Mixed acid-base disorders

Introduction Mixed acid-base balance disorder refers to the simultaneous presence of two or more simple acid-base balance disorders in the same patient. There are 4 types of simple acid-base balance disorder, namely metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis. Since respiratory acidosis and respiratory alkalosis are not possible at the same time, according to the arrangement and combination, there are two types of common acid-base balance disorders: metabolic acidosis + respiratory acidosis, metabolic alkalosis + breathing Alkalosis, metabolic alkalosis + respiratory acidosis, metabolic acidosis + respiratory alkalosis, metabolic alkalosis + metabolic acidosis. The first two are additive types, and the last three are phase-type. There are only two types of three acid-base balance disorders: metabolic acidosis + metabolic alkalosis + respiratory acidosis, metabolic acidosis + metabolic alkalosis + respiratory alkalosis.

Cause

(1) Double acid-base disorders:

1 According to the starting cause:

(1) Respiratory metabolic mixed type:

(Hoh acid + acid, base alkali + base, acid + base, base + acid)

(2) Metabolic mixed type (acid + base)

2 Change according to pH:

(1) Addition type: (call acid + acid, base alkali + base)

(2) Phase-reduction type: (hook acid + base, base alkali + acid, acid + base)

(B), triple acid-base disorders (triple acid-base disorders)

(1) acid + acid + base

(2) Alkali + acid + base

3. Characteristics of blood gas changes:

(1) Additive hybrid ABD:

The two factors change in the opposite direction, and the PH is obviously abnormal.

(2) Destructive hybrid ABD:

The two factors change direction (except for acid + alkali); PH change can be unchanged, normal, high or low.

(3) Mixed ABD:

The degree of change in the compensation factor has exceeded the normal compensation range.

an examination

Related inspection

Arterial oxygen partial pressure (PaO2) sputum pH lung function test (DL) oxygen partial pressure bronchial diastolic test

Medical history and clinical manifestations can provide important clues for determining the type of acid-base balance disorder. Blood gas detection is the main basis for correct diagnosis. According to the blood gas measurement results, the basic type of acid-base balance disorder can be determined, the degree of compensation can be estimated, and whether there is a mixed acid-base disorder. Valuation of serum electrolytes can also provide valuable information. In addition to calculating the AG value to distinguish the type of metabolic acidosis, depending on the serum CL-concentration and Na+ concentration, the effects of excessive water (diluted) or water deficiency (concentrated) may be excluded. If both CL- and Na+ increase, there is a lack of water, both of which decrease the water. However, laboratory test results must be combined with clinical judgment.

(1) Compensation time and compensation limit. No matter what type of acid-base balance disorder occurs, the body will mobilize various compensations, such as blood buffer system, lung, kidney and intracellular and extracellular fluid exchange, etc., but different compensations for its initiation and maximum compensatory capacity. The time required is different. The maximum compensation time is the time required to reach the maximum compensatory ability. In addition, the compensatory capacity of the body has a certain limit, and the compensation limit is manifested in the full compensation of the renal breathing, that is, the maximum compensation range and the maximum limit reached after the maximum compensation time has been reached. The maximum compensatory time, compensation range and compensation limit of various simple acid-base balance disorders are shown in Table 13-15-2. When analyzing the blood gas test results, it is necessary to pay attention to whether the time required for full compensation has been reached. If the time required for the maximum compensation has been reached, the secondary compensatory change exceeds or does not reach the compensation range. It is not a simple acid-base balance disorder, but a mixed acid-base disorder.

(2) The estimated value of compensation. When the simple acid-base balance disorder is in the compensatory stage, according to the formula: PH=6.10+log[HCO3-]0.03×PCO2 (the unit of PCO2 is mmHg), any two of PH, HCO3-PCO 2 parameters are known. It is possible to calculate the actual value of the other. Using this calculation method, the estimated value of compensation can be calculated. The significance of calculating the predicted value of compensation is that the calculated compensation value is a simple acid-base balance disorder within the compensation range, which is beyond the compensation range. Whether it is insufficient or excessive, it indicates a mixed acid-base balance disorder. The predicted value of HCO3- or PCO2 in the simple acid-base balance disorder and the bending of the pH should be calculated according to Table 13-15-3. For example, the blood gas test results of a salicylic acid poisoning patient are: PH=7.45, PCO2=2.6kPa (20mmHg), HCO3-=1.3mmol/L, suggesting that it is respiratory alkalosis. Based on the predicted compensation value, the plasma concentration of PCO2 decreased by 2.5 kPa/L for each 1.3 kPa (10 mmHg). The plasma HCO3- concentration should be reduced to 19 mmol/L when the patient's PCO2 is 2.6 kPa, but the actual measured value is 13 mmol/L. Below the expected value, this patient is a respiratory alkalosis with metabolic acidosis as a mixed acid-base balance disorder, which is the most common type of acid-base disorder in salicylic acidosis.

