1. Fluid and Electrolyte Therapy in the Pediatric Patient
Steve Piecuch MD, MPH
Department of Pediatrics
Lincoln Medical Center

2. Maintenance Requirements

3. Introduction to the Principles of Fluid and Electrolyte Therapy
Important to understand the underlying physiologic principles of a therapy commonly employed in pediatrics
Understanding basic principles essential for the understanding of the management of more complex disorders such as:
Cholera
Dengue
Pyloric stenosis
DKA
Hyperosmotic non-ketotic coma

4. Crystalloid and Colloid
Crystalloid: Water and electrolyte solution
Does not remain within the intravascular space but rather distributes to the entire extracellular space
Only impacts on the intracellular space if it causes a change in extracellular osmolarity
E.g.: 0.9% NaCl, D5 0.3% NaCl
Colloid: Contains large particles which tend to remain within the blood vessels
Colloid preferentially expands the intravascular space because the particles exert oncotic force which retains water within the intravascular space
E.g.: 5% albumin, blood, dextran solution

5. Isotonic Saline Solution
Isotonic saline solution: Solution such as 0.9% NaCl or Ringer’s lactate with a Na concentration similar to that of plasma water
Crystalloid distributes throughout the extracellular space
Infusion of crystalloid will cause a fluid shift into or out of the intracellular space only if it creates an osmotic gradient between the extracellular and intracellular space
Isotonic saline does not change the osmolarity of the extracellular space
Therefore: Isotonic saline solution remains within and expands the extracellular space and has minimal effect on the intracellular space

6. Maintenance Fluid and Electrolyte Requirements
Maintenance: The replacement of normal ongoing losses
Normally serum Na concentration is approximately 140 meq/l and serum K concentration is approximately 4 meq/l
Maintenance solution replaces normal losses
Maintenance solution does not have an electrolyte concentration equal to serum because the electrolyte composition of urine and stool is not equal to that of serum
Maintenance fluids commonly provided as a 5% dextrose solution
Dextrose provides some energy and prevents hypoglycemia
Spares protein
Cannot meet patient’s nutritional requirements with 5% (or 10%) dextrose

7. Maintenance Requirements are a Function of Caloric Requirements
0-10 kg: 100 kcal/kg
10-20 kg: 50 kcal/kg
> 20kg: 20 kcal/kg
Examples:
8 kg: 8 kg X 100 kcal/kg = 800 kcal.
12 kg: 10 kg X 100 kcal/kg + 2 kg X 50 kcal/kg = 1000 kcal kcal = 1100 kcal
20 kg: 10 kg X 100 kcal/kg + 10 kg X 50 kcal/kg = 1000 kcal kcal = 1500 kcal
25 kg: 10 kg X 100 kcal/kg + 10 kg X 50 kcal/kg + 5 kg X 20 kcal/kg = 1000 kcal kcal kcal = 1600 kcal

8. Water and Electrolyte Requirements are Determined by Caloric Requirements
Requirements per 100 kcal:
100 ml water (provided as a 5% dextrose solution)
2-4 meq Na
2 meq K
2 meq Cl
Plasma: Anion is a balance of Cl and base (bicarbonate)
Maintenance solution: Can provide some anion as Cl and some as base (lactate, citrate, phosphate) or can provide all of it as Cl
But: Providing large volumes of fluid (e.g., in DKA or hypovolemic shock) with all of the anion as Cl will promote a hyperchloremic metabolic acidosis

9. Standard Maintenance Solution
D5W with meq/l Na Cl and 20 meq/l KCl (or KAcetate or KPhosphate) will work well as a maintenance solution in most pediatric patients
Can use D5 0.2% (or D5 0.3%) NaCl with 20 meq/l KCl (or KAcetate or KPhosphate) as maintenance solution
Recent article advocated routine use of isotonic saline solution for pediatric maintenance solution
Some disease states: Another solution might be appropriate
E.g.: Sickle cell anemia patients may have a relatively high Na requirement due to high urinary Na losses
0.9% NaCl (without dextrose) in head trauma patients
K should be used with caution or omitted in patients with renal insufficiency

