Chapter 12 Assessment and Care of Patients with Problems of Acid base balance

The pH of a solution may range from

1 (acidic as possible) to 14 (alkaline as possible), with 7 being neutral. A change of 1 pH unit actually represents a tenfold change in free hydrogen ion level.

Liquids with pH ranging from

1.0 to 6.99 have more or stronger (or both) acids compared with bases. The liquids are acidic with more free hydrogen ions released than bound, increasing the amount of free hydrogen ions in the liquid.

Liquids with a pH ranging from

7.01-14.0 have more or stronger (or both) bases compared with acids. These liquids are basic, in which more hydrogen ions are being bound than released, decreasing the amount of free hydrogen ions.

Most body fluids have pH value between

7.35-7.45 even though they contain acidic substances and basic substances. 7.0 is neutral

Maintaining acid base balance is important because changes from normal pH interfere with many functions:

Changing the shape and reducing the function of hormones and enzymes. Changing the distribution of other electrolytes, causing fluid and electrolyte imbalances. Changing excitable membranes, making the heart, nerves, muscles, and GI tract either less or more active than normal. Decreasing the effectiveness of many drugs.

Body fluids contain different types of

acids and bases.

ECF protein buffers are

albumin and globulins

This constant ratio is related to

balancing the production and elimination of carbon dioxide and hydrogen ions.

The most common base in human body fluid is

bicarbonate

The two most common chemical buffers are

bicarbonate (which is active in both ECF fluid and ICF fluid) amd phosphate (which is active in the ICF)

Weak bases bind hydrogen ions less readily. An example of a weak base is

bicarbonate. Bicarbonate ions in the body are critical in preventing major changes in body fluid pH.

A base

binds free hydrogen ions in solution and lowers the amount of free hydrogen ions in solution. Ex. are sodium hydroxide and ammonia

Buffers are critical in keeping

body fluid pH at normal levels because they can react either as an acid (releasing a hydrogen ion) or as a base (binding a hydrogen ion)

Protein buffers are the most common

buffers

The most common acid is

carbonic acid The body keeps these substances at a constant ratio of 1 molecule of carbonic acid to 20 free bicarbonate ions.

Buffers are the first line of defense against

changes in free hydrogen ion levels.

Because the kidneys control bicarbonate levels and the lungs

control CO2 levels, pH is also the result of how well the kidneys are functioning to retain or eliminate bicarbnate divided by how well the lungs are functioning to eliminate carbon dioxide. A problem in either organ system can lead to disturbed acid base balance.

Normal metabolism of carbohydrate, protein, and fat

creates natural waste products.

When excess carbon dioxide is produced, the

equation shifts to the right, causing an increase in hydrogen ions (and a decrease in pH). When very little carbon dioxide is produced, no free hydrogen ions are created by this equation.

This extra CO2 is eliminated during

exhalation, helping to bring the hydrogen ion concentration down to normal. Whenever the CO2 level changes the pH changes to the same degree, in the opposite direction.

Incomplete breakdown of fatty acids occurring when large amounts of

fatty acids are being metabolized forms ketoacids.

the level of free hydrogen ions

formed from acids, must be rigidly controlled

Incomplete breakdown of glucose, which occurs whenever cells metabolize under anaerobic (no oxygen) conditons

forms lactic acid.

Carbon dioxide is a

gas that forms carbonic acid when combined with water, making carbon dioxide a part of carbonic acid.

A major intracellular protein buffer is

hemoglobin

Anaerobic conditions occur with

hypoxia, sepsis, and shock.

When chemical buffers alone cannot prevent changes

in blood pH, the respiratory system is the second line of defense against changes.

Maintaining the pH within the narrow normal range

is critical for life and body function.

When blood pH changes are presistent

kidney actions to increase excretion and reabsorption rates of acids or bases (depending on which way pH changes) start.

These actions are

kidney movement of bicarbonate, formation of acids, and formation of ammonium.

Bicarbonate, a weak base, is the

main buffer of the ECF. It comes from the GI absorption of ingested bicarbonate, pancreatic production of bicarbonate, movement of cellular bicarbonate into the ECF, kidney reabsorption of filtered bicarbonate, and the breakdown of carbonic acid. Once bicarbonate is in the ECF, it is kept at a level 20 times greater than that of cabonic acid.

Acid base balance is the

maintenance of arterial blood pH between 7.35-7.45 through regulation of hydrogen ion production and elimination.

Liquids with a pH of 7.0 are

neutral by having a free hydrogen ion level in which the amount and strength of acids and bases are equal.

Buffers always try to bring the fluid as close as possible to the

normal body fluid pH of 7.35 to 7.45. If the fluid is basic the buffer releases hydrogen ions into the fluid. Fluid is acidic (with many free hydrogen ions), the buffer binds some of the excess hydrogen ions.

One factor that determines blood pH is how much CO2 is

produced by body cells during metabolism versus how rapidly that CO2 is removed by breathing.

A strong acid such as hydrochloric acid

separates completely in water and releases all of its hydrogen ions

A weak acid releases only

some, not all, of its hydrogen ions.

Acids are

substances that releases hydrogen ions when dissolved in water or body fluids, increasing the amount of free hydrogen ions in that solution.

Protein breakdown forms

sulfuric acid. Fat breakdown forms fatty acids and ketoacids.

Therefore carbon dioxide content of a fluid is directly related to

the amount of hydrogen ions in that fluid. Whenever conditions cause carbon dioxide to increase, more free hydrogen ions are created. Likewise, whenever free hydrogen ion production increases, more carbon dioxide is produced.

An increase in bicarbonate causes

the amount of hydrogen ions to decrease and the pH to increase becoming more alkaline (basic). A decrease in bicarbonate causes the free hydrogen ion level to increase and the pH to decrease, becoming more acidic.

When excess hydron ions are present

the carbonic anhydrase equation shits to the left, causing the creation of more carbon dioxide. When the amount of free hydrogen ions in body fluids is low, no extra carbon dioxide is produced.

Respiratory regulation of acid base balance is under

the control of the central nervous system.

The lower the pH value of a fluid

the higher the level of free hydrogen ions in that fluid.

When the CO2 level of a liquid decreases,

the pH rises indicating fewer free hydrogen ions (more alkaline)

Cell destruction allows cell contents to be released, including

the structures that contain acids.

As long as body cells are healthy

they continuously produce acids, carbon dioxide, and free hydrogen ions.

The CO2 level in

venous blood increases with metabolism

Normal body fluid pH remains at this near-neutral value

when the acids and bases are nearly balanced, limiting the total number of free or unbalanced hydrogen ions.

The kidneys are the 3rd line of defense against

wide changes in body fluid pH. Kidney actions are stronger for regulating acid base balance but take 24 to 48 hours to completely respond.