(C), acid and alkali map. The acid-base diagram is a graph based on the correlation between arterial blood pH (or H+ concentration), PCO2, and HCO3-, and is used for the diagnosis of different types including simple and mixed acid-base balance. So far, a wide variety of acid-base diagrams have emerged, providing a simple and reliable means for the diagnosis of acid-base balance disorders. According to the coordinates of any two variables can be reached to a point, such as falling in the simple type of metabolic acidosis, metabolic alkalosis, respiratory acidosis, respiratory alkalosis, is a simple acid-base balance disorder, If it falls between the above areas, it is a mixed acid-base balance disorder.

Differential diagnosis

There are 4 types of simple acid-base balance disorder, namely metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis.

First, respiratory alkalosis. Respiratory alkalosis can cause a range of symptoms, including dizziness, due to increased stress in the central and peripheral nervous systems. The limbs and the area around the mouth are abnormal, muscle spasms, hands and feet, etc., may have swelling or pain in the chest. In addition, various supraventricular and ventricular arrhythmias can occur. Respiratory alkalosis can cause cerebral blood flow to decrease, and cerebral blood flow is also one of the causes of abnormal nervous system function. The experiment reported that when the PCO2 decreased by 2.6 kPa (20 mmHg), the cerebral blood flow could be reduced by 35%-40%. Abnormalities in nervous system function mainly occur in acute respiratory alkalosis, but rarely occur in chronic respiratory alkalosis.

Second, respiratory acidosis. In addition to the symptoms of respiratory diseases and respiratory function compensation, patients with severe respiratory acidosis often have a variety of neurological symptoms, such as headache, blurred vision, restlessness, irritability, further development to tremors, paralysis and lethargy, coma (The so-called carbon dioxide anesthesia). As acidemia causes cerebral vasodilation and increased cerebral blood flow, it can cause elevated cerebrospinal fluid pressure and papilledema. HCO3- in the blood is slow through the blood-brain barrier, and carbon dioxide can quickly cross the blood-brain barrier and reach equilibrium. Therefore, when acute hypercapnia, ie acute respiratory acidosis, the pH in the brain and cerebrospinal fluid is lower than that of chronic respiration. Acidosis is obvious, and the decrease of PH in brain and cerebrospinal fluid is greater than that of arterial blood. Therefore, neurological dysfunction in acute respiratory acidosis is more obvious than chronic respiratory acidosis and metabolic acidosis.

Respiratory acidosis often involves metabolic acidosis, and the combined arterial blood pH can be significantly reduced. For example, lowering to 7.10 or less often causes severe hypotension due to arrhythmia and peripheral vasodilation. At this time, the decrease in pH, that is, acidemia, weakens the contractile reactivity of blood vessels to catecholamines, so it is difficult to increase blood pressure by using a vasculature before the pH is restored to 7.15-7.20. Chronic respiratory acidosis often associated with pulmonary heart disease and systemic edema. However, cardiac output and glomerular filtration rate are often normal or near normal.

Third, metabolic alkalosis. Severe metabolic alkalosis can cause functional abnormalities in the peripheral nerves of the central nervous system, such as paresthesia, muscle spasms, headaches, and irritability. Ankle and disturbance of consciousness, the above-mentioned abnormalities of central nervous function are obvious in patients with alkalosis after hypercapnia, because patients with chronic hypercapnia, increased PaCO2, and increased compensatory HCO3- in plasma and cerebrospinal fluid, when mechanical ventilation is applied After treatment, PCO2 decreased rapidly, and HCO3- could not quickly pass through the blood-brain barrier, resulting in a sudden increase in the pH of the cerebrospinal fluid. Therefore, the speed of correcting chronic respiratory acidosis should not be too fast.

Fourth, metabolic acidosis. Respiratory activity is a compensatory response to the body during acidemia. Examination can reveal that the breathing is deep and fast, and the ventilation per minute can be increased by 4-8 times, even if the patient feels difficulty breathing or respiratory distress. In the case of acidemia, the peripheral blood vessels dilate, so the facial skin is flushed. As cardiovascular susceptibility to catecholamines is reduced, ventricular function is reduced, myocardial contractility is reduced, blood pressure is reduced, and even shock occurs. If a ventricular arrhythmia occurs, the pulse and electrocardiogram will respond. Generally, it is considered that the occurrence of ventricular arrhythmia in acidemia is related to hyperkalemia. In acidemia, anorexia and nausea can cause weight loss, and the nervous system is mild and weak, and severe cases can cause drowsiness and coma.

Long-term or recurrent acidosis can cause various bone diseases. In children, it can affect the growth and development of the body, and even fibrosis and rickets, and osteomalacia or osteoporosis occurs in adulthood. Henderson's test: For patients with deep, fast, and suspected metabolic acidosis, stop breathing and stop breathing as a breath holding. If the breath holding time is less than 20 seconds, it is a virtue. The pine test was positive. This positive generally indicates that the patient is in a severe or severe metabolic acidosis state because the HCO3- is reduced, the pH is lowered, the respiratory center excitability is enhanced, respiratory activity is enhanced, and H2CO3 compensatory discharge is increased.

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