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Arterial Blood Gas
 
 

Overview

  • The arterial blood gas is useful in acutely unwell patients for assessing acid-base balance and oxygen status. This section outlines the approach for collecting an ABG.
  • Indications for arterial blood gas collection include to assess respiratory and acid base status, as well as for detection of carboxyhaemoglobin and methaemglobin.
  • Contraindications include patients with coagulopathy, as they are likely to bleed significantly; and inadequate collateral circulation.

Equipment and Preparation

    • The following equipment is required for collection of an arterial blood gas:
    • Positioning the Patient

      Raise the bed to waist level to allow for comfortable collection; the position of the patient depends on the artery to be used. 
    • Radial artery - ask the patient to place their arm outward with palm up, wrist extended slightly
    • Brachial- ask the patient to place their arm outward as far as possible with the antecubital fossa easily accessible
    • Femoral - ensure privacy, then expose the femoral triangle

Identifying an Artery

  • When looking for an artery, place the index and middle fingers over the desired artery and feel for the area of maximal impulse.
    • Potential sites for arterial blood gas collection are:
    • Radial artery - laterally on the anterior aspect of the forearmThe most commonly used site
    • Brachial artery - medially within the antecubital fossa
    • Femoral artery - centrally within the femoral triangle, between the inguinal ligament, adductor longus and sartorius
    • Tips for Choosing an Artery

    • Do

    • Try to use the radial artery if possible
    • Perform Allen’s test prior to inserting the needle
    • Don't

    • Absolutely do not use the same arm as an AV fistula
    • Don’t use the radial artery on a limb with a fractured wrist
    • Avoid areas with inadequate collateral circulation (e.g. peripheral vascular disease)
    • Avoid inserting a needle through cellulitis, burns or oedema
    • Allen's Test

    • This is a clinical test used to determine the patency of the radial and ulnar arteries, and is used as a predictor of distal ischaemia risk post radial arterial cannulation or catheterisation.
  • Ask the patient to clench their fist, and apply pressure to both the radial and ulnar arteries. Ask the patient to relax their hand, looking for blanching - if the hand does not blanch then both vessels are not occluded. Release pressure on the ulnar nerve, and look for flushing as the hand is reperfused.
  • If the hand does not flush in 10-15 seconds then the ulnar circulation is inadequate - this is a contraindication to radial puncture on this limb.

Specimen Collection

    • Introduction

    • Preparation

    • Collection

    • Finishing Up

Troubleshooting

  • Likely CauseWhat to Do
    No flashbackNeedle not in the arteryInsert the needle slightly deeper, or withdraw slightly and reattempt at a slightly different angle
    Needle is not self-fillingMay be a venous sampleWithdraw and try again
    HaematomaNeedle not in the arteryWithdraw and put pressure on the area for at least five minutes

Complications

    • The potential complications of arterial blood gas collection include:
    • Haemorrhage / haematoma formation
    • Distal ischaemia
    • Nerve damage
    • Haemorrhage / Haematoma formation

    • Due to the high pressure within arteries, there is a high risk of bleeding or bruising around the site. 
  • In order to prevent bleeding, place pressure on the insertion site for 3-5 minutes once the needle is removed. Avoid performing an ABG on a patient with a coagulopathy where possible, or consider reversing anticoagulation / withholding it and waiting. 
  • If bleeding occurs, compress the site for 3-5 minutes the place a compression bandage over the area. Observe the site, and consider reversing anticoagulation if bleeding is major.
    • Distal Ischaemia

    • Ischaemia of a distal limb may occur following arterial blood gas sampling. This may present with pain, pallor, pulselessness, paralysis, paraesthesia or poikilothermia.
  • To prevent distal ischaemia, avoid performing an ABG in a limb with peripheral vascular disease and perform Allen's test before inserting the needle.
    • Nerve Damage

    • Very uncommonly, patients may develop numbness or paraesthesia as a result of nerve damage from an ABG. To prevent this, ensure that the pulse is easily palpable before inserting the needle, and avoid advancing the needle multiple times.
 
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