How to validate hypo/hyper kalemia.

Most nursing programs teach that hypokalemia is associated with tachycardia and hyperkalemia is associated with bradycardia. And although there are conditions where either a slow or fast heart rate can exist with changes in heart rate; understanding the underlying pathophysiology is critical.

Potassium is the major intracellular ion that controls pH balance and water balance inside the cell. When the cardiac cells repolarize (reload) they exchange potassium for sodium and calcium. If the extracellular (serum) level of potassium is high sodium will be displaced and will not be able to enter the cell as readily as when the level is normal leading to bradycardia. When the serum potassium level is low, more sodium can enter making repolarization (reloading) initially more rapid and leading to tachycardia.

Knowing this, there are many confounding variables that may have led to the altered potassium level such as dehydration from vomiting (leading to potassium loss through the stomach), that can cause bradycardia as decompensation from shock; or over-replacement of potassium-rich IV fluids that would lead to tachycardia from volume overload.

Physiologically low potassium levels should cause tachycardia, and high levels should cause bradycardia.However, in clinical practice our patients have many different things going on that can cause an altered heart rate from a variety of mechanisms, such as stimulation of the sympathetic nervous system.

One way to validate which potassium state is present in your patient is to look at their EKG. Due to the increased influx of potassium with high levels, the T-wave will be tall and peaked. The early, but prolonged, repolarization of hypokalemia will be evidenced by flat or bi-phasic T-waves and the production of a U-wave.

The take-home point is that potassium is necessary for cardiac contraction. Alterations in potassium level will negatively affect cardiac conduction, cardiac contraction, and cardiac output.

Source: Anderson, M.E. & Roden, D.M. (2004). Basic cardiac electrophysiology and anatomy. In Crawford, M.H. (ed.) Cardiology (2nd Ed.), Mosby: New York.

Guyton, A. C. & Hall, J.E. (2000). Textbook of Medical Physiology. Saunders: Philadelphia.

Osorio, F.V. & Linas, S.L. (1999) Disorders of potassium metabolism, in Atlas of Diseases of the Kidney, http://www. kidneyatlas.org/book1/adk1_03.pdf.

Yan, G.X., et al. (2003). Ventricular repolarization components on the electrocardiogram: Cellular basis and clinical significance. Journal of the American College of Cardiology; 42(3), 401-9.

David W. Woodruff, MSN, RN, CNS, CEN www.Ed4Nurses.com

Edited version, reprinted with permission