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In medicine, venipuncture or venepuncture is the process of obtaining intravenous access for the purpose of intravenous therapy or for blood sampling of venous blood. In healthcare, this procedure is performed by medical laboratory scientists, medical practitioners, some EMTs, paramedics, phlebotomists, dialysis technicians, and other nursing staff. In veterinary medicine, the procedure is performed by veterinarians and veterinary technicians. Venipuncture is one of the most routinely performed invasive procedures and is carried out for any of five reasons: (1) to obtain blood for diagnostic purposes; (2) to monitor levels of blood components (Lavery & Ingram 2005); (3) to administer therapeutic treatments including medications, nutrition, or chemotherapy; (4) to remove blood due to excess levels of iron or erythrocytes (red blood cells); or (5) to collect blood for later uses, mainly transfusion either in the donor or in another person.
Blood analysis is an important diagnostic tool available to clinicians within healthcare.
Blood is most commonly obtained from the superficial veins of the upper limb. The median cubital vein, which lies within the cubital fossa anterior to the elbow, is close to the surface of the skin without many large nerves positioned nearby.
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 winged infusion needle.
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, UK and Hong Kong is done with an evacuated tube system, (two common systems are Vacutainer (Becton, Dickinson and company) and Vacuette (Greiner Bio-One GmbH). The equipment consists of a plastic hub, a hypodermic needle and a vacuum tube. Under certain circumstances, a syringe may be used, often 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.
Additives and order of draw
The tubes in which blood/serum is transported back to the laboratory contain a variety of additives, or none at all. It is important to know which tube the individual laboratory requires for which test, as reagents vary between laboratories and may be affected by different additives. In general, whole blood needs to be mixed with EDTA — which chelates calcium to prevent it clotting — unless the clotting time is the test to be measured (in such a case, citrates are used). The majority of biochemistry tests are performed on serum, and so either a plain tube or a clotting accelerator is used. This clotting accelerator can interfere with some assays, and thus a plain tube is recommended in these cases, but will obviously delay the result. Some assays may also require whole blood, but are interfered–with by EDTA and, in this case, Lithium Heparin is an alternative.
With the vacuum tube system, the needle pierces the top of the sample tube and will potentially come into contact with the additives in the tube. As it is a hollow needle, some of the substances from the inner surface can be carried into the next tube and contaminate it. The most likely additive to cause trouble is EDTA, which will affect the coagulation time assays (as aforementioned) — and, by chelating some of the metal ions, may interfere with some of the biochemistry results (especially potassium). Thus, EDTA samples should be drawn last in most cases, and plain tubes drawn first.
Venipuncture with evacuated or vacuum tubes
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.
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 impression that using a butterfly needle is easier on their veins and less painful. Using a finer needle is less painful. However, 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 haemolysis. (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.)
Venipuncture in children
Use of lidocaine iontophoresis is an effective method for reducing pain and alleviating distress during venipuncture in pediatric patients. Rapid dermal anesthesia can be achieved by local anesthetic infiltration, but it may evoke anxiety in children frightened by needles or distort the skin, making vascular access more difficult and increasing the risk of needle exposure to health care workers. Dermal anesthesia can also be achieved without needles by the topical application of local anesthetics or by lidocaine iontophoresis. By contrast, noninvasive dermal anesthesia can be established in 5–15 min without distorting underlying tissues by lidocaine iontophoresis, where a direct electric current facilitates dermal penetration of positively charged lidocaine molecules when placed under the positive electrode.
One study concluded that the iontophoretic administration of lidocaine was safe and effective in providing dermal anesthesia for venipuncture in children 6–17 years old. This technique may not be applicable to all children. Future studies may provide information on the minimum effective iontophoretic dose for dermal anesthesia in children and the comparison of the anesthetic efficacy and satisfaction of lidocaine iontophoresis with topical anesthetic creams and subcutaneous infiltration.
Venipuncture with needle and syringe
Some health care workers prefer to use a syringe-needle technique for Venipuncture. Sarstedt manufactures a blood-drawing system S-Monovette that uses this principle. This method can be preferred on elderly patients, oncology patients, severely burned patients, obese patients or patients with unreliable or fragile veins. Because syringes are manually operated, the amount of suction applied may be easily controlled. This is particularly helpful with patients who have small veins that collapse under the suction of an evacuated tube. In children or other circumstances where the quantity of blood gained may be limited it can be helpful to know how much blood can be obtained before distributing it amongst the various additives that the laboratory will require.
