Which of the following sites is commonly used to collect a capillary blood sample?

BACKGROUND AND HISTORY

Venipuncture evolved from the practice of phlebotomy. The word phlebotomy is derived from two Greek words referring to “veins” and “cutting”; thus, phlebotomy can be defined as the incision of a vein for bloodletting or collection. Since early times, humans have appreciated the association between blood and life itself. Many medical principles and procedures have evolved from this belief. Hippocrates (460-377 bc) stated that disease was the result of excess substances such as blood, phlegm, black bile, and yellow bile within the body. It was believed that removal of the excess of these substances would restore balance (McCall, 1998). From this belief arose the practice of bloodletting—the first form of phlebotomy. By the 17th and 18th centuries, phlebotomy was a major therapy for those practicing the healing arts. Lancets were among the primary instruments used by clinicians in the 18th century.

Methods and procedures associated with phlebotomy today are dramatically improved. Only rarely today is phlebotomy used as a therapeutic modality (e.g., for patients with polycythemia). Instead, the primary purpose of phlebotomy is to obtain a sample of blood for diagnostic testing. The development of sophisticated laboratory equipment has reduced the need for venipuncture by requiring smaller quantities of blood for diagnostic assessments, amounts that often can be obtained by simply puncturing the skin without directly accessing the veins. There are many ways to obtain a blood sample using the venipuncture method. The procedures in this chapter describe techniques using Vacutainers, syringes, and infusion sets.

3.05.4.1 Venipuncture

Venipuncture is when a vein is pierced by a needle for either intravenous injection or the removal of blood. Veins are favored over arteries because they have thinner walls, and thus they are easier to pierce. There is also lower blood pressure in veins so that bleeding can be stopped more quickly and easily than with arterial puncture. The most site for venipuncture is the antecubital fossa located in the anterior elbow at the fold. This area houses three veins: the cephalic, median cubital, and basilic veins (Figure 1). The veins may be visible in some individuals but not others, or more easily felt in some, depending on the amount of muscle and fat tissue they have. Vein patterns may also run differently between individuals. Generally, the cephalic vein runs along almost the entire length of the arm and the median cubital vein connects the cephalic vein with the basilic vein. Of these three veins, the preferred one for venipuncture is the median cubital vein because it is larger and has a lower tendency to move or roll when the needle is inserted. There are also fewer nerve endings surrounding this vein making venipuncture less painful at this site. In some people the cephalic and/or basilic veins may be more easily located than the median cubital vein and may be a more appropriate vein to draw blood from. The phlebotomist must take care in anchoring those veins well to prevent rolling.

Sometimes venipuncture is performed on hand veins when the veins in the antecubital fossa are not appropriate. Blood is collected from the dorsal or back side of the hand (Figure 2). Similar to veins in the antecubital fossa, they are prominent in different positions on different individuals. Veins in the hand have a tendency to move or roll; thus, the phlebotomist should ensure that the skin is pulled taut and the vein is well anchored down prior to needle insertion.

a Venipuncture

Venipuncture in woodchucks can be challenging because they lack readily accessible peripheral veins and general anesthesia is usually required. Woodchcucks can be routinely bled from the femoral vein or artery (Fig. 8.5). Following anesthesia, the venipuncture site is clipped and scrubbed with alcohol and an antiseptic. The femoral pulse is palpated in the inguinal region and is used as a reference point since the vessels are not visible. A vacutainer tube and a 22-gauge, 1” needle may be used. Direct pressure is applied following venipuncture to minimize hematoma formation.

Samples can also be obtained from the maxillary or linguifacial veins (Fig. 8.6) which run in close proximity to the clavicle. Here, the woodchuck is placed on its back, head toward the phlebotomist, and a 22-gauge, 1” needle is directed straight into the notch formed where the clavicle meets the sternum. Care must be taken to avoid entering the thorax. Cardiac puncture has been used and is the easiest and quickest method to obtain large amounts of blood, but complications such as cardiac tamponade and death may occur. Small amounts of blood can be obtained from the cephalic veins (on the medial aspect of the front legs) or tarsal veins (on the dorsal aspect of the rear feet).

