Arterial blood gas (ABG) analysis is an essential diagnostic test for assessing a patient’s oxygenation and ventilation status. As a nurse, properly performing the modified Allen test and collecting an ABG sample are critical skills that directly impact patient care. This comprehensive guide will equip nurses with best practices for modified Allen testing, ABG collection supplies and setup, draw techniques, and sample handling.

In this Article:

Understanding the Importance of Arterial Blood Gases

ABG testing measures a patient’s blood pH as well as oxygen and carbon dioxide levels. It provides key information about lung function and helps diagnose acute and chronic respiratory issues like asthma, emphysema, and pulmonary embolism. In critical care settings, ABG analysis is crucial for managing mechanical ventilation and determining the effectiveness of oxygen therapy.

Assessing ABG values can also reveal metabolic problems like diabetic ketoacidosis. Plus, ABG samples may be analyzed to measure electrolytes, hemoglobin, and lactate.Given the breadth of vital information ABG testing provides, nursing expertise in properly collecting these samples is imperative.

Overview of the Modified Allen Test

Prior to drawing an ABG sample from a patient’s radial artery, nurses must first perform a modified Allen test.

This assessment confirms adequate collateral blood flow to the hand via the ulnar artery. Occluding both the radial and ulnar arteries could severely ischemic injury distal to the wrist.The modified Allen test includes the following steps:

Have the patient make a tight fist for about 30 seconds to exsanguinate the hand.
Press firmly on the ulnar and radial arteries at the wrist to occlude both.
Have the patient open their hand. It should appear blanched, indicating interruption of blood flow.
Release pressure on the ulnar artery while keeping the radial artery occluded. Observe as the hand flushes with blood.
If capillary refill takes longer than 5 seconds, collateral ulnar flow is inadequate and the radial artery cannot be used for ABG sampling.

Always document modified Allen test results in the patient’s chart along with the chosen site for the ABG draw.

Gathering the Necessary ABG Collection Supplies

Essential Items for ABG Collection

Nurses must assemble all required equipment before beginning the ABG draw procedure. At minimum, the following supplies are needed:

ABG syringe: Use a heparinized 1mL or 3mL syringe with a thin 25-27 gauge needle. Heparin helps preserve the integrity of the blood sample.
Alcohol wipes: Thoroughly cleanse the draw site to prevent infection.
Gloves: Wear non-sterile gloves as standard contact precaution.
Tourniquet: A latex-free tourniquet aids venous occlusion at the draw site.
Gauze pads: Apply pressure after the blood draw to prevent hematoma formation.
Biohazard sharps container: Responsibly discard used needles.

Additionally, you will need the following for sample analysis:

Heparin tube: Immediately transfer the specimen from the syringe into a heparinized tube after collection.
Tube label: Accurately label each sample with the patient’s name, date, and time of draw.
Transport bag: Place the tube into a biohazard bag for safe delivery to the lab.
Ice pack: Keep the sample on ice until analysis to avoid erroneous results.

Other Recommended Materials:

Hand sanitizer
Adhesive bandage
Penlight
ABG kit: Commercial kits contain all required supplies
Reference chart displaying target values

Assembling all necessary equipment for ABG sampling before approaching the patient exhibits preparedness and helps calm fears about the procedure. It also prevents delays that can falsely elevate CO2 levels from prolonged tourniquet application.

Step-by-Step ABG Collection Technique

1. Identify the Puncture Site

The preferred site for ABG sampling is the radial artery at the wrist. Use the opposite arm from any existing IV lines to avoid interference. Other potential locations include the femoral, brachial, or dorsalis pedis arteries depending on the clinical scenario.

2. Perform Hand Hygiene and Apply Gloves

Thoroughly wash hands or use alcohol-based foam sanitizer before putting on clean, non-sterile gloves. This crucial step prevents transmitting pathogens that could lead to infection.

3. Position the Patient

Have the patient sit in a high Fowler’s position with the wrist extended and slightly supinated. A bedside table or overbed table serves well as an arm rest. Proper positioning provides easier access to the radial pulse.

4. Locate the Radial Pulse

Palpate the radial pulse by placing two fingers lateral to the flexor carpi radialis tendon. Use a penlight to transilluminate and further accentuate the arterial pulse. Mark this spot with a pen.

5. Apply the Tourniquet

Wrap the latex-free tourniquet around the upper forearm about 3-4 inches above the puncture site. Tighten it adequately to obstruct venous flow while maintaining arterial circulation. If unable to palpate the radial pulse with the tourniquet on, it is too tight.

6. Cleanse the Puncture Site

Vigorously swab the marked puncture site with an alcohol wipe using friction for 30 seconds. Let the area fully air dry to prevent hemolysis of the blood sample from residual alcohol.

7. Perform the Blood Draw

A. Anchor the artery by placing one finger distal to the puncture mark. Apply gentle pressure to minimize rolling or sliding of the arterial vessel. Avoid complete occlusion.

