Specimen collection procedures

Chapter 2 Specimen collection procedures


Three major sources of specimen samples are blood, stool, and urine, with most tests performed on blood. The laboratory performs biochemical, DNA, cellular, and microscopic analysis of these body substances to provide objective data about the patient’s health and to identify disease processes. For some specimens, point-of-care testing is used to analyze the specimens at or near the patient’s bedside.


In collection procedures, accurate technique is essential for obtaining a valid specimen and to prevent patient injury. In addition, quality control measures are used in maintaining accuracy in the identification of the patient and the specimen, in the method of obtaining the specimen, and in the transportation of the specimen to the laboratory or site of analysis.


In all instances, the person who collects the specimen has the potential to be in contact with the patient’s blood or body fluids. Gloves must be worn and the person washes his or her hands after the collection is completed.



Blood collection procedures



Arterial puncture




Specimen or type of test:


Arterial Blood



Purpose of the test


Arterial puncture is used to obtain a sample of arterial blood for analysis of blood gases and acid-base balance.



Basics the nurse needs to know


Arterial blood specimens are obtained for blood gas studies, including the measurement of oxygen, carbon dioxide, and pH. The assessment of arterial blood is usually performed on the patient who has an actual or potential problem with oxygenation. The nursing diagnoses may include ineffective airway clearance, ineffective breathing pattern, impaired gas exchange, and altered tissue perfusion: cardiopulmonary.


The procedure of arterial puncture is technically more difficult than that of venipuncture, but arterial blood is far more accurate for the measurement of oxygenation throughout the body. The usual puncture site is either the radial or the brachial artery, with the radial artery being preferred. The femoral artery can be used; however, the risk of hemorrhage at that site is greater.


Before an arterial puncture of the radial artery is carried out, the Allen test is performed to verify the presence of collateral circulation to the hand. If arterial occlusion of the radial artery occurs after arterial puncture, the presence of collateral circulation protects the hand from ischemic damage. The Allen test procedure is presented in the content on Arterial Blood Gases (p. 139).


Some institutions and settings permit the nurse with specialized training to draw blood through an arterial puncture. Refer to the institutional or laboratory protocol to determine who may do this procedure.



How the test is done


A heparinized syringe and needle is used to collect 3 mL of arterial blood. For radial artery puncture, a 23- to 25-gauge needle is used. For brachial artery puncture, an 18- to 20-gauge needle is used. In many institutions, a prepackaged kit provides the equipment for blood gas studies.



Interfering factors



• Poor collateral circulation to the extremities

• Inability to puncture the artery or withdraw blood

• Air mixed in with the blood specimen



Nursing Care



Pretest



• Identify the patient by asking his or her name, checking the identification bracelet, and comparing the two identifications with the name on the requisition form.

• When the radial artery is to be used, palpate the pulse of each wrist to select the site with the stronger circulation. Perform the Allen test to assess the collateral circulation to the hand. Position the hand so that the wrist is in slight dorsiflexion.

• Explain to the patient that a sharp pain will be felt as the needle punctures the blood vessel. In some cases, a local anesthetic may be given beforehand.


During the test



• The interior of the syringe and needle must be coated with heparin. The syringe in the blood gas kit may be heparinized already. If heparin must be added, 1 mL (1000 or 5000 units/mL) is drawn into a 10-mL syringe. After the syringe is rotated to coat the entire interior surface, the heparin is expelled. A small amount of heparin remains in the dead space and within the shaft of the needle.

• Clean the skin over the pulse point with povidone-iodine, using sterile gauze. Remove this solution by wiping the skin with 70% alcohol. Allow the skin to dry.

• With the bevel of the needle up and the syringe placed at a 45- to 60-degree angle, slowly insert the needle into the artery (Figure 3). Blood will pulse into the syringe without your having to draw back on the plunger.

• Once the required amount of blood is in the syringe, remove the needle. The amount is usually 3 mL, but the volume can vary according to the type of syringe and the test protocol.

image

Figure 3. Technique for arterial puncture. Puncture of the radial artery can be performed only when both the radial and ulnar arteries provide adequate circulation to the hand.



Posttest



• Use sterile gauze to apply immediate pressure to the puncture site for 5 minutes. Blood flow from the artery and hematoma formation can develop because of the pressure within the arterial walls. Pressure on the puncture point lessens the tendency of excess bleeding.