Blood

Venipuncture in guinea pigs is difficult because the peripheral veins in this species are small and often covered by layers of fat. It is often necessary to shave the skin and apply alcohol to help visualize peripheral veins in this species (Dyer and Cervasio, 2008).

Small volumes of blood can be obtained in unanesthetized guinea pigs from a variety of peripheral veins using a sterile lancet or a 23G–27G needle. A marginal ear vein can be nicked with a 25G needle and blood drops collected directly into a microhematocrit tube. The lateral saphenous vein runs across the tarsal joint and can be sampled with a 1-ml syringe on a 23G–27G needle after applying digital pressure on the thigh to hold off the vein. The cephalic vein and tarsal vein are also accessible on the guinea pig, although only small volumes can be obtained from these sites, and bruising and hemorrhage often result. Alternatively, a toenail can be cut short using a nail clipper to yield small volumes of blood (Clifford and White, 1999).

Larger volumes of blood can be obtained from anesthetized guinea pigs using large central veins, including the jugular vein, cranial vena cava, and femoral vein. The short neck of the guinea pig makes the jugular vein and cranial vena cava difficult to access, but shaving and proper positioning allow optimal exposure (Pilny, 2008). In the guinea pig, the right jugular vein is larger than the left and will yield up to 2.5 ml of blood. A 24G needle on a 1-ml syringe can be directed caudally to enter the jugular vein just cranial to the clavicle (Shomer et al., 1999). The cranial vena cava can be accessed with a 22G or 23G needle on a 3- or 6-ml syringe that is directed caudally into the sternal notch under the first rib. A ketamine–xylazine mixture has been described as the preferable method of anesthesia for this route of blood sampling (Dang et al., 2008). However, the cranial position of the heart makes cardiac hemorrhage a significant risk when blood is sampled from the cranial vena cava (Joslin, 2009). The femoral vein can be used to collect up to 3 ml of blood with the guinea pig under anesthesia, in dorsal recumbency, and with the rear leg abducted. A 23G needle on a 1–3-ml syringe can be directed at a 45–90° angle to the skin and inserted just ventral to the pulsing femoral artery within the femoral triangle (Joslin, 2009).

Alternative sites for blood collection in a guinea pig under anesthesia include an interdigital vein and the retro-orbital sinus. The interdigital vein technique in the guinea pig is adapted from that described in the rat (Snitily et al., 1991). The foot is disinfected with alcohol and stimulated by rubbing with a methyl salicylate soaked gauze. Approximately 0.4 ml of blood is collected into a capillary tube after puncturing the interdigital vein with a 20G needle. The sample is then transferred into a sodium citrate solution, and pressure is applied to the sampling site for hemostasis (Keino et al., 2002). The retro-orbital sinus will also yield small volumes of blood in an anesthetized guinea pig (Joslin, 2009).

Cardiocentesis can be performed as a terminal procedure in an anesthetized guinea pig. The animal is placed in dorsal recumbency, and a 20G–25G needle is advanced toward the heart under the xiphoid cartilage to enter the left ventricle. Alternatively, up to 15 ml of blood can be obtained from the descending aorta or caudal vena cava following a laparotomy as a terminal procedure in an anesthetized guinea pig (Joslin, 2009). Decapitation, performed by a trained individual, may yield 10–15 ml of trunk blood (Clifford and White, 1999).

Collection

Venepuncture of a cubital vein in an arm is the standard technique used clinically for extracting venous blood. This procedure offers the most convenient yet relatively safest way to draw blood from a live subject. The alcohol content of these samples will represent the systemic blood concentration of alcohol, and the measured value can be readily correlated with the behavioral effects of alcohol.

