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Pediatric Vascular Access and Blood Sampling Techniques
Obtaining vascular access and blood samples in an infant or child can challenge and frustrate even the most skilled emergency clinician and can be especially challenging in children who are dehydrated or in shock. Resuscitation of critically ill and injured children should not be delayed for lack of vascular access, and intraosseous (IO) access is the preferred technique if peripheral vascular access cannot be secured rapidly. This chapter reviews the basic principles and techniques of blood sampling and placement of peripheral and central intravenous (IV) and intraarterial catheters in infants and children, including the use of umbilical catheters in neonates. Hydration techniques for dehydrated children are also reviewed. Though very rarely required, emergency cutdown is occasionally useful in obtaining vascular access, and a section of this chapter is devoted to cutdown techniques.
Patient Preparation and Restraint
Fear and anticipation of procedural pain can make the hospital experience traumatic for children. Before beginning any painful procedure in a stable child, explain the procedure to the parents, as well as the reasons that it needs to be done. For children capable of understanding, explain the procedure in developmentally appropriate language before starting and before each successive step. Parents should generally be present during emergency department (ED) procedures but should not assist with painful procedures. Parental presence is generally comforting to children, and children with a parent present have been shown to demonstrate less stress during procedures. Nonpharmacologic techniques such as music, toys, or being held by a parent may further reduce children's distress during attempts at vascular access. Many applications for smart phones, including some that produce “bubbles” for the child to “pop” on the screen are excellent and typically available distractions.
The success of blood sampling or obtaining vascular access depends in part on proper positioning and restraint of the patient. In most cases this requires the assistance of at least one other staff person and restraint of the extremity a joint above and below the intended insertion site. A significant amount of time may be required to perform venipuncture or vessel cannulation in neonates or young infants. Consequently, they may become hypothermic if disrobed and exposed for a prolonged period, especially if perfusion is compromised due to sepsis or hypovolemic shock. Use overhead lights, warm blankets, or other warming modalities to prevent accidental hypothermia in vulnerable patients. Furthermore, there is some evidence that radiant warmth is effective as an analgesic for minor procedures in newborns.
Anesthesia
Many products are available to decrease the pain associated with vascular access. Do not delay IV access in critically ill or injured children to use these medications or devices, but consider using them in stable patients. These medications and products are discussed in more detail in Chapter 29 . Options include vapocoolants, topical heat-enhanced anesthetic delivery such as lidocaine-prilocaine, 4% liposomal lidocaine, and injection of lidocaine via a needleless jet injector (J-tip), and vibrating devices. Orally administered sucrose solution has been demonstrated to decrease the pain response in young infants during procedures. Procedural sedation is commonly used during central venous and arterial cannulation in children ( Chapter 33 ).
Blood Sampling Techniques
Capillary Blood Sampling
Indications and Contraindications
Capillary blood sampling is frequently used to obtain blood samples from young infants. In infants, the heel is the most common location for capillary blood sampling, whereas in older children and adults, blood samples are more commonly obtained from the finger tip. This technique is useful when repeated measurements such as blood glucose or serial hemoglobin are needed. It is also an option for obtaining “arterialized” blood for blood gas analysis. If a sufficient volume is obtained, blood from a capillary sample can also be sent for other routine laboratory studies. Heel sticks are more painful than venipuncture but are useful in the event of difficult access or when arterialized samples are needed.
Avoid sampling from an area of local inflammation or hematoma. Avoid repetitive sampling from the same site because it may induce inflammation and subsequent scarring. In general, heel stick sampling is not ideal for blood gas analysis when the infant is hypotensive, the heel is markedly bruised, or there is evidence of peripheral vasoconstriction.
Equipment and Setup
Use a 3-mm lancet (Becton-Dickinson, Rutherford, NJ) or an automated disposable incision device (e.g., Tenderfoot, Tenderfoot, Accrivia Diagnostics, San Diego, CA]) to perform this procedure. Perform blood collection with either heparinized capillary tubes or 1-mL Microtainer tubes with a collector attachment (Becton-Dickinson).
Technique
The heel stick method of capillary blood sampling will be described, but capillary blood samples can also be obtained from a finger, toe, or earlobe ( Fig. 19.1 ). Traditional teaching is to puncture only the most medial and lateral portions of the plantar surface of the heel to avoid puncture of the calcaneous. However, newer research has found that although soft tissue thickness is greater on the medial and lateral portions of the heel, if necessary any site can be safely punctured in term infants, as long as automated lancets are used. Prewarm the foot by wrapping it in a hot moist towel (microwaved) for 5 minutes to produce hyperemia and enhance blood flow. Immobilize the foot in a dependent position with one hand. First, cleanse the heel with antiseptic solution and allow it to dry. Next, puncture the skin with the lancet. Allow the alcohol to dry to avoid false elevations in the glucose level. Avoid squeezing the foot because it may inhibit capillary filling and actually decrease the flow of blood. Furthermore, squeezing may lead to hemolysis of the sample. If blood does not flow freely, another puncture may be required.