10. Water and Electrolyte Requirements Based on Weight
0-10 kg: 100 ml/kg
10-20 kg: 1000 ml plus 50 ml/kg
> 20 kg: 1500 ml plus 20 ml/kg
Electrolytes:
Na: 2-3 meq/kg
K: 1-2 meq/kg
Water requirement is the same as with the caloric-based system
Electrolyte requirement is greater than with caloric-based system: Electrolyte requirement is a direct linear function of weight

11. Routine Use of D5 0.45% NaCl as Maintenance Solution in Older Patients
Calculate water and electrolyte requirements on a per 100 kcal basis: Relationship between water and electrolyte requirements is fixed and does not change as weight increases
But: If the water requirement is calculated on a per 100 kcal basis and the Na requirement is calculated on a per kg basis, then as the patient’s weight increases the Na requirement will increase at a greater rate than the water requirement
Heavier children will require a maintenance solution with a higher Na concentration
Why: Because the water requirement does not increase linearly as weight increases: As weight increases the water requirement as expressed on a per kg basis decreases

12. Routine Use of D5 0.45% NaCl as Maintenance Solution (Continued)
Consider Na concentration of maintenance solution if estimate Na requirement to be 3 meq/kg (not 2-4 meq/100 kcal)
10 kg: 30 meq Na in 1000 ml: 30 meq /l:
20 kg: 60 meq Na in 1500 ml: 40 meq/l
40 kg: 120 meq Na in 1900 ml: 63 meq/l
70 kg: 210 meq Na in 2500 ml: 84 meq/l
This explains why commercially available maintenance solutions exist which are designed for children below and above a specific weight
Remember discussion about providing some anion as base: This explains why commercial solutions may contain some anion in the form of lactate or citrate

13. Dehydration

14. Dehydration
Good working definition in pediatrics: Loss of body fluid, usually predominantly from the extracellular space, due to decreased intake and/or increased losses
Most common cause is probably acute gastroenteritis
Failure to replace fluids lost from ostomies and drains with an appropriate solution may cause significant electrolyte imbalance and dehydration
Patients with apparently acceptable intake may develop significant fluid and electrolyte imbalances
E.g.: Infant with a ventricular drain will lose a significant amount of Na in the ventricular fluid
Such an infant may develop severe hyponatremia if exclusively fed human milk (low Na)

15. Classify Dehydration as to Type
Isonatremic dehydration: Serum Na between 130 meq/l and 150 meq/l
Hyponatremic dehydration: Serum Na < 130 meq/l
Hypernatremic dehydration: Serum Na > 150 meq/l
Serum Na and osmolarity
Hypernatremic patients are always hyperosmolar
Isonatremic patients are not always isoosmolar
E.g.: Serum Na 140 meq/l and glucose 600 mg/dl
Hyponatremic patients are not always hypoosmolar
E.g.: Serum Na 129 meq/l and glucose 800 mg/dl
Note: Isonatremic or hypernatremic patient with normal glucose may be hyperosmolar due to mannitol

16. Ongoing Abnormal Losses
Maintenance solution is designed to replace ongoing normal losses
Ongoing abnormal losses: Diarrhea, ostomy drainage, chest tube drainage, ventricular fluid drainage
Possible to measure electrolytes in the fluid but is usually unnecessary
May be useful if there is a large volume of drainage accompanied by significant electrolyte imbalance
Nasogasric drainage: 0.45% (or 0.9%) NaCl with meq/l KCl
Ileostomy drainage: 0.9% NaCl with meq/l KCl or KAcetate

17. Clinical Findings in Dehydration
History: Refusal to feed, vomiting, diarrhea, decreased urine output
Increased risk: Children with defective thirst mechanism, DI, impaired access to water
Physical: Sunken fontanel, decreased tears, decreased skin turgor, tachycardia, weak pulses, cool extremities
Hypotension is a late finding which occurs only after compensatory mechanisms have failed
Laboratory: Metabolic acidosis, increased BUN, increased creatinine, increased urine specific gravity

