Blood gas analysis is a must for the whistle doctor, as a whistle doctor do you master all? Follow the author to review and learn. Does a normal pH mean that there is no acid-base imbalance? pH indicates the indicator of liquid hydrogen ion concentration, which is the most important indicator in arterial blood gas. pH of normal arterial blood is 7.35-7.45, which reflects the result of the combined effect of in vivo whistling and metabolic factors. pH less than 7.35 indicates acidemia and has been lost; pH more than 7.45 is alkalemia and has been lost. If the pH is between 7.35 and 7.45, does it necessarily mean that there is no acid-base imbalance? No! In general, there are 3 possible conditions when pH is normal: no acid-base imbalance, compensated acid-base imbalance and compound acid-base imbalance. The exact situation should be analyzed in a comprehensive manner. Does an elevated PaCO2 value indicate a primary whistling acidosis? PaCO2 is an important indicator of whistling acid-base imbalance, which reflects the effect of alveolar ventilation. The normal value is 35-45 mmHg, and a value above 45 mmHg indicates hypoventilation and CO2 retention. In many patients with AECOPD, PaCO2 is elevated, but this elevated PaCO2 may be caused by primary inspiratory acidosis, because of inadequate ventilation. But it may also be a consequence of compensatory what? Metabolic alkalosis! The body may have a metabolic alkalosis for some reason, and then the respiratory system compensates for it by trying to leave a little bit more CO2 behind, which results in an increase in PaCO2. What does CO2 binding capacity (CO2CP) stand for? CO2 binding capacity is obtained by equilibrating venous blood with air containing 5.5% CO2 (or normal human alveolar gas) at room temperature, measuring the CO2 content of the plasma, and subtracting the physically dissolved CO2. It refers to the amount of CO2 in the plasma in a bound state and reflects the body’s alkaline reserves, but CO2 binding capacity does not reflect changes in CO2 in the blood in a timely manner. An increase in CO2 binding capacity may indicate metabolic alkalosis or whistling acidosis, while a decrease in CO2 binding capacity may indicate metabolic acidosis or whistling alkalosis, so it must be judged in the context of the clinical situation. In units where blood gas analysis is available, CO2 binding is no longer taken seriously. How to determine primary and compensatory alterations? When the alteration of HCO3- and/or H2CO2 exceeds the compensatory capacity of the body, it causes pH abnormalities and an acid-base imbalance. But how to determine whether the acid-base imbalance is primary or compensatory? It is generally considered that the acid-base imbalance with the same pH change is primary change, while the acid-base imbalance with the opposite pH change (that is, making the pH tend to be normal) is compensatory change, and usually the compensation is not sufficient, for example, in whistling acidosis (no matter acute or chronic), there may be renal compensation leading to HCO3- elevation, but no more than 45mmol/L of HCO3- will be compensated ( If this value is exceeded, we should consider the existence of mixed acid-base imbalance, that is, the possibility of simultaneous metabolic alkalosis. Therefore, if there is a significant (beyond the compensatory limit) acid-base balance abnormality at the same time and the pH is normal, you should be alert to a mixed acid-base imbalance, such as whistling acidosis + metabolic alkalosis. Commonly used equations for predicted compensations for simple acid-base imbalance Principles of treatment for whistling acidosis? The most common acid-base imbalance in whistling is whistling acid. Etiological treatment of whistling acid is important because whistling acidosis is mainly due to inadequate ventilation, so what we have to do is to enhance ventilation, not alkaline supplementation. For example, use bronchodilators, whistling stimulants, and if necessary, perform mechanical ventilation to improve ventilation, or if already on mechanical ventilation, then consider adjusting parameters to increase minute ventilation. Whistling acid does not usually require alkaline supplementation. When is alkaline supplementation needed for whooping acid? When the pH is <7.2 or when there is a combination of metabolic alkalosis, or when hypercapnia is allowed during mechanical ventilation to reduce lung injury, NaHCO3 can be supplemented in appropriate amounts (a single supplement of 5% NaHCO3 is usually limited to 80-100 ml). In chronic acidosis, the rate of PaCO2 reduction should not be too fast, so as not to compensate for the increase in HCO3- too late for renal excretion, resulting in severe alkalosis, remember the saying: Better acid than alkali!