Non Invasive and Invasive Blood pressure monitoring RRT

Non Invasive & Invasive
Blood Pressure Monitoring
Presenter- Dr Ranjith R T

Introduction
Blood pressure monitoring is the most commonly
used method of assessing the cardiovascular
system.
The magnitude of BP is directly related to the
Cardiac Output and the Systemic vascular
resistance.
BP = (HR x TPR) x SV
It can be used for diagnosis and treatment of the
patient. This can be achieved by non-invasive or
invasive methods, continuously or intermittently
depending on the requirements of the patient.

Mean Arterial Pressure
Time-weighted average of arterial
pressures during a pulse cycle.
MAP = DBP + (SBP - DBP)/3
or
MAP = [SBP + (DBP x 2)] / 3.
or
MAP = CO x TPR

Non Invasive intermittent BP monitoring
 INDICATIONS and CONTRAINDICATIONS
Requirements:
Three key components:
 1. an inflatable cuff for occluding the arterial supply to the
distal limb;
 2. a method for determining the point of systolic and diastolic
blood pressures;
 3. a method for measuring pressure.

PALPATION
 Inflate the cuff rapidly to 70 mmHg, and increase by 10 mm Hg
increments while palpating the radial pulse. Note the level of pressure
at which the pulse disappears and subsequently reappears during
deflation; will be systolic blood pressure.
 While being easy to perform, this technique has been shown to
underestimate a systolic pressure of 120 mm Hg by 25%.
Diastolic and mean pressures cannot be determined.

DOPPLER
Systolic pressure can also be determined using the Doppler principle.
Blood flow towards or away from the Doppler probe, reflects sound waves causing a change in frequency
that is detected using the same Doppler probe.
As Doppler is so sensitive, this technique is usually reserved for the measurement of low pressures, e.g.
vascular insufficiency.

AUSCULTATION
The cuff should be 20% wider than the diameter of the part of the
limb being used (or cover two-third its length).

OSCILLOMETRY
 The Von Recklinghausen Oscillotonometer uses two cuffs and two bellows
connected to a measurement gauge.
 The two cuffs overlap, one occludes the artery (occluding cuff) and the other
senses the arterial signal (sensing cuff). Pressure from both cuffs is transmitted
to the two bellows which is in turn displayed via a single gauge, alternating
between the two bellows using a lever.
 With the lever in the sensing position, the occlusive cuff is inflated above systolic
pressure. The cuff is then deflated using a bleed valve until the needle suddenly
starts to move vigorously. The lever is then switched to measure the occluding
cuff pressure. This is the systolic blood pressure. With the lever back in the
‘sensing cuff’ position, the occluding cuff is deflated further. The needle will jump
further with maximal oscillations occurring at mean arterial pressure (MAP), as
measured by moving the lever once more.
Diastolic pressure is the point at which these oscillations reduce.

PLETHYSMOGRAPHY
 Blood pressure cuffs or other sensors are placed at different
locations on the arms, legs, fingers, and/or toes. The sensors
record the pulse waves that occur with each heart beat. (This
data is translated into a graphic recording for later review.)
 In some cases, the test also records changes in pulsation
under various conditions, such as exposure to cold or
temporary stoppage of blood flow to the limb (which is done by
inflating a blood pressure cuff in the upper region of the limb
until the blood vessels collapse).
 The test usually takes less than 20 to 30 minutes.

TONOMETRY
In order to obtain a stable bp
signal, the tonometric sensor
must be protected against
movement and other
mechanical artifacts.
The artery wall does not
influence the transmission of
arterial pressure to a sensor
applied to the skin. They have
also been used to determine
arterial elasticity and pulse
wave velocity.
Under favorable conditions, the accuracy of tonometric measurements can be
described by standard deviations of 5mmHg.∼

Indications
 Major surgical procedures involving large fluid shifts or blood
loss
 Surgery requiring cardiopulmonary bypass
 Surgery of the aorta
 Patients with pulmonary disease requiring frequent arterial
blood gases
 Patients with recent myocardial infarctions, unstable angina, or
severe coronary artery disease
 Patients with decreased left ventricular function (congestive
heart failure) or significant valvular heart disease
 Patients in hypovolemic, cardiogenic, or septic shock or with
multiple organ failure

