Electrolyte Disorders

<h1>Electrolyte disorders</h1>
  <h2>Rob Hunter | MBChB Year 5 2026-7</h2>

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    <strong>A question for you:</strong> What substance is being mishandled by the body in patients with hyponatraemia?
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# Learning objectives

1. Apply a **stepwise diagnostic framework** to hyponatraemia, hyperkalaemia, and hypercalcaemia
2. Identify the most likely **underlying cause** from clinical and laboratory data
3. Recognise when an electrolyte disturbance is a **medical emergency**
4. Outline **immediate and subsequent management**, including drug dosing and monitoring
5. Identify key **drugs and risk factors** that predispose to each disorder

<br>

.callout.callout-bottom[
**Session structure:** one clinical case per disorder → small-group discussion → key-points debrief.

The same 4 questions apply to *every* case:<br>
information needed · diagnosis · emergency management · subsequent management

]

???

Reassure: the goal is reasoning, not memorisation.

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# Case 1
## Hyponatraemia

???

Return to question posed at the start!

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.left-panel.top[![](images/case1.png)]

# 79 yo woman with confusion

*Two weeks after coronary artery bypass grafting, she is increasingly confused and cannot recall having had heart surgery. Nursing staff report she has been muddled for 2–3 days and is complaining of a persistent headache.*

<br>

- **PMH:** previous MI, hypertension
- **Social Hx:** lives alone; mobilising with a frame post-operatively

<br>

**Current medications:**
- Dalteparin 5,000 units SC once daily (for VTE prophylaxis)  
- Aspirin 75 mg once daily  
- Amlodipine 5 mg once daily  
- Furosemide 40 mg once daily (started post-op for pulmonary oedema)  
- Sertraline 100 mg once daily (started post-op for low mood)

???
Prompts:

- "What stands out from the **medication** list?" 
- "**What else** in her history predisposes to hyponatraemia?"

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.left-panel.top[![](images/case1.png)]

# 79 yo woman with confusion

.scompact-table[
| Test | Result | Reference Range (Units) |
|:-----|-------:|:------------------------|
| Sodium | **112** | 133–146 mmol/L |
| Potassium | 3.8 | 3.6–5.0 mmol/L |
| Urea | 4.2 | 2.5–6.6 mmol/L |
| Creatinine | 74 | 50–98 µmol/L |
| TCO₂ | 24 | 22–30 mmol/L |
]

.xsmall[Previous Na⁺: 135 mmol/L (4 days ago). **Bold** = outside reference range or clinically significant threshold.]

.callout-question.callout-bottom[
In groups:  
1) 🔍 What **further information** would you like?  
2) 🧩 What is the **differential diagnosis** (cause of electrolyte abnormality)?  
3) 🚨 What is the **emergency management**?  What will you do right now?  
4) 📋 What is the **subsequent management**? 
]

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.left-panel.top[![](images/case1.png)]

# 79 yo woman with confusion

.scompact-table[
| Test | Result | Reference Range (Units) |
|:-----|-------:|:------------------------|
| Sodium | **112** | 133–146 mmol/L |
| Glucose | 8.1 | 4.0–11.1 mmol/L |
| Plasma osmolality | **240** | 275–295 mOsm/kg |
| Urine osmolality | 395 | N/A mOsm/kg |
| Urine sodium | 72 | N/A mmol/L |
| TSH | 2.1 | 0.23–5.6 mU/L |
| Cortisol (09:00) | 520 | >300 nmol/L (adequate) |
]

.callout-question.callout-bottom[
1) 🔍 What **further information** would you like?  
2) 🧩 What is the **differential diagnosis** (cause of electrolyte abnormality)?  
3) 🚨 What is the **emergency management**?  What will you do right now?  
4) 📋 What is the **subsequent management**? 
]

???

Socratic prompts:
- "Why does **urine osmolality** >100 mOsm/kg matter here?"*
- "What is the maximum **safe rate of Na⁺ correction** in 24 hours — and why?"

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# Hyponatraemia: management

Call for senior help immediately
]

<br>

**Hypertonic saline**:

- **1.8% NaCl** 300 mL IV over 30 min   
- green venflon in antecubital fossa (unlicensed)  
- target 5 mmol/L rise...
- ...and no more tham 10 mmol/L in first 24 hours

]

.pull-right[
### This patient (SIADH)
- fluid restriction (e.g. <1 L/day)
- treat precipitating cause = stop sertraline

<br>

### Correction limits:

| Risk group | Max rise / 24 h | Target |
|:-----------|----------------:|-------:|
| standard | ≤10 mmol/L | 6–8 mmol/L |
| high risk* | ≤8 mmol/L | consider ddAVP clamp |

- monitor Na⁺ 4 hrly initially & **urine output**
- if overcorrecting → ? 5%G or ddAVP  
]

???

Hypertonic NaCl for:

- acute hypoNa with any symptoms  
- chronic hypoNa with moderate or severe symptoms (nausea, vomiting, confusion, headache, seizures, coma...)

