• Clinical science

Intravenous fluid therapy (Parenteral fluid therapy)


Parenteral fluid therapy usually involves the intravenous administration of crystalloid solutions, colloidal solutions, and/or blood products. The choice of fluid, the amount of fluid to be infused, and the rate of infusion are determined by the indication for fluid therapy. Fluid therapy with crystalloid solutions is used to resuscitate patients who are hypovolemic, to correct free water deficits in the case of dehydrated patients, to replace ongoing fluid losses, and to meet the fluid requirements of patients who cannot take fluids orally. The use of colloidal solutions is now controversial. However, colloidal solutions (such as albumin solution) may be indicated either as a monotherapy or in combination with crystalloid solutions in severe cases of low oncotic pressure, especially in children. In the case of severe bleeding, the use of blood products must be considered. All patients on fluid therapy should be closely monitored using a combination of clinical parameters and laboratory tests to determine the end-point of fluid therapy.

General indications for parenteral fluid therapy

Fluid resuscitation

Patients who are in hypovolemic shock require rapid fluid infusions in the form of fluid challenges to maintain intravascular volume.

  1. Rapid infusion of a 500 mL –1000 mL bolus; of normal (isotonic) saline (NS) or lactated Ringer's solution (RL) within 15 minutes
  2. Observe the patient for a clinical response
  3. Repeat the fluid bolus infusion if the clinical response is inadequate.
    • An inadequate response to fluid resuscitation is characterized by:
      • Low urine output (< 0.5 mL/kg/hr; best indicator)
      • Increased heart rate
      • Low blood pressure
      • Low CVP (central venous pressure)
  4. If the patient does not respond to multiple fluid challenges:
  • The ideal resuscitation fluid would possess the following characteristics:
    • Predictable and sustained increase in intravascular volume
    • Chemical composition as close as possible to that of plasma
    • Complete metabolism and excretion without accumulation in tissues
    • No adverse metabolic or systemic effects
    • Cost-effective

Replacement of free water deficit

Replacement of ongoing fluid loss

  • Fluids are also indicated in the post-resuscitation phase when the patient is no longer hypovolemic but still has ongoing abnormal fluid loss that cannot be compensated for by oral intake alone.
  • Some common conditions associated with an ongoing fluid loss are:
  • The amount and rate of fluid infusion should ideally match the amount and rate of ongoing fluid loss.
  • The composition of fluid given should ideally match the composition of the bodily fluid lost.
Fluid from the surgical drain Composition Ideal replacement fluid
Na+ K+ Cl- HCO3-
Gastric secretions 50 mmol/L 15 mmol/L 110 mmol/L D5½NS + 20 mEq/L KCl
Pancreatic secretions 140 mmol/L 5 mmol/L 75 mmol/L 115 mmol/L RL ± sodium bicarbonate
BIle 140 mmol/L 5 mmol/L 100 mmol/L 35 mmol/L RL ± sodium bicarbonate
Ileum 140 mmol/L 5 mmol/L 100 mmol/L 30 mmol/L RL ± sodium bicarbonate

Maintenance fluid therapy

The maintenance fluid requirement is higher in children than in adults!

Other indications

  • Correction of electrolyte imbalances (see sodium imbalance, potassium imbalance)
  • As a solvent for IV drugs: e.g., 5% dextrose for noradrenaline infusions


Types of parenteral fluids

Crystalloid solutions

  • Aqueous solutions with varying concentrations of electrolytes
  • The most commonly used fluids in a hospital setting
  • Crystalloids increase intravascular volume. The extent to which they do this depends on the effect on fluid compartments.
Type of crystalloid solution Crystalloid solution Effect on fluid compartments Specific Indications Risks Sodium- free solution Balanced electrolyte solution Potassium-free solution Composition (in mmol/L) Fluid distribution (as a percentage of the administered volume)


Na+ Cl- K+ Ca2+ Lactate Glucose Change in extracellular fluid volume Change in intracellular fluid volume
Hypertonic 3% NaCl
  • ↓ Intracellular volume
  • ↑ Extracellular volume
× × 1026 5.0 513 513 0 0 0 0 + 250% - 150%

