I.  Why do ABGs?
     A.  Precise measurement of acid – base balance of the blood          
     B.  Check lungs’ ability to oxygenate blood and to remove CO2
     C.  Assess respiratory function
           1.  O2 and CO2 levels determined primarily by the lungs

II.  PUNCTURE PROCEDURE
     A. Equipment
          1. HISTORICALLY, RCPs had to gather all the materials necessary to perform an               arterial puncture
              a. 5 10ml glass syringe
              b. 20 22 gauge needles (1 1/2 inch)
              c. Sodium Heparin 1% solution
              d. Cork or syringe cap
              e. Topper pad (sterile gauze)
              f. Alcohol swabs
              g. Ice

   2. TODAY, RCPs simply gather a prepared “kit” off the shelf with everything needed:
               a. 3 cc vented, plastic syringe
                     i.  Improvements in modern plastics overcame problem where gases in blood
                         sample would diffuse through the plastic, compromising the integrity of the
                         ABG results
                    ii.  With today’s plastics, diffusion is negligible
                    iii.  Syringe is pre-heparinized, usually with dry lithium heparin or with a small                          amount of liquid heparin that must be evacuated prior to performing                                    puncture 
               b. 23 gauge 1” needle
               c. 22 gauge 1.5” needle
               d. Vent cap (for evacuation of air bubble)
               e. Usually, some sort of needle guard to prevent accidental needle sticks         
               f. Iodine pad
               g. Alcohol pad
               h. 1”x 1” gauze pad
               i.  plastic bag for icing sample
               j.  Band-aid
               k. Sample label

      B. Prepare Syringe
          1. Assemble needle to syringe
              a. keep needle sterile
              b. eject excess heparin and air bubbles, if using syringe with liquid heparin
              c. pull back syringe plunger to at least 1 cc to give room for blood to fill syringe
                  when puncture is made
              d. NEVER recap needle

     C. Check orders
          1. Check for indications and contraindications
               a. Indications can be wide and varied
               b. No absolute contraindications, mostly just extra precautions and hazards
                     i.  Dialysis shunt – choose another site
                    ii.  Mastectomy – use opposite side
                   iii.  Pt on anticoagulant therapy – MAY have to hold pressure on puncture site
                         longer than normal – includes aspirin therapy
                        
     D. Introduce yourself and explain what is ordered
          1. Patient cooperation needed to help simplify and minimize pain                 
              a. if patient refuses, notify physician

     E. Make positive patient I.D.
          1. Ask patient their name
          2. Check patient I.D. wristband

     F. Select site
          1. Palpate right and left radials
          2. Pick strongest pulse
            a. radials should be used because of collateral circulation                   
                   i. if radial pulse weak on right, move to left
                  ii. if pulse on left weak, then try brachial
              b. brachial used as alternative site
              c. femoral is the last choice in normal situations
                   i. almost every related complication has been with femoral site
                  ii. usually first choice puncture site in code
         3. When using radials, perform Allen's Test for collateral circulation                       
              a. in conscious, cooperative patient:
                 (1) compress ulnar and radial arteries at wrist to obliterate pulse
                 (2) have patient clench and release pulse until hand blanches                      
                 (3) with radial still compressed, release pressure on ulnar artery
                 (4) watch for pinkness to return   (see diagram at end of lesson) –
                       should “pink up” within 10 – 15 seconds
              b. in unconscious:
                 (1) compress ulnar and radials
                 (2) elevate hand above head, squeeze hard
                 (3) release ulnar and lower hand below heart
                 (4) if pinkness returns, collateral circulations adequate – should “pink 
                      up” within 10 – 15 seconds                        
           4. Palpate chosen radial artery noting site with the maximal pulse                     

G. Puncture
          1. Stabilize the wrist in the position that gives maximal pulse               
          2. Rub puncture site with alcohol prep pad
          3. Remove cap from needle
          4. Hold needle at a 30 45 degree angle for radial puncture
                a. Brachial puncture: 45 – 60 degree angle
                b. Femoral puncture:  90 degree angle
                c. Easy to remember:  30 – 60 – 90
          5. Pierce skin at puncture site
                a. keep needle angle constant
                b. Bevel of needle up, or into the arterial flow
                     i.  Bevel faces the heart
                c. slowly advance in one plane
                d. when the artery is punctured, blood will enter the syringe – “flash”                  
                e. slowly allow blood to fill syringe
                   i. if no blood appears, remove, change needles, and start again
           6.  Upon removal of the needle, hold pressure on the puncture site for at least 5 mins
                a. Pressure may need to be held longer if the patient's on an anticoagulant therapy
           7. Check for:
                a. bleeding
                b. movement of fingers and tingling
                c. pulse distal to puncture
                      (1)  if pulse not palpable, notify physician STAT                                                  
H. Post puncture procedure
          1. Remove any air bubbles from sample and cap syringe                   
          2. Roll syringe to mix heparin with sample
          3. Immerse in ice
          4. On lab slip indicate:
              a.  FIO2
              b. patient temperature
              c. ventilator parameters
          5. Deliver to lab

III. COMPLICATIONS OF ABG's
     A. Hematoma
     B. Clotting of artery
          1.  Lack of perfusion
                a.  necrosis of tissue
     C. Laceration of artery
          1.  Bleeding

IV. TECHNICAL CAUSES OF ABNORMAL RESULTS
     A. Room air mixed with sample
          1. PaO2 will equilibrate to above 160
                  a.  Dalton’s Law – Barometric pressure x FiO2
          2. CO2 will be lower due to equilibration
                  a.  By Dalton’s Law, the partial pressure of CO2 in room air is approx. 2mmHg
          3. Diffusion is responsible – diffuse from area of high concentration to low
              concentration    

     B. Delay in running sample
          1. O2 consumption will continue as will CO2 production – pH does what CO2 tells
               it to do                      
          2. Iced, sample will last an hour without a change in the results               
                  a.  un-iced, ABG's can be significantly changed after 10 minutes                   
                
     C. Venous sample drawn
          1. Usually this in shocky patient that you expect low pressures and dark blood
          2. Should doubt when PO2 is significantly lower than expected               
              a. draw venous blood to check comparison or
              b. redraw sample

    D. Capillary samples
          1.  From infants warmed heel
          2.  CAUTION – pay attention to puncture site and sample type
          3.  ONLY diagnostic values are pH and PaCO2
          4.  PaO2 value is NOT diagnostic

 E. Heparin
          1. Sodium Heparin 1% solution should be used
              a.  ammonium heparin will alter pH
              b.  dry lithium heparin is OK
          2. All unnecessary heparin should be ejected from syringe, excess can effect results  

     F. Patient pain
         1. Can cause hyperventilation or breath holding
         2. An anesthetic may be injected prior to stick for pain, although this hurts
             probably as much                    
             a.  Usually 2% lidocaine
             b.  CAUTION – some people allergic to “caines”
                 
     G. Machine errors
          1. Improper calibration
          2. Air bubbles in electrodes
          3. Torn membranes

V.  Quality Control/Performance Improvement
      A.  Quality control levels (high, normal, low) are run every 8 hours to check
            performance of machine
            1. Levey-Jennings chart – assess whether control value falls within acceptable limits
                a.  trend – 6 or more results in an increasing or decreasing pattern
                b.  shift – 6 or more results falling on the same side of the mean
    
      B. The Clinical Laboratory Improvement Act of  1988 (CLIA) requires
           proficiency testing be done through the year

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