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MAINTENANCE FLUID THERAPY
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Maintenance fluid requirements can be estimated by the Holliday–Segar method. Daily water requirements are calculated based on body weight and the assumption that each kilocalorie of energy metabolized results in the net consumption of 1 mL of water (Table 91). Water requirements form the basis for the estimated needs for sodium and potassium (Table 92). This method is not recommended for premature infants or term infants younger than 2 weeks of age.

While several studies argue strongly against the use of hypotonic maintenance fluids across all pediatric populations there are limitations in the evidence including the populations studied, study heterogeneity, and paucity of data on potential adverse events from an increased solute load

It is equally likely that the administration of an inappropriately high fluid administration rate in the context of nonosmotic antidiuretic hormone release is responsible for most cases of iatrogenic hyponatremia

The focus on tonicity of maintenance fluid without adequate study of the rate or volume clearly contributes to wide practice pattern variation

Holliday–Segar maintenance therapy is based on the assumptions that all daily water losses occur as the result of either insensible or urine losses and that all homeostatic mechanisms are intact

Insensible losses in the absence of conditions leading to increased fluid loss (e.g., fever, hyperventilation, prematurity and low birth weight, skin defects, burns) are usually 400–700 mL/m^{2} body surface area (BSA) (higher in neonates, up to 1150 mL/m^{2} BSA)

Holliday–Segar method may not be appropriate in children with urine outputs that are abnormally high (e.g., adrenal failure, diuretic exposure) or low (e.g., hypovolemia, syndrome of inappropriate antidiuretic hormone (SIADH) secretion, renal failure, congestive heart failure, nephrotic syndrome, cirrhosis)

Fever increases metabolic rate and therefore maintenance requirements go up (add about 10% for every °C increase > 38°C for the duration of the febrile episode)

Burns: Increased needs based on percent body surface area involved

Oligoanuria/anuria in a euvolemic/hypervolemic child (e.g., established kidney injury): Maintenance fluid should be prescribed by calculating insensible losses and replacing urine output every few hours

Dextrosecontaining intravenous fluids (IVFs) are used to supply a portion of the caloric needs, to prevent hypoglycemia and starvation ketosis

Stock solutions containing 5% dextrose (D_{5}) are appropriate for most situations, but 10% dextrose (D_{10}) or higher is also available

Dextrose concentrations above 12.5% are usually reserved for central catheters because the increased osmolality is irritating to peripheral veins
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MAINTENANCE ELECTROLYTE CALCULATION
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Sample Maintenance Fluid and Electrolyte Calculation:
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Maintenance fluid, sodium, and potassium requirements for an otherwise healthy 37kg child:
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2 mEq/100 mL/day × 1840 mL/day = 37 mEq/day
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$ 37 mEq / day 1840 mL / day = K + 1000 mL K + = 20 mEq / L $
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Therefore, an order for routine maintenance fluids for this child would be:
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D_{5}/0.2% NaCl with 20 mEq KCl/L to run at 77 mL/h.
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Standard (Stock) Solutions for Routine Maintenance Intravenous Fluids (Table 93)
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REPLACEMENT FLUID THERAPY
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Replacement therapy corrects preexisting deficits (dehydration) and ongoing losses.
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Consider both the extent of the dehydration and the overall balance of water and sodium that is created.
$%dehydration=((Preillness weight\u2212Current weight)/Preillnessweight)\xd7100$

If preillness weight is not available, percent dehydration can be clinically assessed:

✓ Mild Dehydration (up to 3% in older children, 5% in infants): Thirst, normal exam, reduced urine output

✓ Moderate Dehydration (3–6% in older children, 5–10% in infants): Tachycardia, dry mucosa, sunken eyes, delayed capillary refill, irritable, oliguria

✓ Severe Dehydration (>6% in older children, >10% in infants): Thready pulses, low blood pressure, anuria, cold and mottled, lethargy

In acute dehydration (<72 hours), mainly ECF (80% of total losses) is lost. In prolonged dehydration, fluid loss is more evenly lost from both extracellular (60%) and intracellular (40%) compartments

Laboratory findings in dehydration:

✓ Elevation of serum creatinine and urea

✓ Alteration of serum sodium, potassium, and bicarbonate

✓ Increase in urinespecific gravity (except with impaired renal concentration)

✓ Elevation of blood cell counts (hemoconcentration)

Type of dehydration

✓ Isonatremic (serum Na^{+} 135–145 mEq/L): Loss of Na^{+} and water in a balance that does not exceed the body’s ability to maintain isonatremia

✓ Hyponatremic (serum Na^{+} < 135 mEq/L): Retention or replacement of free water in the face of Na^{+} salt and water losses

✓ Hypernatremic (serum Na^{+} > 145 mEq/L): Loss of free water in excess of Na^{+}containing fluid
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The gastrointestinal tract is a common source of ongoing losses from illness, or postoperative drainage. These ongoing losses are replaced with parenteral fluids, in volumes equivalent to the losses at a frequency that will avoid significant depletions (e.g., every 1–8 hours)

The replacement fluid should contain electrolytes in concentrations that approximate the lost fluid. Some recommendations are listed in Table 94
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Consider oral rehydration if patient is hemodynamically stable and if there is no impairment of swallowing function

Oral rehydration solutions (ORS) are best, with concentrations of electrolytes and carbohydrates that approximate the World Health Organization/UNICEF ORS product

Small volumes (e.g., 5–10 mL) frequently (e.g., every 5–10 minutes) are initiated, and increased slowly as tolerated
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PARENTERAL REHYDRATION
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Phase I: Initial Stabilization
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Phase II: After Initial Stabilization

