Paediatric electrolyte and fluid disorders

Dehydration

• Always consider deficit + ongoing losses + maintenance
• Red flags
  • Short gut syndrome
  • Ileostomy
  • Congenital heart disease
  • Renal disease
  • Very young (<6 months)
  • Poor growth
  • Fortified feeds
  • Recent use of hypertonic solutions e.g. Lucozade
  • Repeated presentations

• Bare weight is best indicator
• Mild dehydration (<4%)
  • No clinical signs. Maybe increased thirst.
• Moderate (4-6%)
  • Sunken eyes, increased skin turgor, CRT 2-3 seconds, tachypnoea
• Severe/Shock (>6%)
  • CRT >3 seconds, mottled
  • Tachycardia, irritable, reduced conscious level, hypotension
  • Deep, acidotic breathing
  • Decreased skin turgor

• Modern categorisation is:
  • No clinical signs of dehydration
  • Some signs of dehydration
  • Severe dehydration
• NICE categorisation
  • No clinical signs
  • Clinical dehydration
  • Clinical shock

Treatment

• Replacement of deficit
  • Based on % dehydration and repeat assessment
  • Replace deficit rapidly (in most cases of gastroenteritis), slower in specific patients, over 24-48 hours in DKA and meningitis and over 48 hours in hypernatraemia
• Replacement of ongoing losses
  • Base on previous hours loss OR on previous 4 hours averaged
  • Normally 0.9% N/saline is sufficient
  • However, remember REPLACE WHAT IS LOST

Gastroenteritis

• Consider important differentials
  • UTI
  • Appendicitis
  • Surgical abdomen
  • Other infections
• Consider diagnosis carefully if only vomiting and/or significant abdominal pain
• Red flags
  • Severe abdominal pain
  • Bilious vomiting
  • <6 months
  • Persistent diarrhoea (>10 days)
  • Blood in stool/vomitus
  • Vomiting without diarrhoea

• Who needs investigation?
  • Most children require NO investigation beyond BSL
  • If requiring IV fluids, worth checking electrolytes
  • May collect faecal samples if:
    • Bloody/mucoid stools
    • Recent travel
    • >7 days diarrhoea
    • Suspect sepsis
    • Immunocompromised

• Treatment
  • Ondansetron
    • Not recommended if <2yo or <8kg
    • Only once
    • 2mg if 8-15kg
    • 4mg if 15-30kg
    • 8mg if >30kg
  • Anti-diarrhoeals strongly advised AGAINST

• Oral rehydration
  • Stop any feed fortifications
  • Continue breastfeeding
  • Suggest ORS
  • Early feeding as soon as rehydrated promotes GI tract recovery and slows stool output
  • If diarrhoea worsens and on formula, consider 2 weeks of lactose-free formula due to enteritis-induced lactase deficiency
    • Especially if perianal pruritis associated
    • Can check for reducing substances in stool to confirm

• TOF
  • Mild or no dehydration can be discharged if tolerating any fluids
  • Aim 10-20mL/kg over 1 hour of ORS q5min
  • If significant ongoing losses, consider early NGT
• Nasogastric rehydration
  • If vomiting, consider ondansetron and halve rate temporarily
  • Use ORS
  • Rapid
    • 25mL/kg/hr for 4 hours
    • Suitable for most children with moderate dehydration
  • Slow
    • Infants <6 months, comorbidities, significant abdominal pain
    • Replace deficit over 6 hours then give maintenance over next 18 hours

• IV rehydration
  • Indicated for severe dehydration or if NGTR fails
  • 20mL/kg boluses if shocked
  • Measure BSL and treat hypoglycaemia with 5mL/kg 10% dextrose
  • Rapid IV rehydration
    • If >4yo, moderate dehydration with no significant abdominal pain/electrolyte disorder
    • 10mL/kg/hr (up to 1000mL/hr) for 4 hours N/S + 5% dextrose
    • If serum K <3, add KCl 20mmol/L
    • Measure Na, K and glucose at outset and then 24 hourly

Hyponatraemia

• Differential in children
  • Excessive hypotonic solutions
  • SIADH: Meningitis, pneumonia, bronchiolitis, sepsis, surgery, pain, N&V
  • Exogenous antidiuretic (Desmopressin) with ongoing hypotonic fluid intake
  • GI fluid losses
  • Adrenal insufficiency
  • Renal tubular failure
  • Psychogenic polydipsia