B. Insert the needle with the bevel up at a 30-45 degree angle. Promptly enter the lumen in one deliberate pass to prevent trauma from repeat attempts.

C. Pull back on the plunger to obtain the sample. Draw anaerobically by permitting the pressure gradient to fill the syringe without aspirating. The required volume is usually 1-2 mL.

Note: You may need to adjust the needle’s angle during entry while maintaining the same skin puncture site.

8. Remove the Needle and Apply Pressure

Once sufficient blood volume is obtained, swiftly withdraw the needle and place gauze over the site with pressure. Elevating the arm above heart level also aids hemostasis. Apply an adhesive bandage once bleeding ceases.

9. Transfer the Sample

Immediately expel any air bubbles and transfer the arterial specimen from the syringe into the heparinized tube. Promptly label tube with patient information and deliver to the lab per facility protocol. Don ice packs to maintain temperature during transport.

10. Document the Procedure

Record the ABG draw in the patient’s chart including date, time, sample quality, anatomical site, complications (if any), patient tolerance, and modified Allen test results.

Causes of Unsuccessful ABG Draws

While straightforward in theory, errors can easily occur during ABG collection leading to unusable samples and inaccurate findings.

Common mistakes include:

Prolonged tourniquet time > 1 minute
Inadequate hand cleansing
Hemolysis from tissue trauma or alcohol residue
Clotting due to incorrect syringe-tube ratio
Air bubbles causing oxygenation
Specimen contamination

If faced with an unsuccessful initial attempt, wait at least 10-15 minutes before repeat puncture at a site proximal to the first. This allows arterial spasm to resolve and hematoma formation to become apparent.

Handling ABG Samples After Collection

Maintaining sample integrity from collection through analysis is imperative for reliable test results that guide clinical decision-making.

Follow these post-draw steps:

Place tube on ice, avoiding direct contact with water
Deliver to the lab quickly – samples remain viable for 30 minutes
Load the specimen into the blood gas analyzer promptly
Store on ice again if unable to process immediately

Even brief ambient air exposure can alter the patient’s true pH and gas values. For this reason, keep handling of ABG tubes to an absolute minimum.

Complications Associated With ABG Draws

While generally safe, arterial puncture does incur rare risks of complication such as:

Local trauma:

Hematoma
Arterial dissection
Thrombosis
Compartment syndrome

Systemic:

Vasovagal reaction
Seizure
Distal embolization

Meticulous sterile technique minimizes infectious risks like catheter-associated bloodstream infections. Certain populations have higher incidence of ABG-related complications, including:

Pediatrics
Elderly patients
Those on anticoagulants

If complications arise during the blood draw, immediately apply pressure to the site and elevate the extremity. Consult the provider to promptly assess vascular compromise in the involved limb.

Special Considerations for ABG Collection

While the basic protocol remains unchanged, certain patient-specific factors necessitate additional precautions during ABG sampling.

Patients with oxygen therapy

Remove supplemental oxygen just prior to needle puncture to avoid artificially elevated PaO2 levels. Promptly reapply therapy after specimen acquisition.

Pediatric patients

Warm the site beforehand to promote vasodilation for easier access. Use smaller syringe-needle combinations to reduce tissue injury. Employ distraction techniques while sampling to allay anxiety.

Elderly patients

Assess for adequate collateral circulation via Allen’s test due to higher prevalence of undiagnosed peripheral vascular disease. Expect difficult vessel localization from arterial calcification. Apply warm packs beforehand for vasodilation.

Patients on anticoagulants

Apply direct pressure for at least 5-10 minutes post-draw to prevent hematoma development. Avoid aspirin if possible as this prolongs clotting time.

Integrating Modified Allen Testing Into Routine Nursing Care

While traditionally performed in conjunction with ABG sampling, the modified Allen test also provides beneficial diagnostic information relevant across health care settings. It quickly assesses arterial circulation at baseline and after interventions that could compromise blood flow like wrist fractures, radial catheterization, or arterial puncture. By serving as an easy-to-perform, non-invasive screening tool, nurses can utilize Allen’s testing in various clinical scenarios such as:

Monitoring hand perfusion intraoperatively during lengthier procedures
Evaluating efficacy of vascular surgery to improve circulation
Identifying peripheral artery disease in at-risk individuals

Incorporating modified Allen assessments more broadly into daily nursing workflow facilitates prompt detection of circulatory deficits that prompt further evaluation and treatment to prevent tissue damage.

Conclusion

As detailed throughout this comprehensive guide, arterial blood gas analysis via radial artery puncture plays a crucial role across medical and surgical fields. Sampling errors can lead to detrimental patient outcomes, underscoring the importance of nursing expertise in properly conducting Allen’s tests and collecting ABG specimens.

By honing ABG draw skills, nurses directly enhance diagnostic accuracy that guides time-sensitive interventions for severely ill patients. While the procedure itself may seem straightforward, meticulous technique and finesse only develop over time through repeated practice.

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Mastering Arterial Blood Gas Collection: A Comprehensive Guide for Nurses on the Modified Allen Test and ABG Draws