Most hematology tests, as well as numerous other laboratory tests, require venous blood. Microsamples of capillary blood may be obtained from the fingertips or earlobes of older children and adults and from the heels of infants and neonates. Capillary punctures can also be used instead of venipunctures if the client has poor veins, very small veins, or a limited number of usable veins and if the client is extremely apprehensive about having a venipuncture. When the amount of blood needed is greater than 1.5 mL, however, a venipuncture must be performed.
Blood samples can also be obtained from vascular access devices such as heparin locks, triple-lumen subclavian catheters, and right atrial catheters. In the sick or high-risk neonate monitored in a neonatal intensive care unit, blood samples can be obtained from an indwelling catheter positioned and secured in an umbilical vein and connected to a heparin lock system to prevent clotting in the needle. Such procedures avoid the necessity of repeated skin punctures and must be performed with strict aseptic technique to avoid contamination of the indwelling device or catheter and to prevent possible septicemia. Special techniques are performed when obtaining samples from indwelling devices or catheters to avoid altered results from drugs and intravascular infusions and, in the neonate, to avoid excessive blood loss resulting from the need for numerous laboratory blood analyses.
Recent advances allow fetal blood samples to be obtained to assess fetal health. The samples are obtained by the physician, when special circumstances warrant it, by percutaneous umbilical cord blood sampling (PUBS), in which blood is aspirated from a 20- or 22-gauge spinal needle inserted into the umbilical vessel under the guidance of ultrasonography. Fetal hematologic and metabolic status, genetic disorder identification, and perinatal infection evaluation are the most common tests performed through PUBS.
Tests requiring arterial blood are arterial blood gas analyses and are obtained from the radial or the brachial artery or from arterial lines. The background information and clinical applications data for arterial blood collection are found in Chapter 5 - Blood Chemistry.
Client preparation is essentially the same for all sites and for all studies.
Explain to the client:
- The purpose of the test
- The procedure, including the site from which the blood sample is likely to be obtained
- That momentary discomfort may be experienced when the skin is pierced
- That food, fluids, and drugs are to be withheld before to the test
For children, a doll may be used as the "patient" for demonstration purposes. A laboratory technician's equipment basket may hold the child's attention during the actual procedure. For all clients, encourage questions and verbalization of concerns about the procedure, and provide a calm, reassuring environment and manner.
- For capillary punctures, the skin is assessed for lesions, edema, and temperature, because the site selected should be warm and free of lesions or edema; application of warm compresses for 3 minutes will dilate capillaries if the skin feels cool or looks pale or cyanotic.
- For venipunctures, the condition of the veins should be noted, and the use of tortuous, sclerotic veins or those in which phlebitis has previously occurred should be avoided, as should the use of an extremity with an intravenous (IV) site or heparin lock. If the extremity must be used, obtain the sample from a site distal to the IV or heparin lock. (Extremities with functioning hemodialysis access sites should not be used, nor should the arm on the affected side after mastectomy.)
- The skin is prepared by cleansing with an anti-septic such as povidone-iodine (Betadine) or 70 percent alcohol and is allowed to air-dry or is dried with sterile gauze. (Drying prevents dilution of the sample with antiseptic.) For the immunosuppressed patient, povidone-iodine should be used, followed by a 70 percent alcohol pad taped over the site for 10 minutes—the site should be allowed to air-dry or be dried with sterile gauze before the venipuncture.
- For blood withdrawal from a device or catheter, assess for patency, damage, and type of catheter to determine the need for clot removal, heparinization, or irrigation. If a heparin lock device is in place or attached to an indwelling catheter in the umbilical vein, prepare heparin in saline solution in a syringe with a needle attached. If a right atrial catheter is in place, prepare heparin in saline solution in a syringe with a needle attached or prepare 30 mL saline in a syringe to flush the catheter if blood is to be withdrawn from a Groshong catheter. The injection site is prepared by cleansing the cathetercap junction or hub with povidone-iodine, followed by swabbing with 70 percent alcohol for 2 minutes, and then allowing it to air-dry before the blood withdrawal.
