Healthcare and Medicine Reference
In-Depth Information
CHAPTER 6
Sampling: Arterial Blood Gases
Kathryn Laver 1 and Julian Hull 2
1 Birmingham City Hospital, Birmingham, UK
2 Heart of England NHS Foundation Trust, Good Hope Hospital, Birmingham, UK
Box 6.1 Modifi ed Allen's test
OVERVIEW
By the end of this chapter you should be able to:
understand the indications and contraindications for arterial
Occlude the patient's radial and ulnar arteries by direct pressure
whilst exanguinating the hand through elevation and by asking the
patient to make a fi st. In an unconscious patient the hand can be
squeezed so it blanches. With the hand open, release the pressure
on the ulnar artery and observe the return in colour, which should
occur within 6 seconds.
blood gas sampling
identify the sites used for arterial blood gas sampling
describe different types of arterial blood gas sampling device
describe the procedure of performing an arterial blood gas
interpret the results of an arterial blood gas.
To guide ongoing therapy
Assessment (e.g. of ventilation) in higher dependency environ-
ments and critical care.
Assessment for home oxygen therapy in those with chronic respi-
Introduction
Arterial blood gas (ABG) samples can be used in the assessment
of critically ill or deteriorating patients, and to guide therapy in
specifi c conditions.
ratory and cardiac conditions.
All ABGs should be interpreted in conjunction with careful clini-
cal assessment of the patient's condition.
Absolute contraindications
Puncture through skin with cellulitis.
Indications
All though not an exhaustive list, ABGs are useful in the following
situations.
Puncture of a vessel where there is a graft (e.g. femoral graft).
Presence of an arteriovenous fi stula in the forearm (for radial or
brachial punctures).
Underlying skeletal trauma at wrist or elbow (risk of introducing
Respiratory distress (e.g. asthma, chronic obstructive
pulmonary disease)
Is the patient hypoxic (cyanosis, confusion, hallucinations)?
infection).
A positive Allen test (see Box 6.1 and Figure 6.1) should prompt
Is the patient retaining carbon dioxide (drowsy, fl ap, headache,
the physician to use an alternative site.
bounding pulse)?
Differentiating between type I and type II respiratory failure.
Relative contraindications
Coagulation defects (e.g. liver failure, on warfarin, post
Critically unwell patient (e.g. sepsis, gastrointestinal
bleed, diabetic ketoacidosis, arrhythmias, impaired
consciousness etc.)
Identify and quantify acid-base disturbance.
thrombolysis).
Chronic renal failure. Arterial puncture can hinder the formation
of arteriovenous fi stulae in the future and therefore if possible the
arms should be avoided.
Arterial samples can be taken from the radial, brachial or femo-
ral arteries. Each site has its own advantages and disadvantages
(Table 6.1).
Quick assessment of electrolytes and haemoglobin.
Some machines will measure lactate (a byproduct of anaerobic
respiration).
Global assessment of adequacy of fl uid resuscitation (pH,
lactate).
Anatomy: radial, brachial and femoral
arteries
The radial artery (Figure 6.2) is relatively superfi cial, lying at
0.5-1 cm beneath the skin.
 
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