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💧 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)

Component	Per kg	Total Daily
💧 Water	35–45 mL/kg	2.45–3.15 L
🧂 Sodium	1.5–2 mmol/kg	105–140 mmol
⚡ Potassium	1.0–1.5 mmol/kg	70–105 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

✅ Management: IV isotonic saline

📈 Hypervolaemia

Definition: Sodium and water excess

Note: Rare with normal cardiac & renal function

✅ Management:
• Restrict sodium (50–80 mmol/24h)
• Fluid restriction
• Diuretic therapy

🧂 Sodium Disorders

⬇️ Hyponatraemia Na⁺ < 135 mmol/L

🔍 Causes:

• Renal losses: Diuretics (especially thiazides)
• Adrenocortical failure
• GI losses: Vomiting, Diarrhoea
• Skin losses: Burns

⚠️ CRITICAL: Correction rate ≤ 10 mmol/L/24hrs
Rapid correction → Osmotic demyelination → Permanent brain damage!

⬆️ Hypernatraemia Na⁺ > 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

✅ Management (if acute): IV 5% dextrose or 0.45% saline at 50–70 mL/hr

⚡ Potassium Dynamics

🔄 K⁺ Moves INTO Cells With:

✅ Alkalosis • Insulin • Catecholamines (β₂) • Aldosterone

🔄 Opposite factors cause K⁺ efflux → Hyperkalaemia

⬇️ Hypokalaemia (K⁺ < 3.5 mmol/L)

📉 Reduced Intake
Dietary deficiency, K⁺-free IV

🔄 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

🚫 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

❓ Quick FAQ

Why correct hyponatraemia slowly? ▾

Rapid correction (>10 mmol/L/24h) can cause osmotic demyelination syndrome (central pontine myelinolysis), leading to permanent neurological damage. The brain needs time to adapt to osmotic changes!

When do I use central vs peripheral IV for potassium? ▾

Peripheral lines: Max 40 mmol/L concentration, ≤10 mmol/hr. Central lines: Allow higher concentrations and rates (up to 20 mmol/hr) but require ICU-level monitoring. Always use an infusion pump!

What's the first step in severe hyperkalaemia? ▾

🛡️ IV Calcium Gluconate FIRST - it stabilises the cardiac membrane within minutes. Then shift K⁺ into cells, then remove it from the body. Never skip the calcium in an emergency!

🎯 Test Your Knowledge

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

💡 Clinical Reasoning Tip:
Always ask: What's the volume status? What's causing the imbalance? Treat the underlying cause first!

📚 Keep Learning, Future Doctor!

#ElectrolyteMaster #MedicalStudent #CommunityMedicine #ClinicalPharmacology #PatientSafety #IraqHealthcare #DrAliAlSaedi

"In medicine, balance is everything. Master electrolytes, master life." 💙

⚠️ Disclaimer: Educational content only. Always follow institutional protocols and consult senior clinicians.