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Venipuncture using the BD Vacutainer system. This picture shows a multiple-use BD Vacutainer device that is no longer used. It has been replaced by a single use BD Vacutainer device.

In medicine venopuncture or venipuncture is the process of obtaining intravenous access for the purpose of intravenous therapy or obtaining a sample of venous blood. This procedure will be performed by medical practitioners, some EMTs, paramedics, phlebotomists and other nursing staff.

Blood is most commonly obtained from the median cubital vein, on the anterior forearm (the side within the fold of the elbow). This vein lies close to the surface of the skin, and there is not a large nerve supply.

Minute quantities of blood may be taken by fingersticks sampling and collected from infants by means of a heel stick or from scalp veins with a butterfly needle.

Phlebotomy (incision into a vein) is also the treatment of certain diseases such as hemochromatosis and primary and secondary polycythemia.

[edit] Equipment

There are many ways in which blood can be drawn from a vein. The best method varies with the age of the patient, equipment available and tests required.

Most blood collection in the US and UK is done with an evacuated tube system, such as the BD Vacutainer system or similar blood collection equipment consisting of a plastic hub, a hypodermic needle, and a vacuum tube. Under certain circumstances, a syringe may be used, usually with a butterfly needle, which is a plastic catheter attached to a short needle. In the developing world, a needle and syringe are still the most common method of drawing blood.

[edit] Venipuncture with evacuated or vacuum tubes

Blood draw filling a purple top vacuum tube.

Vacuum tubes were first marketed by U.S. company BD (Becton, Dickinson and Company) under the trade name Vacutainer tubes. Today, many companies sell vacuum tubes as the patent for this device is in the public domain. Some models are a type of test tube that contains a vacuum that automatically aspirates blood into itself. The tubes are made of glass or plastic. The tubes are attached to a needle and hub.

Multiple vacuum tubes can be attached to and removed in turn from a single needle, allowing multiple samples to be obtained from a single procedure. This is possible due to a Japanese invention called the multiple sample sleeve, which is basically a plastic cap fitting over the posterior end of the needle cannula, thus keeping blood from draining onto both health care worker and patient.

BD used this invention to create a system that included the vacuum pressurized sleeve, and a cannula with sleeve attached to a holder that holds the needle/sleeve combination, and guides the negatively pressured collection vial that is inserted once the needle is in the patient. Unfortunately, the sleeve that stops blood from moving until its seal is perforated by the collection tube's insertion, also prevents flashback, the tell-tale sign the vein has been entered properly. If the phlebotomist chooses to use a butterfly needle, the "flash" is still present, and easily visible to the phlebotomy tech as well as the patient.

They are commonly used in US, UK, and Australian hospitals, private doctors' offices and community labs, and are available in various sizes to suit the age of the patient and the type of sample needed.

There are several sized needles for a phlebotomist to choose from. The most commonly used are as follows: a 21g (green top) needle, a 22g (black top) needle, a 21g (green label) butterfly needle, a 23g (blue label) butterfly needle, and a 25g (orange label) butterfly needle (however this needle is only used in pediatrics or extreme cases as it is so small that it can often result in hemolizing the blood sample, thereby invalidating the test). Most lay people are under the mistaken impression that using a butterfly needle is easier on their veins and less painful. However, the opposite is actually true. The hazard of using butterfly needles lies in the fact that as the blood flows through the rubber tubing, it cools significantly, thereby clotting faster. In clotting in the tube, it stops up and reduces or as in most cases, completely stops. When this happens, it is necessary to re-stick a patient in order to obtain the blood sample. This is not the case when using the more common needles. Since the tubing is not a part of the needle, the blood goes through the needle directly into the tube. This method results in a faster, cleaner sample with less chance of hemolization. (When a blood sample is hemolyzed, it means the red cells have ruptured to the extent that they impart a pink/red color to the blood plasma, which is normally pale yellow.)^[1]

[edit] Venipuncture with needle and syringe

A syringe is used to manually extract blood from a patient. This dated method is normally used on elderly patients, or patients with unreliable veins. Because syringes are manually operated, the amount of suction applied may be easily controlled. This is particularly helpful with patients that have small veins that collapse under the vacuum of BD Vacutainer tubes.

The procedure is similar to venipuncture with a vacuum tube. The plunger is then gently pulled outwards, and blood fills the syringe. The blood is usually transferred quickly to a BD Vacutainer tube by inserting the needle into the rubber-capped end of a Vacutainer tube, before clotting sets in. Normally the same order of draw as when using a BD Vacutainer tube, as the same additive cross-contamination issues still exist with this method.

[edit] Blood cultures

Most often, blood cultures are drawn using a syringe, as this is the most efficient way to keep the environment sterile, and as the bottles for the blood cultures do not fit in a Vacutainer holder. When blood cultures are being collected with a winged collection set, phlebotomist are to collect the aerobic sample first, as air in the tubing of the winged collection set can create problems in testing of the anaerobic blood culture.

Aerobic refers to bacteria that grow in the air and anaerobic refers to bacteria that do not grow in the air. Since there is air in the "butterfly" needle tubing anaerobic specimens cannot be drawn without first removing the air from the tubing. The tops of any containers used when drawing a blood culture should be sterilized with the use of iodine that is allowed to dry, seeing that isopropyl alcohol only cleans and does not sterilize. This is disputed in some labs, where iodine is thought to degrade the rubber stopper through which blood enters the bottle, thus allowing contaminates to enter the container, however it is still used in the majority of hospital labs throughout the country.

It is common practice to draw a blood culture by alternating 3 times each alcohol prep pads (new with each swipe) as well as iodine. Then a new alcohol prep pad is placed on top of the blood culture bottle, and the syringe is then directly inserted, thereby sterilizing the culture further. Also, 2 bottles are drawn and tested, as cultures are so easialy contaminated.

The bottles are then incubated in specialized units for 24 hours before a lab technician studies and/or tests it. This step is necessary to grow the specimens being tested to useable levels.

[edit] Blood alcohol tests

It is generally not advisable to use isopropyl alcohol to cleanse the venipuncture site when obtaining a specimen for a blood alcohol test.^{[citation needed]} Using soap and hot water or a povidone iodine swab are advisable alternatives to isopropyl alcohol in this case.

[edit] See also

• Blood donation
• Fingerprick
• Neonatal heel prick
• Vacutainer

[edit] References

[edit] External links

• A video showing phlebotomy
• Phlebotomy details
• Animated Venipuncture tutorial
• "Tips on Blood Testing". American Association for Clinical Chemistry. 2001-08-27. http://labtestsonline.org/understanding/testtips/bloodtips.html.