A few weeks ago one of our lovely interns asked me “how do you know when to put in an ultrasound IV versus a midline?” To which I replied, “blood pressure and vibes.” But in hindsight… I fear that may not be the most helpful answer so I’m going to spend today’s POTD reviewing the various intravenous catheters we place under ultrasound guidance and when to use them.
Ultrasound-guided IV: This is your typical peripheral catheter placed into a vein (usually the upper arm) for the purpose of blood draws, medication administration, and contrast infusion. These are indicated in patients who have poor vasculature such that our excellent nurses can’t obtain IV access. You can theoretically place any size catheter, but most often you will use an 18g or 20g.
Midline: An intermediate between an ultrasound guided IV and a central line. Like an ultrasound IV, they are placed in a large vein in the patient’s upper arm. However, it’s longer and has thicker walls than a peripheral IV catheter which reduces the risk of the line getting dislodged. Thus, midlines can be used for medications with high risk for extravasation (i.e. vasopressors, calcium chloride, hypertonic saline). When placing a midline, you should maintain a sterile field as these can be left in for weeks. At Maimo we have both single lumen (3Fr with one 18g channel x 10cm long) and double lumen (4 Fr with two 18g channels x 20cm long) midlines. Single lumens are slightly easier, faster, and less painful to insert. Double lumens allow you to give multiple medications simultaneously. Before inserting a midline assess the current and anticipated needs of your patient to decide if they need a single or double lumen. Some people opt to place a midline in any north side patient who is ill-appearing and definitely getting admitted to save you and the patient from future pokes.
Now here’s where things can get confusing because we use multiple terms to describe very similar procedures so stick with me here…
Central Venous Line: Triple lumen catheter placed into the internal jugular, subclavian, or femoral vein. These catheters are versatile and can be used for various purposes, including medication administration, blood draws, fluid resuscitation, and hemodynamic monitoring. They are useful for patients who require more secure and definitive access compared to a midline, or when a midline can’t obtained. Triple lumen CVCs are typically 20cm long and have a 7Fr diameter, with one 16g and two 18g channels.
Trialysis: Another triple lumen catheter placed into the internal jugular, subclavian or femoral vein. This catheter is unique from the above CVC due to its larger channels which have a 13Fr diameter, with one 17g and two 12g channels. The larger diameter allows the trialysis to be used for all the typical central line indications plus dialysis.
Cordis: Large bore single lumen catheter placed in the internal jugular, subclavian, or femoral vein. Unlike the CVC and trialysis, the cordis is shorter (10cm long) with a larger diameter (9Fr with one 11g channel). This allows the cordis to have a much higher flow rate compared to other lines, so it is placed in patients requiring rapid transfusion, usually of large volume blood products.
