Acid-Base Balance - Definition and Abnormalities

Understanding PH Balance in the Body and in Disease

Doctor talking to patient in hospital bed. Credit: Caiaimage/Robert Daly

Definition: Acid-Base Balance

Acid-base balance refers to a mechanism developed by the body to keep bodily fluids as close to a neutral pH as possible. In doing so, bodily fluids are kept from becoming too acidic (having too much acid) or too basic (having too much alkaline). A proper acid-base balance allows the body to function in a state of equilibrium, or stability.

What is Normal Body pH?

Body pH is measured on a scale from 1 to 14 with 1 being more acidic and 14 being more basic.

  Normal body pH is between 7.35 and 7.45.

  • If body pH is less than 7.35, the body is "acidotic."
  • If body pH is greater than 7.45, the body is "alkalotic" or "basic."

When healthy, the body regulates the pH carefully through the kidneys (by removing or retaining acids and bases) or through the lungs (by breathing faster or slower.)  Acids are produced by the normal metabolism of carbohydrates, proteins, and fats, for which the kidneys compensate by removing acid.

Body pH Measurement

The body pH is usually measured through a combination of tests that may include the pH of blood in the arteries, plus the level of electrolytes in plasma.

Compensation

If the pH of the body falls outside of the normal range, the body works to restore "homeostasis" or a state of equilibrium.  It does this by:

  • Renal compensation - The kidneys can buffer the pH by excreting acid or by retaining bicarbonate (a base.)
  • Pulmonary compensation - If pH falls, in other words, if the body is acidotic, breathing may increase to blow off carbon dioxide to restore balance.

    Abnormalities in Body Acid-Base Balance/Body pH

    Ordinarily, the PH of the body lies within this small range.  If patients are unable to compensate for a change in pH, for example, due to serious illness, anemia, or malnutrition, a state of excess acid or base may occur.  These can include the following:

    Metabolic Acidosis

    In metabolic acidosis there is an increased amount of body acid - in other words, the pH of the body falls below 7.35.  Conditions which can cause this include:

    Metabolic Alkalosis

    In metabolic alkalosis, the amount of bicarbonate is increased, often due to the loss of metabolic acids.  Conditions which can cause this may include:

    • The use of diuretics (water pills)
    • Vomiting
    • Medications such as steroids
    • Cushing's syndrome

    Respiratory Acidosis

    In respiratory acidosis, the body retains excess carbon dioxide resulting in a more acidic body pH.  Conditions which may cause this include:

    • Hypoventilation - In other words, through shallow or infrequent breathing
    • COPD and other lung diseases
    • Overdoses of opioids and alcohol

    Respiratory Alkalosis

    In respiratory alkalosis,an excess level of carbon dioxide is blown off by the lungs.  Conditions which may cause this include:

    • Liver disease
    • Pregnancy
    • Septicemia and other serious infections
    • Fever
    • Anxiety

    Example:

    The acid-base balance system in a person with COPD is sometimes affected because of ineffective breathing patterns and the build-up of carbon dioxide. This can sometimes lead to respiratory failure, one of the complications of COPD.

    Also Known As: pH balance

    Sources:

    Ayers, P., Dixon, C., and A. Mays. Acid-base disorders: learning the basics. Nutrition in Clinical Practice. 2015. 30(1):14-20.

    Gooch, M. Identifying acid-base and electrolyte imbalances. Nurse Practitioner. 2015. 40(8):37-42.

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