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Rehydration in Pediatrics

Rehydration in Pediatrics is an essential skill for all doctors. The following essay is an easy, step-wise guide to an approach to rehydration. Pediatric Rehydration methods vary, but for a written examination, the following step-wise approach will make the understanding of pediatric rehydration easier.

By Aparajeya Shanker, Faculty of Medicine, Medical University Pleven

www.aparajeya.com

Quick Glance

Rehydration in Pediatrics requires the understanding of the following basic principles:

Glucose and Saline solutions are administered together
Rehydration efforts need to take into account fluid and electrolyte losses, namely Na+ and K+ losses.
Saline is used for Fluid and Na+ replacement
Glucose is used for Fluid and K+ replacement (K+ infusion)

Types of Dehydration

Mild Dehydration → 5% loss of body weight
Moderate Dehydration → 5-10% loss of body weight
Severe dehydration → 10-15% loss of body weight

For ease of calculation and for safety, always assume the higher limit in the range of dehydration, ie, for Mild dehydration assume 5% loss of body weight, for Moderate dehydration assume 10% loss of body weight, and for severe dehydration assume 15% loss of body weight.

Types of Losses

Pathological Losses
1. Calculated by: Pathological losses: 10 X Body weight (in kg) X % of dehydration
2. Daily Requirements
  1. Calculated by the Holiday-Segar formula (Or a variation of the formula)
  1. For a child within 10 kg: 100 ml/kg
  1. For a child between 11 to 20 kg: 1000ml + 50ml/kg, for every kg above the 1st 10 kg
3. 1. For a child above 20kg: 1500ml + 20ml/kg for every kg above 20kgb.
4. 1. Examples of Daily Requirements
  1. For a 5kg child
    1. 100ml X 5= 500ml every day This is because the the child is within 10 kg
  2. For a 15 kg child
    1. 1000ml + 50ml X 5 = 1000ml+ 250= 1250 ml per day This is because the child is 15 kg. The 15 kg are divided into 10kg + 5 kg for the purposes of the formula, and the 1000ml is used for the first 10kg as a standard, plus the 50ml per kilogram is calculated for every kilogram over the first 10 kilogram to give us the daily requirement. Since the child is 15 kilograms, the child is essentially 5 kilograms over the 10 kilogram standard for the formula.
  3. For a 25 kg child
    1. 1500ml + 20ml X 5 = 1600ml per day
  4. Current or Ongoing Losses
    1. For the ease of calculation, assume a standard value of 100ml per day
  1. For a 5kg child
    1. 100ml X 5= 500ml every day This is because the the child is within 10 kg
  2. For a 15 kg child
    1. 1000ml + 50ml X 5 = 1000ml+ 250= 1250 ml per day This is because the child is 15 kg. The 15 kg are divided into 10kg + 5 kg for the purposes of the formula, and the 1000ml is used for the first 10kg as a standard, plus the 50ml per kilogram is calculated for every kilogram over the first 10 kilogram to give us the daily requirement. Since the child is 15 kilograms, the child is essentially 5 kilograms over the 10 kilogram standard for the formula.
  3. For a 25 kg child
    1. 1500ml + 20ml X 5 = 1600ml per day
  4. Current or Ongoing Losses
    1. For the ease of calculation, assume a standard value of 100ml per day

TOTAL FLUID VOLUME PRESCRIBED: PATHOLOGICAL LOSSES + DAILY LOSSES + CURRENT LOSSES

Electrolytes

Electrolytes are lost along with fluids, and we attempt to correct Na+ and K+ electrolytes
Electrolyte losses are a function of pathological losses, daily requirements and current losses

Pathological Losses
1. Na+→ for every 100ml of Pathological loss, 6-8mmol of Na+ is lost For ease of calculation, assume 8mmol for 100ml of Pathological loss
2. K+ → for every 100 ml of Pathological loss, 2-3 mmol of K+ is lost For ease of calculation, assume 2 mmol for 100 ml of Pathological loss
Daily requirements
Daily requirements are calculated based on the body weight of the patient
1. Na+ → 3mmol/kg
2. K+ → 2 mmol/kg
Current Losses Current or ongoing losses are measured as a standard
1. Na+ → 6-8 mmol
2. K+ → 2-3 mmol

