Potassium (K, K⁺) is the most abundant intracellular cation; much smaller amounts are found in the blood. Potassium is essential for the transmission of electrical impulses in cardiac and skeletal muscle. In addition, it helps to maintain the osmolality and electroneutrality of cells, functions in enzyme reactions that transform glucose into energy and amino acids into proteins, and participates in the maintenance of acid-base balance.

Numerous disorders and drugs can affect serum potassium levels. As shown in Table 5-23, the clinical problems associated with altered serum potassium levels may be categorized as (1) inappropriate cellular metabolism, (2) altered renal excretion, and (3) altered potassium intake. False elevations in serum potassium can occur with vigorous pumping of the hand after tourniquet application for venipuncture, in hemolyzed samples, or with high platelet counts during clotting. Falsely decreased levels are seen in anticoagulated samples left at room temperature.

Altered serum potassium levels are of particular concern because of their effects on cardiac impulse conduction, especially when the client also is taking medications that affect cardiac conduction. The combination of low serum potassium (hypo-kalemia) and therapy with digitalis preparations, for example, can produce serious consequences because of increased ventricular irritability.

Note also that potassium is a very changeable ion, moving easily between intracellular and extracellular fluids. An example is seen in states of acidosis and alkalosis. In acidosis (decreased serum pH), potassium moves from the cells into the blood; in alkalosis (increased serum pH), the reverse occurs.

• False elevations may occur with vigorous pumping of the hand after tourniquet application for venipuncture, in hemolyzed samples, or with high platelet counts during clotting.
• Falsely decreased levels are seen in anticoagulated samples left at room temperature.
• Numerous drugs may produce elevated and decreased levels (see Table 5-23).

• Routine electrolyte screening in acute and critical illness
• Known or suspected disorder associated with altered fluid and electrolyte balance, especially renal disease, disorders of glucose metabolism, trauma, and burns (see Table 5-23)
• Known or suspected acidosis of any etiology, because potassium moves from the cells into the blood in acidotic states
• Evaluation of cardiac dysrhythmias to determine whether altered serum potassium level is contributing to the problem (e.g., the combination of low serum potassium and therapy with digitalis preparations may lead to ventricular irritability)
• Evaluation of the effects of drug therapy (e.g., diuretics) on serum potassium levels
• Evaluation of response to treatment for abnormal serum potassium levels

Nursing Alert

• Because of the effects of serum potassium levels on cardiac impulse conduction, abnormal values should be reported to the physician immediately so that treatment may be instituted.

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

• Because many drugs may alter serum potassium levels, a medication history should be obtained. It is recommended that drugs that may alter test results be withheld for 12 to 24 hours before the test, although this practice should be confirmed with the person ordering the study.

A venipuncture is performed and the sample collected in a red-topped tube. Vigorous pumping of the hand after tourniquet application should be avoided, because it may lead to falsely elevated results. The sample should be handled gently to avoid hemolysis, which may also falsely elevate results, and transported immediately to the laboratory.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample.

• Resume any medications withheld before the test.
• Increased levels: Note and report increased levels. Assess for symptoms associated with hyperkalemia such as oliguria, irritability, diarrhea, and ECG tracings for peaked T waves. Assess results of arterial blood gases (ABGs). Prepare client for IV administration of medications (sodium bicarbonate for acidosis, calcium gluconate if calcium level is low) or oral or enema administration of sodium polystyrene sulfonate. Instruct client in low potassium dietary intake and food restrictions (citrus juices, bananas, dried fruits, potatoes, and tomatoes).
• Decreased levels: Note and report decreased levels. Assess for symptoms of hypokalemia such as thirst, vomiting, anorexia, weak pulse, decreased blood pressure, ECG tracings for depressed T waves, or prominent U waves. Administer oral or IV potassium replacement. Instruct client in foods high in potassium, as already listed.
• Critical values: Notify the physician at once of levels less than 2.5 mEq/L or greater than 6.5 mEq/L (greater than 8.1 mEq/L in infants).