12 Fluid and electrolyte

MNJ12-001
Mohan, a 2-year-old child weighing 10 kg, is admitted with loose stools and vomiting with no obvious signs of dehydration. His serum sodium is 161 mEq/L and serum potassium is 3.5 mEq/L. Urine output is adequate:

Calculate the free water deficit.
Write the fluid orders for this child.

Answer

Free Water Deficit (FWD):
$FWD = 0.6 \times weight \times (1 - \frac{145}{current sodium})$
$= 0.6 \times 10 \times (1 - \frac{145}{161}) \approx 560 ml$
Fluid Orders:
- Hypernatremia should be corrected slowly over 48 hours.
- Serum sodium should be monitored serially (6–8 hourly; rate of fall should not exceed 0.5 mEq/L/hr or 10–12 mEq/L/day).
- Fluid order for each day = Maintenance fluid + half of FWD + ongoing losses
- Adequate urine output implies ~2 ml/kg/hour = 480 ml/day
- Maintenance fluid = 1000 ml + half of FWD = 280 ml + ongoing losses = 480 ml $\to$ Total fluid requirement per day = 1760 ml
- Order: 0.45% DNS 440 ml IV Q6H with 5 mEq Inj. KCl in each 500 ml IV fluid, given each day for 2 days.

MNJ12-002
A 2-year-old child weighing 9.2 kg is brought to the hospital with dehydration (8%). Na: 172 mEq/L, K: 4.2 mEq/L, Cl: 101 mEq/L, blood sugar: 80 mg/dL, BUN: 65 mg/dL, serum creatinine: 1.0 mg/dL. Calculate (with formulae) and write final IV fluid orders for the first 24 hours.

Answer

Pre-admission weight: 10 kg (since $10 kg - 8 % = 9.2 kg$ )
Free Water Deficit (FWD): $3 ml/kg \times 10 kg \times 15 mEq (target reduction max 15 mEq) = 450 ml$
Total Fluid Deficit (TFD): $8 % \times 10 kg \times 10 = 800 ml$
Solute Fluid Deficit (SFD): $800 - 450 = 350 ml$
Solute Na deficit: $0.6 \times 145 \times 0.35 = 30.5 mEq$
Solute K deficit: $0.4 \times 150 \times 0.35 = 21 mEq$

Maintenance:

Water: 1000 ml / Na: 30 mEq / K: 20 mEq

First 24 hours:

Fluids: Maintenance + $\frac{1}{2} FWD + SFD = 1000 + 225 + 350 = 1575 ml$
Total Na: $30 + 30.5 = 60.5 mEq$
Total K: $20 + 21 = 41 mEq$
Final Order: 500 ml (5% dextrose) + 7 ml RL (or NaCl) + 7 ml KCl at a rate of 65 ml/hour (or 1575 ml / 24 hr).

MNJ12-003
In relation to hyponatremia in a child:

What is the dreaded complication of overzealous correction of hyponatremia in children?
This complication is more common during correction of chronic than acute hyponatremia — True / False?
What is the advisable rate of correction of hyponatremia to prevent this complication in case of hyponatremia?
When do the clinical features develop in this condition?
What are the neurological features seen?

Answer

Central pontine myelinolysis / Osmotic demyelination syndrome (ODS)
True
Not > 12 mEq/L/day (usually 0.5 mEq/L/hour)
At least 2–6 days after the rapid correction of hyponatremia
Spastic quadri-/paraparesis, locked-in syndrome, obtundation, seizures, dysarthria, pseudobulbar palsy.

MNJ12-004
A 10-year-old child meets with a RTA and has injury to the cervical region. Vitals are as follows: Airway partially obstructed with snoring noises, RR: 22/min, paradoxical breathing, mild retractions, ${SpO}_{2}$ : 95%, HR: 78/min, peripheral pulses are feeble, cold extremities, BP: 88/36 mmHg, GCS: 13/15.

What is the physiological status of this child?
What is the probable cause of shock?
What are the points in favor of your diagnosis?
What are the initial steps in management?

