Disorders of acid-base balance
Disruption of acid-base stability of body fluids due to excessive acid-base load or impaired regulatory mechanisms.
Typing
According to the level of blood pH, <7.35 is acidosis and >7.45 is alkalosis.
HCO3- concentrations that are mainly influenced by metabolic factors are called metabolic acidosis or metabolic alkalosis.
If the H2CO3 concentration is mainly affected by respiratory factors and increases or decreases in a primary way, it is called respiratory acidosis or respiratory alkalosis.
In simple acidosis or alkalosis, the pH is still within the normal range although the HCO3-/H2CO3 value in the body has changed due to the regulation of the body, which is called compensatory acidosis or compensatory alkalosis.
If the pH is abnormal, it is called decompensated acidosis or decompensated alkalosis.
Acid-base balance disorder is mainly divided into the following five types
1, metabolic acidosis.
According to AG value, it can be further divided into AG increased type and AG normal type.
(1) AG increased type of acid replacement: refers to the metabolic acidosis when the plasma concentration of any fixed acid other than chlorine is increased. Characteristics: Increased AG and normal blood chlorine.
(2) AG normal type acid substitute: When the HCO3- concentration is reduced and there is a compensatory increase in Cl- concentration, the metabolic acidosis is AG normal type or hyperchloremic acidosis. Features: normal AG and elevated blood chloride.
2. Respiratory acidosis.
According to the course of the disease, it can be divided into acute respiratory acidosis and chronic respiratory acidosis.
Respiratory acidosis is a disorder of acid-base balance characterized by the retention of CO2 in the body and the original occurrence of increased H2CO3 concentration in plasma.
3. Metabolic alkalosis.
According to the efficacy on saline, metabolic alkalosis is divided into two categories: metabolic alkalosis treated effectively with saline and metabolic alkalosis treated ineffectively with saline.
Metabolic alkalosis is a disorder of acid-base balance basically characterized by primary increase in plasma HCO3- concentration.
4.Respiratory alkalosis.
According to the course of the disease, it can be divided into acute and chronic respiratory alkalosis.
Respiratory alkalosis is a disorder of acid-base balance characterized by a primary decrease in plasma H2CO3 concentration caused by pulmonary hyperventilation.
5.Mixed acid-base balance disorder.
Dual acid-base balance disorder has acid-base consistency and acid-base mixture. In addition there are two forms of triple acid-base balance disorder.
Acid-base consistency: call acid + substitute acid; call base + substitute base.
Mixed acid-base: exhaled acid + substitute base; exhaled base + substitute acid; substitute acid + substitute base.
Triple acid-base homeostasis disorder: exhaled acid+substituted acid+substituted base; exhaled base+substituted acid+substituted base.
Mixed acidosis: high AG surrogate acid + high Cl-ness surrogate acid.
Basic principles of judging acid-base balance disorder
1.Judging acidosis or alkalosis by pH
2.Judging whether it is respiratory or metabolic imbalance by the primary factor
3.Judging whether it is simple or mixed acid-base imbalance according to the compensatory situation
Six steps of arterial blood gas analysis
[Step 1]
Assess the internal consistency of blood gas values according to the Henderseon-Hasselbach formula
[H+] = 24 x (PaCO2)/[HCO3-]
[Step 2]
Determine if alkalemia or acidemia is present?
pH<7.35 is acidemia
pH>7.45 is alkalemia
[Step 3]
Is there a respiratory or metabolic disorder and how does the direction of pH change relate to the direction of PaCO2 change?
[Step 4]
Is there appropriate compensation for the primary abnormality?
[Step 5]
Calculate the anion gap (if metabolic acidosis is present)
AG = [Na+]-[Cl-]-[HCO3-]
[Step 6]
If the anion gap is elevated, evaluate the relationship between the elevated anion gap and [HCO3-].