Arterial Blood Gas Sampling (ABG)
Egan Chapter 18
I. Introduction –
A. What are “blood gases”?
a. They are gases (2) found in the blood
a) O2 for cell metabolism and
b) CO2 which is a by-product of that metabolism
B. Why “arterial” blood gas sampling and not venous blood
gas sampling?
a. All arteries carry blood from a single anatomical part of
the body, the cardiopulmonary system, this is oxygenated blood
that has not been used up by the body
a) veins carry blood from various different
anatomical body parts (i.e.: hand, arm, leg)
with varying metabolic rates. Veins pick up CO2 from
tissue and carry it back to the lung to be expelled from
the body.
C. What is purpose of ABG’s?
a. Diagnostic aid – b/c they reflect the efficiency of the CP system.
a) Assess gas exchange
b) Can diagnose respiratory failure (↑ CO2 with a ↓ pH)
b. Indicator of the effectiveness of therapy.
a) Does the oxygen gas flow have to be turned up, or can it
be turned down (PaO2)?
b) Is the patient ventilating effectively (PaCO2) and
needs the mandatory respiratory rate adjusted when on
mechanical ventilation
D. How is the blood obtained?
a. Arterial Puncture – from peripheral arteries (See Figure 18-2)
B. Indwelling Catheter (arterial, central line, or PA line)
C. Capillary Gas – finger or heel prick
II. Arterial Puncture
A. Blood is drawn through a needle puncture fro a peripheral artery.
a. radial artery is preferred due to collateral circulation
b. it is near the surface and easy to palpate
c. not near any large veins
d. relatively pain free (????)
1. other sites are riskier and only performed by personnel trained to draw fro the
other sites.
2. arterial draws on infants take additional training
3. READ AARC GUIDELINES P. 369
4. READ BOX 18-3 CLINICAL INDICATIONS FOR ABG
B. Preparation and Pre-analytical Considerations
A. Patient status and infection control –
a. Review the chart
a) Doctors Order
b) Primary Diagnosis
c) Respiratory Care Modalities?
1. O2 therapy – ck for steady state
2. ventilator settings – wait 20-30’ post
ventilator changes
d) Anticoagulant Therapy? - reduces the bloods
ability to clot and can ^ the risk of ^ bleeding
following puncture. Use increased compression
time.
1. Sodium Heparin (I.V.)
2. Warfarin Sodium compounds (Oral)
1) Coumadin
2) Prothomadin
3. Dipyridamole (Oral or I.V.)
4. excessive Aspirin ingestion
5. FOR USE in ABG SYRINE ONLY
1) Lithium Heparin or dry heparin
2) Sodium Heparin or wet heparin
e) Thrombolytics – dissolves clots and can ^ the risk
of bleeding following puncture. May need to use more compression
time.
1. Streptokinase
f) Bleeding Disorders?
1. Hemophilia – confirm with Dr. if ABG should be performed.
(Can it be drawn fro a line or a heel stick?)
2. low platelet count (lab rpt) - ^ compression
time
3. prolonged bleeding time – ^ compression
time (lab rpt)
1) PT – Prothrombin Time
Normal is 12 - 14 seconds
** Coumadin trx monitor (oral)
2) PTT - Partial Prothrombin Time
Normal 38 - 42 seconds
** heparin trx monitor (I.V.)
f) Infection Control – Trx all blood as infected.
Always wear gloves, do not contaminate inanimate
objects, wear mask and goggles, wash hands
and observe other standard precautions. Guard
against accidental needle sticks.
1. HIV
2. viral hepatitis
3. syphilis
(CONTINUED…..)
4. Jacob-Creutzfeldt disease
1) rare fatal encephalopathy
5. septicemia
B. “Steady State” – p. 372 - blood gases are dynamic and a period of
continuous therapy (FIO2 and CMV settings) must elapse so that
gases in the blood reach an equilibrium.
a. Normal patient with no chronic condition
a) 5 - 10 minutes
b. Pt with COPD
a) 20 - 30 minutes
C. Document current status - VERY IMPORTANT for data to
be useful
a. FIO2 (or device w flow) x # minutes
b. CMV settings x # minutes
c. puncture site (RB, LB, RR, LR)
d. time and date sample drawn
e. pt. position (V/Q assessment)
D. Materials – See kit contents
READ BOX 18-1 ON PAGE 368
E. Local Anesthetic – NOT OFTEN USED
sometimes used in pediatrics and small
children to allow pt. to calm down, equilibrate and thus get
an accurate sample
a. 0.5% lidocaine (1/4 cc) is injected under the skin and
around the puncture site via a 25G tuberculin syringe
III. Complications of Arterial Puncture (4 plus)–
A. Thrombosis - the formation of a clot within a vessel (thrombus)
a. blockage of a vessel can result in necrosis of distal tissue
a) loss of the thumb and index finger
perform the Allen Test (See handout)
b) loss of a foot or lower leg
B. Hematoma (blood tumor [swelling]) – results from the leakage of
blood into the surrounding tissue.
