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Intravenous fluid therapy

Last updated: April 12, 2021

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Intravenous fluid therapy involves the intravenous administration of crystalloid solutions and, less commonly, colloidal solutions. The type, amount, and infusion rates of fluids are determined based on the indication for fluid therapy and specific patient needs. Crystalloid solutions are used to resuscitate patients who are hypovolemic or dehydrated, correct free water deficits, replace ongoing fluid losses, and meet the fluid requirements of patients who cannot take fluids enterally. The use of colloidal solutions is controversial and should be reserved for special situations (e.g., severe cases of low oncotic pressure). All patients should be closely monitored using a combination of clinical parameters and laboratory tests to determine therapeutic endpoints, and fluid therapy should be appropriately de-escalated for patients in recovery to avoid fluid overload.

Definitions [1][2]

  • Crystalloids: solutions that contain small molecular weight solutes (e.g., minerals, dextrose)
  • Colloids: solutions that contain larger molecular weight solutes (e.g., albumin and starch)
  • Balanced IV fluid solutions: crystalloids or colloids that do not significantly alter the homeostasis of the extracellular compartment [2][3][4]

Osmolarity vs. tonicity of a fluid

  • Osmolality: the concentration of dissolved particles per unit mass of solution (mOsm/kg); preferred term to describe the osmotic pressure of biological systems [5]
  • Osmolarity: the concentration of solutes per unit volume of solvent (mOsm/L); often used interchangeably with osmolality in clinical practice
    • Preferred term to describe the osmotic pressure of parenteral fluids [5][6]
    • Takes into account all osmotically active particles, including those that enter cells (e.g., glucose, urea)
  • Tonicity: the capacity of an extracellular fluid to create an osmotic gradient that will cause water to move into or out of the intracellular compartment; cannot be measured and has no units [7]
Osmolarity vs. tonicity
Solution Osmolarity Tonicity
Isoosmolar Equivalent to the intracellular compartment Can be isotonic or hypotonic
Hyperosmolar Higher than the intracellular compartment Can be hypertonic, isotonic, or hypotonic
Hypoosmolar Lower than the intracellular compartment Can only be hypotonic

The osmolarity and tonicity of a solution are not the same thing! Administering solutions with inappropriate tonicity can lead to life-threatening fluid and electrolyte imbalances. [7]

The osmolarity of a parenteral solution takes into account the concentration of all the solutes, including those that enter cells (e.g., dextrose). The tonicity of a solution is determined by the solutes that do not enter the cell and are, therefore, osmotically active (e.g., sodium, potassium).

Crystalloid solutions [2][8]

  • 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 their tonicity (effect on fluid compartments).
  • Choose a solution based on treatment goals and patient characteristics (see “Principles of IV fluid therapy”).

Isotonic crystalloids

Isotonic IV crystalloids [2][8][9]
Normal saline (0.9% NaCl) Lactated Ringer's solution (LR)

Composition and osmolarity

  • Na+: 154 mEq/L
  • Cl-: 154 mEq/L
  • Osmolarity: 308 mOsm/L
Effect on fluid compartments
  • ↑ Extracellular volume
  • No change in intracellular volume
  • ↑ Extracellular volume
  • Minimally elevated intracellular volume
  • Balanced solution: mild buffer action that counters acidosis
Clinical applications
Risks

Hypotonic crystalloids

Hypotonic crystalloids can be used to correct free water deficits and as a maintenance fluid if there is free water loss. [9]

Hypotonic IV crystalloids [2][8][9]
Dextrose solutions Hypotonic saline solutions

Composition and osmolarity

  • 5% dextrose in water (D5W)
  • 10% dextrose in water (D10W)
Effect on fluid compartments
  • ↑ Extracellular volume
  • ↑ Intracellular volume
  • ↑ Extracellular volume
  • ↑ Intracellular volume
Clinical applications
Risks

Maintenance fluid therapy with hypotonic solutions can cause iatrogenic hyponatremia and cerebral edema. [9]

Hypertonic crystalloids

Hypertonic saline solutions must be administered with extreme caution because of the risk of rapid osmotic changes.

Hypertonic IV crystalloids (hypertonic saline)
3% NaCl 5% NaCl

Composition and osmolarity

  • Na+: 513 mEq/L
  • Cl-: 513 mEq/L
  • Osmolarity: 1027 mOsm/L
  • Na+: 856 mEq/L
  • Cl-: 856 mEq/L
  • Osmolarity: 1711 mOsm/L
Effect on fluid compartments
  • ↓ Intracellular volume
  • ↑ Extracellular volume
Clinical applications
Risks

When administering hypertonic saline, frequent serum sodium controls must be conducted so that treatment can be adjusted accordingly. A rapid increase in serum sodium can lead to osmotic demyelination syndrome.

