Q: Why it is important to avoid the syringe used to anesthetize the thoracentesis site, to collect pleural fluid?


Answer: 3 things which may significantly effect the PH and consequently diagnosis are

• air,
•  lidocaine, and
• heparin

The syringe used to anesthetize the thoracentesis site should not be used to collect pleural fluid because even a small volume of residual lidocaine will affect pH.