Hyperkalemia from Lecturio ;)

Definition

Hyperkalemia is a disorder characterized by serum potassium level greater than 5.5 mEq/L. A level greater than 7 mEq/L leads to a compromised cardiac and neurologic system.

Cardiac arrest and paralysis sets in when the level exceeds 8.5 mEq/L thus necessitating emergency treatment. The normal potassium level varies with age. Neonates less than 10 days old have an upper limit of up to 6.5 mEq/L.

Epidemiology of Hyperkalemia

The worldwide prevalence of hyperkalemia is estimated to be 5 % of the general population and 10 % of the hospitalized patients. Among the general population, hyperkalemia is usually an incidental finding during routine workup or workup for other diseases while among the hospitalized patients iatrogenic hyperkalemia is symptomatic.

The prevalence is even higher with the extremes of ages. Among the elderly, hyperkalemia arises due to chronic diseases such as diabetes and is associated with renal failure. However, in very young children, hyperkalemia is higher due to renal congenital anomalies that lead to insufficiency.

Classification of Hyperkalemia

Hyperkalemia is classified into:

• Mild hyperkalemia: 5.5–6.0 mEq/L
• Moderate hyperkalemia: 6.1–7.0 mEq/L
• Severe hyperkalemia: > 7.1 mEq/L

Etiology and Pathophysiology of Hyperkalemia

Normal control of potassium level

Potassium is the principal intracellular cation that is needed for maintenance of the membrane potential across the cells of nerves and muscles during transmission of impulses. The source of potassium could be from diet rich in potassium, such as intake of bananas, beans and meat, or the intravenous/oral administration of supplemental potassium.

Upon intake or infusion, the cation is absorbed at a rate of 1 mEq/Kg/day. Most of the absorbed ions (up to 90 %) are excreted via the kidneys. This is important in maintaining a normal serum level of potassium as well as a normal storage level.

The total body potassium stored in the muscles is estimated to be 50 mEq/kg. The cations are either intracellular (98 %) or extracellular (2 %). The extracellular potassium is the measurement in reference during laboratory testing and it is maintained at a range of 3.5-5.0 mEq/L via a homeostatic mechanism across the cell membrane aided by the Na+/K+/ATPase pumps.

Etiology

The cause of hyperkalemia is discussed on the following topics:

Increased intake of potassium

It is rarely a single cause of hyperkalemia especially in patients with a GFR> 60 ml/min. However, some situations have been reported, such as massive parenteral administration of potassium supplementation or massive transfusion with packed red blood cells, that may cause a slight increase in potassium level.

Decreased excretion of potassium

Dysfunctional kidneys lead to an elevated serum potassium level in several ways. First, when the removal of the potassium delivered to the kidneys for excretion is impaired, accumulation occurs and hyperkalemia ensues. Also, the majority of patients with renal dysfunctions are on diuretic medications. Most of these medications work by eliminating the water but sparing potassium, thus leading to high concentration of potassium in the body. Moreover, the drugs are not easily removed from the body, and very minimal doses may have a huge impact on the level of potassium.

Shifting of potassium to the extracellular compartment

High levels of glucose around the cell extract water out of the cells. If the water is accompanied by the movement of potassium in the same direction, this leads to hyperkalemia. It is seen in diabetic patients with ketoacidosis who have a compromised renal excretory mechanism.

The shift may also occur with the destruction of cells freeing the intracellular potassium.

This is seen in cases of:

• Trauma
• Burns
• Hemolysis
• Tumor lysis syndrome
• Malignant hyperthermia