Biochemical test for acid-base imbalance disorder

2021-07-05 04:01 PM

Hypoxia is one of the causes leading to disorders of biological oxidation processes, resulting in a lack of cellular energy, leading to cell destruction

Normally, arterial blood pH = 7.38 - 7.41 and the ratio [HCO3-/H2CO3] = 20/1 (PaCO2 = 40 mmHg, HCO3- = 24 mmol/l, BE = 0 ± 2 (mmol/l). ).

When the role of acid-base balance of buffer systems, lungs, kidneys is reduced or
ineffective, it will cause acid-base imbalance.

3 groups of disorders CBAB

Disorders due to respiratory causes (due to changes in PaCO2).

Disorder of metabolic etiology (due to HCO3_ changes).

Mixed disorders of both metabolic and respiratory causes.

To evaluate acid-base disturbances, in clinical practice, Shneerson, Siggar Anderson, Davenport diagrams can be used, in which diagrams.

Davenport is more used.

Davenport's Diagram

Davenport diagram has 2 axes:

The horizontal axis is pH (6.9 - 7.7).

The vertical axis is HCO3- (mmol/l).

The curves are PaCO2 (arterial blood CO2 pressure).

On the diagram there is a circle that is gradually determined the parameters in normal people: pH = 7.38 - 7.42; PaCO2 = 40 mmHg; HCO3- = 25 mmol/l and Hb = 150g/l.

From the 2 lines at pH = 7.38 - 7.42, the PaCO2 curves are cut at 40 mmHg and the Hb = 150 g/l straight lines form 6 areas of acid-base disturbance.

Acid-base balance disorders

6 areas of acid-base disturbance on the Davenport diagram include respiratory acidosis (A), metabolic alkalosis (B), respiratory alkalosis (C), metabolic acidosis (D), mixed acidosis mixed (E), and mixed alkalosis (F).

Respiratory acidosis (A)

The primary disorder of respiratory acidosis is increased PaCO2 due to decreased CO2 excretion in the lungs. Reason:

Decreased alveolar ventilation, bronchial obstruction.

Lung diseases: bronchiolitis, pneumonia, asthma.

Inhale CO2 re-breathes breathed air.

Nervous system: sleeping pills, paralysis, poisoning, traumatic brain injury,
brain tumor ...

Testing the parameters of acid-base balance shows:

pH decreased.

PaCO2 increased.

HCO3- blood increased.

CO2 in the whole blood increases.

Base buffer (BB) decreased, BE negative.

Metabolic alkalosis (B)

The state of excess base or loss of acid other than H2CO3.

Cause: is too much alkali due to too much bicarbonate, or too much alkali, or acid loss in the following cases:

Vomit a lot.

Stomach aspiration.

prolonged diarrhea.

Test results of acid-base balance parameters:

Blood pH increases.

Blood PaCO2 increased.

CO2 in the whole blood increases.

Bicarbonate (HCO3-) blood increased.

Standard bicarbonate (SB) increased.

Base buffer (BB) increased.

The residual base (BE) is positive.

Respiratory alkalosis (C)

Respiratory alkalosis is a disorder triggered by a decrease in PaCO2.


Early-stage of pneumonia.

High fever.

Excessive CPR not tested.

Traumatic brain injury.

Breathe in a low CO2 fractional atmosphere (at altitude). 

When testing the acid-base balance parameters showed:

Blood pH increases.

HCO3- blood decreased.

PaCO2, total CO2 decreased.

BB increases and BE is positive.

Metabolic acidosis (D)

A state resulting from loss of buffer anions, mainly HCO3-, or from the accumulation of "fixed" acids, in fact, strong acids whose anions cannot be excreted by the kidneys.

Test results in metabolic acidosis showed:

Blood pH drops sharply.

PaCO2 dropped sharply.

CO2 in the whole blood decreases.

SB decreased; BB decreased.

BE is negative.

Metabolic acidosis can occur in the following cases:

Diabetes caused by the accumulation of ketone bodies.

Acute pulmonary edema, epilepsy, impaired glucose metabolism cause lactic acidosis.

Kidney diseases: acute and chronic nephritis do not excrete acid.

Acute diarrhea causes loss of HCO3- .

Metabolic acidosis has the highest mortality risk compared with other disorders of acid-base balance.

Mixed acidosis (E)

Mixed acidosis is a combination of metabolic acidosis and respiratory acidosis
Test results in mixed acidosis showed:

Blood pH drops sharply.

PaCO2 increased.

HCO3- decreased.

BE is negative.

Mixed acidosis may occur in the following cases:

Respiratory failure: acute pulmonary edema reduces alveolar ventilation, increases PaCO2, causes hypoxia, and causes lactic acidosis.

Chronic glomerulonephritis associated with bronchial asthma.

Bronchitis bronchiolitis.

Mixed alkalosis (F)

Mixed alkalosis is a combination of respiratory alkalosis and
metabolic alkalosis.

Test results showed:

Blood pH increased sharply.

PaCO2 decreased.

HCO3- increased.

BE is positive.

Seen in cases such as:

Liver coma.

Coma due to hypnotic drugs after combination therapy with artificial ventilation and blood alkalinity to exclude hypnotic drugs.

Lack of blood oxygen

Criteria for hypoxia:

Decreased blood PaO2 (decreased dissolved oxygen, the form of oxygen needed by cells to use).

Hypertonicity: increased blood PaCO2 (as CO2 dissolved in the blood), PaCO2 > 50 mmHg, usually due to decreased ventilation function.

Consequences of hypoxia:

Decreased perfusion of the skin and mucous membranes.


Decreased physiological activity, reduced physical strength, decreased body resistance.

Hypoxia is one of the causes leading to disturbances in biological oxidation processes, resulting in a lack of cellular energy, leading to cell destruction.