In general, the confirmation of a puncture in a blood vessel is made through a visual check of flush back of the blood from the blood vessel into a puncture needle assembly. The conventional puncture needle assembly incorporates a membrane filter permeable to air but impermeable to blood, in order to...http://www.google.es/patents/US4682980?utm_source=gb-gplus-sharePatente US4682980 - Puncture needle assembly