• Corrected sodium
  • = Measured sodium + (Glucose – 5)/3
• Measure urine sodium and osmolality
• Treatment
  • If seizure/ALOC: DRABCDE + 4mL/kg 3% NaCl over 15 min
    • Re-measure Na – Should have risen by 3. If still seizing or <125 – repeat dose
  • Overall should have <8mmol/day rise in Na i.e. if 118 to 126 already. Try to keep it at 126
  • If no symptoms
    • If euvolaemic or hypervolaemic – fluid restrict
    • If moderately dehydrated and sodium 130-135
      • Try NGTR
    • If severe dehydration or sodium <130: N/S + 5% dextrose to slowly rehydrate over 6 hours until child can take enteral feeds

Hypernatraemia

• Causes in children
  • Water loss in excess of sodium: Diarrhoea, hyperosmolar refeeding, severe burns
  • Inability to obtain fluids esp. neonates (e.g. inadequate breast milk intake
  • Impaired thirst drive (hypothalamic lesion)
  • Diabetes insipidus
  • Osmotic diuresis
  • Gain of sodium
    • Large quantities of sodium in inappropriate formula concentration
    • Iatrogenic

• Assessment
  • Lethargy, irritability, doughy skin, ataxia, tremor, hyperreflexia, seizure, ALOC
  • Urine sodium and osmolality
• Treatment
  • Resuscitate with N/S
  • Lower sodium max 12mmol/L in 24 hours
    • Even slower if chronic hypernatraemia
  • Stop any feed fortifications
  • If mild (146-149) just treat underlying cause and repeat Na
  • If moderate (150-169)
    • Replace deficit + maintenance at uniform rate over 48 hours
    • Check U&E and glucose hourly initially
    • Slow rate if Na falling by >0.5mmol/L/hr (i.e. by 20%)
  • If severe (>= 170)
    • Replace deficit _ maintenance over 72-96 hours and arrange transfer to ICU

Hypokalaemia and hyperkalaemia

Hypokalaemia

• If <3, add 20mmol/L KCl and re-measure

Hyperkalaemia

• >5.5 (>6.0 in neonates)
• Causes
  • Reduced excretion: Renal failure, adrenal insufficiency
  • Transcellular shift: Acidosis, DKA, lactic acidosis
  • Increased production: Multitrauma, rhabdomyolysis, haemolysis, tumour lysis, burns
  • Exogenous: Iatrogenic, ingestion, massive transfusion
  • Medication: NSAID, trimethoprim, heparin, chemotherapy, potassium-sparing diuretic, ACEi, beta-blocker, succinylcholine, digoxin, mannitol

• ECG: Peaked T waves, flat P waves, prolonged PR, wide QRS, sine wave, ventricular arrhythmia, asystole
• Investigations
  • FBC, U&E, glucose, VBG, urine electrolytes, CK, cortisol/ACTH/aldosterone
• Treatment
  • Symptomatic/>7/abnormal ECG
    • Discuss dialysis and transfer
    • Salbutamol: 2.5-5mg neb q1h
    • Calcium gluconate 10% 0.5mL/kg slow IV injection over 2-5 min (15-20min if stable)
      • OR Calcium chloride 10% 0.1-0.2mL/kg as above (preferably CVL)
    • Insulin actrapid 0.1U/kg IV + dextrose 10% 5mL/kg IV boluses THEN infusion 0.1U/kg/hr + N/S + 10% dextrose at maintenance rate (careful if hyponatraemic)
    • Bicarbonate if acidotic 1-3mL/kg 8.4% over 5-30 minutes (NOT WITH CALCIUM)
    • +- Resonium PR/PO 0.3-1g/kg q6h
    • Consider hydrocortisone 1-2mg/kg IV if possible adrenal insufficiency
  • Moderate 6-7, asymptomatic, normal ECG
    • Salbutamol, insulin/dextrose IV, resonium and bicarbonate if metabolic acidosis
    • Bicarbonate 1mL/kg 8.4%over 30 minutes
  • Mild (>5.5, asymptomatic, normal ECG)
    • Consider no treatment
    • Salbutamol, resonium, bicarbonate IV if metabolic acidosis
• Contraindications to resonium
  • Ileus, recent abdominal surgery, perforation or hypernatraemia
• Corrected potassium
  • K rise of 0.5 for every 0.1 in pH below 7.4
  • K down 0.3 every 0.1 in pH above 7.4

Last Updated on November 22, 2021 by Andrew Crofton