Self experimentation has led to many important medical discoveries over the years. Even on a local level, self experimentation can be useful to the instructor, for example, one that hooks up cardiac pacer pads to his or her leg and endures electrical stimulation to demonstrate how the device is able to produce heart muscle contraction.
Or the field paramedics evaluating a new CPAP set up and can’t determine if the nebulizer attachment is functional, so they hook up a cardiac monitor to the volunteer paramedic, load up the neb chamber with albuterol and watch the volunteer’s heart rate to determine if the medication is reaching the “patient.”
Werner Forssmann was a surgery resident in Germany in 1929 when he took a long catheter used for certain kidney operations, made an incision in his own arm vein and threaded the catheter through the opening until he thought the tip might be near his heart.
While holding the catheter in place, he walked downstairs to the radiology department and took an X-ray that revealed the catheter tip was in his right atrium.
This was the first central vein cannulation performed on a human1. And we all know where it has gone since then with central line placement and cardiac catheterization a daily occurrence in medical facilities around the world.
Anatomy
The central veins used for central catheter insertion include the jugular, subclavian and femoral veins. Central veins are large diameter vessels that run their course deep in the body and are not visible on the surface.
Most central veins connect directly to the vena cavae. Peripheral vessels lie more distant from the vena cava and tend to be superficial, thus more visible and accessible.
For example, the internal jugular central vein lies deep in the neck and upper chest connecting to the superior vena cava directly on the right side and via the deep innominate vein on the left2.
By contrast, the peripheral external jugular vein is just under the skin of the neck and is often readily visualized in the supine patient. This is the same vein we visualize to determine the presence of jugular venous distention or JVD in conditions like heart failure or cardiac tamponade.
Utility
Central veins are more difficult to access than peripheral veins, but provide a safer route for certain medications such as vasopressors or when long term medication administration is required, as when treating certain infections or providing cancer therapies or for temporary dialysis.
We can also access the right side of the heart via the central veins to monitor heart pressures and function with a pulmonary artery catheter (remember the pulmonary artery carries venous blood) or even float in a temporary pacer wire.
Accessibility
The femoral vein is the easiest to find and cannulate due to its location next to the readily palpable femoral artery. It is also the safest since it is in the groin area and distant from the chest and neck where structures like the lung and major vessels can be damaged during insertion of a central line.
And if bleeding does occur from a femoral vein puncture, direct pressure is easily and effectively applied. The downside is that catheters in the femoral vein are more prone to clot formation3 and thus are useful for initial resuscitation efforts when peripheral intravenous access is inadequate or unobtainable, but not for the long run as in the intensive care setting.
The jugular vein and subclavian vein are more suitable for prolonged use and in the past were cannulated using only anatomic landmarks (use your favorite Internet search engine to find central line placement videos).
However, ultrasound is becoming a standard tool for visualizing a central vein during central line placement. This has increased the procedural safety for femoral and jugular vein access but is less useful for a subclavian vein central line due to the vein’s position behind the clavicle, making ultrasound visualization difficult4.
Out of hospital
Central catheters may be inserted for long-term outpatient use. A central line can be threaded under the skin and into the subclavian vein with the port end remaining exposed for access.
Alternatively, the tunneled catheter can be attached to a port that is placed in a surgically created subcutaneous pouch and is reached with a special needle inserted through the overlying skin and into the port to administer a treatment or obtain a blood specimen.
The PICC, or peripherally inserted central catheter, has simplified the use of central venous lines for patients requiring long-term medication in an outpatient setting.
A long catheter is easily inserted into a peripheral vein in the arm and guided to the superior vena cava, much like Dr Forssmann’s experience in 1929, with the exception that we don’t allow the patient to do the procedure and we keep the catheter tip away from the right atrium where the blood flow may cause it to whip about and potentially induce unwanted dysrhythmias.
Summary
Monitoring central lines and accessing indwelling central catheters or implanted central line ports are increasingly part of the paramedic skill list and requires in-depth training. However, all EMS providers should have a basic understanding of central vein catheterization due to the frequency of patients who benefit from central lines as outpatients. Thanks to Dr. Forssmann, you are more likely to have an encounter of the central venous kind.
References
1. Frossmann-Falck R. Werner Forssmann: A Pioneer of Cardiology. Am J Cardiol 1997;79:651-660.
2. Bannon MP, Heller SF, Rivera M. Anatomic Considerations for Central Liner Placement. Risk Management and Health Care Policy 2011:4;27-39.
3. Desmond J, Teece S. Thrombotic Complications of a Femoral Central Venous Catheter. Retrieved March 7, 2012 from www.emjonline.com .
4. McGee DC, Gould MD. Preventing Complications of Central Venous Catheterization. N Engl J Med 2003:348;1123-1133.
