Arterial Blood Gas (ABG) Sampling: Radial Draw, Line Access & Specimen Integrity
Obtain a bubble-free arterial sample after collateral-flow screening, apply sustained wrist pressure, and deliver on ice for immediate analysis—so ventilation and acid–base decisions rest on trustworthy gas values, not a rejected syringe.
On this page
Quick facts
Key takeaway
ABG sampling is an arterial procedure: confirm collateral hand perfusion before radial puncture, keep the syringe free of air, and analyse without delay. Chart oxygen therapy with the sample, apply longer pressure than for venous draws, and reassess distal pulse and colour—the gas result is only as safe as the wrist you leave behind.
Quick procedure summary
| Item | Detail |
|---|---|
| Procedure name | Arterial blood gas (ABG) sampling |
| Also known as | ABG draw; arterial puncture for blood gas analysis |
| Category | Laboratory / respiratory diagnostics |
| Clinical purpose | Measure arterial pH, PaO₂, PaCO₂, and related values to assess oxygenation, ventilation, and acid–base status |
| Who performs | Registered nurses, physicians, and respiratory therapists per scope, competency, and local authorisation |
| Estimated time | About 10–20 minutes including collateral-flow check, draw, pressure, labelling, and transport |
| Clinical settings | Emergency departments, critical care, respiratory wards, operating theatres, and high-dependency units |
What is arterial blood gas sampling?
When a patient with worsening shortness of breath no longer matches their pulse oximetry trend, the team often orders an arterial blood gas to see what the blood actually carries—oxygen, carbon dioxide, and pH—rather than what the monitor estimates.
ABG sampling collects blood directly from an artery (most often the radial) or from an in-dwelling arterial catheter. Nurses support the pathway by preparing equipment, assisting with or performing authorised draws, documenting oxygen delivery, handling specimens correctly, and monitoring for arterial complications. Interpretation of results belongs to the clinical team; this guide focuses on safe collection aligned with arterial blood gas testing principles.
Technique principles align with Royal Marsden Manual — Arterial puncture: radial artery and Arterial blood gas sampling: arterial cannula on RMM Online. Licensed Marsden Nursing Procedure materials in the project library informed scope alignment; proprietary step text and illustrations are not reproduced here.
Radial puncture vs arterial line sampling
Two routes supply the same analyser—choose based on access, stability, and unit policy.
One-time percutaneous draw
- Requires modified Allen test (or equivalent) before puncture when radial site is used.
- Uses pre-heparinized syringe and needle; higher risk of hematoma and vasospasm than venous draw.
- See also arterial puncture (radial) for focused radial technique.
Continuous monitoring + sampling port
- Many ICU pathways use waste-discard volume before filling the syringe to avoid dilution from flush solution.
- Pair with zero balance adjustment and waveform checks so pressures and samples stay trustworthy.
- Do not confuse with venipuncture or central venous sampling.
Modified Allen test (collateral circulation)
Before radial puncture, confirm the ulnar artery can perfuse the hand if radial flow is compromised. Institutional protocols may vary on technique and timing.
Occlude both arteries
Ask the patient to clench the fist (or assist gently). Compress both radial and ulnar arteries at the wrist.
Release ulnar only
Release ulnar pressure while keeping radial occluded. Pallor should flush within a few seconds as the hand reperfuses via ulnar collateral flow.
Interpret and act
Delayed or absent flushing suggests inadequate collateral circulation—notify the clinician and select an alternative site (e.g. brachial) per policy rather than proceeding with radial puncture.
Correlate with peripheral pulse assessment and capillary refill after the draw.
Specimen integrity: bubbles, heparin, ice, and turnaround
Pre-analytic errors are a leading cause of misleading ABG results. Treat the syringe like a time-critical drug.
| Step | Why it matters | Bedside action |
|---|---|---|
| Heparinized syringe | Prevents clotting before analysis | Use manufacturer-approved ABG syringe; roll gently to mix heparin without haemolysing the sample. |
| Exclude air | Bubbles falsely alter PaO₂ and PaCO₂ | Allow passive fill; expel air per laboratory policy before capping. |
| Immediate analysis | Values change with temperature and delay | Transport on ice when policy requires; hand to blood gas analyzer or point-of-care device without delay. |
| Context on label | Interpretation depends on therapy | Record FiO₂, device, flow, ventilator settings if applicable, and patient temperature when charted. |
Swipe sideways on small screens to read all columns.
Apply two identifiers to the syringe immediately. Follow specimen collection rules—unlabelled arterial samples must not be analysed anonymously.
