ICU · Renal and metabolic
Acute severe hypokalaemia and hypomagnesaemia: ECG, repletion, and refractory causes
Also known as Hypokalaemia · Low potassium · Hypomagnesaemia · Potassium repletion · Refractory hypokalaemia · Gitelman syndrome
Hypokalaemia (K <3.5 mmol/L) is common in ICU (diuretics, GI loss, drugs). SEVERE (<2.5) → cardiac arrhythmia (U waves, VT/VF, torsades), muscle weakness, rhabdomyolysis, ileus. ECG changes: T-wave flattening/inversion, ST depression, U waves (pathognomonic), prolonged QT, ventricular ectopics. Hypomagnesaemia (Mg <0.7) is the 1 cause of REFRACTORY hypokalaemia — renal K-wasting continues until Mg replaced (ROMK channel). Always check + replace Mg in refractory hypokalaemia. Repletion: ORAL preferred (safer — 40-60 mmol/day); IV for severe/symptomatic (max 10-20 mmol/hr via CENTRAL line, max 40 mmol/L peripheral — pain/phlebitis, monitor ECG continuously). NEVER give IV K as a bolus (10 mmol/hr unmonitored → cardiac arrest). Causes: GI (vomiting/diarrhoea), renal (diuretics, mineralocorticoid excess, RTA), drugs (amphotericin, cisplatin), alkalosis (shifts K into cells).
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Target exams
Red flags
Oral vs IV potassium replacement
| Route | Dose | Setting | Rate limit | Notes |
|---|---|---|---|---|
| Oral | 40-60 mmol/day (or 20 mmol per dose) | Mild-moderate; step-down from IV | None | PREFERRED — safe, self-regulating. GI irritation (nausea — give with food). KCl slow-release tabs |
| IV peripheral | Max 40 mmol/L concentration | Severe, no central line | Max 10 mmol/hr | Pain/phlebitis risk (dilute well). Continuous cardiac monitoring if >10 mmol/hr. Avoid extravasation |
| IV central | Higher concentration (e.g., 40 mmol in 100 mL) | Severe, symptomatic, cardiac arrest risk | Max 10-20 mmol/hr | Continuous ECG. Use for rapid repletion (critical). Concentrated via central only. Max 20 mmol/hr in monitored ICU |
| IV BOLUS | NEVER (cardiac arrest) | — | — | NEVER give IV K as undiluted bolus — fatal arrhythmia. Always dilute + infuse over time |
Management of severe hypokalaemia in ICU
- RECOGNISE SEVERITY + ECG — K <2.5 or symptomatic (arrhythmia, severe weakness) = emergency. Get ECG immediately: T-wave flattening, ST depression, U waves (after T — pathognomonic), prolonged QT, ventricular ectopics, VT/VF/torsades. Continuous cardiac monitor. IV access
- CHECK MAGNESIUM — ALWAYS. Hypomagnesaemia (Mg <0.7) is #1 cause of refractory hypokalaemia. If Mg low → replace FIRST (MgSO4 2 g IV over 1-2h, or 8 mmol/day oral). Without Mg correction, K replacement 'leaks' out (ROMK channel stays open) — K won't rise. Recheck K after Mg replaced
- REPLACE POTASSIUM — ORAL preferred if possible (40-60 mmol/day, in divided doses). For severe/symptomatic: IV KCl — PERIPHERAL (max 40 mmol/L, max 10 mmol/hr) or CENTRAL (higher concentration, max 10-20 mmol/hr with continuous ECG). Dilute KCl in compatible fluid (NaCl 0.9% — avoid dextrose which stimulates insulin → shifts K INTO cells → lowers K further)
