- Clinical science
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.
Patients who are in require rapid fluid infusions in the form of fluid challenges to maintain intravascular volume.
- Rapid infusion of a 500–1000 mL bolus; of normal (isotonic) saline (NS) or lactated Ringer's solution (RL) within 15 minutes
- Observe the patient for a clinical response
- Repeat the fluid bolus infusion if the clinical response is inadequate.
- If the patient does not respond to multiple fluid challenges:
- Indicated to treat and/or
- Free water deficit = k × weight (kg) × (Current [Na+]/140 – 1)
- Intravenous fluids that can be used to replace free water deficit
- 5% dextrose
- Hypotonic saline (e.g., ½NS, ¼NS)
- 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.
- Maintenance fluids are indicated in patients who cannot or are not allowed to take fluids orally.
Normal daily maintenance dose
- Adults: 30 mL/kg of water, 1 g/kg of glucose (to prevent starvation ketosis), 1–3 mEq/kg of Na+, 1–3 mEq/kg of Cl-, and 0.5–1 mEq/kg of K+ per day
- Children: Holliday-Segar formula (4,2,1 rule); : 4 mL/kg/hr for the first 10 kilograms + 2 mL/kg/hr for the next 10 kilograms + 1 mL/kg/hr for the remaining weight
- Neonates: 150 mL/kg/day
- Certain conditions may alter the amount of maintenance fluids required.
The maintenance fluid requirement is higher in children than in adults!
- Correction of electrolyte imbalances (see ,
- As a solvent for IV drugs: e.g., 5% dextrose for noradrenaline infusions
- 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|
|Hypertonic||3% NaCl|| || |
½ normal saline (0.45% NaCl)
|Isotonic|| || |
|5% dextrose (D5W)|| || |
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!
- A colloid is a high molecular weight substance; that mostly remains confined to the intravascular compartment; and thus generates oncotic pressure
- Administration: : Their use is controversial, but they may be indicated in combination with crystalloids (for more information, see the table in extra information below).
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!
- IV access: : The intravenous route is most commonly used for administering fluids and/or medication
- Intraosseous (IO) access
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)
- 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
- Measures to reduce risk of infection during placement, e.g. central-line associated blood stream infection (CLABSI)
Technique of insertion: is based on the Seldinger technique, which involves the use of a guide wire to gain access to blood vessels.
- A special, wide-bored needle (trocar) is inserted into either the jugular , subclavian, or the femoral vein with/without ultrasonographic guidance.
- Following needle insertion, a guide wire is passed through a needle into the selected vein
- The needle is removed while maintaining the guide wire in position and the central venous catheter is passed over the guide wire
- Once the central venous catheter is in place, the guide wire is slowly removed
- 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!
- 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:
- 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)