Chloride shifting involves the exchange of bicarbonate (HCO3-) and chloride ions (Cl-) across the red blood cells membrane.
Most carbon dioxide in the body is transported in the form of bicarbonate in the blood. As the blood flows in the tissues, carbon dioxide gas diffuses into the red blood cells and is converted to bicarbonate.
The transport of bicarbonates into the red blood cells is in exchange for chloride ions. Which is referred to as chloride shifting.