Chvostek: Signs, symptoms, causes
There is little value when finding a positive Chvostek sign. However, it is still accepted as a marker in hypocalcemia and increased neuromuscular stimulation.
Tap on the patient's cheek at a point in front of the ear and just below the cheekbone to stimulate the facial nerves, contracting the lateral facial muscles. These are suggestive signs for hypocalcemia and increased neuromuscular stimulation.
Hypocalcemia due to a number of reasons:
Lack of vitamin D.
Disability of fake parathyroid glands.
Increased ventilation / respiratory alkalosis.
Lower Blood Magnesium.
Figure. Mechanism of the Chvostek marker in hyperventilation
All the conditions associated with Chvostek markers cause increased nerve stimulation. This means that when the facial nerve is stimulated (eg, tapping a finger), abnormally strong muscle contractions are caused.
Lower blood calcium
Calcium is required to maintain the normal permeability of nerve cell membranes; thanks to its ability to block sodium channels on it. When the extracellular calcium concentration is low and/or not present to do its job, the sodium channel stability increases. Large amounts of sodium enter the cells; the cell becomes less polar and excitable to an action potential.
Respiratory alkalosis and hyperventilation lead to a decrease in active ionic calcium concentrations - no effect on total calcium concentration. The decrease in active ionic calcium causes increased stimulation.
Respiratory alkalosis usually occurs due to hyperventilation. With increased ventilation, carbon dioxide is lost. The change in CO2 concentration causes the Henderson – Hasselbach equation to change in the direction of increasing CO2 generation to compensate for the loss.
Ultimately reducing the concentration of H + in the blood leads to alkalosis. The amount of ionized and free calcium (no longer bound to plasma proteins) is highly dependent on blood pH. When blood pH increases (alkalosis), the concentration of calcium bound to plasma proteins increases, thereby reducing the concentration of free ionic calcium in the extracellular fluid required for normal activities, such as sodium channel blockers and maintenance. permeability of the cell membrane.
Lower blood magnesium
The mechanism of hypomagnesemia leading to hypocalcemia is still unclear. However, it is clear that magnesium is needed to maintain ion channels and is a carrier in irritable tissues. Magnesium affects several processes in the cell including:
Na + / ATPase pumping action - reducing the magnesium concentration causes a decrease in Na + / ATPase pump activity.
Blocking K + channels on the cell surface - reducing the concentration of magnesium leads to the removal of potassium from the cell.
Reduced magnesium levels inhibit parathyroid hormone and lead to hypocalcemia.
The activity of the calcium channel.
There is little value when finding a positive Chvostek sign. However, it is still accepted as a marker in hypocalcemia and increased neuromuscular stimulation. It is important to note that up to 25% of patients with normal calcium levels are positive.