Clinical indications
| Clinical situation | Why an ABG may be ordered |
|---|---|
| Acute respiratory deterioration | Assess oxygenation and ventilation when hypoxia symptoms, altered mental status, or rising work of breathing appear |
| COPD / asthma exacerbation | Evaluate hypercapnia risk and guide oxygen titration in COPD or asthma |
| Critical illness | Acid–base monitoring in sepsis, ARDS, or ventilated patients |
| Metabolic emergency | Confirm acid–base disturbance in suspected diabetic ketoacidosis alongside lactate and electrolytes |
| Oxygen therapy adjustment | Trend response after changes to oxygen therapy or ventilator settings; pair with capnography when ordered |
Contraindications & pause points
- Positive or equivocal modified Allen test without clinician-approved alternate plan
- Absent radial pulse, prior surgical graft at site, infection, or hematoma at wrist
- Single patent artery to the hand (e.g. prior radial harvest) unless specialist approves
- Therapeutic anticoagulation or coagulopathy—extended pressure and experienced operator
- Agitation or movement disorder—risk of through-and-through injury; plan assistance
- Poorly palpable pulse—consider ultrasound guidance or alternate site per policy
Equipment
Patient preparation
Pediatric / older adult: Smaller syringes and gauges may apply; allow extra reassurance and pressure time. Institutional protocols may vary.
ABG sampling procedure steps
Verify order and collateral flow
Confirm patient, site, and whether sample is from puncture or arterial line. Perform modified Allen test for radial plans. Assemble heparinized syringe.
Palpate pulse and cleanse skin
Locate radial (or ordered) pulse. Disinfect with chlorhexidine in alcohol using friction for product contact time; allow to dry completely.
Sterility checkpoint: Needle must not touch unprepared skin after antiseptic has dried.
Advance into artery
Anchor the artery. Insert at the shallow angle taught in competency training—often toward the pulse at 30–45° for radial sites. Institutional protocols may vary. Arterial blood enters the syringe under pressure; allow passive fill without pulling plunger aggressively.
Withdraw and compress immediately
Remove needle while placing gauze over the site. Activate safety device; dispose in sharps. Apply firm direct pressure—arterial haemostasis takes longer than venous draws.
Expel air, cap, label, transport
Remove bubbles per policy; cap syringe; mix heparin gently. Label at bedside with oxygen context. Transport on ice if required; deliver for immediate analysis.
Line sampling (when applicable)
When drawing from an arterial catheter, discard waste volume per ICU protocol to clear flush or dead space, then fill the ABG syringe from the sampling port. Maintain closed system and document waste volume.
Post-procedure care
- Maintain pressure until bleeding stops—reassess anticoagulated patients frequently
- Check radial pulse, colour, temperature, and capillary refill distal to the site
- Observe for swelling, throbbing pain, or numbness suggesting hematoma or nerve irritation
- Continue respiratory assessment and vital signs measurement; correlate results with clinical picture
- Communicate specimen delivery time to the lab or point-of-care operator
Common complications
| Complication | Bedside clues | Prevention / response |
|---|---|---|
| Hematoma | Rapid swelling, pain, tightness at wrist | Sustained pressure; avoid repeat radial site; escalate if expanding |
| Vasospasm / arterial occlusion | Pale, cool, painful hand; weak or absent pulse | Warmth per policy; notify clinician; may need vascular review |
| Nerve injury | Shooting pain, paraesthesia on insertion | Stop attempt; do not probe; document and notify |
| Inaccurate result | Lab flags sample error | Exclude air, minimize delay, document oxygen settings |
| Vasovagal reaction | Nausea, syncope during procedure | Supine positioning; observe; record orthostatic blood pressure if indicated |
When to escalate
- Hematoma expands despite pressure or distal perfusion deteriorates
- Absent radial pulse, white painful hand, or suspected arterial occlusion
- Persistent bleeding in anticoagulated patients
- Failed Allen test before planned radial puncture—need alternate site plan
- Syncope with injury or haemodynamic instability—activate rapid response per protocol
After maximum attempts per policy, involve a more experienced operator. Delayed or rejected specimens in unstable patients warrant immediate clinical review—not silent recollection hours later.
Nursing documentation
Record date and time, site, method (puncture vs line), modified Allen result, oxygen/ventilator data, attempts, patient tolerance, complications, and transport. Example note:
“22/05/2026 09:10 — ABG via right radial puncture after negative modified Allen test; chlorhexidine dried fully; one attempt; 2 mL heparinized sample, air expelled, capped, sent on ice to blood gas analyser 09:13. Oxygen 2 L/min nasal cannula documented on label. Direct pressure 5 min with haemostasis; radial pulse palpable, fingers warm pink. Patient tolerated; no paraesthesia.”