- ADDRESS CAUSE — stop offending drugs (diuretics? amphotericin? steroids?), treat GI loss (antiemetics, antidiarrhoeal), correct alkalosis (replaces chloride → K stays), investigate mineralocorticoid excess (primary hyperaldosteronism — renin/aldosterone; Cushing; exogenous mineralocorticoid), renal tubular acidosis, Gitelman/Bartter syndrome
- MONITOR AND ADJUST — Recheck K every 2-4h during IV repletion (K shifts are dynamic). Monitor ECG continuously. Watch for overcorrection (hyperkalaemia — especially in renal failure). Once K >3.0 and stable → switch to oral maintenance
- MAINTENANCE + PREVENT — Daily K requirement ~1 mmol/kg/day. Patients on diuretics: add K-sparing (amiloride, spironolactone) or K supplement. Monitor regularly. Correct Mg (prevents recurrence). Address underlying cause permanently
Exam practice — SAQs
SAQ — Severe hypokalaemia with Torsades de Pointes in a malnourished alcoholic
10 minutes · 10 marks
A 56-year-old woman with chronic alcohol misuse and a 5-day history of profuse vomiting, diarrhoea and negligible oral intake is admitted to ICU with dizziness and generalised weakness. She has been taking oral omeprazole 40 mg daily for two years and was started on IV erythromycin and haloperidol on the ward for agitation. Examination: HR 108, BP 88/52, marked proximal and respiratory muscle weakness, bilateral tetany with positive Chvostek sign. Venous gas: K⁺ 1.9 mmol/L, Mg²⁺ 0.32 mmol/L, ionised Ca²⁺ 0.86 mmol/L, phosphate 0.45 mmol/L, pH 7.50, bicarbonate 36. ECG: QTc 580 ms, prominent U waves merging with T waves, and a 20-second run of polymorphic VT twisting around the baseline (Torsades de Pointes) with a pulse.
SAQ — Magnesium replacement in refractory hypokalaemia after cisplatin chemotherapy
10 minutes · 10 marks
A 64-year-old man with locally advanced bladder cancer is admitted to ICU on day 4 of his third cycle of cisplatin-based chemotherapy with generalised weakness, carpopedal spasm and new tremor. He is also on oral frusemide 40 mg daily for lower-limb oedema and has chronic kidney disease stage 3 (baseline creatinine 160 micromol/L). Bloods: K⁺ 2.6 mmol/L (he has received 80 mmol of IV KCl on the ward over 24 h with no rise), Mg²⁺ 0.35 mmol/L, ionised Ca²⁺ 0.82 mmol/L, phosphate 0.55 mmol/L, normal albumin. ECG: prolonged QTc 500 ms with occasional ventricular ectopics. He is oliguric with a urine output of 0.4 mL/kg/h.
Clinical pearls
Red flags
Prognosis
Hypokalaemia and hypomagnesaemia evidence and outcomes
Epidemiology: hypokalaemia in ~20% of hospitalised patients; hypomagnesaemia in ~50% of ICU patients (often undiagnosed). Mortality: hypokalaemia associated with 2-3x increased mortality in MI, heart failure (digitalis toxicity risk), sepsis. Hypomagnesaemia + refractory K: Huang (2017, JASN) — Mg gates ROMK channel; replacing Mg restores K retention. IV potassium safety: max 10 mmol/hr peripheral, 10-20 mmol/hr central (monitored) — bolus causes cardiac arrest. PPI hypomagnesaemia: FDA warning 2011 — chronic PPI → Mg/Ca/K depletion. Diuretic K loss: loop + thiazide → 20-40% develop hypokalaemia — K-sparing diuretic (amiloride) or K supplement prevents. DKA K shift: K falls 0.5-1.5 mmol/L with insulin — monitor every 2h, supplement per protocol.