Indications
 Procedures involving the use of deliberate hypotension or
deliberate hypothermia
 Massive trauma cases
 Patients with right-sided heart failure, chronic obstructive
pulmonary disease, pulmonary hypertension, or pulmonary
embolism
 Patients requiring inotropes or intra-aortic balloon
counterpulsation
 Patients with electrolyte or metabolic disturbances requiring
frequent blood samples
 Inability to measure BP noninvasively (e.g., morbid obesity)

Arterial BP Monitoring
 In short. INDICATIONS:INDICATIONS:
-Anticipated Hypotension
-Wide Blood Pressure Deviations
-End Organ Damage
-Need for multiple ABG
measurements

Sites
Factors that influence the site of arterial cannulation
 Location of surgery,
 The possible compromise of arterial flow due to patient
positioning or surgical manipulations, and
 Any history of ischemia of or prior surgery on the limb to be
cannulated.
 The presence of a proximal arterial cutdown. The proximal
cutdown may cause damped waveforms or falsely low BP
readings due to stenosis or vascular thrombosis.

ADVANTAGES DISADVANTAGES
Radial Artery
Superficial location.
Easy to identify and
cannulate.
Collateral circulation.
CC can be assessed.
Accessible during major
surgeries.
Patient can be mobilized.
Small size artery.
Higher rate of catheter
malfunction.
Not reliable in
vasoconstriction.
Considerable augmentation
of SBP.
Overshoot artifact.

Allen’s test
 5% Patients have incomplete palmar arches. So predispose
them to inadequate blood flow if either artery flow disrupted.
 normal collateral circulation- color returns to the hand in
about 5 seconds.
 >15 seconds to return to its normal color, cannulation is
controversial.
 Variations on allen's test include using a doppler probe or
pulse oximeter to document collateral flow

Other Sites
 The brachial artery lies in close proximity to the median nerve.
Its pressure tracings resemble those in the femoral artery, and
were found to more accurately reflect central aortic pressures
(Kinking problem)
 The femoral artery may be cannulated for monitoring purposes
but is usually reserved for situations in which other sites are
unable to be cannulated or it is specifically indicated (e.g.,
descending thoracic aortic aneurysm surgery for distal
pressure monitoring).
 The femoral artery for hemodynamic monitoring purposes was
as safe as radial artery cannulation
(Atheroma, Pseuaneurysm, Infections, Thrombosis, Rarely-
Aseptic necrosis of head of femur in children)

Other Sites
 The Axillary artery
 Advantages include patient comfort, mobility, and access to a central
arterial pressure waveform.
 Complications appear to be infrequent and similar in incidence to
radial and femoral artery catheterization
 If the axillary approach is chosen, the left side is preferred over the
right because the axillary catheter tip will lie distal to the aortic arch
and great vessels.
 Risk of cerebral embolization is increased whenever more centrally
located arterial catheters are used.
 Dorsalis pedis, Posterior Tibial

Insertion Techniques
 Direct cannulation
 Transfixation
 Seldinger technique
 Doppler assisted technique
 Two dimentional USG assisted method
 Surgical cutdown

Components of Arterial waveform
Notch- Aortic valve closure
as a result of backflow
from already existing
pressure in aorta.
Sometimes a second notch is seen in waveform. Due to rebound of
wave from periphery- Incisure Notch

Arterial Line Waveform Alterations
Pulsus alternans- Alteration of weak
and strong beats with no change in
rate- Left Ventricular dysfunction
Pulsus paradoxus- Large
decrease in SBP and pulse
waveform during inspiration.
– Tamponade, severe lung
disease, advanced CHF

Aortic Stenosis- Dicrotic notch not
well defined from abnormal closure
of leaflet. Narrow pulse pressure
Aortic Insufficiency- Wide pulse
pressure. High blood volume. High
peak systolic pressure during
further systoles.

Atrial Fibrillation- Irregular. Shorter
diastolic filling time. Decreasing
systolic peak amplitude during
premature ventricular complexes.

