Describe the electrocardiographic (ECG) changes seen with hyperkalaemia. (30% of marks) Outline the pharmacologic principles of drugs used in the management of severe hyperkalemia. (70% of marks)
College Answer
In general, knowledge of the ECG changes of hyperkalaemia was lacking. Most candidates could list the drugs used in hyperkalaemia, but few gave adequate detail of their mechanism of lowering potassium, dosing, time to onset and duration of action. Many candidates mentioned dialysis or renal replacement therapy which is not a drug therapy for hyperkalaemia; therefore no points were awarded for this.
Discussion
ECG changes of hyperkalemia:
- Tall peaked T waves with a narrow base
- Shortened QT interval
- ST-segment depression
- P wave widening/flattening, PR prolongation
- Sinus bradycardia, high-grade AV block
- Conduction blocks (bundle branch block, fascicular blocks)
- QRS widening with bizarre QRS morphology
Drugs used to treat hyperkalemia:
- Rehydration (i.e. IV fluids)
- Dosing: 1000-2000ml
- Mechanism: dilution; support of diuresis
- Time to onset: minutes
- Duration of action: hours
- Intracellular movement (temporary)
- Bicarbonate (esp. isotonic bicarbonate)
- Dosing: 100-200mmol
- Mechanism: H+/K+ exchange, using the Na+/K+ ATPase.
- Time to onset: minutes
- Duration of action: 1-2hours
- β-agonists
- Mechanism: increase the activity Na+/K+ ATPase pumps
- Dosing: 5mg nebulised salbutamol
- Time to onset: minutes
- Duration of action: hours
- Insulin
- Dosing: 10-50 units, administered with dextrose
- Mechanism: the insertion of extra Na+/K+ ATPase pumps into cell membranes, thus increased cellular potassium uptake
- Time to onset: seconds/minutes
- Duration of action: hours
- Removal via the urine
- Furosemide, other diuretics
- Mechanism: increased sodium delivery to the distal nephron; exchange of sodium for potassium, and thus kaliuresis
- Dosing: 40-80mg
- Time to onset: 20-40 minutes
- Duration of action: hours
- Removal via the bowel
- Cation exchange resin
- Mechanism: binding of potassium into the resin in exchange for another cation (eg. calcium or sodium)
- Dosing: 10-50g
- Time to onset: hours
- Duration of action: hours
References
Rastegar, Asghar. "Serum potassium." Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition (1990).
Palmer, Biff F. "Regulation of potassium homeostasis." Clinical Journal of the American Society of Nephrology 10.6 (2015): 1050-1060.
Gumz, Michelle L., Lawrence Rabinowitz, and Charles S. Wingo. "An integrated view of potassium homeostasis." New England Journal of Medicine 373.1 (2015): 60-72.
Greenlee, Megan, et al. "Narrative review: evolving concepts in potassium homeostasis and hypokalemia." Annals of internal medicine 150.9 (2009): 619-625.
Stone, Michael S., Lisa Martyn, and Connie M. Weaver. "Potassium intake, bioavailability, hypertension, and glucose control." Nutrients 8.7 (2016): 444.