I2i: Outline the physiological responses to the rapid IV administration of 1L D5W to 70kg euvolemic person

Definition

Dextrose is d-glucose, an isosmotic IV maintenance fluid

1L D5W Components

  • 5% = 50g glucose in 1L
  • No electrolytes
  • pH 4
  • 278mOsm/L

Immediate Distribution

  • Dextrose rapidly metabolised
  • Essentially infusing water
  • 1L Redistributes throughout TBW
  • ICF 66% = 660ml
  • ECF 34% = 340ml
    • 25% ISF – 250 ml
    • 9% plasma = 90ml

Initial Haemodynamic Effects

Redistribution to TBW is too rapid to have any effect on preL/CO

Ultimate Haemodynamic Effects

Starling Forces:  ­ ↑hydrostatic press, but given that it has an oncotic press. of zero it also ↓’s plasma oncotic press.

Excretion of Excess Fluid

  • Pressure Receptors: insufficient sustained MAP increase to activate BaroR
  • Osmoreceptors:
  • Isoosmolar solution
  • Becomes immediately hypoosmolar due to rapid glucose metabolism
  • Drops osmolarity to 280mOsm/kg
  • 2.5% ↓
  • Above the 1-2% threshold Δ for the hypothalamic osmoreceptors
  • ADH release from the PPG is inhibited
  • Excess water excreted in urine
  • Volume Receptors: the 85ml↑ ­ in intravascular vol. which ultimately occurs represents only a 2% Δ (5000ml to 5085ml) and is thus well below the 10% threshold for activation of the atrial stretch ®’s. Thus these will not have a role in excr. of the fluid.
  • Oncotic Pressure: ­ ↑in circulatory vol. is so small, oncotic pressure remains normal (even with the change to Starling’s forces above)