March 8, 2007
Dr. Ramazi Mitaishvili

Dr. Ramazi Mitaishvili

Arterial Blood Gas Sampling

By Dr. Ramaz Mitaishvili


 Alternative names:Arterial Blood Gas Analysis; ABG Sampling; Arterial Blood Gas Test 


Blood is drawn anaerobically from a peripheral artery (radial, brachial, femoral, or dorsalis pedis) via a single percutaneous needle puncture, or from an indwelling arterial cannula or catheter for multiple samples. Either method provides a blood specimen for direct measurement of partial pressures of carbon dioxide (PaCO2) and oxygen (PaO2), hydrogen ion activity (pH), total hemoglobin (Hbtotal), oxyhemoglobin saturation (HbO2), and the dyshemoglobins carboxyhemoglobin (COHb) and methemoglobin (MetHb). 

Outcome Goal
Proper collection of arterial blood samples.

Purpose and indications

The purpose of arterial blood gas sampling is to assess patients respiratory status as well as acid base balance or for laboratory testing when venous blood is unavailable, and is frequently requested for seriously ill patients.  So, an arterial blood gas (ABG) will help in the assessment of oxygenation, ventilation, and acid-base homeostasis. It can also aid in the determination of poisonings (carboxyhemaglobinemia or methemaoglobinemia) and in the measurement of lactate concentration. Arterial puncture is a relatively straight forward technique that is easily performed at the bedside. Pulse oximetry will give a reasonable estimate of the adequacy of oxygenation in many circumstances but does not assess acid-base status or ventilation and should not be used alone in cases where these measurements are important. Apart from helping to establish a diagnosis, blood gases may also help to ascertain the severity of a particular condition (e.g. metabolic acidosis in sepsis). This information can help to establish diagnosis, monitor severity, progression, prognosis as well as guide therapy of:

  • respiratory failure,
  • cardiac failure,
  • renal failure,
  • hepatic failure,
  • diabetic ketoacidosis,
  • poisoning
  • sepsis

 Normal Values in an ABG  report  Values at sea level:

  • Partial pressure of oxygen (PaO2) – 75 – 100 mm Hg
  • Partial pressure of carbon dioxide (PaCO2) – 35 – 45 mm Hg
  • A pH of 7.35 – 7.45
  • Oxygen saturation (SaO2) – 94 – 100%
  • Bicarbonate – (HCO3) – 22 – 26 mEq/liter


NOTE: mEq/liter = milliequivalents per liter; mm Hg = millimeters of mercury At altitudes of 3,000 feet and above, the values for oxygen are lower. The arterial pO2 reduces with age. A rough guideline is that above the age of 40 years, paO2 = 105-age in years/2.

ContraindicationsContraindications are absolute unless specified otherwise.  

  • Cellulitis or other infections over the radial artery
  • Absence of palpable radial artery pulse
  • Negative results of an Allen test (collateral circulation test), indicating that only one artery supplies the hand and suggest to select another extremity as the site for arterial puncture
  • Coagulation defects (relative)


Sampling may be performed by trained health care personnel(6-8) in a variety of settings including (but not limited to) hospitals, clinics, physician offices, extended care facilities, and the home. however, because of the need for monitoring the femoral puncture site for an extended period, femoral punctures should not be performed outside the hospital.  


Arterial blood sampling should be performed under the direction of a physician specifically trained in laboratory medicine, pulmonary medicine, anesthesia, or critical care. A recognized credential MD, DO, CRTT, RRT, RN, RPFT, CPFT, MT, MLT, RCVT, CPT  I, CPT II, or equivalent is strongly recommended.  


The frequency with which sampling is repeated should depend on the clinical status of the patient and the indication for performing the procedure.


NOTE: Repeated puncture of a single site increases the likelihood of hematoma, scarring, or laceration of the artery. Care should be exercised to use alternate sites for patients requiring multiple punctures. An indwelling catheter may be indicated when multiple sampling is anticipated.

Puncture sites

Approved puncture sites include radial, dorsalis pedis, and brachial arteries. The brachial artery will not be used on patients in Children’s Hospital. In the Emergency Department, femoral artery is an approved puncture site. Brachial and femoral arteries should be reserved as a last option.
The radial artery on non dominant hand is the ideal site for an arterial puncture for the following reasons:

  • It is superficial and easily accessible.
  • It is easily compressible with better control of bleeding.
  • There is no nerve near by to worry about.
  • The collateral arch with ulnar artery minimizes the risk of occlusion.

 Anatomical Review

The radial artery runs along the lateral aspect of the volar forearm deep to the superficial fascia. The artery runs between the styloid process of the radius and the flexor carpi radialis tendon. The point of maximum pulsation of the radial artery can usually be palpated just proximal to the wrist.

 Radial Artery(anatomy of wrist)

Local Anesthesia

The use of local anesthetic for arterial puncture is not universal. The proposed reasons for the use of local anesthetic are: To avoid pain The concern that the pain induced hyperventilation or apnea could alter the results of blood gases This issue was specifically studied and the results indicate that an unanesthetized arterial puncture does provide an accurate measurement of resting pH and Pco2. Hence, the only reason to use local anesthetic is to avoid pain to the patient. If you are proficient, the first stick can be tried without the anesthetic. I strongly  recommend the use of local anesthetic for beginners.The syringe has to be heparinized to prevent clotting. It is important to have the right amount of heparin in the syringe. Too much or too little can alter the results. 