Electrolyte deficit, or the amount of electrolytes needed is the sum of all electrolytes needed. It will be separate for Na+ and K+ You will need to calculate it as: Na+ needed→ Na+ lost due to Pathological losses + Na+ Daily Requirements + Current Losses of Na+ K+ Needed→ K+ lost due to Pathological losses + K+ Daily requirements + Current losses of K+

Example of electrolytes needed

Lets assume that a 5kg patient with moderate dehydration has come to the clinic.

Pathological loss in this patient is:

Pathological loss→ 10 X Body Weight in Kg X % of Dehydration
- 10 X 5 X 10 = 500 ml

Na+ Requirements are:
- Pathological losses= Every 100 ml of Pathological loss has 8 mmol of Na+
  - for 500ml= 8 X 5 = 40mmol
- Daily requirements= 3 mmol/kg
  - For a 5kg patient = 3 X 5 = 15 mmol
- Ongoing Losses= Standard of 8 mmol
K+ Requirements are:
- Pathological losses= Every 100 ml of pathological loss has 2 mmol of K+
  - For 500 ml = 2 X 5 = 10 mmol
- Daily Requirements = 2 mmol/kg
  - For a 5kg patient= 2 x 5 = 10 mmol
- Ongoing losses= Standard of 2 mmol

Phases of Rehydration

Phase 1
1. 1/2 of Pathological Losses are infused during this period
2. Only Na+ ions are replaced during this phase
3. This is carried out over 30-60 minutes for immediate resuscitation
4. Preferred method of fluid administration is NG tube or IV. NG is preferred over IV for younger children and is well tolerated in patients with gastroenteritis
Phase 2

1/2 of Pathological Losses + 1/3 of Daily Losses
Na+ and K+ ions
Also called replacement phase

Phase 3
- 2/3 of Daily Losses + Current Losses

The type of fluid chosen (whether glucose or Saline) is determined by the amount of K+ and Na+ ions we need to replace. The Total Fluid Volume that we need to prescribe has to be divided into two specific components, Glucose and Normal Saline, so that we can replace the electrolytes for the patient.

SALINE: 100 ML of saline contains 15 mmol of Na + KCl infusion: KCl is infused into Glucose for K+ electrolytes, 1 ml of KCl contains 2 mmol of K+. This 1 ml is added to the Glucose infusion bag and as such, is not factored in the calculation. Only the volume of the glucose added is factored into the calculation.

Prescribing fluids for rehydration

Utilize the 3 step approach
1. Assess the Pathological Losses
2. Assess the Daily Losses
3. Assess the Electrolyte Requirements
Use the 3 Phase Rehydration method
- Address the Na+ deficit first (The first fluid to be prescribed is saline)
- Whatever is left from the total fluid volume, that volume is the Glucose to be prescribed

At each Phase, whatever volume you calculate= Fluid 1 is Saline, Fluid 2 is Glucose

Phase 1 Volume of liquid required (addressing the Na+ deficit)= Saline Volume Only Phase 2 Volume (addressing the Na+ deficit and the K+ deficit) = Saline Volume + Glucose Volume

Phase 3 Volume (Addressing Na+ Deficit and the K+ deficit)= Saline Volume + Glucose Volume

Example for illustrating the rehydration strategy

Patient weight: 10 Kg

Patient Dehydration: 5%

Pathological Losses: 10 X Body Weight X % of Dehydration

10 X 10 X 5 = 500ml

Daily Losses: 100ml/kg = 100 X 10 = 1000 ml

Electrolyte losses:

