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The chemical reactions that sustain life depend on a delicate balance – or homeostasis – between acids and bases in the body. Even a slight imbalance can profoundly affect metabolism and essential body functions. Several conditions, such as infection or trauma, and certain medications can affect acid-base balance. However, to understand this balance, you need to understand some basic chemistry.
Understanding acids and bases requires an understanding of pH, a calculation based on the concentration of hydrogen ions in a solution. It may also be defi ned as the amount of acid or base within a solution.
Acids consist of molecules that can give up, or donate, hydrogen ions to other molecules. Carbonic acid is an acid that occurs naturally in the body. Bases consist of molecules that can accept hydrogen ions; bicarbonate is one example of a base.
A solution that contains more base than acid has fewer hydrogen ions, so it has a higher pH. A solution with a pH above 7 is a base, or alkaline.
A solution that contains more acid than base has more hydrogen ions, so it has a lower pH. A solution with a pH below 7 is an acid, or acidotic.
A patient’s acid-base balance can be assessed if the pH of their blood is known. Because arterial blood is usually used to measure pH, this discussion focuses on arterial samples.
Arterial blood is normally slightly alkaline, ranging from 7.35 to 7.45. A pH level within that range represents a balance between the concentration of hydrogen ions and bicarbonate ions. The pH of blood is generally maintained in a ratio of 20 parts bicarbonate to 1 part carbonic acid. A pH below 6.8 or above 7.8 is usually fatal.
Under certain conditions, the pH of arterial blood may deviate significantly from its normal narrow range. If the blood’s hydrogen ion concentration increases or bicarbonate level decreases, pH may decrease. In either case, a decrease in pH below 7.35 signals acidosis.
If the blood’s bicarbonate level increases or hydrogen ion concentration decreases, pH may rise. In either case, an increase in pH above 7.45 signals alkalosis.
A person’s well-being depends on their ability to maintain a normal pH. A deviation in pH can compromise essential body processes, including electrolyte balance, activity of critical enzymes, muscle contraction and basic cellular function. The body normally maintains pH within a narrow range by carefully balancing acidic and alkaline elements. When one aspect of that balancing act breaks down, the body can’t maintain a healthy pH as easily, and problems arise.