mmol/l - use 0.45% saline + 10mmol KCl in 500ml
• Intestinal
  
  • Na content = 100-140mmol/l - use 0.9% saline + 10mmol KCl in 500ml

Question 7

Signs of dehydration

Answer 7

• Mild - <5% body weight, Hx, no signs
• Moderate - 5-10% body weight, signs of dehydration
• Severe - >10%, signs of shock

Question 8

Fluid resuscitation

Answer 8

• Fluid bolus = 20mls/kg
• Reassess and readjust

Question 9

Neonates

Answer 9

• High evaporative losses
• Immature renal function
• Expanded extracellular fluid space contracts within 1st week
• Requirements depend greatly on gestation

Question 10

Blood transfusion calculations

Answer 10

• △Hb (g) = Desired - Actual
• Blood volume (ml/kg) = 80 (infants), 90 (neonates), 100 (prems)
• Transfusion volume = △Hb (g) x Wt (kg) x 4

Question 11

Summary

Answer 11