Na+ losses:
- Pathological→ 8 X 5 = 40 mmol
- Daily = 3 X 10 = 30
- Current = 8 mmol
K + losses:
- Pathological→ 3 X 5 = 15 mmol
- Daily = 2 X 10 = 20 mmol
- Current = 3 mmol

3 Phase Rehydration Planning

Phase 1 Rehydration
- 1/2 pathological losses= 1/2 of 500ml = 250 ml → For Liquid rehydration
- 1/2 pathological losses = 1/2 of 40 mmol of Na+ = 20 mmol → For electrolyte balance
- We need to split the 250 ml of fluid into Saline and glucose solution. The glucose here will not be infused with K+. The amount of Saline is dependent on how much Na+ deficit we can correct
- 100 ml of Saline contains 15 mmol of Sodium, therefore:
  - For 20mmol of Na+ we need= 100 X 20/15 = 133 ml of Saline
- Phase 1 Fluid Volume in total= 250 ml, of which 133 ml is Saline
- The rest of it will be Glucose, which is= 250-133ml= 117 ml
- Phase 1 Rehydration Total Fluid for rehydration: 250 ml 0.9 Normal Saline: 133ml
  5% Dextrose Solution (without infusion): 117 ml
  Given over 30 minutes to 2 hours
Phase 2 Rehydration
- 1/2 of Pathological losses + 1/3 of Daily losses
  - 250ml + 333ml = 583 ml
  - Assume 580 ml for easier calculations
- Fluids= 580 ml
- Electrolytes
  - Na+ = 30 mmol
    - 1/2 of Pathological losses + 1/3 of Daily losses
      - 1/2 of 40 + 1/3 of 30 → 20 + 10 = 30 mmol
  - K+ = 30 mmol
    - 1/2 of Pathological losses + 1/3 of Daily losses
      - 1/2 of 15 + 1/3 of 20 → 7 + 6 = 13 mmol
- Saline Required for Na+ Deficit correction= 200 ml
  - 100 X 30/15 = 200 ml
- Glucose Volume= 580 ml -200 ml = 380 ml
- K+ Infusion → 100 ml of Glucose contains 3-4 mmmol of K+ so the above Glucose volume is correct for K+ deficit correction
  Phase 2 Rehydration
  Total Fluid for Phase 2 Rehydration: 580 ml 0.9 Normal Saline: 200 ml
  5% Dextrose Solution with K+ Infusion: 380 ml Given over 8-16 hours
Phase 3 Rehydration
- 2/3 of Daily Losses + Current Losses
- Fluids = 766ml 666 ml + 100 ml (standard measured volume)
- Electrolytes
  - Na+ = 30 mmol
    - 2/3 of Daily Losses + Current Losses
      - 20 + 8 = 28 (round off to 30 for easier calculation)
  - K+ = 15 mmol
    - 2/3 of Daily Losses + Current Losses
      - 13 + 2 = 15
- Saline Amount required for Na+ Deficit correction:
  - 100 X 30 / 15 = 200 ml
- K+ infused glucose amount required for K+ deficit correction
  - 766-200= 566ml
    Phase 3 Fluid Prescription
    Total Fluid Required: 766ml
    0.9 Normal Saline Required: 200ml
    5% Dextrose with K+ Infusion= 566ml
    Given over 8-16 hours

Notes

Please note that realistically, these calculations are not always used in the emergency departments. Oral rehydration solutions are most widely used for patients who are moderately dehydrated and are capable of drinking on their own. Apple Juice and Oral Rehydration Solution have the same outcome according to one randomized control trial
A quick tip for rehydration is to use the formula
- Fluid Volume for Rehydration: 1.5 X Daily Fluids Required
KCl Infusions can also be administered to correct hypokalemia in pediatric patients if rehydration therapy is not working.
It is also important to note that Oral Rehydration Solution contains Na+ and Glucose in the same concentration. This is to allow better uptake of the glucose by the cells through the GLUT1 receptors.
Emergency Administration of Insulin in patients with DKA or with severe dehydration will also improve glucose uptake.