Capillary Punctures (Fingertip, Earlobe, Heel) 
The equipment needed is assembled: sterile lancet, skin disinfectant, gauze pads or cotton balls, collection device, bandage, and materials to label the sample. The client is placed in a position of comfort and safety, either sitting or lying down. If an extremity is to be used, it is supported on the bed or on a table. A small pillow or rolled towel or blanket can be used to improve positioning of the extremity or to promote comfort.
The site is selected and the skin prepared as described previously. The area to be used is grasped firmly. The skin is punctured with the sterile lancet using a quick, firm motion to a depth of approximately 2 mm. With one wipe, the first drip of blood is removed. If flow is poor, the site should not be squeezed, because squeezing may produce more tissue fluid than blood. A hand or foot may be held in the dependent position to improve blood flow.
The sample is collected in microhematocrit tubes or pipettes and evacuated into a container holding the proper reagent. For smears, a drop of blood is placed on a clean microscope slide and spread gently with the edge of another slide. Slight pressure is applied to the puncture site with a small, sterile gauze square until bleeding stops.
The sample is labeled with the patient's name and other required identifying information and is sent promptly to the laboratory.
The equipment needed is assembled: tourniquet; skin disinfectant; gauze pads or cotton balls; syringe and needle or vacuumized tube, holder, and needle; bandage; and materials to label the specimen. A 20-gauge needle is usually used to prevent damage to blood cells. Needles with smaller lumens, such as 21- to 23-gauge, may be used, depending on the age of the client, the size of the vein, and the size of the vacuumized tube. Soft rubber tubing, approximately 1 inch wide, may be used for the tourniquet; however, a rubber tourniquet of the same width with a Velcro closure is preferable.
The vacuumized tubes used in collecting samples of venous blood come in various sizes appropriate to the age of the client or to the type of laboratory analysis equipment and may or may not contain an anticoagulant. The color of the rubber stopper used to seal the tube indicates the presence and type of anticoagulant (Table A-1). Care must be taken to ensure that the correct tube is used for the test to be performed.
A syringe and needle may be used to obtain a venous blood sample if it is felt that the vacuumized tube system will collapse the vein before the volume of needed blood is obtained. In such instances, the sample must be transferred promptly to the appropriate blood tube. To accomplish this transfer, the needle is removed from the syringe and the rubber stopper from the tube, and blood is allowed to flow gently down the inside of the tube. Another approach is to insert the needle into the rubber stopper of the vacuumized tube, allowing the vacuum to draw the blood into the tube. This procedure can be done safely, without hemolysis of blood cells, if the needle is 21-gauge or larger. Most authorities recommend changing the needle before injecting the rubber stopper. If the sample is for a blood culture, the rubber stopper is cleansed with povidone-iodine before the needle is inserted.
The client is placed in a position of comfort and safety, either sitting or lying down. The extremity to be used is supported on the bed or on a table. A small pillow or rolled towel or blanket can be used to improve positioning of the extremity or to promote comfort.
The tourniquet is applied 1 to 1.5 inches above the site to be used, usually the antecubital area, but the dorsum of a hand or foot can be considered. Tourniquets should be applied tightly enough to cause the veins to enlarge but should never occlude arterial circulation. They should not be kept in place for more than 1 minute before the venipuncture or for more than 2 to 3 minutes for the entire procedure. If a vein in the arm is to be used, the client is asked to open and close the hand a few times and then to clench the fist. If the puncture cannot be made within 1 minute, the tourniquet is removed and then reapplied when the puncture site is definitely located. This practice prevents hemoconcentration, which may alter test results.
The skin is cleansed as described previously (see under "Physical Preparation"). If the vein is palpated after the skin is prepared, the site is recleansed.
The needle cover is removed and the needle inserted into the vein approximately one-half inch below the point at which the needle is expected to enter the vein itself. When the needle is smaller than the vein, it is inserted bevel up at a 15- to 45-degree angle through the skin. When the needle is larger than the vein, it is inserted bevel down and almost parallel to the skin. This technique allows the skin to be punctured first and then the vein; it is a useful approach for entering difficult veins.