½ normal saline (0.45% NaCl)

  • ↑ Intracellular volume
  • ↑ Extracellular volume
  • Replacing free water deficit
  • Maintenance fluid therapy: no longer recommended for patients 28 days to 18 years of age in postoperative and medical acute care settings
× × 154 5.0 77 77 0 0 0 0 + 70% + 30%

Normal saline (0.9% NaCl)

  • No change in intracellular volume
  • ↑ Extracellular volume
  • Hyperchloremic acidosis
× × 308 5.0 154 154 0 0 0 0 + 100% no change

Lactated Ringer's solution (RL)

  • ↑ Extracellular volume
  • Minimally elevated intracellular volume
  • Mild buffer action that counters acidosis
  • Lactic acidosis in patients with liver failure
  • Clumping of red cells if RL is co-administered with blood products
× × 275 6.5 130 109 4 3 28 0 + 90% + 10%

Hartmann's solution

  • Similar to RL
  • Similar to RL
  • Similar to RL
× × 279 6.5 131 111 5 2 29 0 + 90% + 10%
5% dextrose (D5W)
  • The sodium-free water becomes evenly distributed among both fluid compartments
    • ↑ Intracellular volume
    • ↑ Extracellular volume
× × 252 4.0 0 0 0 0 0 278 (50 g/L) + 40% + 60%

Patients 28 days to 18 years of age requiring maintenance intravenous fluid therapy should receive isotonic solutions (which have a sodium concentration similar to plasma) with appropriate levels of potassium chloride and dextrose to reduce the risk of hyponatremia!

Colloidal solutions

  • A colloid is a high molecular weight substance; that mostly remains confined to the intravascular compartment; and thus generates oncotic pressure
  • Examples:
  • Effects
    • Colloids have a greater effect on intravascular volume than crystalloids Colloids also persist longer in the intravascular compartment than crystalloids.
    • Decreased blood coagulability
    • Anti-inflammatory effect
  • Administration: : Their use is controversial, but they may be indicated in combination with crystalloids (for more information, see the table in extra information below).
  • Adverse effects
    • Volume overload
    • May interfere with blood grouping and cross matching
    • Impairment of platelet aggregation ("coating") after infusion with a large volume of HES
    • Pruritus with prolonged use
    • Anaphylactoid reactions
    • Nephrotoxicity (especially in the case of pre-existing renal damage)

Although colloids are much more effective than crystalloids as intravascular volume expanders, they are more expensive and are also associated with more side effects than crystalloids without being demonstrably superior. Their use is, therefore, controversial!

Colloidal solution Chemical structure Available forms Increase in intravascular volume Duration of volume expansion Specific indications
  • Naturally occurring colloid in plasma (accounts for 80% of plasma oncotic pressure)
  • + 80% of the administered volume
  • 16–24 hours
  • + 200–400% of the administered volume
  • 6% solution (dextran-40)
  • 10% solution (dextran-70)
  • + 100–150% of the administered volume
  • 6–12 hours
  • To improve micro-circulatory flow in microsurgical re-implantations
  • Priming extracorporeal circulation during cardio-pulmonary bypass
  • Synthesized by the hydrolysis of collagen
  • Succinylated gelatins (e.g., gelofusine, plasmagel)
  • Urea cross-linked gelatins (e.g., polygeline/Haemaccel®)
  • Oxypolygelatins (e.g., gelifundol)
  • + 70–80% of the administered volume
  • < 6 hours
  • Acute management of hemorrhagic hypovolemia
  • Priming extracorporeal circulation during cardio-pulmonary bypass
  • Volume pre-loading before regional anesthesia
Hydroxyethyl starch (HES)
  • Derived from amylopectin (a highly branched starch)
  • 1st generation: hespan
  • 2nd generation: hextend, hetastarch, pentastarch
  • 3rd generation: tetrastarch (side effects are less pronounced in comparison to other colloids)
  • + 100% of the administered volume
  • 8–12 hours
  • Acute management of hemorrhagic hypovolemia

Blood products

The transfusion of packed RBC concentrate is indicated in the case of massive blood loss (see blood transfusion).