<br>

NHSL guidelines as above.

European guidelines:

- 150 ml 3% over 20 mins (2 ml/kg in extremes of BW); repeat up to 3x  
- then 1 ml/kg/hr to target 1 mM rise per hr until symptoms stop  
- stop at 10 mM rise (or 130 mM - whichever is lower)

Look for u/o > 100 ml/hr.

---
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# Case 2
## Hyperkalaemia

???
Transition prompt: *"Hyperkalaemia is dangerous for a very different reason from hyponatraemia — it is primarily a cardiac emergency. The resting membrane potential of cardiac myocytes is critically dependent on the potassium gradient. When that gradient collapses, the heart can stop."*

Activate prior knowledge: *"Which organs and hormones regulate potassium balance?"* (Kidneys — aldosterone-regulated K⁺ secretion in the distal nephron; intracellular buffering by insulin- and β₂-adrenergic-stimulated Na⁺/K⁺-ATPase activity.)

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.left-panel.top[![](images/case2.png)]

# 58 yo man struggling to walk

*An ambulance is called by the patient's partner after he is too weak to stand. He has had profuse watery diarrhoea for 8 days. He describes his legs as feeling "dead".*

<br>

- **PMH:** liver cirrhosis
- **Social Hx:** lives with partner; drinks 2 bottles wine per day
- **Examination:** BP 94/50 mmHg · HR 112 bpm · SaO₂ 99% (room air) · cool peripheries · JVP not visible lying flat · wrinkled skin over ankles

<br>

**Current medications:**
- Lactulose 15 mL three times daily
- Omeprazole 20 mg once daily
- Levothyroxine 75 mcg once daily 
- Spironolactone 100 mg once daily

???
Prompts:

- "He is **'struggling to walk'** — why might hyperkalaemia cause this?"
- "Which single **medication** is most dangerous in this context, and why?" 
- "What does his examination tell you about **volume status**?"
- "Lactulose causes **diarrhoea** — does this protect against or worsen hyperkalaemia?"

---
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.left-panel.top[![](images/case2.png)]

.scompact-table[
| Test | Result | Reference Range (Units) |
|:-----|-------:|:------------------------|
| Sodium | 134 | 135–145 mmol/L |
| Potassium | **7.2** | 3.6–5.0 mmol/L |
| Urea | **32** | 2.5–6.6 mmol/L |
| Creatinine | **306** | 64–111 µmol/L |
| eGFR | **18** | >60 ml/min |
| TCO₂ | **16** | 22–30 mmol/L |
| Albumin | **27** | 36–47 g/L |
| ALT | **68** | 10–50 U/L |
| Bilirubin | **45** | 3–21 µmol/L |
| Haemoglobin | **103** | 130–180 g/L |
]

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# Hyperkalaemia & ECGs

Get an ECG if K⁺ > 6 mmol/L; cardiac monitor if K⁺ > 6.5 mmol/L or unstable.

| K⁺ (mmol/L) | Typical ECG findings | Arrhythmic risk |
|:------------|:---------------------|:----------------|
| 5.5–6.0 | Often normal; may see peaked (tall, narrow) T waves | low-negligible |
| 6.0–7.0 | Peaked T waves; prolonged PR interval; flattened or absent P waves; QRS widening | increasing |
| 7.0–8.0 | Marked QRS widening; sine-wave pattern (QRS merges with T) | very high |
| >8.0 | Ventricular fibrillation; asystole; cardiac arrest | life-threatening |

.callout[
If ECG changes: **calcium gluconate 30 ml IV over 10 mins**.  
Repeat if ECG changes persist.  
]

.callout-warn[
**Absence of ECG changes does NOT exclude risk**; cardiac arrest can occur >6.5 mmol/L with ~ normal ECG.  
Give IV calcium if hyperkalaemia **strongly suspected** (e.g. dialysis patient with ECG changes / cardiac arrest).
]

???

NB Playbook says not to give IV Ca2+ if no ECG changes.  UKKA guidance does say that but recommendation is appropriately nuanced; recognises that some guidelines would recommend this and is within licence.

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background-image: url(images/hyperK_algorithm.png)
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???

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# Case 3
## Hypercalcaemia

???

Transition prompt: *"Hypercalcaemia can be deceptively slow-onset — patients often present with vague, non-specific symptoms that have been present for weeks. The danger is that by the time it is recognised, significant dehydration and renal impairment may already have occurred."*

Activate prior knowledge: *"Which hormone most directly regulates serum calcium, and how?"* (PTH → increases bone resorption, increases renal Ca²⁺ reabsorption, stimulates renal 1α-hydroxylase to produce active vitamin D → increased GI absorption.)

