AIM • STUDENT MEMORY SUPPORT
Electrolyte & Acid–Base Disorders
Final Year MBBS • Renal Module • High-yield memory reinforcement and last-minute revision
1. High-Yield Flashcards
Tap each question to reveal the answer.
What does serum sodium mainly reflect clinically?
The relationship between body sodium and body water.
Why can acute severe hyponatremia cause seizures?
Low extracellular tonicity drives water into brain cells, causing cerebral swelling.
What is the usual basic disturbance in hypernatremia?
A water deficit relative to body sodium.
Why must chronic sodium disorders be corrected carefully?
The brain adapts to chronic tonicity changes; rapid reversal can cause neurological injury.
What is the most immediate danger of severe hyperkalemia?
Cardiac electrical instability and life-threatening arrhythmia.
What does intravenous calcium do in dangerous hyperkalemia?
It stabilizes the myocardium; it does not remove potassium.
How does insulin with glucose lower serum potassium?
It temporarily shifts potassium from extracellular fluid into cells.
Which ECG finding strongly suggests hypokalemia?
Prominent U waves, often with T-wave flattening.
What deficiency can make hypokalemia difficult to correct?
Hypomagnesemia.
Why can severe hypophosphatemia cause respiratory weakness?
Phosphate depletion impairs ATP production and respiratory-muscle function.
What neuromuscular pattern suggests hypermagnesemia?
Neuromuscular depression with reduced deep tendon reflexes.
What neuromuscular pattern suggests hypomagnesemia?
Increased excitability causing cramps, tremor, tetany or seizures.
What is the primary biochemical change in metabolic acidosis?
A primary fall in bicarbonate.
How does the body compensate for metabolic acidosis?
Ventilation increases, lowering PaCO₂.
What suggests a mixed acid–base disorder?
Measured compensation differs substantially from the expected physiological response.
2. Mnemonics
Mnemonic Title: ABG Interpretation Sequence
P-C-B-C
Meaning: PH → CO₂ → Bicarbonate → Compensation.
Mnemonic Title: Hyperkalemia Treatment Logic
P-S-R
Meaning: Protect myocardium → Shift K⁺ into cells → Remove K⁺ from body.
Mnemonic Title: Sodium Brain Effect
LOW = SWELL, HIGH = DRY
Meaning: Low sodium → brain-cell swelling; high sodium → brain-cell dehydration.
3. Memory Tables
Sodium Disorders
| Feature | Hyponatremia | Hypernatremia |
|---|---|---|
| Water shift | Into cells | Out of cells |
| Brain effect | Cellular swelling | Cellular dehydration |
| Important danger | Seizures / neurological deterioration | Neurological dysfunction / dehydration |
| Correction principle | Controlled rise | Controlled fall |
Four Primary Acid–Base Disorders
| Disorder | Primary Change | pH | Compensation |
|---|---|---|---|
| Metabolic acidosis | HCO₃⁻ ↓ | ↓ | PaCO₂ ↓ |
| Metabolic alkalosis | HCO₃⁻ ↑ | ↑ | PaCO₂ ↑ |
| Respiratory acidosis | PaCO₂ ↑ | ↓ | HCO₃⁻ ↑ |
| Respiratory alkalosis | PaCO₂ ↓ | ↑ | HCO₃⁻ ↓ |
4. Rapid Revision Points — Last-Minute Revision
Must Remember:
- Sodium abnormalities primarily disturb the brain through osmotic water shifts.
- Severe symptomatic hyponatremia requires urgent but controlled correction.
- Hypernatremia usually reflects a water deficit rather than simply sodium excess.
- Hyperkalemia with important ECG abnormalities is a cardiac emergency.
- Calcium protects the myocardium in hyperkalemia but does not lower total body potassium.
- Insulin lowers serum potassium by redistribution, so potassium removal is still required.
- Prominent U waves suggest hypokalemia; peaked T waves suggest hyperkalemia.
- Severe phosphate depletion can weaken respiratory muscles.
- Hypermagnesemia depresses reflexes; hypomagnesemia increases neuromuscular excitability.
- Unexpected acid–base compensation indicates a possible mixed disorder.
KMU Exam Trap:
Compensation moves the pH toward normal but does not normally completely normalize it or create the opposite primary disorder.
Compensation moves the pH toward normal but does not normally completely normalize it or create the opposite primary disorder.
5. Clinical Memory Hooks
Seizures with marked hyponatremia
→
Water enters brain cells → cerebral swelling.
→
Water enters brain cells → cerebral swelling.
Peaked T waves with high potassium
→
Cardiac toxicity → stabilize myocardium urgently.
→
Cardiac toxicity → stabilize myocardium urgently.
Hypokalemia not correcting with replacement
→
Check for associated magnesium deficiency.
→
Check for associated magnesium deficiency.
Low HCO₃⁻ with unexpectedly high PaCO₂
→
Metabolic acidosis plus superimposed respiratory acidosis.
→
Metabolic acidosis plus superimposed respiratory acidosis.
6. Starred High-Yield Exam Points
- ⭐ Hyponatremia → reduced extracellular tonicity → cerebral cellular swelling.
- ⭐ Hyperkalemia with ECG toxicity → intravenous calcium protects the myocardium.
- ⭐ Insulin with glucose shifts K⁺ into cells but does not remove total body potassium.
- ⭐ Persistent hypokalemia can be caused by associated hypomagnesemia.
- ⭐ Metabolic acidosis = primary HCO₃⁻ fall with compensatory PaCO₂ reduction.
- ⭐ Respiratory acidosis = primary PaCO₂ rise with renal HCO₃⁻ retention.
- ⭐ Compensation outside the expected range strongly suggests a mixed acid–base disorder.