Chloride shift (also known as the Hamburger shift) is a process which occurs in a cardiovascular system and refers to the exchange of bicarbonate (HCO3−​) and chloride (Cl−) across the membrane of red blood cells.

Carbon dioxide (CO2​) generated in tissues enters the blood and dissolves in water in the red blood cells to form carbonic acid (H2CO3), which then dissociates to form bicarbonate (HCO3−​) and a hydrogen ion (H+). When carbon dioxide levels fall as the blood passes through the lungs, bicarbonate levels fall in the serum because the equilibrium shifts to replace CO2​, and consequently, bicarbonate in the red blood cells will move out into the serum.

To balance the charges when bicarbonate exits the cell, a chloride anion from the plasma enters the red blood cell. Reverse changes occur in the lungs when carbon dioxide is eliminated from the blood. Here, the exchange of bicarbonate for chloride in red blood cells flushes the bicarbonate from the blood and increases the rate of gas exchange. This chloride shift may also regulate the affinity of hemoglobin for oxygen through the chloride ion acting as an allosteric effector.

chloride shift is the shift of chloride ion from plasma to RBC bcoz in RBC CO2 add with H2O to become biocarbonate that is responsible for carbon Di oxide transport. so when this ion goes into plasma then for satisfie the positive charge in RBC chloride ion goes into RBC. this effect also called hamburger effect