Atlas of Procedures in Neonatology, 4th Edition
Capillary Heelstick Blood Sampling
Laura A. Folk
- Automated heel lancing device: Encased, spring-loaded, retractable blade that provides a controlled and consistent width and depth of incision for blood testing.
- Incision depths range from 0.65 to 2.0 mm for micropreemies through toddlers (Tenderfoot, International Technidyne Corporation, Edison, NJ, USA) and from 0.85 to 1.0 mm for preemies and newborns (BD Quickheel Lancet, BD Vacutainer Systems, Franklin Lakes, NJ, USA) (Table 15.1).
- The controlled depths avoid damage to the calcaneus (1,2) while providing greater yield with less pain, hemolysis, and laboratory-value error (3,4,5 and 6). The shallower devices can be used to obtain small samples from larger infants who require frequent point-of-care glucose testing (7).
- Nonautomated (manual) stylet-type lancets and spring-loaded needle-puncture devices designed for adult glucose testing are not appropriate for infants (6).
- Heelwarmer: Chemically activated packet to heat heel prior to capillary testing. If heel warming is used, a commercial prepackaged unit provides controlled temperature. The warmer should be applied for 5 minutes and then removed prior to heelstick.
To obtain capillary blood samples that provide accurate laboratory results with minimal discomfort and potential for injury/infection.
Capillary heel sampling is an easily mastered, minimally invasive technique that, when performed with proper technique and equipment, provides laboratory results within acceptable tolerances compared with samples from arterial catheters (8). Capillary blood sampling conserves veins in premature and critically ill infants, who can be expected to require intravenous access for fluids or medication administration.
- Capillary blood gas sampling
- Routine laboratory analysis (standard hematology, chemistries, toxicology/drug levels) requiring a limited amount of blood in which minimal cell lysis does not alter results
- Newborn metabolic screen
- Edema, because interstitial fluid dilutes the sample and gives inaccurate results
- Injury or anomalies that preclude putting pressure on the foot
- Areas that are bruised or injured by multiple previous heelsticks
- Poor perfusion
- Local infection
- Venous or arterial blood rather than capillary samples should be used for:
- Blood cultures, which require sterile technique
- Tests in which even a minimal amount of hemolysis will compromise results
- Special tests such as coagulation studies (newer coagulation tests that require only a few drops of blood are still not widely available)
- Laboratory tests that require more than 1.5 mL of blood
- Heel-warming device if desired
- Antiseptic (betadine/saline or alcohol swab)
- Pad or other means of protecting bed linens
- Heel-lancing device. Use appropriate size for infant (Table 15.1).
- Specimen collector as appropriate
- Serum separators
- Hematology tubes
- Capillary blood gas tube
- Newborn metabolic screen filter paper
- Capillary tubes for blood transfer to lab tubes if appropriate
- Bandage or gauze wrap
TABLE 15.1 Examples of Automated Heel Lancing Products Based on Infant Size
- Do not use the end of the heel. The calcaneum is superficial at this site, and there is an increased risk of osteomyelitis (1).
- Do not use fingertips, toes, or earlobes of babies.
- Hand position
- Do not squeezethe heel. Squeezing the heel results in greater pain, lower blood yield, and increased cell lysis.
- If using capillary tubes for blood transfer, it is essential to determine whether the tube contains substances such as anticoagulants, and whether those substances have the potential to interfere with lab results. Do not use tubes containing anticoagulants for newborn metabolic screens.
- Scoop-shaped collectors provided with mini–lab tubes are used to guide blood drops to the specimen tube. Avoid repeated “scooping” along the surface of the foot. Microclots that form in blood on the skin can alter lab results.
FIG. 15.1. Appropriate sites for capillary heelstick sampling are along the sides of the heels.
FIG. 15.2. Alternative site for capillary heelstick sampling. If frequent sampling has rendered the sides of the heels unsuitable, the plantar surface between them can be used. Do not incise the end of the heel.