Necessary equipment:

  • Protective eye wear
  • Gloves
  • Iodine swab
  • Alcohol swab
  • Two by two gauze
  • ABG sampling kit is recommended to preserve the integrity of the sample
  • bag with ice, in which sample will be send to lab


Before beginning of a procedure be sure to wash your hands using proper washing technique and follow universal precautions in this procedure.We begin the procedure with performing Allen test, to be sure that collateral circulation is an appropriate.  Before beginning the actual procedure it is a good idea to make sure the patient is seated comfortably. He should rest his arm on a pillow in front of him, palm facing up. This position is necessary to perform the procedure and is the most comfortable for the patient. Try to hyperextend patient’s hand.

NOTE: The artery generally tends to be slippery, especially when it is elongated by arteriosclerosis. Stretching stabilizes the vessel. Let the patient rest his arm on a table, with his hand projecting beyond the edge. Dorsiflex the wrist be gently pressing down on the hand. This maneuver stretches and stabilizes the vessel.


First, we need to palpate by three fingers radial artery, than, on opposite site, the ulnar artery, which can’t be palpated, but we have to palpate area closest to ulnar artery. Than, we should ask patient to make a fist the tighter he or she can. Now I’m going to occlude both arteries and than I’m asking patient to release fist, I’m realizing my grasp from ulnar artery. Normally, within 5 second pale palm turns pink, showing good collateral circulation. With this patient we have good blood return and you’re OK to proceed arterial puncture procedure.

Clean area with iodine swab.


NOTE: Cleaning from center to periphery by circular motion.


You should allow area to dry, than you should wipe away iodine with alcohol swap, again allowing skin to dry and now, you can open ABG kit, which consist, from 3 parts. First peace is sponge cube to expel excessive air from syringe. Second, is black cap, to go over syringe to transport to lab, and last, heparinized syringe with needle attach. Slightly pull plunger back to be sure, that plunger is not stocked and blood can flow inside of syringe from pulsating artery. Remove cap, making sure that you’re seeing bevel. Don’t forget bevel must be up when inserting  facing flow of blood.


NOTE: If you wish to use local anesthesia- draw 2% xylocaine into a syringe. Infiltrate the skin and the area around the radial artery with this local anesthetic.


You should hold syringe little bit differently for ABG. Pretty much like a dart with angle 45 degrees.Palpate area carefully. This is only your landmark to penetrate the skin in going no where.Syringe is ready to be inserted and put your finger on right place, and rolle back on half way this finger and now you can insert needle into the skin. You should watch blood pulsating back into the syringe. When blood return observed, hold needle very steadily, and either allow the syringe barrel to fill or aspirate to pre-determined amount.
Remove needle quickly and apply firm pressure with gauze pad for five full minutes (or longer if the patient is on anticoagulant therapy or is thrombocytopenic double this time). Now, insert needle straight into the cube, than push down on the plunger to expel excessive air. Now, you can remove cube and needle as one and attach black cap to the tip of syringe. Gently mix the specimen by rolling it between your palms

Place the specimen on ice and transport to lab immediately. Last thing to do: Put needle with cube in sharp container.


 NOTE: If needle comes out of the artery during specimen aspiration, withdraw needle, hold pressure, and start over. If no blood is returned, slowly and carefully withdraw needle to re-enter artery. If no blood return after first attempt, withdraw needle to point just below skin surface, change direction and descend needle again. And finally, if unsuccessful after two attempts, withdraw needle completely and carry out post-puncture care.

Complications and How to Avoid

In general, an arterial puncture is an innocuous procedure, but occasionally complications may occur. Awareness of the types of complications and their contributory factors will help us to minimize their occurrence.

  • Pain
  • Bruising
  • Compression Neuropathy
  • Aneurysm
  • Spasms
  • A.V. Fistula
  • Mercury Embolism

Most series who have prospectively evaluated complications of arterial puncture have come to the same conclusion. The procedure is safe, the occurrence of serious complications are rare and most of the complications are minor and temporary.Pain Pain during and following the procedure is a frequent complaint and is reported to occur in 10% of the patient population. When systemically looked for, tenderness at the puncture site was observed in 15% of patients. You can minimize the pain by using thin needles and by the use of local anaesthetic. However, the local anaesthetic is ineffective in preventing late symptoms. Sometimes the pain is felt proximal or distal to the puncture site and this type of pain could be secondary to arterial spasm. In most cases the discomfort following an arterial puncture is temporary and minor.  


Bruising is the most frequently observed complication occurring at 30% of puncture sites. In most, it is mild but in some you could encounter large bruises. The bruising is more common at the radial site. The brachial and femoral arteries lie deep, and this may account for less frequently observed bruising at these sites. A hematoma can occur at the puncture site in patients on anticoagulation. Serious retro peritoneal hemorrhage has been reported. The hematoma formation in anticubital fossa is tolerated poorly and can result in median nerve compression and ischemic changes secondary to compression of the artery.

Compression Neuropathy

Compression neuropathy secondary to hematoma occurs at the cubital fossa and the inguinal region. The facia that holds the neurovascular bundle is tight and any extravasations of blood is tolerated poorly. In the anticubital fossa the brachial artery and the median nerve pass underneath the bicepital aponeurosis. This facia is unyielding and any hematoma formation results in compression of the median nerve and brachial artery. If the faciotomy is not performed, it could eventuate into Volkmann's contracture.


Aneurysm of the punctured vessel has been reported. This occurs with repeated punctures. Fortunately this complication is rare.


Spasms can temporarily decrease the pulse and cause pain. Occasionally the vessel can occlude secondary to thrombosis. Rarely has perivascular fibrosis and occlusion of the vessel been noted. The collateral arch with ulnar artery fortunately prevents any serious ischemic changes.

A.V. Fistula

Iatrogenic arteriovenous fistula has been reported rarely in patients who have hand multiple arterial punctures. This complication is rare.

Mercury Embolism

Mercury embolism has been reported in the days when mercury was used as an aerobic seal and mixing agent. This complication does not occur any more.  




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