18. Classify Dehydration as to Severity
Mild: Earliest signs of dehydration
30-50 ml/kg deficit (3-5% dehydration)
Moderate: Signs of dehydration more pronounced
ml/kg deficit (6-10%)
Severe: Impending or actual circulatory failure
ml/kg deficit (9-15%)
Smaller children (e.g., < 2 years old) use 5%-10%-15% dehydration
In larger children (e.g., > 2 years old) use 3%-6%-9% rather than 5%-10%-15% to avoid providing excessive volumes of fluid
Alternative approach: IV rate of one and a half maintenance for mild to moderate dehydration and twice maintenance for moderate to severe dehydration

19. Severity (Continued)
Can use weight change to estimate the volume of the deficit if the change is recent (i.e., over 24 hours) and you are confident that the weights are reliable
Recent weight loss implies predominantly a water loss
Degree of dehydration is an estimate, not precise (analogous to a visual estimate of serum bilirubin)
Initially underestimating the degree of dehydration is not harmful so long as any existing or impending circulatory failure is recognized and treated appropriately
Initially overestimating the degree of dehydration is not harmful so long as the overestimate is recognized and the fluid regimen is appropriately adjusted

20. Isonatremic Dehydration

21. Traditional Management of Isonatremic Dehydration
24 hour repair: Provide the deficit and one day’s maintenance over a 24 hour period
Give half the total in the first 8 hours
Volume of fluid given during an emergency phase (i.e., bolus) is included as part of the first 8 hour’s fluids
The second half is given over the remaining 16 hours
Emergency phase: One or more 20 ml/kg boluses of 0.9% NaCl in moderate to severe dehydration
Repair solution: Maintenance and deficit requirements combined
In isonatremic dehydration can use D5 0.45% (or 0.3%) NaCl with 20 meq/l KCl (or KAcetate)

22. Repair of Isonatremic Dehydration (Example)
21 kg patient with 10% dehydration
Total 24 hour requirement: 3620 ml
Maintenance: 1520 ml
Deficit: 2100 ml
1810 ml in first 8 hour and 1810 ml in next 16 hours
Emergency phase: 2 isotonic saline boluses for a total of 40 ml/kg (840 ml) over 1 hour
Repair solution: D5 0.45% NaCl with 20 meq/l KCl
1810 ml – 840 ml: 970 ml over next 7 hours: 139 ml/hr
1810 ml in next 16 hours: 113 ml/hr

23. Repair Solution in Isonatremic Dehydration: Assumptions
Deficit is primarily from the extracellular space
Serum Na concentration unchanged:
Therefore the deficit must have Na concentration approximately equal to that of plasma water: 150 meq/l
Na concentration of plasma water is higher than that of serum because serum contains solids such as albumin which reduce the Na concentration
Ignore component of the deficit which consists of intracellular fluid with a low Na and a high K concentration
Ignore maintenance electrolyte requirements because they are relatively insignificant compared with the deficit electrolyte requirements
Some authorities include the maintenance electrolytes in their calculations

24. Repair Solution in Isonatremic Dehydration (Continued)
10 kg patient with 5% dehydration:
Maintenance: 1000 ml water
Deficit: 500 ml water and 75 meq Na
1500 ml water and 75 meq Na: 0.3 % NaCl
10 kg patient with 10% dehydration:
Deficit: 1000 ml water and 150 meq Na
2000 ml water and 150 meq Na: 0.45% NaCl
Remember: Na deficit exists and must be replaced in isonatremic dehydration even though serum Na is normal
Na deficit: Na component of the isotonic volume loss

