Definition
Hypokalemia is the condition when there is too little (lat. “hypo”) potassium in the blood (lat. “-emia”).
Potassium is a metal from the periodic table, which occurs in the blood along with some other metals. Potassium is present throughout the body inside and outside of every cell and, together with sodium and calcium and other charged particles, forms an equilibrium which is often referred to as the “salt balance” or “electrolyte balance”. This equilibrium ensures that each cell maintains an electrical voltage at its shell, its “membrane”.
This means that simply by changing the amounts of potassium (and sodium, calcium, etc. ), processes such as muscle tension, digestion and any other tasks of the cells can take place. If there is an error in this balance in the form of hypokalemia, this can have life-threatening consequences. The normal value of potassium in blood is 3.6 – 5.2 mmol/L. Thus, values <3.6 mmol/L are called hypokalemia, values >5.2 mmol/L are called hyperkalemia.
Symptoms
Muscle cells are particularly sensitive to changes in potassium levels. If the potassium level in blood serum drops, the electrical voltage that exists on the membranes of the muscle cells changes and the voltage drops. The cell becomes more difficult to excite.
In electrophysiological terms, this process is called “hyperpolarization”. In the worst case, this can lead to paralysis (paresis) of the muscles. Deliberate muscle movements are more difficult for the person concerned, resulting in bladder weakness and weakened digestion, which causes constipation.
So-called “muscle reflexes” such as the Achilles or patellar tendon reflex are weakened. The effects on the heart muscle are particularly acute and life-threatening. Initially, there are cardiac arrhythmias, which can be detected when the heart is listened to or when an ECG is recorded.
Severe hypokalemia can lead to ventricular fibrillation, in which acute defibrillation becomes necessary. ECG is the abbreviation for electrocardiogram and is recorded to check the electrical activity of the heart muscle. With every heartbeat, the ions, the “metals”, are shifted between the inner and outer space of the cells.
As a result, the electrical voltage that exists at each cell membrane changes and the cells become excited (“depolarized”), causing the muscle fibers to contract. With the help of electrodes on the skin, the ECG measures the sum of all electrical voltages of the entire heart. This makes it possible to follow how and in which direction the excitation in the heart spreads with each heartbeat.
The ECG can be used to detect all the consequences of hypokalemia. Starting with cardiac dysrhythmia, through disturbances in the reduction of the excitation to life-threatening ventricular fibrillation, the physician can follow all developments in the ECG. The signs of hypokalemia are T flattening, ST depressions, U waves and extrasystoles. However, these ECG signs can also occur without hypokalemia and therefore do not automatically lead to the diagnosis of hypokalemia. The most reliable diagnostic method to detect hypokalemia is blood sampling.