• Remove the needle from the syringe. If there is air in the syringe, expel it. Place the airtight cap on the tip of the syringe. These measures limit or eliminate possible alteration of blood gas values because of contamination of the blood by the oxygen and carbon dioxide gases in the air.

• Place the syringe on ice and arrange for immediate transport of the specimen to the laboratory.

• Once the bleeding from the puncture site has stopped, the nurse applies a small sterile bandage and continues to assess the wrist and hand for signs of complications. It is common for the patient to complain of some temporary discomfort, such as aching, throbbing, or tenderness at the puncture site.





♦ Nursing response to complications


The three complications of arterial puncture are bleeding, infection, and thrombus formation, but the incidence is low.



Bleeding.

The most common sign of bleeding is hematoma formation. The tissue becomes tense and somewhat swollen in the area of bleeding and spreads through the tissue by gravity. The nurse looks for bruising around the puncture site and at the tissue on the underside of the extremity.



Infection.

If the patient develops an infection, the puncture site may become tender, reddened, and swollen. Systemically, the patient develops a fever and the white blood count rises above normal values.



Thrombus formation.

The nurse assesses for signs of an obstruction in the circulation distal to the puncture site. This may include loss of a distal pulse when a brachial or femoral puncture site is used. In addition, the distal parts, such as fingers, feel cool or cold and appear pale or cyanotic. The patient complains of pain in the area where there is loss of circulation.



Capillary puncture


Also called: Finger-stick; Heel-stick




Specimen or type of test:


Capillary Blood



Purpose of the test


Capillary blood collection is used when a small amount of blood is sufficient or the venipuncture method is not feasible.



Basics the nurse needs to know


The capillary puncture is used for patients with small or inaccessible veins. This method is useful in burn patients, in those who are extremely obese, and in patients who have a tendency toward thrombus formation. It is the method of choice for obtaining blood samples from premature infants, neonates, and young children. It may be used to preserve the total blood volume of the infant or small child, particularly when there is a need for repeated blood testing.


Because capillary blood is similar in composition to venous blood, capillary blood collection may be performed for a complete blood cell count, hematocrit determination, blood smear, coagulation studies, and most blood chemistry tests. The specimen source is always identified on the requisition form, because there may be differences between venous and capillary blood values for calcium, glucose, potassium, and total protein.




Site of collection

The available sites for collection of capillary blood are the finger and heel. The finger is often used for adults or older children. The locations most often used are the distal tips of the third and fourth fingers, slightly to the side (Figure 4). Few calluses are located on the sides of the fingers, and the lancet can puncture the skin more easily. The frontal tips or pads of the fingers are not used because many nerve endings are located there, and the puncture would be more painful.


image

Figure 4. Capillary puncture sites in the finger. In adults the middle or ring finger is the preferred site for a capillary blood sample. The sterile lancet punctures the skin in the distal tip, slightly to the side of the finger pad.


The heel is used for premature infants, neonates, infants, and small children and for special cases, such as patients with thermal injury. With the heelstick technique, the medial or lateral plantar surface of the heel is used (Figure 5). The central area of the plantar surface of the foot is never used. There is a risk of damage to the calcaneus bone, Achilles tendon, or other tendons, nerves, and cartilage that are located in the central area of the foot.


image

Figure 5. Heelstick sites for capillary puncture. The shaded areas are appropriate sites in neonates and infants. The central portion of the sole of the foot is never used.


In the selection of the skin puncture site, the tissue should not be edematous, inflamed, or recently punctured. These factors cause increased interstitial fluid to mix with the blood, and they also increase the risk of an infection.


The heelstick method is preferred for sampling blood in the premature baby and infant. It is technically easier to perform and avoids the significant complications that can occur with arterial or venous puncture. Some special considerations including noninvasive alternatives for monitoring must be made when a large number of heelstick punctures are needed. Each puncture is painful and stressful to the baby and the available tissue surface for the capillary punctures is very small. On average, the premature infant experiences 10 painful procedures per day (Berde & Stevens, 2009). The premature infant may weigh as little as 500 g and the heels are small, with little depth to the tissue for the many punctures and tests that are needed. Additionally, blood flow is often inadequate, and two or three punctures may be needed to obtain the required amount.


