Arterial Blood Gas Sampling

ABG Summary

Indications

Acid-base disturbances
PaO₂ and PaCO₂ measurement
Therapeutic response monitoring
Abnormal hemoglobins detection

Contraindications

Abnormal Allen's test
Local infection/thrombus
AV fistula/graft
Severe vascular disease

Site Selection

Radial (most common)
Femoral
Brachial
Dorsalis pedis

Allen's Test

Assess collateral circulation
Abnormal if >10 seconds for color return
Absolute contraindication if abnormal

Complications

Common: Pain, bruising, bleeding
Less common: Hematoma, vasospasm
Rare: Infection, embolism, aneurysm

Technique Tips

30-45° angle for radial artery
90° angle for femoral artery
Use heparinized syringe
Remove air bubbles immediately

Overview

Arterial blood gas (ABG) sampling is a diagnostic procedure that involves collecting blood from an artery to evaluate oxygen and carbon dioxide levels, acid-base balance, and other parameters. It provides critical information about a patient's respiratory and metabolic status.

Indications

Acid-Base Assessment

Identification and monitoring of acid-base disturbances
Metabolic acidosis/alkalosis evaluation
Respiratory acidosis/alkalosis evaluation

Gas Exchange

Measurement of partial pressures of oxygen (PaO₂)
Measurement of partial pressures of carbon dioxide (PaCO₂)
Assessment of oxygenation status

Other Indications

Assessment of response to therapeutic interventions
Detection of abnormal hemoglobins (carboxyhemoglobin, methemoglobin)
Alternative to venous sampling in emergencies

Contraindications

Absolute Contraindications

An abnormal modified Allen's test
Local infection, thrombus, or distorted anatomy at the puncture site
- Previous surgical interventions
- Congenital or acquired malformations
- Burns, aneurysm, stent
Arteriovenous fistula or vascular graft at the puncture site
Severe peripheral vascular disease of the selected artery
Active Raynaud's syndrome (particularly radial site)

Relative Contraindications

Anticoagulants or coagulopathy
Use of thrombolytic agents
Thrombocytopenia
History of Raynaud's disease
Evidence of poor peripheral perfusion

Important Consideration

The presence of a relative contraindication requires careful risk-benefit analysis. In emergency situations, the need for ABG may outweigh the relative risks.

Site Selection

Common sites include the radial, femoral, brachial, dorsalis pedis, or axillary artery. There is no evidence that any site is superior to the others. However, the radial artery is used most often because it is accessible and more comfortable for the patient.

Radial Artery

Most commonly used site
Best palpated between distal radius and flexor carpi radialis tendon
Wrist should be extended during palpation
Good collateral circulation (ulnar artery)

Femoral Artery

Large, easily palpable artery
Palpated just below the mid-inguinal point
Lower extremity extended, patient supine
Higher risk of complications

Alternative Sites

Brachial artery - use with caution (end-artery)
Dorsalis pedis artery - assess collateral flow
Axillary artery - rarely used

Assessing Collateral Circulation

Modified Allen's Test

This test assesses collateral circulation to the hand before radial artery puncture. Although rarely performed in practice, it helps identify patients at risk for ischemia.

Procedure

The patient's hand is initially held high with the fist clenched
Both the radial and ulnar arteries are compressed firmly by the examiner's thumbs
The hand is then lowered and the fist is opened (the palm will appear white)
Pressure is released from the ulnar artery while maintaining occlusion on the radial artery
A pink color should return to the palm, usually within six seconds

Interpretation

Normal: Color returns within 5-6 seconds
Abnormal: Ten seconds or more elapses before color returns
An abnormal test is an absolute contraindication to radial artery puncture

Limitations

The modified Allen's test has poor predictive value for ischemic complications and is not always performed in emergency settings. Clinical judgment should prevail.

Complications

Common Complications

Local pain and paresthesia
Bruising (ecchymosis)
Local minor bleeding

Less Common Complications

Vasovagal response
Local hematoma from moderate or major bleeding
Artery vasospasm

Rare Complications

Infection at the puncture site
Arterial occlusion from a local hematoma
Air or thrombus embolism
Local nerve injury
Needlestick injury to healthcare personnel
Pseudoaneurysm formation
Vessel laceration

Management of Complications

Apply firm pressure for at least 5 minutes (longer if patient is anticoagulated). Monitor for signs of compromised circulation distal to the puncture site. For suspected embolization or severe complications, seek immediate vascular surgery consultation.

Procedure Technique

Preparation

Gather equipment: heparinized syringe, needle (20-23G for radial, 18-20G for femoral), gloves, alcohol swabs, gauze, bandage
Perform hand hygiene and don personal protective equipment
Position the patient appropriately for the selected site
Explain the procedure to the patient

Sampling Technique

Palpate the artery and identify the puncture site
Clean the site with antiseptic solution and allow to dry
Anesthetize the skin if time permits (1% lidocaine without epinephrine)
Hold the needle at 30-45° angle for radial artery, 90° for femoral artery
Advance the needle until arterial blood flashes into the syringe
Collect 1-3 mL of blood
Withdraw the needle and apply immediate firm pressure
Remove air bubbles and cap the syringe
Place the sample on ice if not analyzed immediately

Aftercare

Apply firm pressure for 5-10 minutes (longer if coagulopathic)
Check for bleeding or hematoma formation
Assess distal circulation after the procedure
Label the sample and send for immediate analysis

Special Considerations

Pediatric Patients

Use smaller gauge needles (23-25G)
Consider using topical anesthetics
Radial artery is preferred site
May require sedation or distraction techniques

Coagulopathic Patients

Weigh risks and benefits carefully
Consider using ultrasound guidance
Apply pressure for longer duration (15-20 minutes)
Consider transcutaneous monitoring as alternative

Critical Care Settings

Arterial lines may be preferable for frequent sampling
Use ultrasound guidance for difficult punctures
Consider femoral approach in hypotensive patients
Monitor for complications more frequently