Answer

Airway partially obstructed / respiratory distress / hypotensive (neurogenic) shock / altered level of consciousness.
Neurogenic shock (due to cervical spinal cord injury).
Inappropriate normal/low heart rate (absence of compensatory tachycardia), paradoxical breathing (diaphragmatic breathing due to loss of intercostal muscle innervation), hypotensive shock, and wide pulse pressure.
Initial steps in management:
a. Stabilise airway by jaw-thrust maneuver, C-spine immobilisation.
b. High flow $O_{2}$ by NRBM.
c. Avoid Trendelenburg position; keep supine with spine immobilized.
d. Isotonic fluid NS 20 ml/kg bolus rapidly (up to 3 boluses or until perfusion improves) and inotropes/vasopressors (e.g., norepinephrine/epinephrine) if fluid-refractory.
e. Look for and evaluate other life-threatening conditions like systemic bleeding and tension pneumothorax.

MNJ12-005
Write a total parenteral nutrition (TPN) order for a 3-year-old boy with a weight of 10 kg who is getting all his drugs and infusions in 200 ml of 5% dextrose.

Answer

Total fluid needed: $100 ml/kg = 1000 ml$
Already receiving 200 ml of 5% dextrose ( $200 ml \times 0.05 = 10 g dextrose \times 3.4 cal/g = 34 cal$ )
Total calories needed: ~1000 kcal
Protein: $2 g/kg = 20 g \to 20 % amino acid solution = 100 ml = 80 cal$
Fat: $3 g/kg = 30 g \times 10 = 300 cal \to 20 % fat emulsion (intralipid) = 150 ml = 300 cal$
Remaining fluid: $1000 - 200 - 100 - 150 = 550 ml (or 600 ml)$
Remaining calories needed: $1000 - (34 + 80 + 300) = 586 cal in 600 ml$
25% dextrose 600 ml = $150 g \times 3.4 = 510 cal$
Electrolytes:
- ${Na}^{+}$ : $3 mEq/kg \times 10 = 30 mEq$ ( $30 mEq / 600 ml = N/3$ )
- $K^{+}$ : $2 mEq/kg \times 10 = 20 mEq$ ( $1 ml KCl = 2 mEq$ )
Final TPN Order:
1. 600 ml N/3 in 25% dextrose with 10 ml Inj. KCl (20 mEq) IV over 24 hours.
2. 150 ml 20% Intralipid IV over 18–24 hours.
3. 100 ml 20% Amino Acid solution IV over 24 hours.

MNJ12-006
Serum Na: 136 mEq/L, Cl: 101 mEq/L, and ${HCO}_{3}$ : 10 mEq/L.

What is the anion gap?
What is the normal anion gap?
Classify the following conditions into normal anion gap or high anion gap metabolic acidosis:
- Diarrhea
- Lactic acidosis
- DKA
- ARF
- RTA
- Salicylate poisoning
- Urinary tract diversion
- IEM
- Septic shock
- Post-hypocapnea

Answer

Anion Gap:
$Anion Gap = {Na}^{+} - ({Cl}^{-} + {HCO}_{3}^{-}) = 136 - (101 + 10) = 25 mEq/L$
Normal Anion Gap: $8 - 16 mEq/L$ (or $12 \pm 4 mEq/L$ )
Classification:
- Normal Anion Gap (Hyperchloremic):
  - Diarrhea
  - RTA (Renal Tubular Acidosis)
  - Urinary tract diversion (e.g., ureterosigmoidostomy)
  - Post-hypocapnea
- High Anion Gap:
  - Lactic acidosis
  - DKA (Diabetic Ketoacidosis)
  - ARF (Acute Renal Failure)
  - Salicylate poisoning
  - IEM (Inborn Errors of Metabolism)
  - Septic shock

MNJ12-007
MNJ-P-OSCE 12. Fluid and electrolyte_page_7_Picture_2.jpeg

How will you replace ongoing loss in diarrhea?
What is the average composition of diarrhea and gastric fluid with respect to:
- Sodium
- Potassium
- Bicarbonate
- Chloride

Answer

Replacement of ongoing stool losses:
- Replace stool losses ml-for-ml every 1–6 hours using: $D_{5}$ 0.45% or 0.2% Normal Saline + 20 mEq/L Sodium Bicarbonate + 20 mEq/L KCl (or ORS solution).
Average composition of GI fluids:

Electrolyte	Diarrheal fluid	Gastric fluid
Sodium	55 mEq/L	60 mEq/L
Potassium	25 mEq/L	10 mEq/L
Bicarbonate	15 mEq/L	—
Chloride	45–50 mEq/L	90 mEq/L