Obtaining Arterial Blood Sample

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					                                                                      ABG Lecture Notes

Obtaining Arterial Blood Sample
Egan‟s Chapter 16 / Wyka Chapter 12
AARC Clinical Practice Guidelines

Prior to Obtaining Sample
    Check patients chart for
           o The order (with or without oxygen?)
           o What is the current oxygen order?
           o Is the patient a COPDer?
    If a recent FIO2 change has occurred, you must wait 5-10 minutes before
       performing the puncture. With COPD patients wait 20-30 minutes!
    Is the patient receiving anti-coagulants or thrombolytics? Bleeding disorders?

Ways to Obtain Arterial Blood
   Radial Puncture
   Brachial Puncture
   Femoral Puncture
   Arterial Line Draws

Radial Site
   Near the surface
   Best chance of collateral circulation
   No large veins nearby
   Not too painful

Perform the Allen’s Test Prior to Radial Puncture
    Tests for adequate collateral circulation
    Results can assist in determining which radial artery to use - left versus right
    Have patient make a fist while you tightly squeeze both the radial and ulnar
      arteries; Let go of the ulnar and watch to see if hand is uniformly re-perfused
      (pinks up). If large areas remain pale - check the other hand.

Steps in Performing Arterial Puncture
    Choose site - Radial is first site of choice
    Don gloves & clean site using Betadine &/or alcohol pad
    Prepare syringe - position gauze for holding the site after puncture is completed

                                                                       ABG Lecture Notes

      Palpate site; make sure bevel of needle is pointing up & needle is parallel to
      Insert needle slowly at a 45 degree until blood enters the hub of the needle

Issues in Arterial Puncture
     Blood will enter syringe automatically because it is under pressure
     Arterial blood is generally brighter red than venous blood
     It is best to obtain a 1 - 2 ml of arterial blood. (Most blood gas machines can
        give accurate blood gas values with a sample of low as 0.2 ml of arterial blood.)
     Use supplied 1 inch 22 gauge needle for radial
     Use larger and longer for brachial (can continue to use 22 gauge for brachial)
     Definitely hand brachial needle ( 1 and half inch 20guage) to ER doctor for
        femoral draw
     Use smaller gauge needle for infants and smaller volume sample of blood

Helpful Hints for better technique
    Elevate the wrist for better success – Positioning one of the keys
    Quickly enter the skin and then slowly advance to „flash in the hub‟
    If advance too quickly, can flash and stop – Slowly withdraw – blood may restart
    If miss the artery on first angle of attack, then withdraw to the bevel and redirect
      medially or laterally
    Second key is keep palpating the pulse after first direction unsuccessful
    You will need to decide on which side you missed the artery on
    Some protocols dictate only two redirects

   Handling Syringe after Puncture
    Expel any air present using care not to splatter blood
    Insert exposed needle into “rubber block” or “wax cap”. DANGER! Do NOT re-
     cap needle! (In old days - Scoop with a one-hand-technique)
         o Prevents contact with oxygen in air and inadvertent needle sticks
    Mix blood (with heparin) by rolling syringe between fingers and turning it upside

Post-puncture Issues
    Upon needle removal, immediately hold site with pressure using gauze for 5
       minutes. Inspect site to assure bleeding has stopped. Band-aid is optional
    Ice sample unless it is to be run immediately
    Note patient‟s FIO2 and temperature
    If you have time, return after running sample and check for hematoma or
       occlusion of vessel

Complications of Arterial Puncture
     Arteriospasm                 Air or clotted blood emboli
     Hematoma at site             Hemorrhage
     Pain                         Trauma to artery or nerve

                                                                     ABG Lecture Notes

       Inadvertent needle stick      Loss of feeling below puncture site

Characteristics of Arterial Blood Gas Values
   A standard blood gas machine actually measures only the following values
          o PO2; PCO2; pH
   The following values are calculated by the machine;
          o SO2% (saturation); HCO3; Base Excess
   A special blood gas machine called a CO-oximeter actually measures oxygen
      saturation; carbon monoxide saturation and hemoglobin levels

Normal ABG Values
     pH 7.40 (7.35 – 7.45)
     PaCO2 40 (35 – 45) mmHg
     PaO2 80 – 100 mmHg

ABG Analysis Errors
   Air in sample – Very high PO2; changes PCO2 and pH
   Venous Blood – Higher than normal PCO2 and much too low PO2. Recognize
    with slow fill of dark blood with no pulsations
   Delay in running sample – Increased PCO2 and decreased PO2 and pH. Place on
    ice to slow metabolism and run within 30 minutes

Indwellling Arterial Catheters (Art line)
    Used to measure blood pressure and to obtain blood samples
    Peripheral catheters used to measure systolic blood pressure and to obtain arterial
      blood samples
    Central catheters used to measure heart pressures & to obtain “mixed venous

Example of Peripheral Catheter
Pressurized bag
Flush mechanism
Pressure transducer
Proximal and distal port
Arterial catheter

Hazards of Indwelling Catheters
   Infection
   Thrombus formation on catheter
   Damage to artery on insertion

The End!