Localising the potassium loss — renal vs extrarenal
Renal vs extrarenal (GI/transcellular) K loss — diagnostic workup
| Test | Renal loss (kidney wasting K) | Extrarenal loss (GI / shift) |
|---|---|---|
| 24-hr urine K | >25-30 mmol/day on a normal K diet (inappropriately HIGH despite hypokalaemia — kidney should be retaining K) | <15 mmol/day (appropriately LOW — kidney conserving K as it should) |
| Spot urine K/creatinine ratio | >15 mmol/mmol | <15 mmol/mmol |
| Transtubular K gradient (TTKG) | >3 (often >7) — kidney inappropriately secreting K | <2 — kidney appropriately conserving K |
| Urine chloride | HIGH in diuretic/mineralocorticoid excess (CI correct); LOW in vomiting (<20) | LOW in vomiting/diarrhoea |
| Acid-base | Metabolic alkalosis (diuretic, mineralocorticoid, vomiting); metabolic acidosis (RTA, diarrhoea) | Metabolic alkalosis (vomiting, diuretic); acidosis (diarrhoea) |
| Blood pressure | HIGH in mineralocorticoid excess (Conn's, Cushing, licorice, Liddle, renal artery stenosis); NORMAL in Bartter/Gitelman, diuretic, RTA | NORMAL (GI loss, shift) |
| Common causes | Diuretics (loop/thiazide), Bartter/Gitelman, RTA, mineralocorticoid excess, amphotericin, cisplatin, aminoglycosides, Mg depletion | Vomiting, diarrhoea, laxative abuse, villous adenoma, insulin, beta-agonists, alkalosis, refeeding, periodic paralysis |
Magnesium physiology and repletion
Magnesium replacement formulations in the ICU
| Formulation | Dose | Route | Setting | Cautions |
|---|---|---|---|---|
| MgSO₄ (sulphate) | 2 g IV (= 8 mmol = 16 mEq) over 1-2 h; repeat q6-12h to a total of 8-12 g/24h in symptomatic TdP/seizure | IV (any line) | Symptomatic: torsades, seizure, refractory K⁺/Ca²⁺, eclampsia | Caution in renal failure (reduce dose 50%, monitor reflexes). Hot flush, hypotension if pushed too fast. Slows AV conduction |
| MgSO₄ infusion | 1-2 g/h continuous | IV central | Torsades storm, ongoing renal K wasting | Continuous cardiac monitoring. Target Mg 1.0-1.2 mmol/L (2.0-2.4 mg/dL) |
| Mg oxide | 400-800 mg PO (= 240-480 mg elemental Mg) qid-tid | Oral | Step-down / chronic repletion (Gitelman, post-cisplatin) | Diarrhoea (osmotic) — limits dose. Slow GI absorption. Often split 4-6×/day |
| Mg glycerophosphate / aspartate | 1-2 tabs qid | Oral | When oral oxide causes diarrhoea (better tolerated) | Less commonly stocked |
| No IM route | — | — | Avoid in ICU — painful, erratic absorption | Use IV in critical illness |
Drug-induced potassium and magnesium depletion
ICU drug culprits that waste potassium and magnesium
| Drug class | Mechanism | Typical picture | Management |
|---|---|---|---|
| Loop diuretics (frusemide, bumetanide) | Inhibit NKCC2 in thick ascending limb; increased distal Na delivery + aldosterone → K⁺/Mg²⁺ wasting | Hypokalaemia + alkalosis + hypomagnesaemia + hypercalciuria | Add K-sparing (amiloride); supplement K + Mg; dose-limit by response |
| Thiazides (hydrochlorothiazide, indapamide) | Inhibit NCC in distal tubule; same downstream effect as loops | Hypokalaemia + hyponatraemia (more than loops), hypomagnesaemia, HYPOcalciuria | K-sparing combination; monitor Na (thiazide hyponatraemia common in elderly women) |
| Cisplatin | Direct proximal tubular injury → Fanconi-like syndrome (K⁺, Mg²⁺, phosphate, glucose, amino acid wasting) | Severe persistent hypomagnesaemia (may last years after therapy), hypokalaemia, hypocalcaemia | Pre-hydration, prophylactic IV MgSO₄ with each cycle, oral Mg replacement throughout therapy. Warn patient re nephrogenic DI[19] [20] |
