Arterial Blood Pressure Monitoring

Peripheral intra-arterial catheters ("arterial lines, a-line") offer clinicians a reliable method for continuous and direct monitoring of intra-arterial pressure (IAP). IAP monitoring begins when the left ventricular systole ejects blood from the heart into the aorta creating a fluid pressure wave.  The fluid pressure wave is transmitted from the aorta to the peripheral arterial vasculature. For convenience and safety the arterial pressure wave is usually monitored at the radial, brachial, femoral and dorsalis pedis arteries. (Click for common palpation points)

Indications for IAP monitoring

Contraindications for IAP catheter insertion

Complications

Common insertion sites

Radial artery

The brachial artery divides at the cubital fossa to form the radial and ulnar arteries. The radial artery is commonly used for arterial line placement because it is readily accessible and has a low complication rate (Nutall 2016). "It is palpable at the wrist, proximal to the radial styloid or radial head and slightly lateral. The cannulation site should be at the very distal portion of the arm. The most frequent location for radial artery cannulation is at the proximal flexor crease of the wrist, 1 cm proximal to the styloid process"  (Hager 2021).  The radial and ulnar arteries supply the deep and superficial palmar arches which provide collateral circulation.

Femoral artery

The femoral artery is a large caliber vessel that may facilitate emergent access for severely hypotensive or coding patients.  It provides pressure measurements that are less affected by peripheral vasoconstriction, but significant leakage of blood into the surrounding tissue can occur without detection.

The femoral artery cannulation site is located at the groin, in the inner thigh, at the mid-inguinal point, halfway between the pubic symphysis and anterior superior iliac spine. 

Cannula insertion risk reduction

Identify contraindications and avoid complications, begin with a checklist

Skin changes, scars, sores, discoloration, swelling, excess warmth or swelling etc., could indicate the presence of peripheral vascular disease.

Palpation, capillary refill and the Allen test are necessary steps to determine the suitability of a limb for insertion of an arterial line. The Allen test determines the patency of the arm's radial and ulnar arteries. The Allen test must be done prior to arterial line insertion, in order to reduce the risk of ischemia due to arterial occlusion.

In adults, use of the radial, brachial or dorsalis pedis sites is preferred over the femoral or axillary sites of insertion to reduce the risk of infection.
 
CDC Recommendation Peripheral Arterial Catheters and Pressure Monitoring Devices for Adult and Pediatric Patients
1. In adults, use of the radial, brachial or dorsalis pedis sites is preferred over the femoral or axillary sites of insertion to reduce the risk of infection 
2. In children, the brachial site should not be used. The radial, dorsalis pedis, and posterior tibial sites are preferred over the femoral or axillary sites of insertion.
3. A minimum of a cap, mask, sterile gloves and a small sterile fenestrated drape should be used during peripheral arterial catheter insertion.
4. During axillary or femoral artery catheter insertion, maximal sterile barriers precautions should be used.
5. Replace arterial catheters only when there is a clinical indication.
6. Remove the arterial catheter as soon as it is no longer needed.
7. Use disposable, rather than reusable, transducer assemblies when possible.
8. Do not routinely replace arterial catheters to prevent catheter-related infections.
9. Replace disposable or reusable transducers at 96-hour intervals. Replace other components of the system (including the tubing, continuous-flush device, and flush solution) at the time the transducer is replaced.
10. Keep all components of the pressure monitoring system (including calibration devices and flush solution) sterile.
11. Minimize the number of manipulations of and entries into the pressure monitoring system. Use a closed flush system (i.e., continuous flush), rather than an open system (i.e., one that requires a syringe and stopcock), to maintain the patency of the pressure monitoring catheters.
12. When the pressure monitoring system is accessed through a diaphragm, rather than a stopcock, scrub the diaphragm with an appropriate antiseptic before accessing the system.
13. Do not administer dextrose-containing solutions or parenteral nutrition fluids through the pressure monitoring circuit.
14. Sterilize reusable transducers according to the manufacturers’ instructions if the use of disposable transducers is not feasible.

Centers for Disease Control and Prevention. (2015, November 5). BSI. Centers for Disease Control and Prevention. Retrieved December 27, 2021, from https://www.cdc.gov/infectioncontrol/guidelines/bsi/index.html#rec17

Set-up checklist:

  • Sterile barrier precautions (surgical mask, sterile gloves, cap, sterile gown, and sterile drape)
  • Skin cleaning with alcohol-based chlorhexidine(rather than iodine)
  • Specified staff for line insertion, i.e. competency training/assessment
  • Standardized insertion packs
  • Checklist completion by trained observer
  • Prepare ultrasound guidance for insertion
  • Verify that the pressure tubing/transducer assembly is:
  • properly connected to the monitoring equipment
  • connected to 500ml saline in IV fluids cuff with gauge & pump set to 300mmHg
  • properly flushed of all air and functioning, i.e. square wave when flushed.
    •

    Aseptic Insertion by approved personnel

    Waveform evaluation is the best method to determine correct placement.

    The normal peripheral arterial waveform will display the peak systolic pressure after the QRS. This phenomenon reflects the time it takes the cardiac systolic pressure wave to reach the peripheral catheter and sensor. The dicrotic notch reflects the closure of the aortic valve. Of course, the aortic valve has closed prior to the display of the notch.

    The time delay is a function of both distance and compliance and elasticity of the vessels. The waveform of a patient with arteriosclerotic disease would be steeper in ascent and descent, therefore shorter in duration and the notch would be less well defined.

    Correlation of pressure readings with contralateral blood pressure cuff should be done periodically, if possible.

    Instant Feedback:

    The normal arterial waveform will display a "dicrotic" notch, reflecting the closure of the aortic valve.

    True
    False

    References

    Hager HH, Burns B. ( 2021)  Artery Cannulation. [Updated 2021 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing;  Available from: https://www.ncbi.nlm.nih.gov/books/NBK482242/

    Nuttall G., Burckhardt J., Hadley A., Kane S., Kor D., Shirk Marienau M. , Schroeder D.R., Handlogten K., Wilson G., Oliver W.C. (2016) Surgical and Patient Risk Factors for Severe Arterial Line Complications in Adults. Anesthesiology; 124:590–597 doi: https://doi.org/10.1097/ALN.0000000000000967

    O'Horo JC, Maki DG, Krupp AE, Safdar N. Arterial catheters as a source of bloodstream infection: a systematic review and meta-analysis. Crit Care Med. 2014 Jun;42(6):1334-9. doi: 10.1097/CCM.0000000000000166. PMID: 24413576.

    Riangwiwat T, Blankenship J.C. (2021). Vascular Complications of Transradial Access for Cardiac Catheterization. US Cardiology Review 2021;15:e04. DOI:https://doi.org/10.15420/usc.2020.23

    Rickard, C. M., Marsh, N. M., Larsen, E. N., McGrail, M. R., Graves, N., Runnegar, N., Webster, J., Corley, A., McMillan, D., Gowardman, J. R., Long, D. A., Fraser, J. F., Gill, F. J., Young, J., Murgo, M., Alexandrou, E., Choudhury, M. A., Chan, R. J., Gavin, N. C., … Playford, E. G. (2021). Effect of infusion set replacement intervals on catheter-related bloodstream infections (RSVP): A randomised, controlled, equivalence (central venous access device)–non-inferiority (peripheral arterial catheter) trial. The Lancet, 397(10283), 1447–1458. https://doi.org/10.1016/s0140-6736(21)00351-2

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