When should you avoid intravenous cannulation ?

As such there is no absolute contraindications for doing an intravenous cannulation . 

When its difficult to access the vein we can take the help of ultrasound and do the intravenous cannulation  process ultrasound guided.

However in certain situations iv cannulations are avoided like-

  1. When there is skin infection or rash on the site we want to cannulate, its better to avoid the affected area and do at another site.
  2. When doctor plans to start hemodyalisis for some reason, iv cannulation is avoided in one of the hands to make a fistula between the artery and vein.