An alternative to venous blood is capillary blood obtained by finger-tip puncture. This blood, obtained from the fleshy tissue of the finger-tips, represents a transition from arterial to venous blood. As such, the alcohol concentration more closely represents the concentration in arterial blood. The major disadvantage of finger-tip blood is the very limited quantity that can be extracted. The amounts extracted are usually just sufficient to perform an initial analysis with no chance of repeat if subsequently required. Thus, venous blood has become the predominant choice for forensic purposes, since the extraction is relatively more comfortable for the subject, allows more than sufficient quantity of blood for repeated analyses, and easy correlation with behavioral effects.

In deceased subjects, a wider selection of sites for blood collection becomes available. However, the wider selection is counterbalanced by the complications in interpretation arising from the differences in alcohol concentration among the sites. As for living subjects, venous blood extracted from a vein in the arm or leg provides the optimum sample for interpretive purposes. The least desirable site is an open chest cavity that results from an autopsy examination.

Blood of uncertain origin (heart, vein or artery) may gather in the chest and mix with the interstitial fluid that bathes the organs of the chest. This mixed fluid is often scooped up and submitted for alcohol analysis as a ‘blood’ sample. The alcohol analysis produces a result which presents difficulties in interpretation since the sample does not truly reflect a genuine blood origin.

In forensic work, the collection of a blood sample must observe certain precautions related to the integrity and security of the sample. This is particularly so when the result will be used in the prosecution of an offense charged against an individual, such as the operation of a motor vehicle while under the influence of alcohol. Precautions are most crucial when the offense is that of exceeding a specified statutory blood alcohol concentration (BAC) in the operation of motor vehicles.

Swabbing the injection site with an alcoholic antiseptic solution is a common practice in clinical settings. Alcohol swabbing compromises the integrity of a blood sample taken for alcohol analysis and is discouraged for forensic purposes. Unfortunately, microorganisms residing on the skin, potentially on the surfaces of apparatus used for taking the blood, or suspended in the ambient air, can contaminate the blood sample. Such microorganisms utilizing blood sugars can produce alcohol through a fermentation process. Conversely, microorganisms could also use alcohol present in the blood from drinking as an energy source. Either way, the true BAC of the person is compromised, leading to difficult interpretations.

Blood alcohol kits, such as pictured in Fig. 1, have been developed expressly for forensic purposes. These kits are self-contained, requiring no additional apparatus whose cleanliness and alcohol-free status may be open to question. The kits contain tubes that are sterile and contain a preservative, such as sodium fluoride with an anticoagulant. Tubes used in Canada contain sodium fluoride to produce a final concentration of 1% w/v and potassium oxalate as anticoagulant to produce a final concentration of 0.2% w/v. The preservative stabilizes the blood sample for an indefinite period of up to several months, if required. The anticoagulant prevents clotting, an undesirable feature when analyzing the blood. Although not essential, the anticoagulant nevertheless simplifies the analysis by eliminating the step of homogenizing clotted blood. This step would otherwise require the use of homogenizing apparatus, a messy and somewhat cumbersome procedure when dealing with whole blood. Refrigeration of the blood samples at approximately 4°C is recommended for prolonged storage. Experimental data have shown that blood concentrations decrease slightly over time when stored at room temperatures. The exact cause of the decrease is not certain but is thought to be either evaporation of the alcohol around the rubber stopper, or oxidation to acetaldehyde using oxygen from oxyhemoglobin (the red pigment in the blood). Refrigeration stabilizes the blood alcohol for periods of up to six months. The preservative, sodium fluoride, and the commonly used anticoagulants, do not interfere with the analytical procedures in current forensic use.

