The invention provides an improved cannula assembly comprising a first cannula having a first length and first inner diameter, the first cannula having at least a flexible distal portion； a trochar having a second length and second diameter, the trochar having a sharp distal position capable of puncturing through skin and one or more blood vessels of a patient and sized such that the trochar may be inserted within the first cannula and extend beyond the flexible distal portion thereof； and at least one flexible second cannula for insertion in the first cannula, each second flexible cannula sized to extend beyond the distal portion of the first cannula for a predetermined length.
