---

📚 Chapter 16 - Fluids Therapy: MCQ & YVA High-Yield Points

---

🔢 FLUID COMPARTMENTS (Classic MCQ Numbers)

MCQ trap: TBW is lower in obesity (fat has less water than lean tissue)

• Na+ in ECF = 140 mmol/L | in ICF = 8 mmol/L
• K+ in ECF = 4 mmol/L | in ICF = 151 mmol/L
• ECF anions = Cl- and HCO3- | ICF anions = Proteins + Glycogen
• Gibbs-Donnan equilibrium - intracellular large anions draw in K+ to maintain electrical neutrality
• Oncotic (colloid osmotic) pressure ≈ 25 mmHg - draws fluid INTO capillary
• Hydrostatic pressure pushes fluid OUT of capillary

---

💊 CRYSTALLOIDS - Compositions (Extremely High-Yield)

• 5% Dextrose = 50g glucose/L = 200 kcal energy
• 10% Dextrose = 100g glucose/L
• Peads solution (0.18% + 4% dextrose): contains 30 mmol Na and Cl + 40g glucose

---

🩸 COLLOIDS - Key Facts

• Contain high molecular weight substances (proteins, branched polysaccharides)
• Cannot cross the capillary membrane - exert osmotic pressure
• Stay in intravascular space for 6-24 hours (removed by reticuloendothelial system)
• 1 liter of colloid = adds exactly 1 liter to intravascular compartment
• In burns (capillary integrity lost) → colloids leak into interstitium → worsen edema → use crystalloids instead
• In severe hypovolemia with normal capillary integrity → colloids preferred
• Risks of large volume colloid: CHF, pulmonary edema, anaphylaxis, coagulopathy

---

📊 FLUID DISTRIBUTION - Where Does It Go? (Calculation MCQs)

1000 ml 5% Dextrose infused:

• Glucose metabolized → behaves like free water → distributes to total body water
• ICF gets 2/3 = 660 ml | ECF gets 1/3 = 330 ml
• Of ECF: Interstitial = 220 ml, Intravascular = 110 ml (only 11%)
• ⭐ D5W is useless for resuscitation - only 11% stays intravascular

1000 ml 0.9% Saline (or Ringer's/Hartman's) infused:

• Na+ is extracellular ion → goes entirely to ECF
• Interstitial gets 2/3 = 660 ml | Intravascular gets 1/3 = 330 ml (33%)
• Same applies to Ringer's lactate and Hartman's (Na-rich = extracellular)

1000 ml Colloid infused:

• Stays entirely in intravascular space → adds 1 liter to intravascular compartment

---

⚠️ HIGH-YIELD CLINICAL PRINCIPLES

Large volume 0.9% Normal Saline risk:

• Causes hyperchloraemic metabolic acidosis → renal impairment
• Avoid in large volumes except for gastric losses

Balanced solutions (Ringer's / Hartman's):

• Lactate used instead of bicarbonate (bicarbonate is unstable in solution)
• Lactate metabolized → generates bicarbonate in body
• Decrease risk of hyperchloraemia

Hypertonic saline (1.8%, 3%):

• Causes fluid shift ICF → ECF
• Used for: cerebral edema and hyponatraemic seizures

Safe isotonic alternative for maintenance:

• 4% dextrose in 0.18% saline (isotonic, safe)

---

📋 PRINCIPLES OF FLUID THERAPY

1. Resuscitation - blood/plasma/GI loss
2. Maintenance - daily baseline requirements
3. Replacement - ongoing losses (NG aspirate, drain, fistula, diarrhea)

• Start with 500 ml bolus normal saline, then reassess
• Blood transfusion if ≥30% blood loss
• Avoid large volumes of NS → use balanced solutions (except gastric losses)
• Endpoint: normal pulse, BP, urine output, lactate level

• Water: 35-40 ml/kg/day (~2.5 L/day)
• Na+: 1-2 mmol/kg/day (70-150 mmol)
• K+: 0.6-1 mmol/kg/day (50 mmol/day typical)
• Ca: 5 mmol/day | Mg: 1 mmol/day

