Arterial Puncture/Arterial Blood Gas Sampling

Indications for arterial puncture

any time an arterial blood sample is required

Indications for arterial blood gas sampling

- evaluation of dissolved gases in the arterial system, or pH

- diagnosis of acute dysfunction in CO2/O2 exchange or acid-base balance

- monitoring of response to therapy aimed at correcting these imbalances

- specific lab tests that are more accurate with arterial sample

- unable to get venous sample

How do the levels of dissolved gases differ between the arterial and venous systems?

constant level throughout the whole arterial system, unlike the venous system

What lab tests are more accurate with an arterial sample?

ammonia, CO, lactate

Why might one be unable to get a venous sample?

hypovolemia

Absolute contraindications to ABGs

- non-palpable arterial pulse

- NEGATIVE modified Allen's Test (for radial puncture)

- arterial disease (atherosclerosis, aneurysm, inflammation)

- overlying skin issue (i.e., cellulitis)

Relative contraindications to ABGs

- coagulopathy (anticoagulated or thrombocytopenia)

- renal disease with need for AV fistula in the future

What does the modified Allen's test check for?

collateral circulation (prior to using the radial artery)

How do you perform the modified Allen's test?

occlude both ulnar and radial arteries, have the patient make a tight fist, then open hand (hand should appear fully blanched), release pressure over the ulnar artery

What is a normal (positive) modified Allen's test?

hand regains its normal color within 15 seconds

What is an abnormal (negative) modified Allen's test?

hand does not regain its normal color within 15 seconds

What are the implications of a negative modified Allen's test?

- do NOT use this site

- risk for ischemia/gangrene of the hand

What are the potential complications of ABGs?

- hemorrhage or hematoma formation at the puncture site (MOST COMMON)

- thrombosis +/- embolus (distal occlusion can lead to ischemia/gangrene)

- transient arterial spasm (during or after procedure)

- nerve damage (direct or due to hematoma)

- infection

How can you avoid hemorrhage or hematoma formation at the puncture site?

apply constant pressure for 10 minutes and use the smallest needle

In which patient populations is the risk of hemorrhage or hematoma formation at the puncture site higher?

severe HTN or coagulopathy

What puncture sites are hemorrhage or hematoma formation most common in?

brachial & femoral sites

What puncture site is thrombosis +/- embolus most common in?

radial site

What should you do if a patient has signs of thrombosis +/- embolus and ischemia?

vascular surgery consult STAT

What should you do if a patient has transient arterial spasm?

monitor closely (if persistent, vascular surgery consult STAT)

What is the most frequently used/preferred site?

radial artery

Why is the radial artery the preferred site?

- close to the skin surface

- lowest complication rate

Where should you perform the puncture at the radial site?

point of maximal pulsation, 1-2 cm proximal to the wrist crease, with the wrist slightly hyperextended

What should you do before performing an arterial puncture at the radial site?

Modified Allen's Test

What angle do you use for an arterial puncture at the radial site?

40-60 degrees

When is the brachial artery used?

if radial artery is unavailable

Why does the brachial artery have a greater risk of complications?

Trama to the basilica vein or median nerve

What angle do you use for an arterial puncture at the brachial site?

40-60 degrees

Which puncture site is least preferred?

femoral artery, used when radial and brachial are not available (severe volume depletion/shock)

How should you position the patient to perform an arterial puncture in the femoral artery?

hip extended and externally rotated

What angle do you use for an arterial puncture at the femoral site?

60-90 degrees

What materials do you need to perform an arterial puncture?

- ABG syringe & needle

- iodine-containing skin preparation pads

- rubber stopper for syringe

- bag or cup of ice for transport

- small towel rolled up for positioning

- sterile gloves

- sterile gauze pad, tape

Most of the ABG syringes come pre-assembled and heparinized. If not, what do you need to collect?

- 3-5 mL syringe

- hepatin

- 21- to 25-gauge, 1/2 to 5/8 inch needle

How do you prepare yourself and the patient for the arterial puncture procedure?

- gather supplies (note date, time, and amount of oxygen on order or sticker)

- identify patient & ask about allergies

- wash hands, put on nonsterile gloves

- assess the potential site, perform Allen test

- position patient (use towel roll for radial site)

How do you prepare to perform the arterial puncture procedure?

- prepare supplies on a sterile area

- put on sterile gloves

- clean with iodine solution, +/- alcohol, let AIR DRY

- palpate artery with nondominant hand; find site of maximal pulsation (hold index and middle finger there, will puncture DISTALLY)

How do you perform the arterial puncture?

- hold syringe like a dart, insert needle through skin

- slowly, at a 40- 60-degree angle, advance the needle until blood is seen entering hub

- hold position and allow blood to fill into the syringe (3-5 mL)

- aspiration should NOT be needed

- remove needle in swift motion, cover puncture area with gauze and hold pressure for 10 MINUTES

What should you do with your sample after you obtain it?

- hold upright, allow for any air to rise, gently tap and expel from syringe

- put safety cover over needle, remove needle, and place stopper on syringe

- roll syringe between palms to distribute heparin

- place on ice and send/transport immediately to lab for most accurate results

How should you tend to your patient after the procedure?

- place pressure dressing on the patient with gauze and tape

- check on the patient in 5 and 15 minutes post-procedure

How long should you wait to take a sample after any adjustments in oxygen therapy?

15 minutes

What does a delay in analysis or improper chilling cause?

The blood dissociates from hemoglobin, affecting O2 levels

What might air in the syringe cause?

air in syringe may dissolve and decrease PCO2 & increase PO2

What might severe leukocytosis or thrombocytosis cause?

falsely low O2 and falsely high CO2 readings (delay in chilling or analysis increases this risk

What might excess heparin in the syringe cause?

decrease in pH

Follow-up care after arterial puncture

- monitor to ensure hemostasis is achieved

- educate patient; small amount of tenderness and ecchymosis can be expected

- avoid rigorous activity x24 hours

What are the things to watch for after arterial puncture?

increased pain, redness, coolness/paleness of hand/extremity