A brief forethought. This post we will stray from the usual whimsical rants regarding recent literature in Emergency Medicine. Instead we will focus on the far more practical topic of the insertion of the Midline catheter. Of note, I am overwhelmingly biased in favor of these devices and have taken such a fanciful liking to them I can't possible be an objective critic. With this in mind…
The dichotomy that is venous access has become far more ambiguous since the establishment of ultrasound (US) to identify vascular targets. Prior to US, admission to the circulatory system was gained via superficial peripheral veins located by direct visualization, palpation or through central veins large enough to cannulate by blindly sticking a needle in the area of their anticipated anatomic location.
Since employing US to sonographically identify a deeper set of peripheral veins, the clear-cut boundaries that once separated central and peripheral access have become blurred. Not only has US improved our success in both these traditional techniques (1,2), it has introduced a new target for our blood hungry beveled needle tips to pursue. A larger set of peripheral veins that were once too deep for direct visualization and too small for blind exploration now, thanks to US, have become an appealing target. To our surprise and dismay these deep peripheral lines are far less durable than their size and integrity would suggest (3). In fact, the rate of line failure within the first 24-hours (46%) is unacceptably high for clinical use (3,4).
This failure is due, more likely to a deficit in our equipment rather than a deficiency in these anatomic structures. Our current line of peripheral catheters is not designed to access such deep vessels. These catheters were intended to cannulate superficial veins. When employed on deeper veins they typically do not have adequate length to sufficiently seat the catheter tip in the vessels. This creates two problems. First the catheter will often become dislodged by even the smallest movement from the patient, as the elastic recoil of the soft tissue surrounding the precariously placed catheter pulls it from its target vessel. Second the steep trajectory taken to ensure the catheter reaches these vessels often results in the needle damaging the posterior wall of the vessel. This would not be of great importance if the catheter possessed the necessary length to thread beyond the damaged endothelium. Unfortunately even our long peripheral catheters lack the required length and end up sitting right next to this damaged portion of the vessels. These deficits have led to an abnormally high failure rate.
The deep venous or Midline catheters offer a viable solution to these obstacles. A number of recent studies have demonstrated the successful use of a small wire to thread a single lumen catheter into the deep veins of the upper extremity. This technique allows for secure access to these deeper vessels, avoiding the risks associated with central line insertion. These studies, examining the insertion of such lines, have confirmed their superior durability when compared to standard catheters and far fewer line related infections than observed with central venous catheterization(7).
The most recent of these trials, by Meyer et al, examines the use of arterial catheters inserted into either the cephalic or basilic veins (5). In this study’s participating hospital it was routine for the ICU to provide “line consultations”, during which the Critical Care physician would be called to the ward to obtain venous access on particularly difficult patients. Difficult access was defined in this cohort as three failed attempts to insert a peripheral line by an experienced nurse. After which all lines were inserted by a single operator, the study’s second author, Dr. Pierrick Cronier, using either 18 or 20 gauge arterial catheters that were 8 to 11 cm in length. Catheters were placed using the Seldinger technique under full aseptic conditions.
All 29 lines were placed successfully, the majority in the basilic vein (66%) and the remainder in the cephalic vein (34%). Only three catheters were removed early. One was accidently removed by the patient up until which point it had been functioning normally. The remaining two catheters were removed due to absence of blood return and were found to be occluded. Two additional catheters were found to be colonized with coagulase. Using ultrasound, no thrombophlebitis was visualized on any catheter prior to their removal.
The small sample size and use of a single skilled operator limit the conclusions that can be drawn from such a study and thus this trial does very little to answer the more pertinent questions Emergency Physicians have regarding the use of Midlines.
What is the optimal catheter for Midline insertion?
In the Meyer et al cohort the authors studied catheters intended for arterial use (5). In earlier cohorts both Elia et al and Mills et al employed single lumen central venous catheters of varying sizes (12 and 15 cm respectively) with equal success. While others have used catheters specifically designed for Midline insertion (3,6,7), no one study directly compares the various catheter choices, but all demonstrate similar efficacy and safety profiles in their independent cohorts. There is a Goldilocks effect in the sense that the longer the catheter inserted the greater the durability of the line, and yet if the catheter tip extends proximally enough to be seated in the subclavian vein, the rate of catheter related infections approaches numbers associated with the use of central line catheters (8). Seemingly no one catheter type appears superior to any other. It is important to remember that unlike central lines we are inserting catheters into much smaller, thin walled vessels and thus should choose a catheter insertion kit nimble enough to navigate such delicate structures.
Can vasopressors be safely administered through Midline catheters?
