Instrument delivery device with nested housing

A medical device, comprising:

• an instrument having a proximal end and a distal end;
• an introducer configured to moveably receive the instrument and having:
• an outer housing having a proximal end, a distal end, and a sidewall therebetween defining an inner volume, the sidewall comprising a plurality of alternating first and second regions, the first regions having a first inner diameter and the second regions having a second inner diameter that is less than the first inner diameter;
• and
• an inner housing having a proximal end, a distal end, and a sidewall therebetween defining an inner volume and an outer diameter, wherein the outer diameter of the inner housing is substantially equal to the second inner diameter of the outer housing, the inner housing slidably received within the outer housing;
• the distal end of the introducer configured to couple the introducer to an intravenous line;
• and
• wherein the inner housing is configured to move relative to the outer housing to move the instrument between a first position, in which the instrument is disposed within the outer housing, and a second position, in which the distal end of the instrument is disposed beyond the distal end of the outer housing such that at least a first portion of the instrument is disposed within the intravenous line when the introducer is coupled to the intravenous line.