Question

acidosis and alkalosis will cause shifts of the serum potassium that may produce serious cardiac rhythm abnormalities. discuss the shift into and out of the cell that occurs with both alterations of the pH. describe what the body is trying to accomplish by such shifts (these are compensatory mechanisms.) Provide appropriate pathophysiology and then a brief discussion of the potential cardiac dysrhythmias resulting from each shift. How does that shift affect the cardiac action potential?

Answer 1

Potassium is the major intracellular electrolyte; in fact, 98% of the body's potassium is inside the cells. The remaining 2% is in the ECF. Potassium influences both the skeletal and cardiac muscle activity. The normal serum potassium ranges from 3.5 to 5.5mEq/L.

Hypokalemia:

Hypokalemia usually indicates an actual deficit in total potassium stores. When alkalosis is present, a temporary shift of serum potassium into the cells occurs. Alterations in acid-base balance have a significant effect on potassium distribution. The mechanism involves the shift of hydrogen and potassium ions between the cells and the ECF. Hypokalemia can cause alkalosis, and in turn, alkalosis can cause hypokalemia. For example, hydrogen ions move out of the cells in alkalotic states to help correct the high PH, and potassium ions move in to maintain an electrically neutral state.

Thus the disturbance of decreased potassium level will raise the resting membrane potential. The refractory period and action potentials are prolonged. the ECG shows changes of ST depression, T-wave flattening suggesting ischemia, the appearance of U wave(specific to hypokalemia) and arrhythmias. Hypokalemia increases sensitivity to digitalis., predisposing the patient to digitalis toxicity at lower digitalis levels.

Hyperkalemia:

Hyperkalemia is greater than the normal serum potassium concentration. Hyperkalemia is more dangerous because the cardiac arrest is more commonly associated with high serum potassium levels. In acidosis, potassium moves out of the cells into the ECF. This occurs the hydrogen ions move out of the cells, a process that buffers the PH of the ECF.

The most consequence of hyperkalemia is its effect on the myocardium. As the plasma potassium level rises, disturbances in cardiac conduction occur. The earliest changes, often occurring at a serum potassium level greater than 6mEq/L are peaked, narrow T waves; ST-segment depression; and a shortened QT interval. If the serum potassium level continues to rise, the PR interval becomes prolonged and is followed by the disappearance of P waves. finally, there is a decomposition and prolongation of the QRS complex. Ventricular dysrhythmias and cardiac arrest may occur at any point in this progression.