Arterial B lood Gas

 

Brian C. Kitamura, MD

John Sarka, MD

Key Points

• Arterial puncture for blood gas ana lysis is a common

procedure performed in the emergency department

(ED).

• Blood obtained from the radial artery can be used

to quickly provide qua ntitative information on the

INDICATIONS

The primary indication for obtaining an arterial blood

sample is for the assessment of the partial pressures of

oxygen and carbon dioxide and accurate assessment of

arterial pH. Secondarily, arterial blood can be analyzed

for carboxyhemoglobin, methemoglobin, and basic elec ­

trolytes depending on the capabilities of the laboratory.

Under certain circumstances it may be necessary to

obtain a sample of arterial blood for other routine laboratory tests, such as in patients who are obese or have a

history of intravenous drug abuse, in whom the radial

artery is palpable, but venous access is difficult or may be

delayed.

CONTRAINDICATIONS

There are few absolute contraindications for arterial puncture for blood gas analysis. Trauma, infection, or abnormalities of the overlying skin such as a burn are

contraindications because of concern for infection or further damage to the vascular structures. Patients with

known coagulopathies, taking anticoagulants, or who may

require thrombolytic agents should be approached with

caution because of the increased risk of bleeding, hema ­

toma formation, or rarely, compartment syndrome. Finally,

a known history of insufficient blood flow through the

4

patient's acid-base status and carboxyhemoglobin,

methemoglobin, and electrolyte levels.

• Arterial puncture is a useful way to obta in blood for

ana lysis when traditional phlebotomy is limited or difficult on the basis of patient characteristics.

palmar arch or previous surgery to the radial or ulnar

arteries should also be considered a contraindication. The

Allen test, described later, has been used as a way to determine adequacy of collateral circulation, however, its necessity has been questioned.

EQUIPMENT

Many commercially prepared kits for arterial puncture are

available, and if a commercial kit is not available, then

equipment is easily found in most EDs. The following

equipment is typically used to perform the procedure

(Figure 2-1).

� Required Equipment

Alcohol, chlorhexidine, or iodine prep pads

2- to 3-rnL heparinized syringe with a 23- to 25-gauge

needle

Syringe cap

Appropriate personal protective equipment

Gauze or other dressing

� Suggested Equipment

Anesthetic (eg, lidocaine)

Ultrasound or Doppler (if the artery is difficult to palpate)

ARTERIAL BLOOD GAS

Figure 2-1. Eq ui pment used for an arterial puncture.

Rolled towel or kidney basin (to stabilize and extend

the wrist)

Ice (for specimen process times > 10 minutes)

Local anesthesia is not strictly required for the procedure;

however, studies have shown that pain, as well as the

number of attempts required to obtain a sample, are

reduced when appropriate anesthesia is provided.

Traditionally, 1% lidocaine is used, avoiding epinephrine

because of concern for vasospasm. Recent studies have

suggested that jet-injected 2% lidocaine also provides

reasonable anesthesia.

PROCEDURE

Before selecting an appropriate wrist, the Allen test may

be used to assess collateral circulation. Manually occlude

the radial and ulnar arteries using your fingers. Ask the

patient to clench the fist to increase venous drainage

from the hand for approximately 30 seconds. Ask the

patient to open the hand, which should be noticeably

pale. At this point, release only the ulnar artery. Rapid

return of color signifies adequate collateral flow.

Although the necessity of the test for arterial puncture is

questioned, common sense dictates that if collateral flow

in one wrist is noticeably decreased compared with the

other, the wrist with better collateral flow should be

accessed. In the absence of good collateral flow in both

wrists, the necessity of the procedure should be weighed

against the remote risk of serious vascular injury and

distal extremity ischemia.

The radial artery is easily palpated in a majority of

patients. It runs down the radial aspect of the forearm,

generally located between the styloid process of the

radius and the flexor carpi radialis tendon at the

.A. Figure 2-2. Position of the forea rm for puncture of

the radial artery. A kidney basin or rol led towel may

be helpful to hold the patient's wrist in this position.

proximal crease of the wrist. The patient's wrist should

be extended to bring the artery to a more superficial

position. A kidney basin or rolled towel as well as tape

may be helpful to hold the patient's wrist in this posi ­

tion ( Figure 2-2). The skin overlying the artery should

be cleaned. The skin and immediate subcutaneous

tissue should then be appropriately anesthetized. The

authors recommend massaging the area or letting it rest

for 1-2 minutes for the anesthetic to take complete

effect. This time may be used to prepare your other

equipment.

After locating the impulse of the artery with the nondominate hand, take the syringe and needle in your dominate hand and slowly advance the needle toward the

impulse at a 30- to 45-degree angle proximally toward the

patient. If the impulse is difficult to detect, an ultrasound

or Doppler may be helpful to locate the artery (Figure 2 - 3) .

Some practitioners use a direct 90-degree angle to the skin,

but this is largely a matter of preference. When the artery

is accessed, blood will passively fill the syringe. It should

not be necessary to draw back on the syringe. Pulsatile or

bright red blood signals the correct vessel has been

accessed; however, this may not be apparent in the criti ­

cally ill patient. If blood is not obtained, withdraw the

needle to just below the skin and reattempt the procedure

after slight adjustments have been made. Do not move the

needle in an arc deep in the skin, as this risks damage to

the vascular structures.

After blood is collected, the needle should be removed

and disposed of appropriately. Remove air from the syringe

and place the syringe cap, ensuring that blood contacts the

cap. Maintain pressure over the arterial site for approxi ­

mately 5 minutes to prevent development of a hematoma,

and dress the wound appropriately.

CHAPTER 2

Radial vein

Tendon

Radial vein

8

Radial artery Tendon

Radial artery Tendon

A. Figure 2-3. The radial artery on ultrasonography. A. A high-frequency linear transducer is used to locate the vessel

based on anatomic landmarks. The ultrasound probe is oriented toward the patient's thumb. B. If there are other

vascu lar structures in the image, color Doppler can be used to locate the artery by identifyi ng pulsati le flow.

ARTERIAL BLOOD GAS

COMPLICATIONS

Complications from this procedure are rare but include

infection, bleeding, arterial laceration, pseudoaneurysm or

arteriovenous malformation, and nerve injury.

SUGGESTED READING

Dev SP, Hillmer MD, Ferri M. Arterial puncture for blood gas

analysis. N Engl J Med. 20 11; 364:e7.

Giner J, et al. Pain during arterial puncture. Chest. 1 996; 1 1 0:

1443-1445.

Hajiseyedjavady H, et al. Less painful arterial blood g as sampling

using jet injection of 2o/o lidocaine: a randomized controlled

clinical trial. Am ] Emerg Med. 20 1 2;30:1 1 00-1 104.

Haynes JM, Mitchell H. Ultrasound-guided arterial puncture.

Resp Care. 2010;55:1 754-1 756.

Shiver S, Blaivas M, Lyon M. A prospective comparison of

ultrasound-guided and blindly placed radial arterial cathe ­

ters. Acad Emerg Med. 2006;13:1 275-1279.