Arterial Line Insertion and Waveforms

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Tyler Jones
Critical Care Nurse Practitioner in Cleveland, Ohio. With a passion for teaching, POCUS and shock. I am a Husband to an amazing Wife/Nurse, dog father, world traveler and volunteer high school baseball coach.

The Pre-brief

If you have ever been in the intensive care unit (ICU) or operating room (OR), you know that arterial lines are vital and frequently used to aid in the monitoring of blood pressure (BP). This article will give you an inside look at the rationale for use, setup tips and tricks, and the waveform’s information.

Indications and contraindications for arterial line 

Arterial lines are placed at the bedside in the ICU or in the OR frequently and typically without complications. However, some complications that can occur are ischemia, bleeding/hematoma, pseudoaneurysm or infection. As a generalized recommendation (and please follow your facility’s policy for insertion of invasive lines), before placement, make sure to complete a procedural time out. Time out should include coagulation study evaluation, allergies, consent, indication, and site of placement.

Site rational

The radial artery is the most favored site typically due to reliable anatomy, superficial/easily palpable, and suitable caliber for cannulation. Therefore, this is the most common site of insertion. However, the risk for hematoma and occlusion can be higher in the radial artery.

The femoral artery is typically more significant in caliber and more reliable anatomy with landmarks. This is one reason why in an emergency, femoral access may be chosen over radial. Things to consider in femoral access placement, in obese patients, excess adipose tissue could obscure point of insertion along with its deeper anatomy. In addition, there is a higher risk for infection, large hematoma, and pseudoaneurysm formation.

The brachial artery is not typically chosen due to NO collateral flow, and if it becomes occluded, this could lead to increased limb ischemia and all-around badness. If radial and femoral cannot be accessed, can consider axillary.

Nursing Setup (Before insertion)

The supplies that you will need before setup are a 500cc-1L NS bag, pressure bag, transducer set, transducer holder, pressure cable, and IV pole.

  • Open transducer and pressurized tubing set 
  • Tighten all connections on the set
  • If a syringe is present on your facility’s tubing (As shown above), close it until you feel/hear a click while priming.
  • Hang your NS and spike pressurized tubing (Want to fill the drip chamber about halfway full)
    • Place NS into a pressure bag and pump up until 300 mmHg is achieved or you see green on the pressure gauge; turn stop cock up to turn it off.
    • Pull up on the blue tab on the transducer to prime your tubing.
      1. One crucial aspect is not to allow any air to remain in the tubing. Connections such as the transducer can hold air bubbles; giving it a slight tap on the counter or cabinet as you flush can help encourage the air bubbles to come out of the tubbing.
    • Once the tubing is flushed, place the transducer on the IV pole or your facility’s transducer holder.
    • You want to make sure that your transducer is level with the phlebostatic axis. Also known as leveling. This is different from zeroing and is dependent on position.
      1. This is the intersection of the 4th ICS and the maxillary line.
    • After the provider obtains arterial access, keep sterility and attach pressure tubing to the arterial line.
    • Now it’s time to “Zero” this is the pressure relative to atmospheric pressure.
      1. You will want to turn the stop cock off to the patient and open up the white cap to “zero” to atmospheric pressure.
    • Once you have zeroed the transducer, turn the stop cock back off to open to the patient and for continuous readings.
    • You should see a waveform on the monitor, as seen below

Troubleshooting for Nurses

The Square Wave test is used to help with the interpretation of values for arterial lines. This test is nothing more than a fast flush that exposes the transducer to high pressure creating a square waveform. This high pressure creates vibrations in the transducer, then it is followed by a damping coefficient, or how fast the vibrations stop. This typically gives us three results, which we can use to interpret what is going on with the arterial line. As the bedside nurse, you want to count how many oscillations happen after the square wave.

Normal wave: 1-2 Oscillations before returning to baseline is deemed normal.

Over-dampened: Air bubbles, kinks, clots, spasms, stopcock closed/loose connections, or no volume or low pressure in pressure bag and tubing. This can underestimate systolic pressure and/or overestimate diastolic pressure. 

Under-dampened: Increased vascular resistance (SVR), extended or non-compliant extension tubing, hypothermia or tachycardia, or tachyarrhythmias all can cause. This can lead to false high systolic or false low diastolic pressures.

The Debrief

  • What’s the reason/indication for the arterial line and is it appropriate? Remember that unnecessary a-lines can lead to infection
  • The setup is key
  • Prime tubing before successful placement and make sure the pressure bag is inflated correctly.
  • Know your waveforms and how to troubleshoot them.
  • If unsure what is going on with waveform, complete a flush test and troubleshoot with your newfound knowledge. 

References

  1. Blackburn, J., & Walton, B. (2016, November 10). Risks associated with arterial LINES; time for a National safety standard? Journal of Anaesthesia Practice. http://japractice.co.uk/2016/11/risks-associated-arterial/12248#google_vignette.
  2. Nguyen Y, Bora V. Arterial Pressure Monitoring. [Updated 2021 May 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK556127/
  3. Swaminathan MD, A. (2019, March 18). How to set up an arterial line. Core EM. https://coreem.net/procedures/how-to-set-up-an-arterial-line/.
  4. Zarbiv, S., & Pisani, M. (2018, October 4). When is a Peripheral Arterial Catheter (a-line) indicated in My Icu patient?When Is a Peripheral Arterial Catheter (A-Line) Indicated in My ICU Patient? – American College of Chest Physicians. https://www.chestnet.org/News/Blogs/CHEST-Thought-Leaders/2018/10/Arterial-lines. 

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