What causes Carpopedal spasms during respiratory alkalosis?

Acute respiratory alkalosis also causes cerebral vasoconstriction and decreased blood supply to the brain, which can lead to syncope and altered mental status. Calcium levels also decrease in respiratory alkalosis, which can cause numbness, tingling and spasms of the patient's hands and feet, known as carpopedal spasm.

Why does hyperventilation cause tetany?

Low levels of carbon dioxide cause tetany by altering the albumin binding of calcium such that the ionized (physiologically influencing) fraction of calcium is reduced; one common reason for low carbon dioxide levels is hyperventilation. Low levels of magnesium can lead to tetany.