Arterial Puncture

Arterial blood samples are necessary for arterial blood gas (ABG) determinations or when it is not possible to obtain a venous blood sample. Arterial sticks are usually performed by a primary provider or a specially trained nurse or respiratory therapist because of the potential risks inherent in this procedure. Samples are normally collected directly from the radial, brachial, or femoral arteries. If the patient has an arterial line in place (most frequently in the radial artery), samples can be drawn from the line. Be sure to record the amounts of blood withdrawn in order to track and total the amounts that are removed when frequent samples are required.

ABG determinations are used to assess the status of oxygenation and ventilation, to evaluate the acid–base status by measuring the respiratory and nonrespiratory components, and to monitor effectiveness of therapy. ABGs are also used to monitor critically ill patients, to establish baseline laboratory values, to detect and treat electrolyte imbalances, to titrate appropriate oxygen therapy, to qualify a patient for home oxygen use, and to assess the patient’s status in conjunction with pulmonary function testing.

Arterial puncture sites must satisfy the following requirements:

Sites must have available collateral blood flow.
Sites must be easily accessible.
Sites must be relatively nonsensitive as periarterial tissues.

For patients requiring frequent blood draws, an indwelling arterial catheter (line) may be inserted. Follow agency protocols for obtaining arterial line blood samples. The procedure varies for neonate, pediatric, and adult patients (see Arterial Blood Gas Tests in Chapter 14).

Pretest Patient Care

Assess patient for the following contraindications to an arterial stick or indwelling arterial line in a particular area:
- Absence of a palpable radial artery pulse
- Negative modified Allen test result, which indicates obstruction in the ulnar artery (i.e., compromised collateral circulation)
- Cellulitis or infection at the potential site
- Presence of arteriovenous fistula or shunt
- Severe thrombocytopenia (platelet count 20,000/mm³)
- Prolonged PT or PTT (more than 1.5 times the control is a relative contraindication)
A Doppler probe or finger pulse transducer may be used to assess circulation and perfusion in dark-skinned or uncooperative patients.
Before drawing an arterial blood sample, record the patient’s most recent Hb concentration, mode and flow rate of oxygen, and temperature. If the patient has recently undergone suction or been placed on a ventilator or if delivered oxygen concentrations have been changed, wait at least 15 minutes before drawing the sample. This waiting period allows circulating blood levels to return to baseline levels. Hyperthermia and hypothermia also influence oxygen release from Hb at the tissue level.

Intratest Patient Care

Observe standard precautions and follow agency protocols for the procedure.
Place the patient in a sitting or supine position.
Perform a modified Allen test by encircling the wrist area and using pressure to obliterate the radial and ulnar pulses. Watch for the hand to blanch and then release pressure only over the ulnar artery. If the result is positive, flushing of the hand is immediately noticed, indicating circulation to the hand is adequate. The radial artery can then be used for arterial puncture. If collateral circulation from the ulnar artery is inadequate (i.e., negative test result) and flushing of the hand is absent or slow, then another site must be chosen. An abnormal Allen test result may be caused by a thrombus, an arterial spasm, or a systemic problem such as shock or poor cardiac output.
Elevate the wrist area by placing a small pillow or rolled towel under the dorsal wrist area. With the patient’s palm facing upward, ask the patient to extend the fingers downward, which flexes the wrist and positions the radial artery closer to the surface.
Palpate for the artery and maneuver the patient’s hand back and forth until a satisfactory pulse is felt.
Swab the area liberally with an antiseptic agent such as chlorhexidine.
OPTIONAL: Inject the area with a small amount (less than 0.25 mL) of 1% plain lidocaine, if necessary, to anesthetize site. Assess for allergy first. This allows for a second attempt without undue pain.
Prepare a 20- or 21-gauge needle on a preheparinized, self-filling syringe; puncture the artery; and collect a 3- to 5-mL sample. The arterial pressure pushes the plunger out as the syringe fills with blood. (Venous blood does not have enough pressure to fill the syringe without drawing back on the plunger.) Air bubbles in the blood sample must be expelled as quickly as possible because residual air alters ABG values. The syringe should then be capped and gently rotated to mix heparin with the blood.
When the draw is completed, withdraw the needle, and place a 4 × 4 inch absorbent bandage over the puncture site. Do not recap needles; if necessary, use the one-handed mechanical, recapping, or scoop technique, or commercially available needles. Maintain firm finger pressure over the puncture site for a minimum of 5 minutes or until there is no active bleeding evident. After the bleeding stops, apply a firm pressure dressing but do not encircle the entire limb, which can restrict circulation. Leave this dressing in place for at least 24 hours. Instruct the patient to report any signs of bleeding from the site promptly and apply finger pressure if necessary.
Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Indicate the type and flow rate of O₂ therapy or if the patient was on room air. Place the sample in an ice slurry and transport to the laboratory in a biohazard bag. Do not use blood for ABGs if the sample is more than 1 hour old.
In clinical settings such as the perioperative or intensive care environment, ABG studies usually include pH, PCO₂, SO₂, total CO₂ content (TCO₂), O₂ content, PO₂, base excess or deficit, HCO₃, Hb, hematocrit (Hct), and levels of chloride, sodium, and potassium.

Clinical Alert

Metabolizing blood cells can quickly alter blood gas values (primarily PaO2) at normal body temperature (37 °C). This occurs much slower at 0 °C (i.e., temperature of ice water). An iced sample should remain stable for at least 1 hour. Any sample not placed in ice should be tested within minutes after it is drawn or else discarded. The main effect of cellular metabolism decreases PO2. Several studies have shown a remarkable fall in PaO2 if the blood contains more than 100,000 WBCs/mm3 (i.e., leukocyte larceny), even when the sample is on ice. A WBC count of this magnitude (usually in leukemia) should mandate special handling, such as testing the sample immediately. Alternatively, check the patient’s oxygen saturation by pulse oximetry, which is not affected by extreme leukocytosis

Clinical Alert

Some patients may experience lightheadedness, nausea, or vasovagal syncope during the arterial puncture. Treat according to established protocols

Posttest Patient Care
Posttest assessment of the puncture site and extremity includes color, movement, sensation, degree of warmth, capillary refill time, and quality of the pulse.
The arterial puncture site must have a pressure dressing applied and should be frequently assessed for bleeding for several hours. Instruct the patient to report any bleeding from the site and to apply direct pressure to the site if bleeding occurs.
Frequently monitor the puncture site and dressing for arterial bleeding for several hours. Instruct the patient not to use the extremity for any vigorous activity for at least 24 hours.
Monitor the patient’s vital signs and mental function to determine adequacy of tissue oxygenation and perfusion.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

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Introduction ⬇

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