Sodium bicarbonate is the chemical name for baking soda, a common household salt that is also an important part of your blood chemistry, because it occurs naturally in the blood. In general, sodium bicarbonate has the effect of acting as a buffer, meaning it helps to stabilize the blood pH.
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Sodium bicarbonate has the chemical formula NaHCO3. It's a salt with both acidic and basic properties, but most importantly, it acts as a chemical buffer. A buffer is a chemical that can react with small amounts of either acid or base, helping to prevent changes in solution pH, where pH is a measure of solution acidity. This is very important in your bloodstream, because to maintain cellular health, the pH of your blood must remain relatively constant.
Though the most common bicarbonate salt is sodium bicarbonate, the sodium itself has no part in the buffering chemistry; bicarbonate is the reactive part of the salt. The most important source of bicarbonate in blood is metabolic. When your cells burn nutrient molecules for energy, they generate carbon dioxide. This reacts with water in the bloodstream to make carbonic acid, which further reacts in the bloodstream to produce bicarbonate. In this way, you continually produce a pH-stabilizing buffer as you respire.
Maintaining the stability of the blood pH depends upon not only the production of carbon dioxide, but its elimination as well. If you don't exhale CO2 regularly, it starts to build up in your blood. This leads to overproduction of carbonic acid, which can start to affect blood pH despite the presence of the bicarbonate buffer. In simple terms, while some bicarbonate in the blood is helpful, too much can lead to acidosis.
The complex buffering chemistry of bicarbonate means that sodium bicarbonate is sometimes used as an ingredient in dialysis solutions. Dialysis is a mechanism for cleansing the blood if the kidneys aren't functioning correctly. If kidney failure leads to buildup of too much acid in the blood -- which it can -- sodium bicarbonate in dialysis solution can help to remove some of the excess acid and bring the blood pH back to appropriate levels.