If the vacuumized tube system is used, the tube is pushed into the holder until the rubber stopper is punctured and blood flows into the tube. If more than one tube of blood is required, the filled tube is removed from the holder and another inserted until the desired number of samples is obtained. The sequence for obtaining multiple samples using different types of tubes is as follows: (1) blood culture tubes (the rubber stopper must be cleansed before insertion into the holder to prevent contamination of the sample), (2) tubes with no additives, (3) tubes for coagulation studies, and (4) tubes with additives (see Table A-1).
If a syringe is used, pull back on the plunger until the desired amount of blood is obtained. The sample is then transferred into the desired blood tubes as described previously.
The tourniquet is released and the client is instructed to unclench the fist. It should be released within 1 minute after the start of blood withdrawal if multiple samples are needed. The needle is removed and pressure is immediately applied to the puncture site with a gauze pad or cotton ball. Pressure should be maintained for 3 minutes to prevent hematoma formation. If the puncture site is on the dorsum of the hand, the hand is elevated while pressure is applied. Pressure is maintained until bleeding has stopped.
The sample is labeled with the client's name and other required identifying information and sent promptly to the laboratory.
Pediatric venous blood sample collections are considered and performed only when a capillary puncture cannot provide the amount of blood needed or when a test is needed that can be performed only on whole blood, blood serum, or plasma. Modifications such as needle lumen, mentioned previously, are made according to the child's age. The site for older children is the same as for adults. The site for infants can be a scalp vein or a superficial vein of the wrist, hand, foot, or arm. Infants and very young children require some restraint, which can be provided by the caregiver or nurse. Venous samples can also be obtained by aspiration from an IV infusion site, depending on the type or components of the fluid being infused. Children have a particular need for reassurance that the blood loss is not a threat to their life and that the body produces blood that replaces the blood withdrawn. Also, a Band-Aid can provide assurance that more blood will not leak out of the body through the puncture site.
Indwelling Devices and Atrial Venous Catheters
Assemble all necessary equipment: disinfectant swabs (povidone-iodine and alcohol), sterile gauze pads, sterile injection cap, 10-mL syringe, blood collection tubes, vial of heparin with syringe and needle or Tubex unit dose of heparin, normal saline in a 50-mL syringe, sterile gloves, and materials to label the specimen.
The client is placed in a position of comfort and safety, usually semi-Fowler's, for blood withdrawal from a right atrial catheter, with the cap or hub exposed at the site of insertion, that is, right upper chest or neck. A sitting or lying position with the extremity supported on a small pillow or towel can be used for blood withdrawal from a heparin lock. If the client is a neonate, the heparin lock system is positioned next to the neonate, taped in place, and connected to tubing that leads to an indwelling catheter placed in an umbilical vein. It is important to note that frequent removal of blood from the neonate for laboratory testing can deplete blood volume and is the most common indication for transfusion therapy. The development of microtechnology and electronic devices that facilitate in vivo testing and monitoring allows continuous laboratory evaluation with a minimum of blood sampling.
All of the procedures for blood withdrawal from a device or catheter are performed using strict sterile technique. The heparin is prepared in a syringe or the unit dose heparin is placed in a Tubex and the medication allowed to warm to room temperature for better tolerance as it enters the blood flow. The heparin prevents obstruction of the needle or tubing by clotting the blood. Dosage varies for the sick neonate with an umbilical catheter in place. If a Groshong right atrial catheter is in place, irrigation takes place instead of heparinization. For this type of catheter, a syringe is prepared with 30 mL of sterile normal saline to flush the catheter. This irrigation is performed before blood withdrawal and after total parenteral nutrition. A syringe prepared with 20 mL of sterile normal saline is used after blood withdrawal.