Mixed crystalloid solutions

The following list is not exhaustive, but it includes some very commonly used formulations.

The tonicity of a mixed solution is determined by the concentration of solutes that cannot cross the membranes freely (e.g., Na+ and Cl-).

Concentrated crystalloid solutions

Concentrated crystalloids are typically administered like medications rather than fluids, e.g., as an antidote to a toxin or a reversal agent for an acute metabolic disturbance.

Colloidal solutions [3][19][20][21]

Avoid the use of colloids unless guided by a specialist or under specific circumstances (e.g., albumin for cirrhosis). [3]

Natural colloids

Artificial colloids [3][8]

The use of artificial colloids is controversial because their advantage over crystalloids has not been proven and their side effects, e.g., decreased blood coagulability, pose certain risks. They should only be prescribed in consultation with a specialist. [20][21]

  • Hydroxyethyl starch (HES): derived from amylopectin (a highly branched starch)
  • Dextran: highly branched polysaccharide molecules
  • Gelatins: synthesized through the hydrolysis of collagen

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!

References:[26]

General indications for parenteral fluid therapy

Intravenous fluid management is one of the most common in-hospital interventions. Patients may present with multiple indications for IV fluid therapy, which can evolve over the course of their illness and response to treatment. These include: [2][3]

Hypovolemic patients with significant or active bleeding should receive transfusions of blood products as soon as possible. Parenteral fluids are only a temporizing measure in the management of hemorrhage.

Prescribing parenteral fluids

  • IV fluids should be prescribed as any other drug.
  • The phases of IV fluid treatment and the 4 Ds can be used as guiding principles.
  • Patients receiving IV fluids should be evaluated continuously (at least daily).

The 4 Ds of fluid prescription: [3]
Drug: Prescribe the type of fluid.
Dosing: Indicate the amount of fluids and the rate.
Duration: Monitor the response and determine the minimum and maximum duration of therapy.
De-escalation: Taper and eventually discontinue the fluid.

Dynamic phases of IV fluid treatment [2][3][8]

  • Patient rescue phase (minutes): life-saving intervention for patients with severe shock (i.e., fluid resuscitation)
  • Organ rescue phase (hours): maintenance of tissue perfusion in patients with or at risk of hemodynamic instability (i.e., IV fluid challenges , titration of maintenance fluids to maintain tissue perfusion)
  • Organ support phase (days): management of IV fluids in stable patients (i.e., maintenance fluid therapy, replacement of ongoing losses) and prevention of unnecessary fluid accumulation (i.e., switch to oral/enteral hydration)
  • Organ recovery phase (days to weeks): reduction of IV fluids and evacuation of fluid overload

Monitoring and evaluation of parenteral fluid therapy

Monitoring and evaluation include baseline evaluations and frequent reassessments of clinical (e.g., pulse, blood pressure, capillary refill time, JVP assessment) and diagnostic parameters (e.g., biomarkers, imaging) depending on the patient's status, therapeutic goals, and response.

Clinical evaluation

Consider a fluid challenge to differentiate between hypovolemia and euvolemia if other clinical signs are unclear or cannot be assessed.

Clinical assessment of volume status
Volume status Clinical signs
Hypovolemia (fluid deficit)
Euvolemia (fluid balance)
Hypervolemia (fluid overload)
Fluid balance monitoring [27]
Parameter Measurements
Intake
  • Enteral fluids: e.g., dietary oral intake, tube feeding
  • Parenteral fluids: e.g, IV fluid therapy, medication infusions, blood products
  • Fluid creep from fluids administered in addition to the parenteral fluid prescription [2]
Output
Both
  • Consider daily weight and abdominal circumference measurements.

Diagnostic evaluation

Approach [2][8][19]

Approach to fluid management
Clinical scenario Fluid management strategy Goal

Hypovolemic shock

Aggressive fluid resuscitation (see also “Shock”)

Patient rescue

Mild to moderate hypovolemia or dehydration

Fluid resuscitation (e.g., with IV fluid challenge)

Organ rescue

Ongoing fluid loss

Replacement of ongoing fluid loss

Organ support

Free water deficit

Correction of free water deficit

Inability to meet daily fluid requirements enterally

Maintenance fluid therapy

Recovering patients

De-escalation of IV fluid therapy

Organ recovery

Fluid resuscitation [2]

Patients who are in hypovolemic shock require rapid fluid infusions. Other patients can be hypovolemic without frank shock, i.e., have decreased total body water in a compensated state without severe intravascular fluid depletion.

