تابع سحب عينات الدمArterial Puncture

من طرف **المسلمانى** الثلاثاء مارس 16, 2010 6:58 pm

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. â€œArterial sticksâ€‌ are usually performed by a physician or a specially trained nurse or technician 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 Be sure to record the amounts of blood withdrawn because significant amounts can be removed if frequent samples are required.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. The 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.

Interventions
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
- Positive Allen's test result, which shows only one artery supplying blood to the hand
- Negative modified Allen's test result, which indicates obstruction in the ulnar artery (ie, compromised collateral circulation)
- Cellulitis or infection at the potential site
- Presence of arteriovenous fistula or shunt
- Severe thrombocytopenia (platelet count 20,000/mm³)
- Prolonged prothrombin time or partial thromboplastin time (>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 hemoglobin concentration, mode and flow rate of oxygen, and temperature. If the patient has been recently suctioned or 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 hemoglobin at the tissue level.

Intratest Patient Care

Observe standard precautions and follow agency protocols for the procedure.
The patient assumes a sitting or supine position.
Perform a modified Allen's 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 (ie, negative

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test result) and flushing of the hand is absent or slow, then another site must be chosen. An abnormal Allen's 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 Chloraprep.
OPTIONAL: Inject the area with a small amount (<0.25 mL) of 1% plain Xylocaine, if necessary, to anesthetize site. Assess for allergy first. This allows for a second attempt without undue pain.

Note
Do not use Xylocaine that contains epinephrine; it causes blood vessel constriction and makes the arterial puncture difficult.