It should be noted that analysis for forensic purposes requires whole blood. Hospital and clinical labs routinely separate the fluid portion, plasma, from the blood. The plasma can be conveniently analyzed for a number of chemicals, including alcohol, using automated equipment specifically designed for that purpose. Forensic or toxicology laboratories, however, are more likely to analyze whole blood for alcohol since statutory limits for legal operation of motor vehicles are expressed in terms of whole blood, e.g. 80 mg of alcohol in 100 ml of blood. Alcohol concentrations expressed in terms of plasma have to be converted into the equivalent concentration in whole blood. Since this conversion is directly related to the water content of the blood of the individual, a degree of uncertainty is introduced at this point. The water content, or hematocrit value, varies not only among individuals but within the same individual. Hence, the equivalent whole blood concentration cannot be predicted precisely, but only within a range of values with acknowledgment to possible values outside that range.

Percutaneous Femoral Vein Puncture

Femoral vein puncture is performed like the arterial puncture, as described in The Cardiac Catheterization Handbook, 5th edition, chapter 2. Indications for femoral venous sheath placement in patients undergoing PCI include the need for additional intravenous access for fluids and medications, a temporary pacemaker, or pulmonary artery pressure monitoring. Caution should be used to avoid inadvertent additional arterial punctures. For this reason, if femoral vein access is needed, start with the vein access before arterial puncture. If the artery is inadvertently accessed, place the arterial sheath and then angle slightly more medially with the next puncture.

Disadvantages

1.

Venipuncture is necessary. Although most adult patients tolerate venipuncture with little or no difficulty, some patients are psychologically unable to “handle” needles anywhere in their body. Children may be particularly difficult to manage via this route because veins are proportionally smaller in smaller patients, making venipuncture itself more difficult. Younger children requiring IV moderate sedation will usually pose severe management problems (the “precooperative” patient) or be physically unable to control themselves. Not all patients, even adults, have veins that are easy to visualize and gain access to with a needle. Probably the most significant challenge facing the dentist learning IV moderate sedation is to develop a degree of proficiency at venipuncture. Venipuncture is a learned skill, one that becomes easier to perform as experience is gained.

Complications may arise at the venipuncture site. As discussed in Chapter 27, a variety of minor and some major complications can develop at the venipuncture site. These include hematoma, phlebitis, and intraarterial injection of a drug.

Monitoring of the patient receiving IV moderate sedation must be more intensive than that required in most other moderate sedation techniques. Because intravenously administered drugs act rapidly, the entire dental team must be trained to assess the physical and mental status of the patient throughout the procedure. The greater the depth of sedation (deep > moderate > minimal), the greater is the need for increased patient monitoring.

Recovery from intravenously administered drugs is not complete at the end of the dental treatment. All patients receiving any intravenously administered CNS depressant must be escorted from the dental office by a responsible adult companion.

Although the depth of sedation provided by intravenously administered drugs can be increased rapidly (by administration of additional drug), the converse is not true. Many intravenously administered drugs cannot be reversed by specific drug antagonists. Although antagonists do exist for several drug groups, specifically opioids, benzodiazepines, and anticholinergics, they are not recommended for routine administration.3–5 Should a patient become overly sedated (deep instead of moderate; moderate instead of minimal), the initial, and most effective, management in all situations is the maintenance of basic life support: assess the patient's airway, assist or support ventilation, and provide for the effective circulation of oxygenated blood. Following these steps (P-C-A-B [basic life support]), consideration may be given to antidotal drug therapy.

Box 21.1 summarizes the advantages and disadvantages of the IV route of drug administration.