• Pancreatic fistula: replace with fluid + 50 mmol NaHCO3 per liter lost

---

🌡️ FACTORS AFFECTING FLUID REQUIREMENTS

---

🧴 GI SECRETION COMPOSITION (Replacement fluid guide)

---

💧 DROP RATE CALCULATION (MCQ Formula)

• Blood set = 10 drops/ml
• Regular set = 15 drops/ml
• Micro drop = 60 drops/ml

---

🧪 SODIUM & WATER BALANCE (YVA Favorites)

Water Depletion (ECF):

• Pure water loss with maintained electrolytes → serum Na+ and osmolarity increase
• Causes: diminished intake, tracheostomy losses, excessive sweating
• Features: intense thirst, dry tongue, low urine output, elevated serum Na+
• Urine osmolality > serum osmolality; urine Na+ < 20 mEq/L
• Treatment: oral rehydration first; IV fluids if severe

Water Intoxication (ECF):

• Excess hypotonic solution → dilutional hyponatraemia
• Causes: excessive 5% glucose, TURP syndrome, SIADH
• Features: drowsiness, weakness, convulsions, coma, nausea/vomiting, markedly decreased serum Na+
• Treatment: stop water intake (best therapy); hypertonic saline only with intensive monitoring

---

🧂 HYPONATRAEMIA (Na+ < 135 mmol/L)

Types & Causes:

• ADH causes renal tubular water reabsorption independently of Na+
• Urine: inappropriately concentrated (>100 mOsm/L)
• Diagnosis: serum Na+ <135, plasma osmolality <280, urine Na+ >20 mEq/L, urine osmolality >100 mOsm/L
• Treatment (asymptomatic): water restriction to 1 L/day; refractory → Demeclocycline

Correction of Chronic Hyponatraemia - ⭐ YVA point:

• Rapid correction → central pontine myelinolysis (osmotic demyelination)
• Rate of correction should not exceed 10 mmol/L/day
• Mechanism: brain cells adapt to hypo-osmolality; rapid correction causes water to shift OUT of neurons → detachment from myelin sheaths → fatal

Pseudohyponatraemia:

• Caused by extreme elevation of plasma lipids or proteins (no true Na+ decrease)

---

📝 SCENARIO-BASED YVA ANSWERS (Exam Favorites)

Persistent vomiting / Gastric outlet obstruction:

• Expected: Hypochloraemic, hypokalaemic, metabolic alkalosis with paradoxical acidification of urine
• Mechanism: HCl + K+ loss → alkalosis → kidney excretes HCO3 with Na+ → hyponatraemia → kidney reabsorbs Na+ (losing H+ in urine) → acidic urine despite systemic alkalosis
• Fluid of choice: 0.9% saline (restores Na+ and H+ via kidney Na+/H+ exchange); add KCl supplementation

Early post-operative period fluid:

• Pain and narcotics → powerful stimulus for SIADH → risk of hyponatraemia with hypotonic fluids
• Use 0.9% saline or dextrose saline for first 24 hours post-op
• After 24 hours: add maintenance + replacement fluids with potassium

Intestinal obstruction:

• Ideal fluid: Ringer's lactate (composition closest to plasma and to fluid lost in obstruction)

Hypovolemic shock (burns/severe depletion):

• Normal capillary integrity → colloids preferred
• Capillary integrity lost (burns) → crystalloids preferred

---

🧒 PAEDIATRIC FLUID FORMULA (4/2/1 Rule)