Significant ongoing losses (e.g., continued vomiting and/or diarrhea) will require additional fluid replacement

Modifications to the rate and nature of the IVF should be guided by:

✓ Urine output: goal = 1–2 mL/kg/h

✓ Weight, vital signs, clinical appearance

✓ Repeat serum electrolytes: If needed
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Phase III: Resolution

Trials of oral/gastric feeds usually begin with clear liquids if vomiting is present

If vomiting is resolved, or not a factor, prompt advancement to regular diet is encouraged (including breast milk or infant formula)

Avoid foods high in simple sugars (e.g., juices, sodas) that can worsen or prolong diarrheal symptoms

Wean IVF rate or hold IVF for short periods to encourage oral intake
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ISONATREMIC DEHYDRATION
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Fluid lost has sodium concentration similar to blood

Although the entire fluid deficit must be corrected sodium repletion should only be considered for fluid lost from the ECF (intracellular fluid sodium concentration is negligible)

In acute dehydration (illness <72 hours) 80% of the fluid lost is from the ECF, in chronic dehydration (illness >72 hours) 60% of the fluid lost is from the ECF

Don’t forget that maintenance fluid should also be included in total fluid calculations

In general the ideal IVF solution in isonatremic dehydration will usually approximate D _{ 5 } /0.45% NaCl

Some clinicians prefer to use D_{5}/0.9% NaCl in this circumstance because of the risk of hyponatremia in a subset of patients with high circulating antidiuretic hormone levels. This approach must be used cautiously in patients with acute kidney injury/oligoanuria
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Oneyearold with 10% dehydration, with current weight 9 kg, presents with 5 days of diarrhea. Serum sodium concentration is 140 mEq/L.
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Preillness weight: (Current weight (kg) × 100)/100 − % dehydration
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= (9 × 100)/100 – 10 = 900/90 = 10kg
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Calculation of fluid deficit:
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Fluid deficit = Preillness weight (kg) – Current weight (kg)
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Calculation of sodium deficit from ECF losses:
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Calculation of maintenance fluid and sodium requirements:
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Total fluid and sodium requirement:
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Optimal fluid: Fluid containing 117 mEq Na/2000 mL = 58.5 mEq/L
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Available fluid: D_{5}/0.45% NaCl (77 mEq/L) at a rate of 83 mL/h (2000 mL/24h)
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HYPONATREMIC DEHYDRATION
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Sodium deficit in excess of water deficit

Start calculations as if the patient had isonatremic dehydration and then calculate the additional sodium deficit

Sodium is freely distributed throughout the TBW (60% of the patient weight) and therefore the volume (factor) of distribution of sodium is 0.6 of the total body weight

In general the ideal IVF solution in hyponatremic dehydration will usually range between D _{ 5 } /0.45% and D _{ 5 } /0.9% NaCl
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Oneyearold with 10% dehydration, with current weight 9 kg, presents with 2 days of diarrhea. Serum sodium concentration is 123 mEq/L.
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Preillness weight: (Current weight × 100)/100 – % dehydration
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= (9 × 100)/100 – 10 = 900/90 = 10 kg
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Calculation of fluid deficit:
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Fluid deficit = Preillness weight (kg) – Current weight (kg)
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Calculation of sodium deficit from ECF losses (identical to isonatremic example):
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Calculation of additional sodium deficit (specific to the hyponatremic patient):
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(sodium (mEq) desired – sodium (mEq) actual) × volume (L) of distribution
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Calculation of maintenance fluid and sodium requirements:
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Total fluid and sodium requirement:
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Optimal fluid: Fluid containing 218 mEq Na/2000 mL = 109 mEq/L
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Available fluid: May alternate between D_{5}/0.45% (77 mEq/L) NaCl and D5/0.9% (154 mEq/L) NaCl every 12 hours at a rate of 83 mL/h (2000 mL/24h)
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HYPERNATREMIC DEHYDRATION
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Free water deficit (FWD) in excess of salt deficit

Assumption: FWD = 0.6 × weight (kg) × [(actual sodium/140) – 1]

In general the ideal IVF solution in hypernatremic dehydration will usually range between D _{ 5 } W and D _{ 5 } /0.2% NaCl
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Oneyearold with 10% dehydration, with current weight 9 kg, presents with 5 days of diarrhea. Serum sodium concentration is 155 mEq/L.
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Preillness weight: (Current weight × 100)/100 – % dehydration
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= (9 × 100)/100 – 10 = 900/90 = 10kg
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Calculation of fluid deficit:
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Fluid deficit = Preillness weight – Current weight
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10 kg – 9 kg = 1 kg or 1 L
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Calculation of FWD:

FWD = 0.6 × weight(kg) × [(actual sodium/140) – 1]

Example: Sodium = 155 mEq/L, weight = 10 kg; FWD = 0.6 × 10 kg × [(155/140) –1]/140) – 1] = 0.64L = 640 mL
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Calculation of sodium deficit from ECF losses:

Total fluid deficit is 1000 mL, 640 mL should be replaced as free water and the remaining 360 mL should be replaced as in isonatremic dehydration

Calculation of sodium deficit in remaining 360 mL of ECF losses:

Sodium deficit = Fluid deficit (L) × Percentage of fluid loss from ECF × Average ECF sodium concentration (145 mEq/L)

0.36 (L) × 0.6 × 145 mEq/L = 32 mEq
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Calculation of maintenance fluid and sodium requirements:
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Total fluid and sodium requirement:
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Optimal fluid: Fluid containing 62 mEq Na/2000 mL = 31 mEq/L
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Available fluid: D_{5}/0.2% NaCl (34 mEq/L) at a rate of 83 mL/h (2000 mL/24h)