Intravenous fluids

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Intravenous fluids

Lactated Ringer's solution

Lactated Ringer's Solution is often used for fluid resuscitation after a blood loss due to trauma, surgery, or a burn injury. Previously, it was used to induce urine output in patients with renal failure.

Lactated Ringer's Solution is used because the byproducts of lactate metabolism in the liver counteract acidosis, which is a chemical imbalance that occurs with acute fluid loss or renal failure.

The intravenous dose of Lactated Ringer's Solution is usually calculated by estimated fluid loss and presumed fluid deficit. For fluid resuscitation the usual rate of administration is 20 to 30 ml/kg body weight/hour. Lactated Ringer's Solution is not suitable for maintenance therapy because the sodium content (130 mEq/L) is considered too high, particularly for children, whereas the potassium content (4 mEq/L) is too low, in view of electrolyte daily requirement.

Other commonly used intravenous solutions include normal saline and hespan (used in hypovolemic shock). Lactated Ringer's is also used as a conduit for the delivery of drugs. Lactated Ringer's is usually given intravenously, but if a suitable vein is not found, it can be taken orally (although it has an unpleasant taste).

One liter of Lactated Ringer's Solution contains:

Generally, the sodium, chloride, potassium and lactate come from NaCl (sodium chloride), NaC3H5O3 (sodium lactate), CaCl2 (calcium chloride), and KCl (potassium chloride).

There are slight variations for the composition for Ringer's as supplied by different manufacturers. As such, the term Ringer's Lactate should not be equated with one precise formulation.

Normal saline solution

Normal saline (NS) is the commonly-used term for a solution of 0.9% w/v of NaCl, about 300 mOsm/L. Less commonly this solution is referred to as physiological saline or isotonic saline, neither of which is technically accurate. NS is used frequently in intravenous drips (IVs) for patients who cannot take fluids orally and have developed or are in danger of developing dehydration or hypovolemia. NS is typically the first fluid used when hypovolemia is severe enough to threaten the adequacy of blood circulation and has long been believed to be the safest fluid to give quickly in large volumes. However, it is now known that rapid infusion of NS can cause metabolic acidosis [1] . NS is 9g NaCl dissolved in 1 liter water. The mass of 1 milliliter of NS is 1.009 grams. The molecular weight of sodium chloride is approximately 58 g/mole, so 58g NaCl is 1 mole. Since NS contains 9 grams NaCl, the concentration is 9g/L divided by 58g/mole = 0.154 mole/L. Since NaCl dissociates into two ions - sodium and chloride - 1 molar NaCl is 2 osmolar. Thus, NS contains 154 mEq/L of Na+ and Cl−. It has a slightly higher degree of osmolarity (i.e. more solute per litre) than blood (hence, though it is said to be isotonic with blood in clinical contexts, this is a technical inaccuracy).

Other concentrations commonly used include

1. Half-normal saline (0.45% NaCl), often with "D5" (5% dextrose), contains 77 mEq/L of Na and Cl and 50 g/L glucose. 2. Quarter-normal saline (0.22% NaCl) has 39 mEq/L of Na and Cl and always contains 5% dextrose for osmolality reasons. 3. Dextrose (glucose) 4% in 0.18% saline is used sometimes for maintenance replacement.

Common intravenous solutions

Hartmann’s solution

Hartmann's solution or Compound Sodium Lactate is a solution that is isotonic with blood and intended for intravenous administration.

One litre of Hartmann's Solution contains:

  • 131 mEq of sodium ion = 131 mmol/L.
  • 111 mEq of chloride ion = 111 mmol/L.
  • 29 mEq of lactate = 29 mmol/L.
  • 5 mEq of potassium ion = 5 mmol/L.
  • 2 mEq of calcium ion = 2 mmol/L .

Generally, the sodium, chloride, potassium and lactate come from NaCl (sodium chloride), NaC3H5O3 (sodium lactate), CaCl2 (calcium chloride), and KCl (potassium chloride).

Phosphate buffered saline

Phosphate buffered saline (abbreviated PBS) is a buffer solution commonly used in biological research. It is a salty solution containing sodium chloride, sodium phosphate, and (in some formulations) potassium chloride and potassium phosphate. The buffer helps to maintain a constant pH. The osmolarity and ion concentrations of the solution usually match those of the human body (isotonic).

Volume expanders

When blood is lost, the greatest immediate need is to stop blood loss. The second greatest need is replacing the lost volume. This way remaining red blood cells can still oxygenate body tissue. Normal human blood has a significant excess oxygen transport capability, only used in cases of great physical exertion. Provided blood volume is maintained by volume expanders, a quiescent patient can safely tolerate very low hemoglobin levels, less than 1/3rd of a healthy person.

The body automatically detects the lower hemoglobin level and compensatory mechanisms start up. The heart pumps more blood with each beat. Since the lost blood was replaced with a suitable fluid, the now diluted blood flows more easily, even in the small vessels. As a result of chemical changes, more oxygen is released to the tissues. These adaptations are so effective that if only half of the red blood cells remain, oxygen delivery may still be about 75 percent of normal. A patient at rest uses only 25 percent of the oxygen available in his blood. In extreme cases, patients have survived with a hemoglobin level of 2 g/dl, about 1/7th the norm, although levels this low are very dangerous.

With enough blood loss, ultimately red blood cell levels drop too low for adequate tissue oxygenation, even if volume expanders maintain circulatory volume. In these situations the only alternatives are blood transfusions, packed red blood cells, or oxygen therapeutics (if available). However in some circumstances hyperbaric oxygen therapy can maintain adequate tissue oxygenation even if red blood cell levels are below normal life sustaining levels.

Common crystalloid solutions

Composition of Common Crystalloid Solutions
Solution Other Name [Na+](mmol/L) [Cl-](mmol/L) [Glucose](mmol/L) [Glucose](mg/dl)
D5W 5% Dextrose 0 0 278 5000
2/3D & 1/3S 3.3% Dextrose / 0.3% saline 51 51 185 3333
Half-normal saline 0.45% NaCl 77 77 0 0
Normal saline 0.9% NaCl 154 154 0 0
Ringer's lactate Lactated Ringer 130 109 0 0

Ringer's lactate also has 28 mmol/L lactate, 4 mmol/L K+ and 3 mmol/L Ca2+. Ringer's acetate (ASERING) also has 28 mmol/L acetate, 4 mmol/L K+ and 3 mmol/L Ca2+.

Effect of Adding One Litre
Solution Change in ECF Change in ICF
D5W 333 mL 667 mL
2/3D & 1/3S 556 mL 444 mL
Half-normal saline 667 mL 333 mL
Normal saline 1000 mL 0 mL
Ringer's lactate 900 mL 100 mL

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