Wipe away the first small drop of blood with gauze and allow a second drop to form. Place a heparinized capillary tube in the drop of blood and invert the proximal end of the tube to allow it to fill by capillary action. Fill the capillary tube until blood reaches the demarcation line on the tube. Over- or underfilling may result in clotting or erroneous test results. If 1-mL Microtainer tubes are used, hold the tube at an angle of 30 to 45 degrees from the surface of the puncture site. Touch the collector end of the tube to the drop of blood and allow the blood to drain into the tube. Gently tap the tube to facilitate flow to the bottom. Once filled, seal the tube with the accompanying cap. After an adequate specimen is obtained, apply a dry dressing to the puncture site.
When a heel stick is performed for an arterialized blood sample, use the same technique, but take care not to introduce ambient air into the sample. Place the tip of the tube as near the puncture site as possible to minimize exposure of the blood to environmental oxygen. Fill the tube as completely as possible and avoid collecting air in the tube. When the tube is full, occlude the free end with a gloved finger to prevent the entry of air, and cap both ends. Excessive squeezing of the foot may artificially lower the partial pressure of oxygen (P o 2 ).
Complications
When performed properly, heel sticks are associated with a low incidence of complications. Use an automatic incision device to prevent lacerations. Rare complications include infection, scarring, and calcified nodules.
Interpretation
Multiple studies have demonstrated a good correlation between arterial and capillary specimens for determining pH and partial pressure of carbon dioxide (P co 2 ) in hemodynamically stable patients. However, determination of P o 2 is not reliable when performed on blood obtained by capillary sampling.
Venipuncture
Indications and Contraindications
Venipuncture is used to obtain larger quantities of blood from infants and children and to obtain blood for culture. When collecting blood for culture, prepare the area of venipuncture with an appropriate antiseptic solution and allow the skin to dry. Wash off the cleanser promptly after blood has been collected because antiseptic solutions can irritate infant skin.
Equipment and Setup
A small-gauge butterfly or straight needle with a syringe are generally preferred for specimen collection in infants and young children because the negative pressure generated by standard specimen collection tubes (e.g., Vacutainer, Becton-Dickinson) may collapse small veins. A 3-mL or 5-mL syringe is less likely than a 10-mL syringe to cause vein collapse. Many providers find that it is easier to control needle position with a butterfly needle rather than a straight needle. If other access is not available, the butterfly needle may also serve as an infusion line after an adequate amount of blood is obtained. A 23-gauge butterfly needle will generally suffice for venipuncture, regardless of patient size.
Technique
As in adults, the usual site for venipuncture in infants and children is the antecubital fossa. However, any reasonably accessible or easily visible peripheral vein that will not be needed for IV cannulation may be used. Veins on the hands, feet, or scalp are frequently visible in young children ( Fig. 19.2 ). Imaging devices (e.g., ultrasound, transillumination, or infrared devices) may also be used to locate and identify veins for venipuncture. These devices are discussed later in this chapter (see section on Vascular Line Placement: Venous and Arterial ).
Assemble all necessary equipment, especially needles, out of sight of the child and have equipment within easy reach before beginning. Ask an assistant to help immobilize the patient when drawing blood from infants and small children. If an extremity vein is to be used, apply a tourniquet proximal to the selected vein. In small infants a rubber band can be used as a tourniquet. Be sure that the tourniquet is not so tight that it impedes arterial filling.
Cleanse the area surrounding the chosen site of skin penetration with antiseptic solution and allow it to dry. Apply slight distal traction to the skin to immobilize the vein. Insert the needle quickly through the skin and advance it slowly into the vein at an angle of approximately 30 degrees with the bevel facing up ( Fig. 19.3 ). Successful vessel penetration is heralded by a flashback, or flow, of blood into the needle hub or butterfly tubing. Apply gentle suction by slowly withdrawing the plunger of the syringe. If the required amount of blood is greater than the capacity of the attached syringe, pinch off the tubing, remove the filled syringe, attach a new syringe, and apply gentle suction again after releasing the pinched tubing. Remove the tourniquet. After the required amount of blood is withdrawn, remove the needle and apply a sterile dressing and direct pressure to the puncture site.
