According to the 2016 Infusion Therapy Standards of Practice, a midline catheter is defined as “a catheter inserted into the upper arm via the basilic, cephalic, or brachial vein, with the internal tip located at or near the level of the axilla and distal to the shoulder.” The axilla is the armpit and this tip location describes placement in the upper arm. A midline catheter must remain in the upper extremity for adults and should never go into the shoulder or chest area.
There are 3 axillary lines used for guidance on many procedures like thoracentesis and for placement of various ECG leads. Look at the drawing and notice that all axillary lines are on the chest and do not involve the arm. The anterior axillary line would be the closest to a midline tip location, however using this axillary line would put the midline tip location directly in the shoulder where joint motion will lead to catheter complications. The midclavicular line was the tip location of a midclavicular catheter, however studies in the late 1990’s showed that tip location to have a greater risk of vein thrombosis. For this reason, the INS Standards have never included the midclavicular tip location.
To achieve the midline tip location as defined by the INS Standards, place your index finger in the patient’s armpit and bring your thumb around the circumference of the upper arm at that level. This is the correct midline catheter tip location. Choose your insertion site and measure between these 2 points. Insert that length of catheter and you will have a correctly placed midline catheter meeting the definition in the national standards. For clinicians with a bad experience with midline catheters, could this be the reason for their failure?