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Rules of interpretation of AAB indices AAB indices in the norm

RULE 1. Primary metabolic disorders are possible if:

A. pH and PC0₂ are changed in one direction.

If pH and PC0₂ are changed in one direction and pH differs from the norm, then primary disorders are metabolic.

B. pH is changed, and PC0₂ is in the norm that indicates at the disturbance
of compensation mechanisms.

RULE 2. Associated respiratory disorders are defined by the following equations:

A. For metabolic acidosis

It means that if PC0₂ is greater than the expected value, then the state is due to respiratory acidosis, and if it is less, then it is due to respiratory alkalosis.

RULE 3. Primary respiratory disorders develop as a result of pH and PC0₂ changes in opposite directions.

RULE 4. A relationship between the changes of PC0₂ and pH may be used for revealing metabolic disorders or incomplete compensation reactions.

Metabolic acidosis is the most frequent form of AAB disorders. It is observed in massive hemotransfusions (citrated blood), infusions of cold solutions, circulatory disorders, crush syndrome and so on.

The causes of metabolic acidosis:

1. Hypoxia and formation, as a result, of great amounts of lactic, pyruvic and other organic acids.

2. ARF, CRF accompanied by a retention of phosphates P0₄³" and hydrophosphates HP0₄²".

3. Dehydration as a result of significant loss of the small intestine content, bile or pancreatic juice (loss of bases).

4. Diabetes mellitus, prolonged starvation or persistent fever.

5. Grave adrenal insufficiency.

6. Intake of great amounts of acids with food.

A compensation of metabolic acidosis occurs through respiratory and renal tracts.

In clinic a metabolic acidosis is mostly encountered in oxygen deprivation of tissues and formation of underoxidized products of metabolism — in massive blood loss, progressing cardiovascular insufficiency. A particularly great number of underoxidized products is formed in clinical death, and with the onset of restoration of blood circulation these products are ejected into a general blood flow.

Basic signs of metabolic acidosis are a decrease of pH, HC0₃~, inten­sification of pulmonary ventilation and decrease of PC0₂, SB, BB, BE (-), elevation of K⁺ content with simultaneous decrease of Na⁺ ions content.

Metabolic acidosis is compensated by respiratory alkalosis. Here, pH, pC0₂, BE are significantly reduced (there is an excess of nonvolatile acids in the organism). Concentration of HC0₃" is decreased, Na⁺ is excreted with urine. Elevation of K⁺ level is rather pathognomonic.

Respiratory acidosis develops in excess of C0₂ in the organism as a result of its excessive formation or decrease of the alveolar ventilation volume. In the process, PC0₂ increases and pH decreases.

The causes of respiratory acidosis:

1. Hypoventilation as a result of bronchial asthma.

2. Pulmonary ventilation disorders in the early postoperative period (pain, dynamic ileus with compression of diaphragm, inadequate APV in the regimen of hypoventilation etc.).

Main compensation of respiratory acidosis is implemented by the kidneys in the form of forced elimination of H⁺ and Cl" ions, as well as by means of bicarbonates retention that is reflected by an increase of AB, SB, BE.

Such compensation is expedient until metabolic alkalosis is added.

PC0₂ and BE are moderately elevated, Cl" content is decreased (excreted with the urine), Na⁺ is elevated, concentration of K⁺ increases in blood plasma at the expense of its release from the cells in exchange for H⁺.

Respiratory acidosis is combined with oxygen deprivation, in this connection underoxidized products arise in the organism in excess amounts that leads to metabolic acidosis.

So, a respiratory acidosis, as a rule, is combined with metabolic acidosis.

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