Anticoagulation During Device Implantation

Femoral venous puncture does not necessitate withdrawal of anticoagulant therapy. Nevertheless, most operators aim to perform the procedure with normal-level INR at baseline and then use intravenous antithrombotic agents (mostly unfractionated heparin) during the procedure (Table 36.4). The antithrombotic protocol of the PROTECT AF study [43] mandated an INR < 2.0 at the onset of the procedures. ASA 81–325 mg was initiated at least 1 day before the procedure (we recommend a loading dose if the patient is not on chronic aspirin therapy). In patients who are candidates for postprocedure therapy with DAPT, a loading dose of aspirin and clopidogrel is indicated unless they are already receiving this treatment. Weight-adjusted heparin (70–100 IU/kg) is administered after transseptal puncture to maintain an activated clotting time (ACT) > 200 s for the procedure duration [60]. However, some operators perform the procedure while the patient receives OAC with a therapeutic level of the INR, a practice analogous to the widespread use of warfarin during AF ablation. Several small studies showed that the combined procedures of catheter ablation for AF and Watchman LAA implant—while warfarin or NOACs are onboard—appear to be feasible and safe, with excellent rates of LAAO and an observed stroke rate of 0.5% per year during midterm follow-up; this without a significant increase in bleeding risk [89,90]. Intravenous administration of antithrombotic agents is generally provided (at the latest) immediately after traversing the interatrial septum. A weight-adjusted bolus of unfractionated heparin (70–100 IU/kg) is most commonly used, thus maintaining an ACT ≥ 250 s. LAAO may be performed as part of a combined procedure while a different type of antithrombotic medication is used, e.g., the direct thrombin inhibitor bivalirudin. This approach requires no further anticoagulation. Upon completion of the procedure the heparin is not reversed and various hemostatic techniques are used for safe sheath removal.

Specimen Selection and Collection in Living Subjects

Currently accepted venepuncture consists of cutaneous application of a nonalcoholic antiseptic (e.g., povidone iodine) and withdrawal of a sufficient aliquot of cubital venous or fingertip capillary whole blood by a sterile needle to a sealed sterile vial. Anticoagulants and microorganism-inhibiting chemicals are typically added. Importantly, venous blood does not precisely reflect the cerebral BAC, which ultimately defines the biochemical effects of EA, unless absorption and distribution of EA are complete at collection (Table 6).

Table 6. Accepted collection, transport, and storage of blood from living persons

EDTA, ethylenediaminetetraacetic acid.

Randomly collected, first-voided urine is generally valuable only in confirming the presence of EA, because the urine alcohol concentration (UAC) is subject to multiple uncontrolled variables. Since the 1990s saliva, or oral fluid, has gained acceptance as a satisfactory matrix for on-the-spot testing for EA, both qualitative and semiquantitative, applicable to workplace or clinical settings such as emergency departments.

Specimen Selection and Collection – Living Subjects

Currently accepted venipuncture (World Health Organization, 2010) consists of cutaneous application of a nonalcoholic antiseptic (e.g., povidone iodine) and withdrawal of a sufficient aliquot of cubital venous or finger tip capillary whole blood by sterile needle to a sealed sterile vile (Table 6). Anticoagulants and microorganism-inhibiting chemicals are typically added. Importantly, venous blood does not precisely reflect the cerebral BAC, which ultimately defines the biochemical effects of EA, unless absorption and distribution of EA is complete at collection (Williams and Leikin, 1999a,b; World Health Organization, 2010).

Table 6. Accepted collection, transport, and storage of blood from living persons

•

Cutaneous application of nonvolatile antiseptic

Percutaneous venipuncture of cubital vein or finger tip capillary

Withdrawal of sample by sterile needle to sterile container

Vacuum glass collection tubes are acceptable legally

Filling container sufficiently to avoid evaporation

Use of clean container without anticoagulant allowing blood to clot (for serum)

1–2% NaF

EDTA or potassium oxalate

Proper labeling, laboratory request form, and chain of custody on or with container

Refrigeration (4 °C) or prompt delivery to analytical laboratory

Recording of receipt and disposition of specimen by receiving analyst

Analysis or storage (refrigeration or frozen (−20 °C)) of specimen

Abbreviations: C, centigrade; EDTA, ethylenediaminetetraacetic acid; NaF, sodium fluoride.

Randomly collected, first-voided urine is generally valuable only in confirming the presence of EA because the concentration (UAC) is subject to multiple uncontrolled variables (Jones, 2006; Payne et al., 1967). Over the last decade saliva, or oral fluid (Choo and Huestis, 2004), has gained acceptance as a satisfactory matrix for on-the-spot testing for EA, both qualitative and semiquantitative, applicable to workplace or clinical settings such as emergency departments.