The labeled blood tubes are placed in an upright position in a small glass. The catheter-cap junction or hub is cleansed with a povidone-iodine swab and a 70 percent alcohol swab for 2 minutes. Sterile gloves are donned, the cap is removed, and a 10-mL syringe is attached to the connector. Blood in the catheter can cause inaccurate test results, so 6 mL of blood is withdrawn with the syringe and the catheter is then clamped. Clamping is not necessary if a Groshong catheter is in place because it has a special valve that eliminates the need for clamping. This blood is discarded with the syringe. Another 10-mL syringe is attached, and the needed amount of blood is withdrawn, using only a moderate amount of suction. The appropriate amount of blood is placed in the tubes (usually 7 to 10 mL in each tube), and blood withdrawal is continued until the tubes are filled. Color-coded stoppers are applied to the tubes as they are filled, and specimens that require the blood to be mixed with substances in the tube are gently rotated.
At the conclusion of the blood withdrawal, heparinization of the device or catheter or flushing of the Groshong catheter with saline is performed. Heparinization is performed by inserting the needle into the cap or hub and slowly injecting the prepared syringe of medication into the device or catheter. The catheter is then clamped 2 inches from the cap or hub as the last of the medication is injected. The needle is removed from the cap or hub, and the catheter is unclamped. A new sterile injection cap or hub is attached if the old cap is discarded. To irrigate the Groshong, a solution of 20 to 30 mL of sterile normal saline is gently injected through the injection cap with moderate force. The needle is then removed, but some positive pressure is maintained on the plunger of the syringe during withdrawal to prevent the solution from backing up into the syringe.
The client is left in a comfortable position after the procedures, and the labeled specimens are promptly sent to the laboratory.
Nursing Care After the Procedure
- After bleeding has stopped, apply an adhesive bandage.
- Application of an adhesive bandage on the finger of a child under 6 years of age is not recommended because the child may swallow the bandage and choke on it.
- Apply a new dressing to the catheter site using a sterile 2- × 2-inch gauze pad. Coil the catheter on the dressing with the cap or hub directed upward, cover with a transparent dressing, and tape in place.
- Rebandage and tape a heparin lock device if necessary.
Nursing Observations and Problem-Solving Activities
- Assess the client's understanding of the explanations provided.
- Assess the client's degree of anxiety about the procedure.
- Assess the infant's or child's need for restraint and reassurance.
- Ensure that food, fluid, and medication restrictions have been followed.
- Fill out the requisition accurately and include all information that is requested on the form.
- Note the client's response to the procedure and provide support if needed.
- Obtain the blood sample using proper technique and standard precaution procedures.
- Avoid possible invalid testing caused by prolonged use of a tourniquet; excessive suction on the syringe; vigorous shaking of the specimen in a tube or expulsion from the syringe into a tube; moisture in the syringe or tube; leakage of air into the syringe or tube; contamination of the site, equipment, or blood.
- Provide support to the client if the puncture is not successful and another must be performed to obtain the blood sample.
- Select appropriate evacuated tubes or syringe, needle, and laboratory tubes, depending on tests to be performed.
- Note obstruction of vascular access device or catheter caused by blood clotting, and notify the physician.
- Apply the necessary pressure to the puncture site until the bleeding stops. If oozing continues, elevate the extremity and apply a pressure type of dressing.
- Remain with the client until the bleeding has completely stopped.
- If the client is experiencing excessive and lingering pain or syncope, allow the client to lie down and rest.
- Assess for extreme anxiety and signs of possible shock state such as tachycardia and hypotension.
- Check the venipuncture site in 5 minutes for hematoma formation. If the client is immunosuppressed, check the puncture site every 8 hours for signs and symptoms of infection or septicemia, such as fever, chills, petechiae, and inflamed joints.
- Monitor vascular device or catheter insertion site for redness, swelling, pain, and purulent drainage indicating infection and monitor for sepsis caused by contamination during the procedure.
- If the specimen cannot be transported to the laboratory within a reasonable time or if analysis is delayed, arrange for proper storage to prevent deterioration or contamination that can cause inaccurate results.
- Client Preparation
- The Procedure
- Nursing Care After the Procedure
- Nursing Observations and Problem-Solving Activities