Healthcare and Medicine Reference
Monitoring: Arterial Line
Mersey Rotation, Liverpool, UK
status should be considered as haemorrhage may be diffi cult to
control and a haematoma can also lead to distal ischaemia. Arterial
cannulation should be avoided:
in limbs where the collateral circulation has been demonstrated
By the end of this chapter you should be able to:
understand the indications and contraindications for insertion of
an arterial line
understand the anatomy of the relevant sites of insertion
to be poor
where there is active infection or ischaemia
describe the two commonly used types of arterial cannulae
where there is a surgical shunt, such as for renal dialysis.
describe the procedure of inserting an arterial line
interpret an arterial waveform.
Anatomy and sites
A number of superfi cial arteries are suitable for catheterisation
with an arterial cannula. The most commonly used site is the
radial artery at the wrist, ideally of the non-dominant hand.
Other sites include brachial, axillary, ulnar, dorsalis pedis and
femoral arteries. The radial artery is preferred due to its ease of
location in its superfi cial position at the distal end of the radius
between the tendons of the brachioradialis and fl exor carpi
radialis. The cannula site can also be readily inspected. Importantly
the tissues supplied by the radial artery have a collateral circu-
lation, via the ulnar artery, which helps to minimise the risk of
ischaemic damage should the radial artery thrombose following
The collateral supply of the ulnar artery can be demonstrated
using the modifi ed Allen test (see Box 20.1 and Figure 20.1) or
by using a Doppler probe, before cannulation of the radial artery.
However, the Allen test has been demonstrated to have a poor
sensitivity and specifi city for ischaemic complications.
Arterial lines are routinely used in the operating theatre and
intensive care settings in the monitoring of critically ill patients.
They allow beat-to-beat display of heart rate and blood pressure, as
well as sampling of arterial blood for analysis without the need for
repeated arterial puncture.
Major surgical cases.
Moderate or severe ischaemic heart disease.
Acid-base disturbances (particularly emergencies).
Likely need for inotropic (or vasopressor) support.
Failure of non-invasive blood pressure measurement.
Inotropic (or vasopressor) support.
The monitoring system consists of the arterial cannula, connected
to a pressurised column of fl uid with an inbuilt pressure transducer,
and a monitor for display of the waveform.
Frequent arterial blood gas sampling.
Monitoring of waveform for cardiac output and end-diastolic
Box 20.1 Modifi ed Allen's test
The risks associated with arterial cannulation must be balanced
with the benefi ts that can be gained. The patient's coagulation
Occlude the patient's radial and ulnar arteries simultaneously 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.