25. Repair Solution in Isonatremic Dehydration (Continued)
D5 0.45% (or D5 0.3%) NaCl with 20 meq/l KCl or KAcetate works well as a repair solution
The Na requirement is determined by the deficit
The greater the deficit relative to the maintenance requirements, the greater the Na concentration needs to be
Moderate to severe dehydration: D5 0.45% NaCl preferred over D5 0.3 % NaCl
Chronic dehydration associated with a significant intracellular loss: Some patients may develop hypokalemia and require meq/l of K in the repair solution

26. Actual Calculations: Modified Finberg Technique
Example: 12 kg patient with 10% isonatremic dehydration
Maintenance volume: 1100 ml
Deficit volume: 1200 ml
Deficit Na: 1.2 liters X 150 meq/l = 180 meq
Repair the dehydration: Give 2300 ml of water and 180 meq of Na over a 24 hour period
Technique: Give half over first 8 hours and the remainder over the next 16 hours
Give 20 ml/kg isotonic saline bolus if have deficit > 10%

27. Modified Finberg Technique (Continued)
12 kg patient with 10% dehydration: Require 2300 ml of water and 180 meq of Na over a 24 hour period
Emergency phase: 20 ml/kg X 12 kg = 240 ml of 0.9% NaCl
240 ml of water
37 meq of Na
Repair solution
Water: 2300 ml ml = 2060 ml
Na: 180 meq - 37 meq = 143 meq
2060 ml of water with 143 meq of Na
5% dextrose solution with 69 meq/l of Na
Give 1150 ml over first 8 hours and 1150 ml over following 16 hours
1150 ml – 240 ml (bolus) = 910 ml
910 ml/8 hr = ml/hr
1150 ml/16 hr = 71.8 ml/hr

28. Summarize: 12 kg patient with 10% Isonatremic Dehydration
Emergency phase: 20 ml/kg of isotonic saline
240 ml of 0.9% NaCl
Dextrose free fluid bolus: Correct hypoglycemia separately if necessary
Repair solution: 5% dextrose solution with 69 meq/l of Na
D5 0.45% NaCl close enough (77 meq/l Na)
Repair solution should include meq/l of K to meet K needs and to replace any intracellular deficit
First 8 hours: 2300 ml/2 = 1150 ml ml = 910 ml/8 hr = 114 ml/hr
Subsequent 18 hours: 1150 ml/16 hours = 72 ml/hr

29. Alternative Approaches to the Repair of Isonatremic Dehydration
Give maintenance evenly over 24 hours but give half the deficit over the first 8 hours and the rest of the deficit over the next 16 hours
Complicated: Either use different IV bags for the maintenance and deficit fluids or change the electrolyte composition of the repair solution after the first 8 hours
Estimating relative contributions of the extracellular and intracellular fluid to the overall deficit
Extracellular fluid: Na concentration of 150 meq/l
Intracellular fluid: K concentration of 150 meq/l
Unnecessary if K is provided in repair solution and is increased if hypokalemia develops during the repair

30. Alternative Approaches to the Repair of Isonatremic Dehydration (Continued)
Give one or more 20 ml/kg boluses of isotonic saline as needed and then run D5 0.45% (or 0.3%) NaCl at 1.5 or 2 times maintenance
Commonly done, not an unreasonable approach
Remember: Na concentration of D5 0.45% and D5 0.3% NaCl is significantly greater than maintenance requirements
True maintenance solution contains inadequate Na to effectively correct significant isonatremic dehydration
Rapid correction of the deficit over less than 24 hours
E.g.: Give 100 ml/kg of isotonic saline solution over 3-6 hours to replace the deficit
Provide maintenance separately or by the oral route
May avoid hospitalization or shorten hospital stay

31. Correction of Abnormal Osmolarity
So long as actual or impending circulatory failure is treated appropriately with isotonic saline solution, the kidney will usually compensate if the degree of the water or Na deficit is underestimated or overestimated
Excessive urine output: May be a protective measure in a patient who is being rehydrated at an excessive rate
Rapid correction of abnormal osmolarity
Potentially harmful
Hyponatremia: Central pontine myelinolysis
Hypernatremia: Seizures
DKA: Cerebral edema
Kidney will not protect against this