intravenous (iv) fluids

see also:

• dehydration
• diabetic ketoacidosis (DKA)
• http://emcrit.org/pulmcrit/crystalloid/

• ideally a iv crystalloid would be close to physiologic and minimise incompatibilities with blood transfusions and other medications, these means:
  • no calcium
  • an osmolarity close to blood of 285mOsm/L
  • K of around 4mM to reduce risk of either hypokalaemia or hyperkalaemia
  • Na of 136mM
  • Cl 109mM
  • lactate 28-34
  • Mg 1.5mM as most hospitalised patients have low Mg
• to avoid incompatibilities, most of us still use the less than ideal 0.9% saline

• perhaps the least physiologic of the common crystalloids but it is the default iv fluid for many despite theoretic disadvantages of:
  • acidotic
    • thus may increase hyperkalaemia due to transcellular shifts
    • large volumes rapid infusion of NS can cause hyperchloraemic metabolic acidosis
  • hyperchloraemic, which theoretically risks renal impairment
  • slightly hypertonic at 286 mOSM/L
• Na 154mM, Cl 154mM and thus not “normal” at all when compared to blood as 0.6% saline is closer to blood levels of NaCl
• “saline” solutions were first used IV in the 1830's to Rx cholera in Europe

• similar to Lactated Ringer's solution
• slightly hypotonic with osmolarity of 274 mOsm/L
• Na 131mM, K 5mM, Cl 111mM, lactate 29mM, calcium 2mM, pH 6.5
• although its pH is 6.5, it is an alkalizing solution as lactate is metabolised to bicarbonate
• the calcium limits its compatibility with other iv agents including blood transfusions
• the slightly higher K concentration may not be as good as LR in patients at risk of hyperkalaemia

• Sydney Ringer developed his Ringer's solution in the 1880's as a fluid which maintained contractility of a frog heart muscle tissue, but not widely used in medicine until decades later
• Na 130mM, K 4mM, Cl 109mM, lactate 28mM, Ca 1.5mM
• slightly hypotonic with osmolarity of 273 mOsm/L
• although its pH is 6.5, it is an alkalizing solution as lactate is metabolised to bicarbonate
• the calcium limits its compatibility with other iv agents including blood transfusions

• a commonly used maintenance fluid, often with KCl added

• to make 500mL:
  • inject 35mL of 50% D into the 500mL bag of 10% D

• to make 500mL:
  • withdraw 70ML from the 500mL bag of 10% D and inject 35mL of 50% D and 23mL 20% saline

• to make up 500mL:
  • inject 25mls of NaCl 20% into the 500ml bag of 10% D
• to make up 1000mL:
  • inject 49ml of NaCl 20% into the 1000ml bag of 10% D

• to make up 500mL:
  • inject 25mL 0.9% saline into the 500mL bag of 5% D