Although peripheral sites for venous blood sampling are preferable in infants, the external jugular and femoral veins may also be used for venipuncture during resuscitation or when peripheral sites are inadequate. The external jugular vein lies in a line from the angle of the jaw to the middle of the clavicle and is usually visible on the surface of the skin ( Fig. 19.4 ). When the infant is crying, this vein is more prominent. Ask an assistant to restrain the infant in a supine position with the head and neck extended over the edge of the bed. Alternatively, place a towel roll or pillow under the child's shoulders. Turn the head approximately 40 to 70 degrees from the midline. Cleanse the skin surrounding the area to be punctured with alcohol or another antiseptic solution. Apply finger pressure just above the clavicle to help distend the jugular vein. Use a 21- to 25-gauge straight needle or a 21- to 25-gauge butterfly needle attached to a syringe. Puncture the skin and then advance the needle slowly until the jugular vein is entered and a flashback of blood is observed. Keep the syringe connected to the needle at all times to maintain constant negative pressure and avoid air embolism. After the appropriate amount of blood is obtained, withdraw the needle and apply slight pressure to the vessel. Place the child in an upright position if possible after the needle is removed, and hold pressure over the puncture site for 3 to 5 minutes. Observe the puncture site closely afterward to identify persistent bleeding.
In most patients, the femoral vein lies medial to the femoral artery and inferior to the inguinal ligament ( Fig. 19.5 A ). Ask an assistant to position the patient's hips in mild abduction and extension while you palpate the artery. Identify its location by placing a mark on the skin just superior to the femoral triangle. If available, use ultrasound to assess the position of the femoral vessels. Prepare the femoral triangle with alcohol or another antiseptic agent. Use a povidone-iodine or chlorhexidine scrub when obtaining blood for culture. Puncture the skin and then direct the needle or catheter toward the umbilicus at a 30- to 45-degree angle to the skin and just medial to the pulsation of the femoral artery (see Fig. 19.5 B ). Apply slight negative pressure constantly throughout insertion. After the needle enters the femoral vein, withdraw the desired blood samples. Afterward, remove the needle or catheter unless an IV catheter for venous access is desired in this location. Apply pressure over the puncture site in the femoral triangle for a minimum of 5 minutes. Observe closely for recurrent bleeding.
Scalp veins can be very useful for venous sampling in small infants when other options are not possible or readily available. The anatomic considerations and technique are discussed later (see sections on Peripheral Venous Catheterization: Percutaneous and Peripheral Venous Catheterization: Venous Cutdown ).
Complications
Complications of venipuncture include hematoma formation, arterial puncture, local infection, injury to adjacent structures, and phlebitis. Serious complications are uncommon. Use special care when attempting to puncture the external jugular or femoral vein. Inadvertent deep puncture in the neck can injure the carotid artery, vagus nerve, phrenic nerve, or apex of the lung. The femoral artery or nerve can be injured during puncture of the area around the femoral triangle. Fortunately, these injuries are unlikely when proper technique is used.
Arterial Blood Sampling
Indications and Contraindications
Arterial blood sampling is most often indicated to obtain an arterial blood gas (ABG) analysis. Consider sending venous blood for blood gas analysis because all parameters except P o 2 may be clinically useful. Arterial blood may be drawn for routine laboratory analysis or blood culture if venous blood is difficult to obtain. Avoid puncture of an artery if the overlying skin is infected, burned, or otherwise damaged. In addition, consider the presence of adequate collateral circulation and any potential coagulation disorders.
Equipment and Setup
For arterial puncture in infants and children, a small-gauge butterfly needle is preferable to a needle and syringe. A 23-gauge butterfly needle is used most often, although a 25-gauge butterfly needle may be preferable in newborns. Some clinicians prefer to use a 25-gauge needle connected to a syringe, but a butterfly allows better control of the needle while an assistant aspirates the syringe. This technique may also permit a larger volume of blood to be withdrawn.
Technique
Potential sites for arterial blood sampling include the radial, brachial, dorsalis pedis, and posterior tibial arteries. In newborn infants the umbilical arteries are also available. The radial artery has several advantages that make it the most commonly used artery for blood sampling. First, its location makes it easy to palpate and puncture ( Fig. 19.6 A ). The ulnar artery is more difficult to locate. Second, no vein or nerve is immediately adjacent to the radial artery, minimizing the risk of obtaining venous blood or damaging a nerve. Another advantage of the radial artery is the presence of good collateral circulation from the ulnar artery. The brachial artery has little collateral circulation and should be avoided unless an arterial sample is absolutely necessary and no other options are available. Limit use of the ulnar artery to preserve collateral circulation to the hand. As a general rule, do not use the femoral artery for obtaining routine blood samples.
Because the radial artery is used most frequently to obtain percutaneous arterial blood samples, the technique for radial artery puncture will be described. (See Chapter 20 for a discussion of the Allen test and the effect of heparin on arterial blood sampling.)
