Pediatric Fluid Management

Anatomy and Physiology

Children vary in required fluid intake due to increased metabolic rates, which cause increased fluid loss.[5] Tonicity applies to the concentration of carbohydrates and electrolytes. It is related to its effect on the volume of a cell. Tonicity is related to both the impact on a cell of a fluid and the osmolality of the fluid. It is controlled by the release of antidiuretic hormone (ADH) from the posterior pituitary causing water retention, and by the thirst mechanism.

An isotonic solution does not change the volume of a cell. The isotonic solution has a sodium concentration similar to plasma. A hypotonic solution results in swelling of the cell and administration of a hypertonic solution cause a shrinkage of the cell due to extracellular fluid shift.[5] Electrolytes are responsible for determining tonicity; dextrose generally does not substantially affect tonicity as it is rapidly metabolized by insulin upon entering into intravascular space unless diabetes exists.[5] Solutions with a 1 to 1 glucose to sodium ratio (75 mEq/L according to WHO recommendations) work with physiological glucose and sodium transporters to increase intestinal mucosa absorption. Hyperosmolar solutions, those with excessive carbohydrates, can also cause osmotic diarrhea, which worsens fluid loss. As a result, studies have shown oral rehydration therapy (ORT) in this manner is as effective as IV rehydration when oral fluids are tolerated.[6]

Indications

Acute gastroenteritis commonly causes dehydration in children. This causes vomiting, diarrhea, or reduced oral fluid intake and is, therefore, can develop dehydration.

This causes extracellular fluid depletion through either diarrhea or vomiting. Oral fluid replacement is preferred in children with mild to moderate dehydration unless any contraindication exists. The intestinal solute transport mechanisms develop the osmotic gradients due to the movement of electrolytes and nutrients through the cell. The passive movement of water follows this. The transport of sodium and glucose occurs at the intestinal brush border.

Oral solutions contain adequate sodium, glucose, and osmolarity to maximize this co-transportation and to avoid problems of excessive sodium intake or additional osmotic diarrhea. Oral rehydration is a safe and cost-effective method for the management of children with dehydration. However, oral rehydration therapy has been underused.[7] A Cochrane review reports only 4% had true indications in children who received intravenous hydration.[2] 

Research demonstrates ORT is as effective as intravenous hydration in children with moderate dehydration.[8] A meta-analysis showed no clinically significant difference when oral rehydration was compared with intravenous rehydration in terms of safety and efficacy.[7]

The administration of intravenous fluid usually occurs when oral rehydration has failed. In such situations, an IV fluid administration may be more efficient for rehydration. This may be more relevant in infants and young children, especially if there is vomiting associated with diarrhea. Oliguria also indicates that dehydration is severe, and requires intravenous fluids.

The presence of severe dehydration and children in shock should be given IV fluids due to the need for rapid restoration of intravascular volume.[9] This will restore adequate tissue perfusion. Children with respiratory distress should also receive IV fluids.[5]

Contraindications

Oral rehydration is a preferred method of fluid administration in mild to moderate dehydration in the absence of any contraindication. It is not appropriate in children with severe dehydration and shock. 

Other contraindications include:

• Circulatory instability or shock
• Altered mental status (risk of aspiration)
• Persistent vomiting
• Bloody diarrhea
• Acute abdomen, intestinal obstruction, or paralytic ileus
• Electrolyte abnormalities such as hyponatremia
• Significant underlying illness
• Severe respiratory distress

Equipment

In a dehydrated child, there are many ways of enteral hydration and different solutions when intravenous fluid replacement is needed.

• Alternate forms of enteral hydration
  • Nasogastric tube
  • Nasoduodenal tube
  • Orogastric tube
  • Gastric tube
  • Gastrojejunal tube
• Normal plasma sodium rates are 135 to 144 mEq/L.
• Normal saline has plasma sodium of 154 mEq/L and 1/2 and 1/4 normal saline are a fraction of 154 mEq/L.
• Lactated Ringer's has a sodium concentration of 131 mEq/L.

Technique or Treatment

The three steps in treating dehydration are as follows:

1. Correction of fluid deficit; this includes fluid loss
2. Maintenance therapy; this involves physiologic requirements of fluid and electrolytes
3. Sustained replacement of continuing fluid losses

It is as effective as intravenous fluid in replacing fluid and electrolyte losses and has many advantages. The amount of fluid deficit should depend upon the change in weight (if available) or clinical signs.

The recommended rate is 50 mL to 100 mL/kg over 2 to 4 hours for oral fluids.[10] It is recommended to use an oral rehydration solution rather than free water or a commercial sports drink.[10] Nasogastric administration is another route for rehydration with similar rates and fluids recommended for oral administration. The implementation of an evidence-based algorithm based on the clinical dehydration score can decrease the frequency of intravenous fluid administration and reduce emergency room length of stay.

An isotonic solution should be administrated for the correction of volume depletion, regardless of the plasma sodium concentration. Frequent and periodic re-evaluation should be performed to ensure appropriate fluid volume is being administered. The fluid balance should be monitored in all children receiving IV fluids. This includes body weight and fluid input and output. In some children, when the physical examination is otherwise unremarkable, Ondansetron may be administered to control vomiting. This can reduce the need for intravenous therapy and hospitalization.