There are times where a patient may require a blood culture collection. The culture will determine if the patient has pathogens in the blood. Normally blood is sterile. When drawing blood from cultures use a sterile solution such as Betadine rather than alcohol. This is done using sterile gloves, while not wiping away the surgical solution, touching the puncture site, or in any way compromising the sterile process. It is vital that the procedure is performed in as sterile a manner as possible as the persistent presence of skin commensals in blood cultures could indicate endocarditis but they are most often found as contaminants. It is encouraged to use an abrasive method of skin preparation. This removes the upper layers of dead skin cells along with their contaminating bacteria. Povidone-iodine has traditionally been used but in the UK a 2% chlorhexidine in 70% ethanol or isopropyl alcohol solution is preferred and time must be allowed for it to dry. The tops of any containers used when drawing a blood culture should also be disinfected using a similar solution. Some labs will actively discourage iodine use where iodine is thought to degrade the rubber stopper through which blood enters the bottle, thus allowing contaminates to enter the container.
The blood is collected into special transport bottles, which are like vacuum tubs but shaped differently. The blood culture bottle contains transport media to preserve any microorganisms present while they are being transported to the laboratory for cultures. Because it is unknown whether the pathogens are anaerobic (living without oxygen) or aerobic (living with oxygen), blood is collected to test for both. The aerobic bottle is filled first, and then the anaerobic bottle is filled. However, if the collection is performed using a syringe, the anaerobic bottle is filled first. If a butterfly collection kit is used, the aerobic bottle is filled first, so that any air in the tubing is released into the oxygen-containing bottle.
Specially designed blood culture collection bottles eliminate the need for either the syringe or butterfly collection method. These specially designed bottles have long necks that fit into the evacuated tubes holders that are use for regular Venipuncture collection. These bottles also allow for collection of other blood specimens via evacuated tubes, to be collected without additional Venipuncture.
The amount of blood that is collected is critical for the optimal recovery of microorganisms. Up to 10mL of blood is typical, but can vary according to the recommends of the manufacturer of the collection bottle. Collection from infants and children are 1 to 5 mL. If too little blood is collected, the ratio of blood-to-nutrient broth will inhibit the growth of microorganisms. If too much blood is collected from the patient, the patient risks a hospital-induced anemia and the ratio of blood-to-nutrient broth will tilt in the opposite direction, which also is not conductive to optimal growth.
The bottles are then incubated in specialized units for 24 hours before a lab technician studies and/or tests it. This step allows the very small numbers of bacteria (potentially 1 or 2 organisms) to multiply to a level which is sufficient for identification +/-antibiotic resistance testing. Modern blood culture bottles have an indicator in the base which changes color in the presence of bacterial growth and can be read automatically by machine. (For this reason the barcoded stickers found on these bottles should not be removed as they are used by the laboratorys automated systems.)
Taking blood samples from animals
A) Blood collection not requiring anesthesia: Saphenous vein (rat, mice, guinea pig); Dorsal pedal vein (rat, mice).
B) Blood collection requiring anesthesia (local/general anesthesia): Tail vein (rat, mice); Tail snip (mice); Orbital sinus (rat, mice); Jugular vein (rat, mice); Temporary cannula (rat, mice); Blood vessel cannulation (guinea pig, ferret); Tarsal vein (guinea pig); Marginal ear vein/artery (rabbit).
C) Terminal procedure: Cardiac puncture (rat, mice, guinea pig, rabbit, ferret); Orbital sinus (rat, mice); Posterior vena cava (rat, mice).
The volume of the blood sample collection is very important in experimental animals. All nonterminal blood collection without replacement of fluids is limited up to 10% of total circulating blood volume in healthy, normal, adult animals on a single occasion and collection may be repeated after 3 to 4 weeks. In case repeated blood samples are required at short intervals, a maximum of 0.6 ml/kg/day or 1.0% of an animal’s total blood volume can be removed every 24 hours. The estimated blood volume in adult animals is 55 to 70 ml/kg body weight. Care should be taken for older and obese animals. If blood collection volume exceeds more than 10% of total blood volume, fluid replacement may be required. Lactated Ringer’s solution (LRS) is recommended as the best fluid replacement by National Institutes of Health (NIH). If the volume of blood collection exceeds more than 30% of the total circulatory blood volume, adequate care should be taken so that the animal does not suffer from hypovolemia.
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. This has been related largely to the potential legal implications associated with use of alcohol based cleaners that could theoretically impact analysis. Numerous police alcohol collection kits have been marketed that incorporate a sodium fluoride/potassium oxalate preservative and non-alcohol based cleansing agents to ensure proper collection. Using soap and hot water or a povidone iodine swab are advisable alternatives to isopropyl alcohol in this case.
- Blood donation
- Neonatal heel prick
- Arterial blood gas is taken from an artery instead of a vein.
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