To help prevent injury to the calcaneus, the depth of the lancet must be controlled, and careful selection of the tissue site must be carried out. To help prevent infection and hematoma, aseptic technique and gentle handling of the tissue are needed whenever blood is drawn. Because of repeated trauma to the heels of the premature infant, the nurse assesses this tissue for signs of localized complications. These complications can occur during the stay in the neonatal unit, or they can develop years later.



How the test is done


A sterile lancet is used to collect capillary blood from a skin puncture site. The blood is blotted onto special filter paper (Figure 6) or collected in a narrow-diameter glass tube called a micropipette, microtube, or capillary tube.


image

Figure 6. Capillary blood filter paper. Droplets of blood are blotted onto the filter paper at each circle. Each circle must be filled before moving on to fill the next circle. Do not partially fill some circles and then return to complete them later. To promote blood flow, the hand is kept lower than the heart, and the finger is stroked in a distal direction.



Interfering factors



• Reduced cardiac output

• Vasoconstriction



Nursing Care



Pretest



• Identify the patient using the patient’s identification bracelet. For infants or small children, the parent or nurse can be the second identifier. Check the requisition form to be certain that the identifiers are the same as the name on the form.

• Particularly with small children, provide reassurance to help limit anxiety.

• If pretest fasting or dietary restriction is required, verify that the instructions were followed for the correct time period.

• The patient may be seated or in the supine position.


During the test



• Assess the skin site for color and temperature and the absence of infection and edema. If the skin is cool or pale, the circulation may be diminished. Put the hand in warm water or apply a warm, moist compress to the site for a few minutes. This helps increase circulation to the skin.

• Use gauze and 70% alcohol to cleanse the skin site. Allow the skin to dry.

• Holding the tissue between the thumb and the forefinger, use a firm, quick stroke to puncture the skin with the sterile lancet.

• Wipe away the first drop of blood, because it contains tissue fluids. Collect the subsequent drops of blood in capillary tubes or on the blotting paper.

• To help obtain more blood, the finger or heel may be massaged gently. The tissue near the puncture should not be squeezed because tissue fluids will mix with the blood, and the blood will clot quickly.

• The capillary tubes are held horizontally to prevent air bubbles. They should be filled two-thirds to three-quarters full and then sealed with clay.

• The circles on the filter paper are filled one at a time, until they are fully saturated. Allow the blood on the paper to air-dry for 10 minutes before it is placed in a collection envelope.


Posttest



• Once the specimen collection is completed, wipe the puncture site with alcohol.

• Place sterile gauze on the site and instruct the patient to apply pressure until the bleeding stops.

• If the infant or small child is crying, the nurse or family member provides comfort, such as by rocking, cuddling, or pacifier, as appropriate.

• Before leaving the patient’s side, the label is applied directly to the specimen container. The specimen is promptly transported to the laboratory.





♦ Nursing response to complications


The nurse inspects the infant’s feet daily for damage to the skin in the sites of capillary punctures. The laboratory findings are documented in the patient’s record and abnormal results are reported to the physician.



Infection.

The most serious but infrequent complication of heelstick puncture is infection. The infection is usually localized in the soft tissue, and the most common causative organism is Staphylococcus aureus. Weeks later, the infection can develop into osteomyelitis. The source of the infection is poor aseptic technique, a contaminated lancet, or injury to the bone during the skin puncture.


Infection is characterized by localized redness and swelling. The area is tender or painful. In more advanced infection, there may be purulent drainage or abscess formation. Because of the risk that the infection could spread to the bone, x-rays of the heel and foot may be ordered.



Hematoma and bruising.

Bruising, pain, scarring, and hematoma formation are more frequent complications. They occur from frequent skin punctures or excessive squeezing of the tissues during the collection of the blood samples.


When blood has leaked from the puncture site into tissue, the area becomes bruised and discolored. There may be leakage of blood onto the skin. The nurse should handle the baby’s foot gently during the examination because the heel tissue will be painful.



Venipuncture


Also called: Phlebotomy; Venous Blood Collection




Specimen or type of test:


Whole Blood, Serum, Plasma



Purpose of the test


Venipuncture is used to obtain a venous blood sample for laboratory analysis. The serum component of the blood is used for most of the chemistry analyses.

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Feb 18, 2017 | Posted by in NURSING | Comments Off on Specimen collection procedures

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