Route of parenteral fluid therapy

General principles

  • The route of fluid infusion depends on the amount of fluid to be infused, the nature of the fluid (blood products vs. crystalloids), and the required flow rate
  • A wider lumen and a shorter catheter tube allow for a higher flow rate

Routes of fluid infusion

  • IV access: : The intravenous route is most commonly used for administering fluids and/or medication
    • Rapid introduction of large volumes of fluid through multiple large-bore (16G or wider) peripheral venous catheters is required to resuscitate patients with hypovolemic shock
  • IO (intraosseous) access
    • In “difficult/collapsed” peripheral veins, IO (intraosseous) access is preferred to central venous access for resuscitation.
    • A 15G IO needle allows for a flow rate of 60–100 mL/min.
    • Technique of insertion
      1. The leg is slightly externally rotated at the hip joint and the thigh is fixed with the hand.
      2. The needle should be inserted 2 cm distal and 1 cm medial to the tibial tuberosity.
  • Central venous access
    • Central venous catheters are longer and hence permit a slower flow rate than peripheral venous catheters; with the same lumen diameter. However, a much higher flow rate can be achieved with special large bore central venous catheters (e.g., high-flow Hickman catheters, Shaldon catheters)
    • Indications
      • Fluid resuscitation in a patient with “difficult/collapsed” peripheral veins (when IO access in not feasible)
      • Hemodynamic monitoring: measurement of central venous pressure, pulmonary artery catheterization
      • Administration of veno-irritant substances: vasopressors, chemotherapeutic drugs, prolonged parenteral nutrition
      • Therapies requiring high-volume extracorporeal circulation: plasmapheresis, emergent hemodialysis
      • Certain procedures: placement of inferior vena caval filters, transvenous cardiac pacing
    • Measures to reduce risk of infection during placement (e.g., CLABSI)
      • Use a cap, mask, long-sleeved sterile gown, sterile gloves, and a sterile full body drape.
      • Prepare skin with chlorhexidine and alcohol before inserting the catheter.
      • Systemic anticoagulation and antibiosis may be considered in oncology patients who require long-term central venous access.
    • Technique of insertion: is based on the Seldinger technique, which involves the use of a guide wire to gain access to blood vessels.
      1. A special, wide-bored needle (trocar) is inserted into either the jugular , subclavian, or the femoral vein with/without ultrasonographic guidance.
      2. Following needle insertion, a guide wire is passed through a needle into the selected vein
      3. The needle is removed while maintaining the guide wire in position and the central venous catheter is passed over the guide wire
      4. Once the central venous catheter is in place, the guide wire is slowly removed
      5. Proper positioning of the central venous catheter (in the case of jugular or subclavian approaches)

The flow rate is subject to Poiseuille's law: The flow rate is 16 times slower if a lumen's diameter is halved, but flow rate doubles if the catheter's length is halved!


Parameters for controlling parenteral fluid therapy

  • The indication for fluid therapy determines the amount of fluid administered and the rate of fluid therapy (see “General indications for fluid therapy” above).
  • Hemodynamic measures: pulse, blood pressure, capillary refill time, jugular venous pressure (or central venous pressure)
  • Monitor for complications of IV fluid therapy, which include:
    • Signs of fluid overload; : pedal edema; , fine crackles on pulmonary auscultation
    • Electrolyte imbalances: (see sodium imbalance and potassium imbalance)
  • Fluid balance charts: These charts should record the fluid intake (total amount of fluid administered) and fluid output (urine output, output from surgical drains, and, if applicable, the volume of loose stools or vomit)
  • Infusion rates may be adjusted in wards using drop rates: 15 drops = 1 mL in a macrodrip, 60 drops = 1 mL in a microdrip