Technical Aspects
 The SBP, DBP and MAP are all displayed. But it is the MAP that
tends to guide practice. Provides overall indication of peripheral
tissue perfusion. In critically ill patients, MAP is maintained >70
mm Hg in order to maintain adequate renal and cerebral
perfusion.
 Usefulness of information depends on accuracy.
Accuracy depends on responsibility to maintain that accuracy.
Responsibilities:
Patency, Levelling, Zeroing, Square wave testing

Patency
 Soft Tubing to bag of NaCl containing 500mL flush solution placed in
pressure bag and inflated to 300 mm Hg. Why 300 mm Hg?
Leveling
 Minimises effect of hydrostatic pressure on the transducer.
Too High- lower pressure. Abnormally low pressure,
Too Low- greater pressure. Abnormally high pressure.
Zeroing
 Negates influence of external pressures on monitoring system.

Square wave testing
 Helps identify if arterial line is over or under damped.
 Method:
-Activating the fast flush
-Observe arterial waveform square off at the top and then drop to
zero as the flush is released.
 Normal- Immediate downstroke with just 1 or 2 oscillations within
0.12 seconds and rapid return to baseline.
 Overdamped- slurred upstroke or downstroke with no oscillations
above or below the baseline. Underestimates SBP and falsely high
DBP. CORRECTION- check for air bubbles, clots, kinking.
 Underdamped- Numerous oscillations above or below the baseline.
Over estimates SBP. Under estimates DBP. CORRECTION-
excessive tubing, multiple stopcocks. (Tachycardia, High CO)

Natural Frequency, Damping
Coefficient, and Dynamic Response
A crude arterial waveform that
displays a systolic upstroke,
systolic peak, dicrotic notch, and
so forth can be reconstructed
with reasonable accuracy from
two sine waves

Natural Frequency, Damping
Coefficient, and Dynamic Response
 As a general rule, 6 to 10 harmonics are required to provide
distortion-free reproduction of most arterial pressure
waveforms

Damping
 Most catheter-tubing transducer systems are underdamped but
have an acceptable natural frequency that exceeds 12 Hz.
 If the system's natural frequency is lower than 7.5 Hz, the
pressure waveform is often distorted, and no amount of
damping adjustment can restore the monitored waveform to
adequately resemble the original waveform
 If the natural frequency can be increased sufficiently (e.g., 24
Hz), damping will have minimal effect on the monitored
waveform

Components
 The intra-arterial catheter, extension tubing, stopcocks, in-line
blood sampling set, pressure transducer, continuous-flush
device, and electronic cable connecting the bedside monitor
and waveform display screen.
 The flush device provides a continuous, slow (1 to 3 mL/hr)
infusion of saline to purge the monitoring system
Transducers
 Most transducers are resistance types that are based on the strain
gauge principle: stretching a wire or silicone crystal changes its
electrical resistance.
 The sensing elements are arranged as a Wheatstone bridge circuit
so that the voltage output is proportionate to the pressure applied to
the diaphragm

Arterial BP Gradient
Various pathophysiologic disturbances may produce generalized
arterial pressure gradients in the body.
 Large differences in peripheral and central arterial pressure may be
seen in patients in shock.
Other vasoactive drugs, anesthetics (particularly neuraxial blockade),
and changes in patient temperature produce pressure gradients.
 During hypothermia, thermoregulatory vasoconstriction causes radial
artery systolic pressure to exceed femoral artery systolic pressure,
whereas during rewarming, vasodilation reverses this gradient and
causes radial artery pressure to underestimate femoral artery pressure.

Pulse Pressure Variation
Inspiration Expiration

Complications
 Hematoma/blood loss (Diagnostic also)
 Thrombosis/Embolisation: Fibrin/Particulate/Air
 Distal ischemia
 Retrograde emboli to brain
 Vascular insufficiency:
 Large catheter small vessel
 Radial>Femoral
 Peripheral vascular disease
 DM
 Extended duration
 Ischaemic necrosis of overlying skin
 Arterial injury
 Infection
 Accidental intraarterial injection of drugs
 Pseudoaneurysm
 HIT
 Bowel perforation
 AVF

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Care
 Aseptic precautions
 Daily inspection & dressing
 Pressure bag
 Transducer to be changed every 72 hours
 Arterial line to be changed/removed after 1 week
 Joint near the cannulation site: neutral position
 Prompt removal if signs of ischaemia

Non Invasive and Invasive Blood pressure monitoring RRT

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