RSPT 1410 Arterial blood gas sampling

What does an ABG Measure?

pH - acid-based balance

SpCO2 in arterial blood - alveolar ventilation

PaO2 in arterial blood - oxygen tension (pressure) of O2 that has dissolved in plasma

Advantages and disadvantages of sticking radial artery?

Advantages - easily accessible, has collateral circulation, reduced chance of nerve damage or venous puncture.

Disadvantages - small size, may be difficult if patient has hypotension

Advantages and disadvantages of sticking brachial artery?

Advantages - Easily palpated, large size

Disadvantages - Inadvertent venous sampling, accidental contact with nerve, less collateral circulation

Advantages and disadvantages of sticking the femoral artery?

Advantages - Very large, used during state of low cardiac output (CPR)

Disadvantages - Close proximity of major vein, lack of collateral circulation, may be difficult to locate (deep).

Two other stick location options?

Dorsalis pedis, posterior tibial artery

What is the Modified Allen’s Test used? Steps

Used to assess collateral circulation through the ulnar artery. 

Must be performed and results recorded prior to puncture

Procedure: Make a fist, occlude radial and ulnar arteries until blanching occurs, release pressure on the ulnar artery, color returns within 5-10 seconds

Supplied needed for puncture

ABG kit, or:

Syringe and needle (20-25 gauge needle)

Rubber stopper

Gauze and band-aid

Alcohol prep pad

Plastic bag or cup of ice

2 lidocaine or ELMA cream if ordered (j-tip)

PPE

What is the size needle used for radial artery stick? 

20-25 gauge 1 inch 

The use of anesthetic for stick

Use if ordered. Wait a few minutes for effect to begin (longer with EMLA)

What are the steps for puncture?

BE PREPARED AND ORGANIZED

Prepare syringe

Arrange supplies

Put on PPE - gloves, gown, mask and goggles if required/wanted

Perform modified Allen’s test if radial stick

Palpate site and clean with alcohol

Hold syringe like a pencil with needle bevel up 

While palpating the artery, puncture skin

     Radial/Dorsalis Pedis - 45 degree angle

     Brachial/Femoral - 90 degree angle

Once below surface, slowly advance needle towards artery

Observe needle hub for “flash” of blood.  

Once flashed, do not move, let needle fill up, quickly withdraw needle, apply firm pressure with gauze pad (3-5) min. - 10 min if on anti-coagulant meds.

Expel excess air in syringe and insert needle into rubber stopper or use needle guard

Label properly including stick location, how many advances, how long pressure held. 

Place sample in ice slush - decreases metabolism

What are sampling errors and what about them? 

Air bubbles - CO2 will go into the bubble. May increase/decrease PaO2, will decrease PaCO2 and increase pH. 

Delay in Sample Analysis - should use ice to inhibit metabolizing. Decreases PaO2, decreases pH, increases PaCO2.

Venous Sampling Dark in color. Common with hypotension/poor CV status, if in doubt repeat stick, PaO2 decreased, PaCO2 increased, pH decreased. 

Patient Anxiety - Work quickly to prevent hyperventilation, Increased PaO2, decreased PaCO2, increased pH

Hazard and Complications

Arterial spasm

Hematoma

Hemorrhage

Trauma to vessel

Air or blood emboli

Pain

Infection

How long do you wait between any type of modality adjustment before getting a ABG?

20-30 minutes, latest exam for peds said 10 minutes

2 things to do before an ABG?

check ID, check to see if on blood thinners, usually stroke people are on this medication.

IStat

Most popular blood analyzer