Clinical pearls
- Chart the oxygen prescription on the specimen label—ABG interpretation without FiO₂ context can mislead therapy.
- If blood “pulses” into the syringe then stops, you may have penetrated through the artery—withdraw slightly rather than digging.
- Never send a syringe with visible air “to see what happens”—recollect when policy allows.
- Pair trending gases with clinical assessment: a normal PaO₂ does not rule out fatigue from work of breathing.
- When CBC and ABG are both ordered, clarify whether one radial puncture can supply both—many services use separate venous and arterial collections.
NCLEX practice questions
On a respiratory ward, a “normal” SpO₂ can still hide rising CO₂—practice NCLEX-style clinical judgment practice with priority action, select-all-that-apply preparation, post-draw trend interpretation, matrix escalation, and documentation cloze focused on ABG sampling, Allen testing, bubble-free syringes, and wrist perfusion checks.
Unfolding case — respiratory bay. Mrs. Chen, 71, has COPD with a charted SpO₂ target of 88–92%. She is on 2 L/min nasal cannula. SpO₂ reads 96%. She is newly drowsy with accessory muscle use and RR 28. An ABG is ordered. Radial pulse is palpable; you plan a right radial draw after modified Allen test.
Answer key & rationale
Frequently asked questions
Why is the modified Allen test done before radial ABG sampling?
It screens whether ulnar collateral flow can perfuse the hand if the radial artery is injured or spasms after puncture. An abnormal test should prompt an alternative site or clinician review before radial puncture.
How is ABG sampling different from venipuncture?
ABG sampling enters an artery under higher pressure, requires heparinized equipment, must minimise air bubbles, and needs rapid analysis. Venipuncture targets veins for general laboratory tests with different tubes and pressure control.
Why must air bubbles be avoided in an ABG syringe?
Air alters PaO₂ and PaCO₂ readings and can make results misleading for ventilation and oxygen decisions. Expel bubbles per laboratory policy before analysis.
How long should pressure be applied after radial artery puncture?
Until haemostasis is achieved—often longer than venous draws. Anticoagulated patients may need several minutes of firm pressure with reassessment for hematoma. Institutional protocols may vary.
Can nurses draw ABGs from an existing arterial line?
When an in-dwelling arterial catheter is present, many teams sample from the line using a waste-discard technique to avoid dilution. Scope, waste volume, and flush policy vary by unit—follow competency and protocol.
When should the nurse escalate after ABG sampling?
Escalate for expanding hematoma, persistent bleeding, absent distal pulse, new numbness, severe pain, vasospasm with poor perfusion, or syncope. Failed collateral testing should be reviewed before radial puncture.
References
Authoritative sources used to develop this guide. Royal Marsden procedure principles are attributed to official RMM Online pages aligned with licensed Marsden Nursing Procedure materials in the project library; proprietary step text and illustrations are not reproduced. Each citation lists the source first; the URL is the page used for content alignment.
-
The Royal Marsden Manual of Clinical Nursing Procedures — Arterial puncture: radial artery (RMM Online).https://www.rmmonline.co.uk/manual/c13-fea-0006
-
The Royal Marsden Manual of Clinical Nursing Procedures — Arterial blood gas sampling: arterial cannula (RMM Online).https://www.rmmonline.co.uk/manual/c13-fea-0007
-
Royal Marsden Manual of Clinical Nursing Procedures — Procedures (RMM Online hub).https://www.rmmonline.co.uk/contents/procedures
-
British Thoracic Society. Emergency oxygen use in adult patients (guideline hub).https://www.brit-thoracic.org.uk/quality-improvement/guidelines/emergency-oxygen/
-
Centers for Disease Control and Prevention. Hand hygiene in healthcare settings.https://www.cdc.gov/infection-control/hcp/hand-hygiene/index.html
-
StatPearls [Internet]. Allen test — NCBI Bookshelf.https://www.ncbi.nlm.nih.gov/books/NBK536984/
-
OpenStax. Clinical Nursing Skills — specimen collection and vascular access chapters.https://openstax.org/details/books/clinical-nursing-skills
Local Marsden Nursing Procedure PDFs in the project library informed scope alignment; refer to the RMM Online equivalents above for authoritative web citations.
Editorial standards & medical review
About the author: Sid A. Abdala Balal, RN, writes evidence-based nursing education focused on practical bedside skills, patient safety, and clinical decision support for nurses.
Medical review: This guide is reviewed by a licensed physician for clinical accuracy, clarity, and alignment with current arterial blood gas sampling and specimen-handling standards.
Policies: Medical Review Process · Editorial Policy · Correction Policy