Changes in extracellular ion concentrations following ischemia. Extracellular pH begins to decrease immediately after the onset of ischemia. This change is accompanied by slight increases in the extracellular concentrations of K⁺, Cl⁻ and Na⁺. After about 1 min of ischemia, a dramatic shift of ions occurs, with K⁺ leaving cells and Ca²⁺, Cl⁻ and Na⁺ leaving the extracellular space. (From [1], with permission.)