💧 Water & Electrolyte Disturbances

Essential Clinical Guide for Medical Students

🎓 Community Medicine • First Year

📊 Total Body Water (TBW) Basics

Adult Male TBW

~60% of Body Weight

Infants: Higher • Women: Slightly Lower

🔬 Intracellular vs Extracellular Ions

🧫 INSIDE CELLS (ICF):
⚡ Cation: Potassium (K⁺)
⚡ Anions: Phosphates, Proteins

💧 OUTSIDE CELLS (ECF):
⚡ Cation: Sodium (Na⁺)
⚡ Anions: Chloride (Cl⁻), Bicarbonate (HCO₃⁻)

📋 Daily Requirements (70 kg Adult)

ComponentPer kgTotal Daily
💧 Water35–45 mL/kg2.45–3.15 L
🧂 Sodium1.5–2 mmol/kg105–140 mmol
⚡ Potassium1.0–1.5 mmol/kg70–105 mmol

🩸 Volume Disturbances

📉 Hypovolaemia

Definition: Reduction in circulating blood volume

Common Causes:
• Loss of sodium-containing fluids
• Acute blood loss
• Sequestration of fluids

Lab Finding: ↑ Serum urea (low urine flow → ↑ tubular reabsorption)

✅ Management:
IV isotonic (normal) saline to expand ECF volume

📈 Hypervolaemia

Definition: Sodium and water excess

Note: Rare in patients with normal cardiac & renal function
✅ Management:
• Restrict dietary sodium (50–80 mmol/24h)
• Fluid restriction
• Diuretic therapy (pivotal role)

🧂 Sodium Disorders

⬇️ HyponatraemiaNa⁺ < 135 mmol/L

🔍 Causes:

  • Renal losses: Diuretics (especially thiazides)
  • Adrenocortical failure
  • GI losses: Vomiting, Diarrhoea
  • Skin losses: Burns
⚠️ CRITICAL: Correction rate should NOT exceed 10 mmol/L/24hrs
Rapid correction → Osmotic demyelination (myelinolysis) → Permanent brain damage!

⬆️ HypernatraemiaNa⁺ > 145 mmol/L

🔍 Causes:

  • Renal losses: Loop diuretics + water restriction
  • Glycosuria (hyperosmolar state)
  • GI losses: Colonic diarrhoea
  • Skin losses: Excessive sweating
  • Diabetes insipidus (central/nephrogenic)
🚨 Clinical: Dizziness → Delirium → Weakness → Coma → Death (if untreated)
✅ Management (if acute):
IV 5% dextrose or 0.45% saline at 50–70 mL/hr

⚡ Potassium Dynamics

🔄 K⁺ Moves INTO Cells With:

✅ Extracellular alkalosis
✅ Insulin • Catecholamines (β₂) • Aldosterone

🔄 Opposite factors cause K⁺ efflux → Hyperkalaemia

⬇️ Hypokalaemia (K⁺ < 3.5 mmol/L)

📉 Reduced Intake
Dietary deficiency, K⁺-free IV fluids
🔄 Redistribution
Alkalosis, Insulin, β-agonists
🚽 Urinary Loss
Cushing's, Glucocorticoids
🤢 GI Loss
Vomiting, NG aspiration, Diarrhoea
⚠️ Clinical Features:
• Muscular weakness & fatigue
• Ventricular ectopic beats / arrhythmias
• ⚡ Potentiates digoxin toxicity!
✅ IV Replacement Guidelines:
• Standard: ≤ 10 mmol/hour
• Severe/Life-threatening: Up to 20 mmol/hour with continuous ECG monitoring
• Always dilute • Use infusion pump • Monitor site

⬆️ Hyperkalaemia (K⁺ > 5.0 mmol/L)

🍽️ Increased Intake
Dietary K⁺, K⁺-containing IV fluids
🔄 Redistribution
Acidosis, Insulin deficiency, β-blockers, TLS
🚫 Reduced Excretion
AKI, CKD, Addison's disease
🚨 ⚠️ Silent Killer: May have NO symptoms until cardiac arrest!

🚑 Emergency Treatment (K⁺ > 6.5 mmol/L)

1
🛡️ Stabilise Cardiac Membrane
IV Calcium Gluconate 10mL of 10%
💡 Works within minutes - cardiac protection
2
🔄 Shift K⁺ Into Cells
• Inhaled β₂-agonist (salbutamol)
• IV Glucose 50mL 50% + Insulin 5-10 IU
• IV Sodium Bicarbonate
💡 Onset: 15-30 minutes
3
🗑️ Remove K⁺ From Body
• IV Furosemide + Normal Saline
• Ion-exchange resin (oral/rectal)
• Dialysis (definitive for renal failure)
💡 Actually eliminates potassium

🎯 Test Your Knowledge

Remember: Electrolyte management isn't just about numbers—it's about understanding the patient's overall clinical picture!

❓ Quick FAQ

Why correct hyponatraemia slowly?

When do I use central vs peripheral IV for potassium?

What's the first step in severe hyperkalaemia?

⬆️

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