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.left-panel.top[![](images/case3.png)]

# 66 yo man: "just not right"

*Over the past few weeks this ex-smoker has become generally unwell: persistently thirsty, constipated, and sleeping poorly due to back pain. He has stopped playing golf. His wife reports he seems low in himself.*

<br>

- **PMH:** Hypertension, gallstones; ex-smoker (40 pack-years); no known malignancy
- **Social Hx:** Retired; lives with wife; alcohol within recommended limits
- **Examination:** BP 159/88 mmHg · HR 92 bpm · Pale · Clinically dehydrated

<br>

**Current medications:**
- Enalapril 10 mg once daily

???
Prompts:

- "What are the **classical symptoms** of hypercalcaemia?" (Mnemonic: 'bones, stones, abdominal groans, psychic moans' — bone pain, renal stones/polyuria, constipation/nausea, confusion/depression)
- "Which symptoms does **this patient** have?" (Thirst/polyuria, constipation, back pain, low mood — all consistent with hypercalcaemia)
- "What does 40 pack-years + **thoracic back pain** + general malaise suggest to you?" (Malignancy — lung cancer with bone metastases, or myeloma)
- "Why is his **BP still elevated** if he is dehydrated?" (Hypertensive background from enalapril; hypercalcaemia can cause vasoconstriction)

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.left-panel.top[![](images/case3.png)]

.scompact-table[
| Test | Result | Reference Range (Units) |
|:-----|-------:|:------------------------|
| Sodium | 142 | 135–145 mmol/L |
| Potassium | 3.9 | 3.6–5.0 mmol/L |
| Urea | 7.0 | 2.5–6.6 mmol/L |
| Creatinine | 108 | 64–111 µmol/L |
| TCO₂ | 25 | 22–30 mmol/L |
| Adjusted calcium | **3.36** | 2.20–2.60 mmol/L |
| Albumin | 37 | 36–47 g/L |
| Phosphate | 0.9 | 0.8–1.4 mmol/L |
| ALP | **289** | 50–250 U/L |
| Haemoglobin | **94** | 130–180 g/L |
]

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.left-panel.top[![](images/case3.png)]

# 66 yo man: "just not right"

???

---

# Hypercalcaemia — diagnostic pathway

.callout[
**PTH** is the single most important discriminating test in hypercalcaemia.  
Low = appropriate parathyroid respnse.  
]

- **Primary hyperparathyroidism (PHPT)**:  
    - most common cause in the community
    - often mild and chronic
    - refer to endocrine

<br>

- **Familial hypocalciuric hypercalcaemia (FHH)**  
- **Tertiary hyperparathyroidism** (ESKD)

]

- **Malignancy** *(until proven otherwise)*:  
    - PTHrP secretion (SCLC, renal, breast)
    - osteolytic bone metastases (→ ↑ ALP)
    - myeloma (→ anaemia, back pain, AKI/CKD)

<br>

- **Vitamin D excess** (exogenous or granulomatous)
-  **Sarcoid / TB / lymphoma** (ectopic 1α-hydroxylase)
- **Drugs** (thiazides, lithium, vitA)  
- thyrotoxicosis · immobilisation

]

???

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# Hypercalcaemia — management

**IV 0.9% sodium chloride** ~ 3–4 L over 24 hours:

- adjust for age, cardiac function etc.  
- target u/o 100 - 150 ml/hr  
- two mechanisms of action

<br>

#### Step 2 — Anti-resorptives

**Zoledronic acid** 4 mg IV over 15 min:

- onset 2–4 days; duration 2–6 weeks
- check eGFR before administration

**Alternative:** Pamidronate 60–90 mg IV

**Sometimes:** Denosumab, calcitonin (specialist only)
]

| Cause | Intervention |
|:------|:-------------|
| Lymphoma / sarcoid / Vit D XS | glucocorticoids |
| Primary HPT | surgery / cinacalcet |
| severe + AKI | haemodialysis |

<br>

#### For this patient:

- admit; IV 0.9% NaCl; ECG (check QT shortening)
- hold enalapril 
- zoledronic acid 
- CT chest/abdomen/pelvis & myeloma screen

]

???

Fluids:  
1. Corrects volume depletion from hypercalcaemia-driven nephrogenic DI
2. Drives **calciuresis** via sodium-coupled calcium excretion in the proximal convoluted tubule

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# Close
## Take-home points & reflection

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# Take-home points

.pull-left[
## Hyponatraemia
- a **water** problem — not sodium depletion
- plasma Osm → is it hypotonic (dangerous)?
- urine Osm → is ADH active?
- acute + symptomatic → **hypertonic saline**

<br>

## Hyperkalaemia
- **ECG** if K > 6 mM (cardiac monitor if K > 6.5 mM)
- protect heart → shift into cells → eliminate  
- watch for hypoglycaemia  
]

.pull-right[
## Hypercalcaemia
- **PTH** is the single most discriminating test
- high Ca + suppressed PTH → ? malignancy
- **IV 0.9% NaCl** first

<br>

## All three disorders
- Is it an **emergency**?
- **Drugs** are a common precipitant
- Think through the **physiology**
]

???

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# Reflection

## Tell yourself....

- 💡 The most important thing I learned today

-  ✅ One clinical situation where I will apply this

- ❓ My muddiest point — one thing I am still unclear on