Overview.
Mixed acid-base imbalance is defined as the simultaneous presence of two or more simple acid-base imbalances. In mixed acid-base imbalance, the original compensatory response no longer exists, while the pathophysiologic changes are complex and the clinical manifestations are atypical. Therefore, a preliminary diagnosis is made by taking a history and analyzing the results of blood gas analysis.
Etiology
The following five types of mixed acid-base balance disorders are common:
(i) Respiratory acidosis combined with metabolic acidosis
1. Chronic respiratory acidosis
If obstructive pulmonary disease, toxic shock with lactic acidosis occurs at the same time.
2. Acute respiratory acidosis due to cardiac and respiratory arrest and lactic acidosis due to hypoxia.
This mixed acid-base balance disorder may cause a significant decrease in plasma pH, a decrease in plasma [HCO3-], and an increase in PCO2.
(ii) Respiratory acidosis combined with metabolic alkalosis
In chronic obstructive pulmonary disease hypercapnia, but also due to pulmonary heart disease heart failure and the use of diuretics such as tachycardia, diuretic acid and other metabolic alkalosis caused by patients. The patient’s plasma PH may be normal or mildly elevated or decreased, but both [HCO3-] and PCO2 are significantly elevated. Elevated [HCO3-] is a characteristic of metabolic alkalosis, while elevated PCO2 is a characteristic of respiratory acidosis, but the ratio of the two can remain unchanged or change little.
(C) Respiratory alkalosis combined with metabolic acidosis
1. Patients with renal insufficiency
Patients with metabolic acidosis and respiratory alkalosis caused by hyperventilation due to fever, such as acute renal failure caused by gram-negative bacillus sepsis with high fever.
2. Patients with hepatic insufficiency
Hyperventilation due to NH3 stimulation and lactic acidosis due to metabolic disorders.
3. Metabolic acidosis caused by excessive dose of salicylic acid.
At the same time, it stimulates the respiratory center and leads to hyperventilation. The plasma PH value can be normal, mildly increased or decreased, but plasma [HCO3-] and PCO2 are significantly decreased. The decrease in [HCO3-] is a characteristic of metabolic acidosis, and the decrease in PCO2 is a characteristic of respiratory alkalosis, but the ratio of the two can remain unchanged or change little.
(D) Respiratory alkalosis combined with metabolic alkalosis
1. Patients with fever and vomiting
Respiratory alkalosis caused by hyperventilation and metabolic alkalosis caused by vomiting.
2. Cirrhotic patients with ascites
When hyperventilation due to NH3 stimulation is accompanied by diuretics or vomiting, this type of plasma PH is significantly elevated, plasma [HCO3-] may be elevated, and PCO2 may be decreased. Elevated [HCO3-] is a characteristic of metabolic alkalosis, and decreased PCO2 is a characteristic of respiratory alkalosis, but the ratio of the two may remain unchanged or change little.
(E) Metabolic acidosis combined with metabolic alkalosis
Respiratory acidosis and alkalosis cannot exist at the same time, but metabolic acidosis and alkalosis can coexist. For example, in acute renal failure patients with vomiting or gastric suction. However, plasma PH, [HCO3-], and PCO2 can be within the normal range or slightly high or low.
Symptoms.
There are clinical manifestations of the original disease, but the pathophysiologic changes are complex and the clinical manifestations may be atypical.
Examination
Mainly do blood gas analysis.
1. Respiratory acidosis combined with metabolic acidosis
Plasma pH is significantly decreased, plasma [HCO3-] may be decreased, and PCO2 may be increased.
2. Respiratory acidosis combined with metabolic alkalosis
Plasma pH may be normal or mildly increased or decreased, but both [HCO3-] and PCO2 are significantly elevated. Elevated [HCO3-] is a characteristic of metabolic alkalosis, while elevated PCO2 is a characteristic of respiratory acidosis, but the ratio of the two can remain unchanged or change little.
3. Respiratory alkalosis combined with metabolic acidosis
Plasma pH can be normal, mildly increased or decreased, but plasma [HCO3-] and PCO2 are significantly decreased. The decrease of [HCO3-] is the characteristic of metabolic acidosis, and the decrease of PCO2 is the characteristic of respiratory alkalosis, but the ratio of the two can remain unchanged or change little.
4. Respiratory alkalosis combined with metabolic alkalosis
Plasma pH is significantly elevated, plasma [HCO3-] may be elevated, and PCO2 may be decreased.
5. Metabolic acidosis combined with metabolic alkalosis
Plasma pH, [HCO3-] and PCO2 may be within the normal range or slightly higher or lower.
Diagnosis
The diagnosis of mixed acid-base balance disorders is complex and must be made on the basis of a thorough study and analysis of the disease process. A small number of mixed acid-base balance disorders remain difficult to identify.
Treatment
Treatment is directed at the primary cause of the disease. During the course of treatment, changes in acid-base balance are monitored and a decision is made as to whether appropriate treatment should be given.