a. can be large and compress the artery
C. Arteriospasm – due to pain or anxiety
a. can cause blockage of the artery
b. time or a warm compress can relax the spasm
D. Other
a. extreme pain
b. infection
c. peripheral nerve damage
d. Vasovagal (vascular & vagal) response
1) precordial distress – discomfort over the heart &
2)
3)
4)
5)
stomach
anxiety
feeling of impending doom
nausea
respiratory difficulty
IV. Anatomical Landmarks for Puncture Site & Local Nerve
A. Radial Puncture Site
a. above the crease of the wrist: 1 - 2 cm or
0.4 - 0.8 inches (about a half of an inch)
b. extend wrist to about 30°
c. 450 angle or steeper - needle to surface of the skin.
d. depth is just below the surface of the skin to 0.5 inch (obesity)
e. Radial Nerve is lateral to the puncture site and generally.
behind the radial bone.
B. Brachial Puncture Site
a. above the crease of the elbow. Just above.
b. medial in relation to the anterior elbow (normal
anatomical position)
0
c. 60 degree angle or steeper - needle to the surface of the skin.
d. depth is just below the surface of the skin (cachexia) to 0.8 inch
(obesity)
e. Medial Nerve is lateral and VERY close to the puncture site
C. Femoral Puncture Site
a. below the fold of the groin. 0.25 to 0.5 inch (must miss the
inguinal ligament)
b. middle of the superior side of the femoral triangle
c. 900 angle - needle to the surface of the skin
d. depth is 0.5 (cachexia) to 2.0 inches or more (obesity)
e. Femoral Nerve is lateral and against the femoral artery
f. Femoral Vein is medial and against the femoral artery
V. Arterial Puncture Technique – READ BOX 18-2 ON PAGE 370
A. STUDY "ABG Sampling Laboratory Performance" for proper
techniques for three puncture sites
B. ALWAYS –
* Do modified Allens test (SEE Figure 18-3)
* Get comfortable (sit in a chair, lower bedrails) and do not rush.
* Hold syringe with dominant hand
* Place gauze near non dominant hand.
* Place needle stopper near dominant hand. Avoids accidents.
* NEVER LOOSEN GRIP on syringe (control your breathing and
avoid any movements once blood begins to flow) as the arterial
puncture will be lost and hematoma can result.
* As syringe fills with blood, place gauze over needle entry point
and wait for barrel to fill.
* Place FAIR pressure upon puncture site and quickly withdraw
needle.
* Place FIRM pressure (above systolic mm Hg) on puncture site.
* HOLD PRESSURE for a minimum of FIVE MINUTES (watch
time).
* Most hospital policies allow for only TWO advances of the needle
after which another RCP must be called
C. Allen Test – a test for collateral circulation around the Radial
puncture site (via the Ulnar and Palmer Arch arteries)
* There is NO collateral circulation around the Brachial or Femoral Artery
puncture sites.
VI. Procedure for Drawing Gases from Indwelling Catheters
READ BOX 18-4 ON PAGE 374
VII. PROCEDURE FOR CAP GAS SAMPLING
READ BOX 18-5 ON PAGE 376
AARC GUIDELINES P. 375
VIII. Advantages and Disadvantages for each Puncture Site
A. Radial Puncture Site
a. closest to the surface of the skin
b. little chance of nerve trauma
c. no esthetic objections (also spelled aesthetic taste or conscious of something)
d. easy to detect hematoma
e. easy to compress - one finger
f. smallest of 3 puncture sites
g. can test for collateral circulation
B. Brachial Puncture Site
a. not as deep as femoral site
b. much greater (than radial) chance of nerve trauma
c. no esthetic objections (vs. femoral site)
d. more difficult (than radial) to detect hematoma
e. harder than radial to compress - 2 or three fingers
f. larger than radial vessel
g. can NOT test for collateral circulation
C. Femoral Puncture Site
a. deepest of all three puncture sites
b. greatest chance of nerve trauma
c. esthetic objections do exist
d. can NOT detect hematoma
e. hardest to compress - hand over 4 fingers or palm
f. largest of all three vessels
g. can NOT test for collateral circulation
IX. Troubleshooting and Problem Solving
A. Getting a Good Sample
a. READ p. 371
b. Always withdraw needle before redirecting in case you have gone through the
artery.
c. If the needle is completely withdrawn you must open a new ABG kit.
d. If you must apply suction it is probably a venous sample unless it is smaller
than a 23 gauge needle. Due to the size of these small needles you may have a apply a very small
amount of pull on the syringe barrel.
B. Pre Analytical Errors Table 18-1 p. 371
a. Most Preanalytical errors can be avoided by:
*obtaining sample anaerobically (without air)
*it is properly anticoagulated
* any air bubbles are immediately expelled
* analyzed within 15 minutes
C. Read paragraph on blood cell metabolism on p. 371 (chill or not to chill)
X. PROCEDURE FOR ANALYZING A BLOOD GAS SAMPLE
READ BOX 18-6 ON PAGE 378
-END-