Medical and endocrine disease05 / 30
Primary hyperaldosteronism with severe hypokalaemia for ankle fixation47-year-old woman, 68 kg, for urgent open fixation of a displaced bimalleolar ankle fracture
From memory: the diagnosis and the notes are hidden. Answer each question aloud, then press Show.
Know this first
- Conn's: sodium retention, potassium loss, hypokalaemic metabolic alkalosis and hypertension.
- Severe hypokalaemia is below 3 mEq/L, with flat T waves, U waves, QT prolongation and ST depression.
- Her total-body potassium deficit may exceed 300 mEq; magnesium is replaced alongside it.
- Hyperventilation lowers plasma potassium and should be avoided.
- Shockable arrest: adrenaline once the first shocks fail; amiodarone 300 mg for refractory pulseless VT.
The patient
47-year-old woman, 68 kg, for urgent open fixation of a displaced bimalleolar ankle fracture, booked for tomorrow.
Primary hyperaldosteronism awaiting adrenalectomy; BP hard to control; cramps and weakness this week.
Drugs: spironolactone (started 5 days ago), amlodipine.
Labs: K 2.6 mmol/L, Mg 0.5 mmol/L, HCO3 32 mmol/L, Na 145 mmol/L. ECG: flat T waves and U waves.
Vitals: BP 172/104, HR 84, SpO2 98% on air, RR 14.
The examiner asks
Answer aloud, then press Show.
Consider
What are your concerns?
Show the answerHide the answer
- A 47-year-old with Conn's syndrome, potassium 2.6 and low magnesium, for urgent ankle fixation. Patient
- Aldosterone excess gives her salt retention, potassium loss, alkalosis and hard-to-treat hypertension. Disease
- Her 2.6 is severe hypokalaemia, and her ECG already shows flat T waves and U waves.
- Her body's total potassium deficit may be over 300 mEq, far more than the serum suggests.
- The ankle can wait some hours; anaesthesia at 2.6 with ECG changes can't be justified. Surgery
Prepare
How do you prepare her?
Show the answerHide the answer
- Magnesium 1–2 g over 15 minutes first; without it her potassium won't stay up. (Disease)
- Concentrated potassium by central line: 20–40 mEq over 30 minutes by pump, ECG monitored.
- Spironolactone acts slowly, so her potassium may keep rising after surgery.
- I proceed once she's in the mild range, 3.0–3.5, with her ECG settling.
- Treatment may leave her relatively dry, so I expect hypotension when she's anaesthetised.
Plan
How will you anaesthetise her?
Show the answerHide the answer
- Popliteal sciatic and saphenous blocks let her breathe for herself, with no ventilator-driven alkalosis. Surgery
- If she needs GA, normal ventilation only; hyperventilation and alkalosis push potassium into cells. Disease
- I avoid insulin, gentamicin and acid–base swings that lower her potassium.
- Low potassium changes her response to relaxants, so I use quantitative neuromuscular monitoring.
- Potassium and magnesium rechecked in recovery and the next morning. After surgery
Crisis
Forty minutes into a GA, she has frequent multifocal ectopics, then the monitor shows pulseless VT. Your actions?
Show the answerHide the answer
- Adult arrest algorithm, shockable rhythm: pulseless VT in a woman with severe hypokalaemia. (Crisis)
- Call for help, start CPR and shock: biphasic 120–200 J, then 2 minutes of CPR.
- Still shockable: shock again, then adrenaline 1 mg, repeated every 3–5 minutes.
- After the third shock: amiodarone 300 mg, then 150 mg if needed.
- Her reversible cause is hypokalaemia: 20–40 mEq over 3–10 minutes centrally, plus magnesium 1–2 g.
- Ventilate at 10 breaths a minute, not faster; alkalosis would drop her potassium further.
Fatal mistakes
- Inducing her with potassium 2.6 and ECG changes when a few hours' delay is safe.
- Hyperventilating her and driving her potassium lower.
- Delaying the shock for pulseless VT while drugs are drawn up.
Checked against: Miller 10e · Barash 9e · Stoelting 8e · AHA guidelines: adult advanced life support (2025)
Report a problem with this case
Mark Got it only if you said every point. Again brings the case back tomorrow; Got it brings it back in 3, then 7, 14 and 30 days.