5. • An arterial vessel is cannulated under
aseptic conditions with a 20 guage
cannula using seldinger (guideline)
technique.
• The arterial catheter is connected to a
1000ml flush bag of NaCl and
pressurised to 300mmHg (also required
for KVO running @ 3ml/hr).
• At the mid point in the pressurised
connecting tube there is a transducer
point and this is connected directly to
the patients monitoring device.
6. • The pressure transducer converts the patients
arterial blood pressure oscillations into an electrical
waveform that is readable on the monitoring device.
• The resulting arterial pressure wave differs
depending on the site of vascular cannulation i.e.
radial, femoral, etc. this is due to several factors
including
– Fluid status
– Vessel pathology
– Cannulation quality (including thrombus, phlebitis
and/ or vasospasm)
– Reflection waves throughout the arterial tree
(more evident in the more distal catheters).
7. • The following slide shows the effects of wave
reflection/deflection on the systolic and
diastolic arterial blood pressure.
• Note that the mean arterial blood pressure is
fairly constant.
• Wave reflection/deflection occurs as the
blood passes through the arterial tree under
pressure.
• If all of the vessels were straight, and had no
branches, then the flow of blood would be
direct and the pressure at each end would be
the same.
8. • However, as arteries are under constant
pressure adjustment (musclular wall
adjustment) and as they have bends and many
branches, the flow of blood becomes less
laminar – it becomes turbulent
This turbulance that causes
• the systolic pressure to rise
and the diastolic pressure
to fall slightly in the more
distal arteries.
9. Arterial trace at different sites
BLOOD turbulance that
causes
the systolic pressure to
rise and the diastolic
pressure to fall slightly in
the more distal arteries.
10. Before we analyse the arterial
waveform,
Always make sure that the gain on
the monitor is correctly set!!!!
11. Is it accurate?
• Failure to notice this may lead to
unnecessary, or missed treatments
for our patients.
• There are 2 main abnormal tracing
problems that can occur once the
monitor gain is set correctly.
13. Dampened: wide, slurred, flattened tracing
• Dampening occurs due to:
– air bubles
– overly compliant, distensible tubing
– catheter kinks
– clots
– injection ports
– low flush bag pressure or no fluid in the flush bag
• This type of trace UNDERESTIMATES blood
pressure.
15. Resonant: ‘spiked’ tracing
• Resonance occurs due to:
– long tubing
– overly stiff, non-compliant tubing
– increased vascular resistance
– reverberations in tubing causing harmonics that distort the
trace (i.e. high systolic and low diastolic)
– non-fully opened stopcock valve
• This type of trace OVERESTIMATES blood pressure.
17. End diastole - systole
• Anacrotic limb reaches from point (a) to point
(b)
point (y) is
known as the
anacrotic
notch
y
a
b
18. Anacrotic limb
• The anacrotic limb represents the
first phase of the arterial pulse cycle
• It occurs as the ventricles eject the
blood into the arterial tree and gives
a visual record of the arterial
pressure rising to that of the end
systole.
19. Anacrotic limb
• The steepness of the ascending
phase can be affected by heart rate,
increased systemic vascular
resistance, and through the use of
vasopressors such as noradrenaline
(more steep incline)
• And vasodilators such as GTN (less
steep incline).
20. Anacrotic limb
• Myocardial contractility also effects the
steepness of the anacrotic limb – during
impaired contractility (post MI for
example) the up-sweep, or the rate of
pressure increase can be prolonged.
• As the pressure reaches maximum, and
the wave makes sharp turn to level off,
this is called the anacrotic notch
21. • The black line represents the rate of
pressure increase
22. Anacrotic notch abnormality
• In some patients, a second systolic notch can
be seen (as point (a) in the next slide).
• It is detected when aortic insufficiency exists
in association with aortic stenosis, and may be
found in hypertrophic obstructive
cardiomyopathy.
• It may OVERESTIMATE systolic blood
pressure slightly.
24. End systole – diastole
• Dicrotic limb reaches from point
(b) to point (c)
b
c
25. Dicrotic limb
• Descending limb of the arterial pressure trace
as the pressure falls to that of the end
diastolic pressure
• Dicrotic means ‘twice beating’ – meaning that
this phase of the arterial pressure pulse
should have a second, smaller wave, known as
the dicrotic notch
27. Dicrotic notch
• Can occur at any point that there is a
fluctuation in pressure during the
descending arterial limb.
• The most common time for this to occur
is when the aortic and pulmonary valves
snap shut causing pressure
reverberations through the arterial
30. Dicrotic notch – continued..
• Flat or non-existent notch can mean that the
patient is dehydrated (line trace will also
‘swing’)
• Low notch can also mean high pulse pressure
(due to the low diastole in septic shock for
example)
• Flattened notch can be present in
cardiopulmonary valve insufficiency.
31. Dicrotic limb: 2
• The rate of dicrotic ‘fall-off’, or the rate at
which the arterial line trace falls from end-
systole to early-diastole changes in relation to
systemic vascular resistance.
• In patients with a severely reduced arteriolar
resistance, fall-off time is rapid. This occurs as
soon as end-systole finishes due to the greatly
reduced pressure in the arterial tree
(representing reduced afterload). The arterial
waveform in this clinical state looks thin and
pointed (don’t confuse this with resonance).
32. Dicrotic limb: 2
• In patients with increased vascular
resistance, such as main vessel stenosis
for example, the dicrotic fall-off time is
greatly increased.
• This occurs due to the length of time it
takes to return to end-diastolic pressure.
The arterial waveform in this clinical state
may be normal, or quite fat!
34. Stroke volume variance
• The systolic blood pressure reading can vary
from time to time – this is known as ‘arterial
line swing’ and occurs more in dehydrated
patients.
• This phenomenon occurs during respiration –
both spontaneous and mechanically
ventilated, although is more pronounced
during volume controlled mechanical
ventilation (SIMV).
35. Stroke volume variance
• During spontaneous respiration, at the
beginning of inspiration, the intrarthoracic
pressure briefly drops before building up and
becoming much higher than before due to the
expansion of the lungs.
• This increased pressure causes a reduction in
transmural blood flow back to the heart by
compressing the intrarthoracic veins (reduced
pre-load) causing stroke volume to drop.
36. Stroke volume variance
• As expiration begins, after a brief period of
further increased pressure as the muscles
contract, the pressure drops significantly as
the air leaves the lungs greatly increasing
transmural blood flow (increased pre-load)
causing stroke volume to rise.
• This can also be noted in the systolic blood
pressure figure as it fluctuates with
respiration.
37. Stroke volume variance
• During positive pressure ventilation there is
always a reduced transmural blood flow – this
is why blood pressure is always lower during
mechanical ventilation.
• Stroke volume variance is much more
pronounced in relation to higher VTi and peak
airways pressures.
• Of the next 2 slides, slide 1 represents
changes during spontaneous respiration and
slide 2 during mechanical ventilation.
39. Ventilated arterial ‘swing’
• (A) = the expiratory phase – or the period
where the only pressure in the chest is due to
PEEP.
• (B) = the inspiratory phase, ASB + PEEP
40. Pulse contour analysis: swing
• The use of pulse contour analysis is available
in the ICU and this can help in the selection of
vasoactive drugs and/ or fluids.
• LiDCO also analyses arterial trace stroke
volume variance and translates this into a
visual percentage to determine if a patient will
be pre-load responsive or not.
• LiDCO IS USELESS IF THE ARTERIAL LINE TRACE
IS INACCURATE – please remember this.