| Amphotericin B (deoxycholate) | Pore-former in tubular cell membrane → cation leak (K⁺, Mg²⁺, H⁺); afferent arteriolar vasoconstriction → AKI | Distal RTA (normal anion gap), hypokalaemia, hypomagnesaemia, non-oliguric AKI | Use liposomal formulation (lower nephrotoxicity); pre-hydrate with NaCl; replace K + Mg aggressively; avoid concurrent nephrotoxins[21] |
| Aminoglycosides (gentamicin, amikacin, tobramycin) | Inhibit proximal tubular protein synthesis → Fanconi-like + Bartter-like wasting | Hypokalaemia + hypomagnesaemia + hypocalcaemia; non-oliguric AKI at 5-7 days | Once-daily extended-interval dosing; limit course <5-7 days; daily Mg/K; therapeutic drug monitoring |
| Corticosteroids / mineralocorticoids | Direct mineralocorticoid effect → Na retention, K loss | Hypokalaemic alkalosis, hypertension, hyperglycaemia | Lowest effective dose; K-sparing diuretic; K/Mg supplement |
| Amphotericin + diuretic + aminoglycoside | Synergistic renal injury in septic/neutropenic patient | Refractory hypokalaemia | STOP unnecessary nephrotoxin; switch antifungal class; aggressive replacement |
| Carbenoxolone, licorice | Inhibit renal 11β-HSD2 → apparent mineralocorticoid excess | HTN + hypokalaemia + alkalosis + LOW aldosterone | Stop agent; spironolactone |
| β₂-agonists (salbutamol, terbutaline, ritodrine) | Stimulate β₂-receptor → activate Na⁺/K⁺-ATPase → K⁺ INTO cells | Acute hypokalaemia in status asthmaticus (high-dose nebs), tocolysis | Monitor K + Mg (Mg also falls); supplement; consider lower β₂ dose |
| Insulin | Activates Na⁺/K⁺-ATPase → K⁺ INTO cells | Acute fall in K when treating DKA/HHS (0.5-1.5 mmol/L) | Check K before insulin — hold if <3.3; supplement in infusion fluids |
| PPIs (omeprazole, pantoprazole, esomeprazole) | Reduce intestinal TRPM6-mediated Mg absorption | Chronic (months-years) hypomagnesaemia → refractory hypokalaemia + hypocalcaemia | Stop PPI, switch to H2 blocker; IV Mg then oral; may take weeks[11] [26] |
| Foscarnet, cidofovir, tenofovir | Proximal tubular injury (Fanconi-like) | Hypokalaemia + hypomagnesaemia + AKI + Fanconi | Hydrate; monitor renal indices; replace electrolytes; consider alternative antiviral |
| Ifosfamide | Toxic metabolite chloroacetaldehyde injures proximal tubule | Fanconi syndrome (K⁺, Mg²⁺, phosphate, glucose), RTA | Mesna co-administration; aggressive electrolyte replacement; dose modification[14] |
| Piperacillin-tazobactam, high-dose penicillins | Non-reabsorbable anion in distal tubule → increased distal Na delivery → K⁺ secretion | Dose-related hypokalaemia (often in high-dose ICU therapy) | Monitor K; supplement; reduce dose if possible |
Cardiac arrhythmia, long QT and torsades de pointes
[1]Management of torsades de pointes in the ICU
- RECOGNISE — polymorphic VT with QRS twisting around the baseline, rate 200-250/min, long QT-sensor preceding beat. If PULSELESS → immediate defibrillation (unsynchronised 200 J biphasic), CPR. If a pulse AND tolerating → proceed below
- STOP every QT-prolonging drug — macrolide/fluoroquinolone, antipsychotic, methadone, ondansetron, antifungal, antiemetic, haloperidol. Review all infusions. Check potassium-sparing diuretic, antiarrhythmic
- GIVE MAGNESIUM — MgSO₄ 2 g IV bolus over 1-2 min (the single most effective agent in TdP, even with normal Mg — Mg suppresses EADs by blocking L-type Ca channels). Repeat 2 g after 5-15 min if TdP recurs. Infusion 1-2 g/h thereafter
