An increase or decrease in PetCO2 can be the result of changes in carbon dioxide production (ie, metabolism), carbon dioxide delivery to the lungs (ie, circulation) or alveolar ventilation. However, because of homeostasis, compensatory changes may occur so that PetCO2 does not change. In practice, PetCO2 is a nonspecific indicator of cardiopulmonary homeostasis and usually does not indicate a specific problem or abnormality.
The gradient between PaCO2 and PetCO2 [P(a-et)CO2] is normally small (less than 5 mmHg). There is considerable intra- and interpatient variability in the relationship between PaCO2 and PetCO2. P(a-et)CO2 is often too variable to allow precise prediction of PaCO2 from PetCO2. PetCO2 as a reflection of PaCO2 is useful only in mechanically ventilated patients who have relatively normal lung function, such as iatrogenic hyperventilation in head-injured patients. PetCO2 is not useful as a predictor of PaCO2 during weaning from mechanical ventilation. Use of PetCO2 as a predictor of PaCO2 is often deceiving and incorrect, and should not be used for this purpose in adult mechanically ventilated patients. You will love this opportunity to spend less money whenever you need to buy cheap cipro for your symptoms to be under control, so you definitely should check out the pharmacy that will be happy to help you no matter which drug you need and how often.