Hold the infant's wrist and hand in your nondominant hand (see Fig. 19.6 B ). Hold the hand fully supinated with the wrist slightly extended (i.e., dorsiflexed). Palpate the arterial pulsation just proximal to the transverse wrist creases. Do not overextend the wrist because this can cause loss of the arterial pulse during palpation. Make a small indentation in the skin with a fingernail to mark the insertion site. Cleanse the area with antiseptic and allow the skin to dry. The topical anesthetic options discussed previously may be used if the clinical situation permits. Penetrate the skin at a 30- to 45-degree angle. As the plunger of the syringe is gently withdrawn by an assistant, advance the needle slowly until the radial artery is punctured or resistance (bone) is met ( Fig. 19.7 ). In contrast to performing the procedure in adults, provide continuous, but gentle suction with the plunger of the syringe in infants. Pulsating or rapidly flowing blood that appears in the hub of the needle is a good indication that the radial artery has been punctured. Some clinicians prefer to attach the syringe to the butterfly needle only after blood return is noted. Suction can be applied afterward.
If resistance is met while pushing the needle deeper, withdraw the needle slowly because both walls of the artery may have been punctured, but the tip may reenter the lumen on withdrawal. If no blood returns, withdraw the needle slowly to the point at which only the distal tip of the needle remains beneath the skin. Repeat the procedure after checking the location of the pulse and reorienting the needle. After the desired amount of blood is obtained, remove the needle and apply pressure for 5 minutes or longer to prevent hematoma formation.
Complications
Complications of radial artery puncture include infection, hematoma, arterial spasm, tendon injury, and nerve damage. With proper technique, however, the complication rate is extremely low. If the infant starts to cry before blood is obtained, the P o 2 and P co 2 values may not reflect the infant's true steady state.
Vascular Line Placement: Venous and Arterial
Intravascular lines are indicated when ongoing access to the venous or arterial circulation is necessary. Remember to consider using local anesthetics or procedural sedation if the clinical situation permits.
Peripheral Venous Catheterization: Percutaneous
Indications and Contraindications
In general, peripheral IV lines are indicated when the patient is unable to attain medical and nutritional goals with enteral therapy. These lines are used to provide fluids for resuscitation and maintenance needs and for the administration of medications.
Equipment and Setup
Over-the-needle catheters such as the Angiocath, JELCO I.V. (Smiths Medical, Dublin, OH) are the mainstay of peripheral venous catheterization. These thin-walled, flexible catheters range in size from 14 to 24 gauge. Select the appropriate gauge and length of the catheter based on the size of the child and the clinical situation. Larger-diameter catheters allow more rapid administration of fluids in emergency situations but may decrease the success of cannulation in young children with small veins. In general, use the smallest-gauge catheter that is appropriate for the clinical situation. For infants, a 22- to 24-gauge catheter is generally appropriate.
Attach T-connector extension tubing to the catheter after insertion to facilitate blood collection. This device makes flushing the catheter easier, especially while taping and securing the IV line. It also allows dressing changes without disturbing the IV insertion site.
Use either a homemade or commercially available device to protect the IV site from a child's attempts to remove the line. An arm or leg board appropriate for the size of the child provides stabilization of the extremity after insertion. Macrodrip tubing and liter bags are inappropriate for use in infants because they can result in the inadvertent infusion of large amounts of fluid. An infusion pump is an ideal way of limiting fluid infusion while keeping the vein open.
Vein Imaging Devices
A variety of imaging modalities, including ultrasound, transillumination, and infrared technologies, can be used to help locate peripheral veins for cannulation. In adults, data support the use of ultrasound to facilitate peripheral vein cannulation in those with difficult access. The data is more limited in children. Several small pediatric studies demonstrated a modest benefit of ultrasound, especially in patients with difficult access and other studies have shown no benefit.
Transillumination has been shown to facilitate peripheral venous cannulation in infants and small children. These devices work by projecting a high-intensity light into the patient's subcutaneous tissue, causing the veins to contrast with surrounding tissue, and making them easier to locate. Newer vein imaging technology, available as VeinViewer (Christie Medical Holdings, Memphis, TN), AccuVein (Cold Spring Harbor, NY), Vein-Eye (Newmaw Medical Ltd, Liverpool, United Kingdom), Veinsite (VueTek Scientific, Gray, ME), Vasculuminator (De Koningh Medical Group, Arnhem, the Netherlands) and others, uses near-infrared technology to project an enhanced image of the subcutaneous veins onto the patient's skin. Theoretically, knowledge of the location of the venous valves and the course of the vessel can assist the clinician in selecting the best area to be cannulated. However, multiple studies have not demonstrated improved overall success rates in obtaining IV access.
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