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.

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 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:
   • Try and identify the underlying cause of hypovolemic shock if it is not clinically apparent.
   • Consider the use of vasopressors and/or inotropes
   • Consider other causes of shock besides hypovolemia (e.g., cardiogenic shock, sepsis).

• 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

• Indicated to treat dehydration and/or hypernatremia
• 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)

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:
  • Burns
  • Polyuria (high output renal failure, diabetes insipidus)
  • Surgical drainage
  • Significant ongoing gastrointestinal loss (vomiting, diarrhea)
• 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

• 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.
  • ↑ Maintenance fluids: fever , tachypnea
  • ↓ Maintenance fluids: congestive cardiac failure, low output renal failure

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

References:^{[1][2][3][4][5][6]}

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)
								Osmolality	pH	Na+	Cl-	K+	Ca2+	Lactate	Glucose	Change in extracellular fluid volume	Change in intracellular fluid volume
Hypertonic	3% NaCl	↓ Intracellular volume ↑ Extracellular volume	Acute severe hyponatremia	Osmotic myelinolysis	×	×	✓	1026	5.0	513	513	0	0	0	0	+ 250%	- 150%
Hypotonic	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	Cerebral edema Pulmonary edema	×	×	✓	154	5.0	77	77	0	0	0	0	+ 70%	+ 30%
Isotonic	Normal saline (0.9% NaCl)	No change in intracellular volume ↑ Extracellular volume	Fluid resuscitation Maintenance fluid therapy	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	Fluid resuscitation Maintenance fluid therapy	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	Replacing free water deficit Maintenance fluid therapy Total parenteral nutrition	Hyperglycemia in diabetic patients	✓	×	×	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:
  • Natural colloids: albumin, fresh frozen plasma (FFP)
  • Artificial colloids; : gelatins, dextrans, hydroxyethyl starch
• 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
Albumin	Naturally occurring colloid in plasma (accounts for 80% of plasma oncotic pressure)	5% albumin (iso-oncotic)	+ 80% of the administered volume	16–24 hours	Acute management of severe burns Hypoalbuminemic states (following paracentesis, liver cirrhosis) Spontaneous bacterial peritonitis Acute lung injury Diuretic resistant nephrotic syndrome In plasmapheresis as an exchange fluid
		25% albumin (hyperoncotic)	+ 200–400% of the administered volume
Dextrans	Highly branched polysaccharide molecules	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
Gelatin	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).

References:^[7][6]

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 tip of the catheter is correctly positioned in the superior vena cava with the help of ECG leads by observing the changes occurring in the P wave
       • A chest x-ray must be taken after the placement of a central venous line

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:^[8]