- Identify site; the preferred areas for capillary heel testing are the outer aspects of the heel (Fig. 15.1).
- Vary sites to prevent bruising and skin damage.
- The plantar surface can be used if the preferred areas are compromised by previous frequent testing (Fig. 15.2) (1,8). The skin-to-calcaneal perichondrium distance is at least 3 mm in most term babies
and in 91% of babies at 33 to 37 weeks' gestation, but is at least 3 mm in only about 60% of babies <33 weeks' gestation (1).
- Apply heel warmer or warm towel for 5 minutes. Remove just before procedure.
- Provide comfort measures—Facilitated tucking/swaddling and the use of pacifiers combined with administration of a concentrated sucrose solution results in less measurable pain and faster resolution of discomfort in the infant following the procedure (9,10) (Fig. 2.1).
- Prepare automated device by removing release clip.
- Don gloves.
- Cleanse site with betadine followed with saline wipe or alcohol wipe.
- Position hand with fingers along the calf and thumb at ball of foot to stabilize. Apply pressure along calf toward heel (Fig. 15.3).
- Place automated device on site and activate.
- Apply pressure to leg with counterpressure to ball of foot and allow blood drop to form.
- Wipe away first drop of blood with gauze or clean wipe.
- Using capillary action, fill blood gas tube, holding tube horizontally (Fig. 15.4).
- Release pressure, allowing capillaries to refill.
- Guide blood drops into tube or collect with capillary tube for transfer to laboratory tube.
- If blood stops flowing, wipe site to remove clot with alcohol swab, gauze, or clean wipe, ensure time for capillary refill, and then reapply pressure to leg. If blood does not flow, choose another site and repeat procedure or consider venipuncture.
- When samples have been collected, apply pressure to puncture site and wrap with gauze or apply adhesive bandage.
- Continue comfort measures.
FIG. 15.3. Position for hand and automated lancing device. Position heel in the apex of the angle of the thumb and forefinger with fingers along the calf and thumb along the ball of the foot. Position automated lancing device in appropriate position. Apply pressure along the calf with counterpressure by the thumb. Do not squeeze the heel.
FIG. 15.4. Capillary blood gas sampling.
- Specimen Handling
- Collect blood gas sample first, then hematology samples, then chemistry/toxicology samples.
- Ensure that blood gas samples are free of air bubbles.
- Place the tube horizontally so that the blood is drawn by capillary action and does not collect air bubbles that can alter results. Apply caps to ends of tube.
- Capillary blood gas samples should be analyzed within 10 minutes or should be kept horizontally on ice for up to 1 hour, and the tube must be rolled prior to analysis. Consult institution laboratory for guidance on blood gas sample storage and transport.
- Flick side of hematology microtube during collection process to activate anticoagulant and prevent clotting.
- Newborn metabolic screen: specific collection guidelines (11)
- Minimum 24 to 48 hours after birth
- Integrity of collection medium: Avoid touching filter paper, as oils from finger can compromise results.
- Single (no overlapping) drops on filter paper. Position infant so that incision is down, allowing a large drop of blood to form. Blood should drop freely onto designated circle on filter paper. Repeat for each circle.
- Do not apply blood using capillary tubes that contain anticoagulants or other materials that can interfere with lab results.
FIG. 15.5. Cellulitis of heel—complication of capillary heelstick sampling.
- Provide oral sucrose, swaddling/tucking, and pacifier.
- Use proper equipment.
- Make incisions in designated areas of the heel.
- Infection (cellulitis, abscess, perichondritis, osteomyelitis) (Fig. 15.5) (12,13)
- Tissue loss and scarring
- Calcified nodules (14)
- Inaccurate laboratory results
- Hyperkalemia secondary to excessive hemolysis
- Use proper technique and procedures to minimize cell lysis.
- Erroneous blood gas results
- Ensure that sample is free of air bubbles.
- Avoid delay in analysis.
- Use proper technique and procedures to minimize cell lysis.
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