The causes of increased CO2 may be excessive CO2 load, hypermetabolism, HCO3- titration, or, more commonly, reduction of alveolar ventilation. An excessive CO2 load rarely causes increased PCO2 in spontaneously breathing subjects, as the CO2 is a strong stimulus to ventilation. However, an extra CO2 load may cause respiratory acidosis in mechanically ventilated patients.
The most common cause of increased PCO2 is CO2 retention which may be due to changes in any of the organs involved in normal ventilation: the central nervous system, the conductive system (airways), the lung parenchyma, the inspiratory muscles, and the chest wall.
The most common causes of CO2 retention, which may be acute or chronic, are summarized in JableJ?.
Table 2 The most common causes of ventilatory impairment
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