---

⚡ QUICK MCQ TRAPS SUMMARY

1. 5% Dextrose → only 11% stays intravascular (useless for resuscitation)
2. 0.9% Saline → 33% stays intravascular
3. 1 L Colloid → 100% stays intravascular (6-24 hours)
4. Large NS → hyperchloraemic metabolic acidosis
5. Balanced solutions (RL/Hartman's) use lactate, NOT bicarbonate (bicarbonate is unstable)
6. Hypertonic saline treats cerebral edema + hyponatraemic seizures
7. Rapid correction of chronic hyponatraemia → osmotic demyelination syndrome
8. SIADH refractory treatment → Demeclocycline
9. Fever → +200 ml/day per °C above 37°C
10. Blood transfusion threshold: ≥30% blood loss
11. Post-op fluid of choice first 24h: 0.9% saline (SIADH risk from narcotics)
12. Paradoxical aciduria = metabolic alkalosis from vomiting (hypochloraemia)
13. Gibbs-Donnan equilibrium = K+ drawn in by intracellular large anions

---

📚 Chapter 16 (Pages 114-116) - MCQ & Viva Points

---

🧂 HYPONATRAEMIA - Diagnostics & Deficit Calculation

Urine Na+ and Osmolality Interpretation (Classic MCQ)

Sodium Deficit Formula ⭐ (Viva favorite)

Na deficit = (140 - measured Na) × 0.2 × weight (kg)

• The 0.2 = 20% ECF space (because Na+ is the main ECF cation)

Effects of Hyponatraemia (metabolic encephalopathy):

---

🔺 HYPERNATRAEMIA (Na+ > 145 mmol/L)

Causes:

• Water loss (hypovolaemic): Fasting, vomiting, diarrhea, diuretics, burns, insensible loss, Diabetes Insipidus (head injury)
• Sodium gain (hypervolaemic): Excessive hypertonic IV fluids

Effects: Nausea, vomiting, confusion, convulsions (severe)

Treatment - ⭐ Key MCQ trap:

• Acutely developed → neuronal shrinkage → relatively rapid correction safe
  • Use 5% dextrose or 0.45% saline at 50-70 ml/hour
• Slowly/chronically developed → extreme caution → rapid correction risks cerebral oedema
• Always treat underlying cause

---

🟡 POTASSIUM BALANCE - Key Numbers

• K+ is essential for neuromuscular control and regulates skeletal, cardiac, and smooth muscle activity

---

🔻 HYPOKALAEMIA (K+ < 3.5 mmol/L)

Causes:

• Inadequate intake: K+-free IV fluids, dietary deficiency, K+-deficient TPN
• Excessive excretion: Hyperaldosteronism, diuretics, steroids, aminoglycosides
• GI losses: Diarrhea (direct K+ loss); vomiting/NG suction → renal K+ wasting (kidney conserves Na+ at expense of K+)

---

🔺 HYPERKALAEMIA

Drug causes (especially with renal insufficiency): ⭐

• Potassium-sparing diuretics (Spironolactone)
• ACE inhibitors
• NSAIDs
• Mechanism: these drugs block aldosterone activity → impair renal K+ excretion

Effects (GI + Neuromuscular + Cardiovascular):

• GI: nausea, vomiting, intestinal colic, diarrhea
• Neuromuscular: weakness → ascending paralysis → respiratory failure
• Cardiovascular: ECG changes → arrhythmia → cardiac arrest

ECG Changes in Hyperkalaemia ⭐ (Must know sequence):

1. Peaked/tall T waves (earliest)
2. Widened QRS
3. Flattened P wave
4. Prolonged PR interval (1st degree block)
5. Sine wave formation
6. Ventricular fibrillation (terminal)

Management of Hyperkalaemia ⭐:

MCQ trap: 5% glucose given during treatment will also shift K+ from ECF into cells (insulin-mediated)

---

🦴 HYPOCALCAEMIA

Definition:

• Serum calcium < 8.5 mEq/L OR ionized calcium < 4.2 mg/dL
• Symptoms don't occur until ionized Ca2+ falls below 2.5 mg/dL

Causes ⭐:

• Pancreatitis - chelation of Ca2+ with free fatty acids (saponification)
• Massive soft tissue infections / Necrotizing fasciitis
• Renal failure
• Pancreatic and small bowel fistulas
• Hypoparathyroidism
• Toxic shock syndrome
• Abnormal magnesium levels / Tumour lysis syndrome
• After parathyroid adenoma removal - transient hypocalcaemia (atrophy of remaining glands)
• Breast/prostate cancer with increased osteoblastic activity (bone formation traps Ca2+)
• Note: dietary deficiency alone rarely causes it (bone reabsorption compensates)

Clinical Features ⭐ (Classic Viva):

• Paresthesia (face + extremities)
• Muscle cramps, carpopedal spasm
• Stridor (laryngeal spasm)
• Tetany
• Seizures
• Hyperreflexia
• Decreased cardiac contractility → heart failure

Two Classic Signs ⭐ (High-yield viva):

• Chvostek's sign = facial spasm from tapping over the facial nerve
• Trousseau's sign = carpopedal spasm from inflating BP cuff on upper arm

ECG Changes in Hypocalcaemia:

• Prolonged QT interval (most classic)
• T-wave inversion
• Heart block
• Ventricular fibrillation

---

🧲 HYPOMAGNESAEMIA ⭐ (Short but High-Yield)

• Causes both hypocalcaemia AND persistent hypokalaemia
• When hypoK+ or hypoCa2+ persists despite replacement → suspect and correct hypomagnesaemia first
• Rule: if hypoK+ or hypoCa2+ coexists with hypoMg2+, aggressively replace magnesium to restore the other electrolytes

---

📊 FLUID THERAPY ALGORITHM (NICE Guidelines Summary)

Algorithm 1 - When to resuscitate? (Indicators):

• Systolic BP < 100 mmHg
• Heart rate > 90 bpm
• Capillary refill > 2 seconds
• Respiratory rate > 20/min
• NEWS ≥ 5
• Passive leg raising test positive

Algorithm 2 - Resuscitation Protocol:

1. High-flow O2 + large bore IV access
2. 500 ml crystalloid bolus → reassess (ABCDE)
3. Still needs fluid? → give 250-500 ml bolus → reassess
4. If > 2000 ml given with no response → seek expert help urgently
5. Signs of shock still present → seek expert help urgently

Algorithm 3 - Routine Maintenance Requirements:

• Water: 25-30 ml/kg/day
• Na+, K+, Cl-: 1 mmol/kg/day each
• Glucose: 50-100 g/day (5% glucose contains 5g/100ml)
• Prefer NG/enteral feeding over IV if maintenance needed > 3 days

Algorithm 4 - Replacement/Redistribution:

• Estimate deficits/excesses and add/subtract from daily maintenance
• Check ongoing losses: vomiting, NG tube, biliary drain, fistulas, diarrhea, bleeding, sweating, post-AKI polyuria
• Complex issues (gross oedema, severe sepsis, hypo/hypernatraemia, renal/liver/cardiac impairment) → seek expert help promptly

---

⚡ QUICK MCQ TRAPS SUMMARY

1. 75% of body K+ is in skeletal muscles
2. Earliest ECG change in hyperkalaemia = tall peaked T waves
3. Calcium gluconate in hyperkalaemia = protects heart only, does NOT lower K+
4. Insulin + glucose = shifts K+ INTO cells
5. Chvostek = facial nerve tap | Trousseau = BP cuff
6. Hypocalcaemia ECG = prolonged QT (vs hyperkalaemia = peaked T)
7. Pancreatitis causes hypocalcaemia via saponification with free fatty acids
8. After parathyroid adenoma removal → transient hypoCa2+ (gland atrophy)
9. Breast/prostate cancer + osteoblastic mets → hypocalcaemia (bone formation traps Ca2+)
10. Persistent hypoK+ or hypoCa2+ not responding to replacement → think hypoMg2+
11. Na deficit formula: (140 - Na) × 0.2 × weight (0.2 = 20% ECF)
12. Hypernatraemia from Diabetes Insipidus = associated with head injury
13. Resuscitation bolus = 500 ml crystalloid; if >2000 ml given → seek expert help