Fluid resuscitation according to hemodynamic status
Hemodynamically unstable Hemodynamically stable
Indications
  • Mild to moderate hypovolemia
  • Optimization of treatment after stabilization of shock
  • Patients who do not respond to oral rehydration strategies with or without ORS
Fluid regimens
Next steps
  • Optimize treatment; proceed with management for hemodynamically stable patients.

Patients in shock require monitoring of hemodynamic parameters, e.g., heart rate, blood pressure (MAP), CVP, lactate, and urine output.

The steps required for a fluid challenge can be recalled with TROL: Type of fluid, Rate, Objective, and Limits.

Replacement of ongoing fluid loss

Fluids are also indicated in the postresuscitation phase, when the patient is no longer hypovolemic but still has ongoing abnormal fluid loss that cannot be compensated for by oral intake alone.

Estimated composition of enteral fluid losses [19]
Source of ongoing fluid loss Composition
Na+ K+ Cl- HCO3-
Gastric secretions 50 mEq/L 15 mEq/L 110 mEq/L
Pancreatic secretions 140 mEq/L 5 mEq/L 75 mEq/L 115 mEq/L
Bile 140 mEq/L 5 mEq/L 100 mEq/L 35 mEq/L
Ileum 140 mEq/L 5 mEq/L 100 mEq/L 30 mEq/L
Jejunum 140 mEq/L 5 mEq/L 100 mEq/L 8 mEq/L

Correction of free water deficit

Replacement of free water is indicated to treat hypernatremia (organ support phase).

Maintenance fluid therapy [3][9]

For most patients that require maintenance IV fluids, dextrose in isotonic crystalloids is a reasonable choice that prevents starvation ketosis as well as iatrogenic hyponatremia. However, maintenance fluids alone with dextrose do not fulfill a patient's nutritional requirements.

If potassium is added to a solution, it cannot be infused at a rate > 10 mEq/hour via a peripheral line or > 40 mEq/hour via a central line, as it may lead to cardiac arrhythmias if infused too quickly.

Maintenance fluid therapy calculation according to age group
Age group Suggested maintenance fluid rate
Neonates [30]
  • Calculate hourly rate based on daily fluid requirements
    • Birth to day 1: 40–60 mL/kg/day
    • Day 2: 50–70 mL/kg/day
    • Day 3: 60–80 mL/kg/day
    • Day 4: 60–100 mL/kg/day
    • Days 5–28: 100–140 mL/kg/day
Children (28 days to 18 years of age) [31]
  • Holliday-Segar formula (4,2,1 rule) :
    • 4 mL/kg/hour for the first 10 kg
    • + 2 mL/kg/hour for the next 10 kg
    • + 1 mL/kg/hour for the remaining weight
Adults [19][32]
  • Can be estimated with one of the following:
  • Use IBW for fluid rate calculations in patients with obesity.
Subtract other sources of fluid intake from the required daily fluid volume to avoid fluid creep (e.g., IV medication, enteral fluids, blood products).

The maintenance fluid requirement per kg of weight is higher in children than in adults.

Special patient groups [9]

  • Conditions with decreased water (and potentially decreased solute) requirements, including:
  • Conditions with increased water (and potentially increased solute) requirements, including:
Daily fluid requirements for special patient groups [9]
Condition Free water requirements Examples Modification to daily fluid requirements
Edematous states
CNS diseases
Euvolemic states with ADH
  • Pulmonary disease
  • Cancer
  • Postoperative setting
Oliguric or anuric states
  • ↓ (sodium requirements can also be decreased)
Concentrating defects
  • ≥ 120% of the calculated maintenance fluid requirement; ∼ 1.2 × maintenance
  • Consider the use of hypotonic fluids to make up for the free water requirements (e.g., D5½NS).
Solute diuresis
  • ↑ (sodium requirements may also be increased)
  • Goals (organ recovery phase) [2][3]
    • Weaning from IV fluids
    • Mobilization of accumulated fluid to achieve normovolemia
    • Prevention of prolonged or worsening fluid overload
  • Indications: patients in recovery
    • Hemodynamically stable, with adequate tissue perfusion
    • Capable of enteral/oral feeding and hydration
  • De-escalation: Continue oral/enteral hydration and consider restricting IV fluids until they are suspended completely.
  • Evacuation of excess fluids: Strategies should be tailored to the patient. [2]
    • Allow spontaneous diuresis of excess fluid in patients with adequate kidney function.
    • If spontaneous diuresis is deficient:
      • Consider diuretics with or without albumin.
      • Consult nephrology for early RRT if there is intractable fluid overload.
      • Set objective goals and monitor carefully to prevent harm from excessive fluid removal (e.g., hypotension, acute kidney injury).

De-escalate IV fluids in patients who are stable (e.g., weaned from ventilator and vasopressors) and are capable of meeting their fluid needs orally/enterally.

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