Rate

Parental fluid administration includes bolus and maintenance rates. Fluid bolus should be rapidly infused at 10 to 20 mL/kg of isotonic saline (0.9%).[2] This should be infused over 20 minutes in children with moderate dehydration and as fast as possible in the presence of severe dehydration. A hypotonic fluid or dextrose-containing fluid should not be used for bolus unless the rapid correction of hypoglycemia is needed. A single 20-mL/kg bolus improves circulation but cannot normalize the hemodynamic status. Therefore, it can be repeated as needed until adequate perfusion is restored with careful monitoring of the clinical condition and vital signs. An improvement in clinical status and resolution of signs of dehydration, such as tachycardia and dry mucous membranes, can be easily monitored.  A fluid requirement of more than 60 ml/kg without improvement in clinical status indicates other causes such as septic shock or hemorrhage.

The fluid administration rate is determined by maintenance requirements, estimated fluid deficit, and ongoing fluid losses. The maintenance rate can be calculated using the Holiday-Segar method.[11] This estimates physiologic losses of water scaled to the metabolic rate based on the weight of the child. The recommended rates are the following: 100 ml/kg for the initial 10 kilograms of weight, 50 ml/kg for each kg between 10-20 kg, 20 ml/kg for each additional kg.[11]

Tonicity

Historically hypotonic IV fluids have been administered; however, several cases of morbidity and mortality were reported.[5][12][13][14] In most hospitalized children who developed hyponatremia, it was related to the administration of hypotonic fluid. Therefore, hypotonic fluid is not appropriate in children with volume depletion.

In 2018, the American Academy of Pediatrics published a key action statement that states, “children between twenty-eight days to eighteen years of age requiring maintenance intravascular fluids should receive isotonic solutions with appropriate potassium chloride (KCl) and dextrose.” This can significantly reduce the risk of hyponatremia.”[5] Based on this key action statement, the standard of care is for potassium chloride to be added to maintenance fluids unless hyperkalemia is present or renal function is compromised. Also, if the duration of IV fluids will be short, fluids without potassium can be given. The guidelines for potassium vary greatly, and some recommended 10 mEq/L for children less than 10 kg, but the majority recommend 20 mEq/L of KCl regardless of weight.[11] 

Care must be taken not to correct hypernatremia rapidly. A free water deficit in children with hypernatremia should be corrected slowly to avoid seizures and cerebral edema. It should be replaced over 48 hours to ensure a slow and gradual fall in the serum sodium concentration. The rapid administration of fluid can cause fluid shifts and a rapid fall in the extracellular fluid sodium concentration resulting in cerebral edema due to a large intracellular shift of fluid.

An update of a Cochrane review in 2018 concluded that the use of starches, dextrans, albumin, or gelatins as opposed to crystalloids has little if any effect on mortality.[15] Small randomized and nonrandomized studies in term and preterm neonates showed some benefit with the use of albumin vs. crystalloids. These studies showed decreased edema, negative fluid balance, and less weight gain; however, no difference in length of intensive care unit stay, ventilation days, or mortality was noted.[16][17]

Dextrose

In children, who are not taking adequate calories orally, 5% dextrose (D5) should be added to maintenance fluids. If hypoglycemia is present, it should be appropriately corrected.

Complications

Hyponatremia, hypernatremia, and hypoglycemia may occur in children with dehydration as a result of illness or complication of fluid replacement therapy.

Hyponatremia

Although isonatremic dehydration is most common, hyponatremia or hypernatremia can occur. Hyponatremia is defined as a plasma sodium concentration less than 135 mEq/L. It is a common electrolyte abnormality in children receiving IV fluids. It is caused by a deficit of sodium or an excess of free water. In hospitalized children, there is an excessive release of ADH. This may require adjustment of water or sodium replacement. Hyponatremia may occur due to the administration of hypotonic solutions. It has been found with both 0.2% and 0.45% normal saline.[5] The serum sodium level estimates water balance; a normal sodium level does not assess the adequacy of volume status.

Fluid Overload

Generally, kidneys are capable of maintaining euvolemia; however, aggressive fluid administration can cause fluid overload.[5] Avoiding excessive fluid administration is critical; this is particularly more important in infants. An overly fluid administration can cause clinically significant over-hydration. It is, therefore, vital to assess for signs of fluid overload such as edema or excessive weight gain. Many specific chronic comorbidities can increase the risk of fluid overload. This includes protein loss due to liver or renal disease, congestive heart failure, and renal failure.[5]

Hypernatremia

Hypernatremia is a serum sodium level of more than 145 mEq/ L. It suggests water loss over sodium loss. There is a total body sodium deficiency despite elevated sodium concentrations. However, with the administration of isotonic fluids, the risk of hypernatremia is low.[5] 

In general, infants are at particular risk because of inadequate water replacement. This typically occurs with diarrhea or poor breastfeeding. In such a situation, the degree of dehydration may be underestimated; fluid shifts from the intracellular to the extracellular compartments. This preserves plasma and interstitial fluid volumes. Beware that the common signs of intravascular dehydration such as tachycardia, or weak pulse occur when severe dehydration is present. Since the intravascular space is relatively maintained, shock may occur late and may be sudden.

Clinical Significance

Dehydration is common in children. The clinical findings of dehydration are a manifestation of extracellular volume loss. Fluid and electrolyte issues can be challenging. The ability to correctly identify dehydration has important clinical implications. Clinical features of dehydration lack sensitivity and specificity to estimate the degree of dehydration in children. Therefore, diagnosing dehydration requires a high index of suspicion.

Enhancing Healthcare Team Outcomes

The monitoring of children with hypovolemia is a team approach. This includes body weight and fluid input and output. Early recognition is crucial for the provision of the correct combination of fluid and electrolytes at the appropriate time and rate. Monitoring is essential for the patient’s safety while adjusting the rate of rehydration.