- CORRECT POTASSIUM — aim for HIGH-NORMAL (4.5-5.0 mmol/L). IV KCl 10-20 mmol/h via central line. Hypokalaemia is the most modifiable QT risk factor
- CORRECT MAGNESIUM and CALCIUM — recheck Mg, target >1.0 mmol/L (give MgSO₄); check ionised Ca, replace if low
- ACCELERATE THE HEART — overdrive pacing. Bradycardia lengthens QT; increase HR to 90-110 (isoprenaline infusion if pacing not available, or temporary transvenous/transcutaneous pacing). Atrial pacing > ventricular — preserves atrial contribution
- REMOVE TRIGGER — treat ischaemia, hypoxia, electrolyte disturbance, sepsis. Stop all offending agents. Consider temporary mechanical support if deteriorating
- DEFINITIVE THERAPY — if recurrent despite the above, escalate: isoprenaline infusion, ventricular pacing at 100-110 bpm, lidocaine (may terminate via Na channel), and ultimately ICD if congenital/structural long QT
Common ICU drugs that prolong QT (and synergise with hypokalaemia)
| Drug class | Examples | QT risk | Notes |
|---|---|---|---|
| Macrolides | Erythromycin, clarithromycin, azithromycin | High (especially erythromycin IV) | Avoid with other QT-prolongers; check K/Mg |
| Fluoroquinolones | Moxifloxacin, ciprofloxacin, levofloxacin | Moderate (moxi > cipro) | Caution in elderly; ADR-injury risk |
| Antipsychotics | Haloperidol IV (high), droperidol, quetiapine, olanzapine | High | Haloperidol IV restricted in many ICUs for this reason |
| Antiemetics | Ondansetron, droperidol, domperidone | Moderate | FDA warning ondansetron; ECG if >16 mg IV |
| Antifungals | Fluconazole, voriconazole, posaconazole | Moderate | Often combined with macrolide (double risk) |
| Methadone | — | High (dose-related) | ECG on admission, dose ceiling |
| Antiarrhythmics | Sotalol, amiodarone (lower), quinidine, procainamide, ibutilide, dofetilide | High (class Ia, III) | Class III in CICM — check K/Mg first |
| Antidepressants | Citalopram/escitalopram, TCAs | Moderate-High | Citalopram >40 mg dose ceiling |
| Others | Trimethoprim, tacrolimus, arsenic trioxide, halofantrine | Variable | Treat K + Mg before dosing |
Refeeding syndrome — the overlooked ICU hypokalaemia
[1]Prevention of refeeding hypokalaemia in the ICU
- IDENTIFY HIGH-RISK PATIENT — BMI <16; unintentional weight loss >15% in 3 months; little/no intake >10 days; low K/Phosphate/Mg BEFORE feeding; history of alcohol misuse, anorexia, chemotherapy, post-bariatric
- CHECK BASELINE ELECTROLYTES — K⁺, Mg²⁺, phosphate, Ca²⁺. Replace to high-normal BEFORE feeding starts (do not start feed with K⁺ <3.5 or phosphate <0.6)
- GIVE THIAMINE BEFORE THE FIRST FEED — thiamine 200-300 mg IV/PO daily × 5 days. (Carbohydrate metabolism consumes thiamine; deficiency → Wernicke, lactic acidosis)
- START FEED SLOWLY — 10 kcal/kg/day (max 20); increase by ~third every 24-72 h if electrolytes stable
- SUPPLEMENT ROUTINELY — oral/IV K⁺ (2-4 mmol/kg/day), phosphate (15-30 mmol if falls), Mg²⁺ (8-16 mmol/day), and a multivitamin/trace element supplement. Restrict Na + fluid (low Na, weight daily)
- MONITOR EVERY 6-12 h × 72 h — K⁺, Mg²⁺, phosphate, glucose, ECG (QT). STOP/reduce feed if K⁺ <2.5, phosphate <0.3, or arrhythmia
- ESCALATE IF SYMPTOMATIC — IV replacement as above; cardiac monitoring; treat arrhythmia (Mg for torsades); respiratory support if diaphragm weakness (phosphate-driven)
