Why does the pressure signal appear to drift a few mmHg after my PV catheter is inserted into a biological environment?

The pressure signal may drift a few mmHg if the pressure sensor has not been properly prepared before inserting it into the biological environment. Presoak the catheter tip in saline or distilled water at body temperature for at least 30 minutes prior to use. Only soak the catheter tip, do not submerge the catheter connectors, as doing so will damage the sensitive electronics housed inside! 
The presoak helps prepare the pressure sensor diaphragm for the "wet" biological environment. Presoaking the catheter tip in body-temperature fluid also helps prevent pressure signal drift and negative pressure recordings. The presoak can be done by gently inserting the catheter tip into a beaker, dish, or through the tip of a syringe.