Most of the trials examining Midline catheters focused on the rate of successful insertion and line safety. All of these trials examining Midlines treated them as if they were peripheral lines (3,4,5,6,7), and as such there is no specific evidence evaluating the safety of administering vasopressor medication. This lack of evidence does not invalidate their use. The most commonly cited concern is that due to the depth of these venous structures, a delay in recognition of an infiltrative event may occur causing significant damage before the infusion could be stopped. This would be a valid concern except that unlike their more superficial cousins, Midlines very rarely infiltrate. When compared to traditionally inserted peripheral lines, Midlines fail far less often and in far different ways. Peripheral lines tend to infiltrate or become dislodged because of the short distance between insertion site and distal catheter tip in conjunction with the delicate nature of the vessels. Conversely Midlines fail later in their course, primarily due to distally located occlusions. The failure rate of Midline catheters is approximately 14% with a median time to failure of 6.19 days (3). In all the cohorts examining the insertion and use of Midlines only two infiltrative events occurred. In Mills et al, this event transpired directly after a difficult insertion performed by one of their less experienced practitioners (6). In El-Shafey et al, a single Midline catheter infiltrated shortly after its insertion (4). Both of these events occurred soon after insertion and quickly became clinically obvious. The much feared “occult” infiltration, has yet to manifest in any cohort examining the use of Midline catheters. That being said it is important to note that all Midlines are not created equal. The small tortuous vein in which one experiences great difficulty threading a catheter is a far different line than a large easily compressible vein that threads easily with adequate blood return.
Finally the generalizability of these trials is limited by the expertise of the practitioners inserting these lines. The majority of these trials called upon a few experienced practitioners to perform each catheterization. Only one trial, Elia et al, utilized a variety of practitioners (attendings, residents and nurses) with varying levels of experience (3). This variability is reflected in the lower success rate when compared to similar cohorts (86% vs 93% and 100%) (5,6). From my personal experience there is a learning curve when first beginning to insert these types of lines. The delicate act of threading the wire is far more difficult than the insertion of a central line. Because of the small size of these vessels there is a greater likelihood for the tip of the needle to become dislodged when detaching the syringe. Once this skill is perfected the placement of the lines becomes far simpler.
Our threshold for changing practice is frustratingly fickle. We have accepted that the use of US to identify deeper peripheral vessels will both improve peripheral line insertion and decrease the need for central line placement. Yet our success is limited by our use of traditional techniques and unsuitable equipment neither of which were intended to cannulate such deep vasculature. Likewise we incorrectly apply the rules that govern superficial peripheral vasculature to these deeper more durable vessels. In order to optimize our success with US guided peripheral access, it is imperative we realize these vessels are unlike their more superficial brethren and we must adapt our ideology, methods and tools accordingly.
1. Leung J, Duffy M, Finckh A. Real-time ultrasonographically-guided internal jugular vein catheterization in the emergency department increases success rates and reduces complications: a randomized, prospective study. Ann Emerg Med. 2006;48(5):540-7.
2. Costantino TG, Parikh AK, Satz WA, Fojtik JP. Ultrasonography-guided peripheral intravenous access versus traditional approaches in patients with difficult intravenous access. Ann Emerg Med. 2005;46(5):456-61.
3. Elia F, Ferrari G, Molino P, et al. Standard-length catheters vs long catheters in ultrasound-guided peripheral vein cannulation. Am J Emerg Med. 2012;30(5):712-6.
4. Eid Mohamed El-Shafey, Tarek F. Tammam. Ultrasonography-Guided Peripheral Intravenous Access: Regular Technique Versus Seldinger Technique in Patients with Difficult Vascular. European Journal of General Medicine. 2012; Vol. 9, No. 4 .
5. Meyer P, Cronier P, Rousseau H, et al. Difficult peripheral venous access: Clinical evaluation of a catheter inserted with the Seldinger method under ultrasound guidance. J Crit Care. 2014;29(5):823-7.
6. Mills CN, Liebmann O, Stone MB, Frazee BW. Ultrasonographically guided insertion of a 15-cm catheter into the deep brachial or basilic vein in patients with difficult intravenous access. Ann Emerg Med. 2007;50(1):68-72.
7. Mermel LA, Parenteau S, Tow SM. The risk of midline catheterization in hospitalized patients. A prospective study. Ann Intern Med. 1995; 123:841-4.
8. Kearns PJ, Coleman S, Wehner JH. Complications of long arm-catheters: a randomized trial of central vs peripheral tip location. JPEN J Parenter Enteral Nutr. 1996;20(1):20-4.