Potassium management during DKA and HHS treatment
DKA/HHS potassium management — the rules that prevent death
- CHECK K⁺ BEFORE ANY INSULIN — at DKA presentation, total body K⁺ is depleted (often 3-6 mmol/kg deficit from osmotic diuresis + vomiting), but serum K⁺ may be NORMAL or HIGH because acidosis (H⁺/K⁺ shift) and insulin deficiency move K⁺ OUT of cells. The serum K⁺ will FALL by 0.5-1.5 mmol/L once insulin starts
- K⁺ <3.3 mmol/L → HOLD INSULIN, give K⁺ FIRST — IV KCl 20-30 mmol/h via central line until K⁺ >3.3, then start insulin. Giving insulin at K⁺ <3.3 risks lethal arrhythmia (this is the leading cause of death in DKA treatment)
- K⁺ 3.3-5.2 mmol/L → give K⁺ WITH insulin — add 20-30 mmol KCl per L of maintenance fluid. Start insulin at 0.05-0.1 unit/kg/h (DKA) or 0.025-0.05 (HHS, lower insulin sensitivity)
- K⁺ >5.2 mmol/L → hold K⁺, monitor — recheck every 2 h; once K⁺ <5.2, add to fluids as above
- CHECK K⁺ EVERY 2 h DURING DKA TREATMENT — and any time the ECG changes; replace IV aggressively if falling
- CHECK AND REPLACE Mg²⁺ — DKA patients have Mg²⁺ depletion; without Mg, K⁺ replacement is partly wasted (ROMK)
- SWITCH TO ORAL once eating + anion gap closed — K⁺ 40-60 mmol/day oral, taper over 24-48 h
Refractory hypokalaemia — diagnostic workup
Workup of refractory hypokalaemia (K⁺ does not rise despite adequate replacement)
- CONFIRM ADHERENCE AND DOSE — is the patient actually receiving the prescribed K⁺? (missed doses, dilution errors, line blocked, extravasation, vomiting oral K)
- CHECK MAGNESIUM — and replace it FIRST. Hypomagnesaemia is the #1 cause (up to 40% of refractory cases). Give MgSO₄ 2 g IV, recheck. Without Mg, K⁺ will not rise
- LOCALISE THE LOSS — renal vs extrarenal. Spot urine K/Cr ratio (>15 = renal); 24-hr urine K (>25-30 mmol/day = renal); TTKG (>3-7 = renal). Acid-base: alkalosis (mineralocorticoid excess, diuretic, vomiting, Bartter/Gitelman) vs acidosis (RTA, diarrhoea)
- MEASURE BLOOD PRESSURE — hypertension + hypokalaemia → mineralocorticoid excess workup (renin/aldosterone, dexamethasone suppression, 24-hr urine cortisol, CT adrenal)
- DRUG HISTORY — diuretics, β₂-agonists, amphotericin, cisplatin, aminoglycosides, PPIs, penicillin, steroid, laxative, licorice. STOP culprit if possible
- MEASURE URINE CHLORIDE — <20 mmol/L = vomiting (chloride-responsive alkalosis); >20 = diuretic, mineralocorticoid excess, Bartter/Gitelman (chloride-resistant)
- CALCIUM + PHOSPHATE + GLUCOSE + ABG — hypocalcaemia + hypokalaemia → Mg deficiency; hypophosphataemia → Fanconi/cisplatin; metabolic acidosis + urine pH >5.5 → distal RTA; hyperglycaemia → insulin/Cushing
- CONSIDER INHERITED TUBULOPATHIES — Gitelman (adult, hypocalciuria, hypomagnesaemia) or Bartter (childhood, hypercalciuria) if metabolic alkalosis + renal K loss + normal BP + no diuretic
- RE-EVALUATE THE FLUIDS — never dilute K⁺ in 5% dextrose (insulin shifts K⁺ IN); always use NaCl 0.9% or balanced crystalloid (Plasma-Lyte, Hartmann)
- ESCALATE — IF STILL REFRACTORY — admit/continue in ICU, central line, IV KCl up to 20 mmol/h with continuous cardiac monitoring, simultaneous Mg replacement, treat underlying cause. Consider amiloride 5-10 mg PO (blocks ENaC — reduces renal K loss even in mineralocorticoid excess)
K-sparing diuretics and mineralocorticoid receptor antagonists (MRA)
K-sparing diuretics / MRAs in the ICU
| Agent | Site / target | Use | Dose | Cautions |
|---|---|---|---|---|
| Amiloride | ENaC blocker (collecting duct) | Adjunct in diuretic hypoK, Gitelman, Liddle, mineralocorticoid excess | 5-10 mg PO daily | Hyperkalaemia, GI upset. First-line in Liddle (does not require intact aldosterone axis) |
| Triamterene | ENaC blocker | Adjunct to thiazide/loop (combo products) | 50-100 mg PO daily | Crystalluria, kidney stones |
| Spironolactone | Mineralocorticoid receptor antagonist | Resistant HTN, primary hyperaldosteronism (hyperplasia), HFrEF (NYHA III-IV), ascites | 12.5-50 mg PO daily | Gynaecomastia (10%), impotence, menstrual irregularity, hyperkalaemia. Slow onset (lag 48-72 h) |
| Eplerenone | Selective MRA (less anti-androgen) | HFrEF post-MI, mild-moderate HFrEF, hypertension | 25-50 mg PO daily | Hyperkalaemia (less gynaecomastia). Contraindicated with strong CYP3A4 inhibitors (ketoconazole, clarithromycin) |
| Finerenone | Non-steroidal MRA | Diabetic kidney disease + albuminuria (FIDELIO/FIGARO) | 10-20 mg PO daily | Hyperkalaemia (less than spironolactone). CYP3A4 caution |
Potassium binders — NOT for the acute hypokalaemic patient
[1]Special ICU contexts
[1] [1] [1] [1]Extended clinical pearls
Extended red flags
Evidence and trials
Landmark trials in hypokalaemia, hypomagnesaemia and K⁺/Mg²⁺ modulation
RALES (1999, NEJM) — Spironolactone 25-50 mg added to standard therapy in severe HFrEF (NYHA III-IV, EF ≤35%): 30% reduction in all-cause mortality (HR 0.70, p<0.001), 35% reduction in hospitalisation. Hyperkalaemia manageable with monitoring. Established MRA as standard-of-care in advanced HFrEF.[7]
EPHESUS (2003, NEJM) — Eplerenone 25-50 mg vs placebo 3-14 days post-acute-MI with LV dysfunction (EF ≤40%) + HF signs: 15% reduction in all-cause mortality, 21% reduction in sudden cardiac death. Established eplerenone in post-MI LV dysfunction.[8]
EMPHASIS-HF (2011, NEJM) — Eplerenone 25-50 mg vs placebo in NYHA II HFrEF (EF ≤35%): 37% reduction in CV death or HF hospitalisation (primary), 24% reduction in all-cause mortality. Extended MRA indication to mild symptomatic HFrEF.[9]
Huang (2017, JASN) — Mg²⁺ gates the ROMK channel; low Mg removes the brake on renal K⁺ secretion. Replacing Mg restores K⁺ retention. The mechanistic basis for 'Mg first' in refractory hypokalaemia.[3]
FDA Drug Safety Communication (2011) — Long-term PPI use associated with hypomagnesaemia (and secondary hypocalcaemia + hypokalaemia) that may be refractory to supplementation until PPI withdrawn. Mechanism: TRPM6 channel requires acidic milieu.[11]
Kraft (2005, Am J Health Syst Pharm) — Comprehensive review of electrolyte disorders in ICU; replaces K⁺ in saline (not dextrose), max 10 mmol/h peripheral, 20 mmol/h central with continuous ECG.[10]
Noronha & Matuschak (2002, ICM) — Magnesium is the 4th most abundant cation; hypomagnesaemia present in up to 65% of ICU patients; serum Mg underestimates total body deficit. Mg supplementation reduces arrhythmia in multiple ICU settings.[23]
Whang & Ryder (1984) — 42% of hypokalaemic inpatients have concurrent hypomagnesaemia; hypomagnesaemia is the strongest predictor of refractory hypokalaemia. The 'Whang rules' that every ICU trainee should know.[12] [13]
Gennari (2002, Crit Care Clin) — For every 0.1 unit pH rise, serum K⁺ falls ~0.6 mmol/L; both metabolic and respiratory alkalosis drive intracellular K⁺ shift. Mechanistic basis for the inseparability of alkalosis and hypokalaemia.[14]
Ayuk & Gittoes (2014, AJKD) — Treatment of hypomagnesaemia: IV MgSO₄ for symptomatic (2 g over 1-2 h); oral Mg oxide 400-800 mg daily for chronic. Serum Mg underestimates total body deficit; replace until serum normal AND symptoms resolve.[17]
If you remember nothing else
[1]References
- [1]Unwin RJ, et al. Pathophysiology and management of hypokalemia: a clinical perspective. Nature Reviews Nephrology, 2011.PMID 21278718
- [2]Viera AJ, et al. Potassium Disorders: Hypokalemia and Hyperkalemia. American Family Physician, 2015.PMID 26371733
- [3]Huang CL, et al. Mechanism of hypokalemia in magnesium deficiency. Journal of the American Society of Nephrology, 2007.PMID 17804670
- [4]Schaefer TJ, et al. Disorders of potassium. Emergency Medicine Clinics of North America, 2005.PMID 15982543
- [5]Upala S, et al. Hypomagnesaemia and mortality in patients admitted to intensive care unit: a systematic review. QJM, 2016.PMID 27016536
- [6]Walsh SB, et al. Clinical hypokalemia and hyperkalemia at the bedside. Journal of Nephrology, 2010.PMID 21170866
- [7]Pitt B, et al. The effect of spironolactone on morbidity and mortality in patients with severe heart failure (RALES). New England Journal of Medicine, 1999.PMID 10471456
- [8]Pitt B, et al. Eplerenone, a selective aldosterone blocker, in patients with left ventricular dysfunction after myocardial infarction (EPHESUS). New England Journal of Medicine, 2003.PMID 12668699
- [9]Zannad F, et al. Eplerenone in patients with systolic heart failure and mild symptoms (EMPHASIS-HF). New England Journal of Medicine, 2011.PMID 21073363
- [10]Kraft MD, et al. Treatment of electrolyte disorders in adult patients in the intensive care unit. American Journal of Health-System Pharmacy, 2005.PMID 16085929
- [11]Liamis G, et al. Proton pump inhibitor-associated hypomagnesaemia: what do FDA data tell us? Annals of Pharmacotherapy, 2013.PMID 23632281
- [12]Whang R, et al. Magnesium deficiency: causes and clinical implications. Drugs, 1984.PMID 6499696
- [13]Whang R, et al. Predictors of clinical hypomagnesemia. Hypokalemia, hypophosphatemia, hyponatremia, and hypocalcemia. Archives of Internal Medicine, 1984.PMID 6476998
- [14]Gennari FJ, et al. Disorders of potassium homeostasis. Hypokalemia and Hyperkalemia. Critical Care Clinics, 2002.PMID 12053834
- [15]Agus ZS, et al. Mechanisms and causes of hypomagnesemia. Current Opinion in Nephrology and Hypertension, 2016.PMID 27219040
- [16]Agus ZS, et al. Cardiovascular actions of magnesium. Critical Care Clinics, 2001.PMID 11219228
- [17]Ayuk J, et al. Treatment of hypomagnesemia. American Journal of Kidney Diseases, 2014.PMID 24100128
- [18]Ayuk J, et al. Contemporary view of the clinical relevance of magnesium homeostasis. Annals of Clinical Biochemistry, 2014.PMID 24402002
- [19]Solak I, et al. Importance of magnesium sulfate supplementation in the prevention of hypomagnesemia and hypocalcemia during chemoradiation in head and neck cancer. Journal of Trace Elements in Medicine and Biology, 2018.PMID 30262299
- [20]Koc S, et al. Cisplatinum nephrotoxicity in oncology therapeutics: retrospective review. Pediatric Nephrology, 2014.PMID 25171948
- [21]Laniado-Laborin R, et al. Amphotericin B: side effects and toxicity. Revista Iberoamericana de Micologia, 2009.PMID 19836985
- [22]Ziemann DA, et al. Digoxin toxicity with normal digoxin and serum potassium levels: beware of magnesium. Journal of Emergency Medicine, 2013.PMID 23685098
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