Ppt deals shortly about various invasive monitoring modalities of cardiology for an anesthetist! This is just an overview and each topics is itself an area of deep learning! Ideal for a basic presentation for residents of anesthesiology!

1. Presenter: Dr. S. Sk. Mohd Malik
Moderator: Dr. Debdutta Behera

2. DIRECT MEASUREMENT OF ARTERIAL BLOOD PRESSURE
Percutaneous Radial Artery Cannulation
• The radial artery is the most common site for invasive blood pressure monitoring because it is
technically easy to cannulate and complications are rare.
Modified Allen’s test:
• The radial and ulnar arteries are both compressed while the patient makes a tight fist to
exsanguinate the palm and then slowly reopens it.
• As occlusion of the ulnar artery is released, the color of the open palm is observed.
• Severely reduced collateral flow is present when the palm remains pale for more than 6 to 10
seconds.
The diagnostic accuracy of the modified Allen test with a 5-second threshold is only 80% with 76%
sensitivity and 82% specificity.

3. Alternative Arterial Pressure Monitoring Sites:
• Ulnar artery (has been used safely even following failed attempts to access the ipsilateral radial
artery.)
• Brachial artery
• Axillary artery (has the advantages of patient comfort and mobility.)
• femoral artery (is the largest vessel in common use for blood pressure monitoring.)
• Less commonly used alternatives include the dorsalis pedis, posterior tibial, and superficial
temporal arteries.

4. Technical Aspects of Direct Blood Pressure Measurement
• Most invasive blood pressure monitoring systems are underdamped second-order dynamic
systems that demonstrate simple harmonic motion dependent on elasticity, mass, and friction.
• System operating characteristics (i.e., frequency response or dynamic response) are characterized
by natural frequency and damping coefficient.

5. Natural Frequency,
Damping Coefficient,
and Dynamic Response
of Pressure Monitoring
Systems
• The displayed pressure
waveform is a periodic
complex wave produced via
Fourier analysis of a
summation of multiple
propagated and reflected
pressure waves
• The sine waves that sum to
produce the final complex
wave have frequencies that
are multiples or harmonics of
the fundamental frequency
(i.e., pulse rate).
• Natural frequency and
damping coefficient are
intrinsic characteristics of all
monitoring systems.

6. • Dynamic Response is a function of
Natural Frequency and Damping Coefficient
• The Natural Frequency: the frequency at
which the system will oscillate in the absence
of a driving or damping force, i.e. how fast the
system vibrates in response to a single
disturbance.
• The Damping coefficient: How quickly those
vibrations come to rest in the system
• The dynamic response of an arterial line system
is tested using the "fast flush" test, where the
transducer is briefly exposed to pressure
straight from the counterpressure bag.
• When the fast flush abruptly ends, the
transducer system oscillates at its natural
frequency.
• This can be measured and assessed for
adequacy. The time between oscillation
"peaks" gives you the natural frequency of the
system; (i.e. a system with 50 msec between
peaks has a natural frequency of 20Hz.)

7. Fast-flush test/The Square Wave Test:
• Provides a convenient bedside method for determining system dynamic response and assessing
signal distortion.
• When squeezed the fast flush valve, the transducer is exposed to some of the 300mmHg in the
pressurized saline bag.
• This produces a waveform that rises sharply, plateaus, and drops off sharply when the flush valve
is released again.
This is the "square wave".
• The transducer system returns to baseline by "bouncing" a couple of times before coming to rest.
• This "bounce" can be used to determine the resonance characteristics of the system.
(continued..)

8. The accurate, responsive, adequately damped arterial line waveform will have the following
features:
• The time between oscillations will be short. This is the natural frequency of the system, and it
should be less than 20-30 msec in order to resolve the details.
• There should be at least one "bounce" oscillation. If the system does not oscillate, there is too
much damping.
• There should be no more than two oscillations; a system which oscillates too much is
underdamped.
• There should be a distinct dicrotic notch. The dicrotic notch is resolved from high-frequency
waveforms, which are usually of low amplitude and therefore more susceptible to damping.

10. The over-damped arterial line
waveform
• The over-damped trace will lose its dicrotic
notch, and there won't be more than one
oscillation.
• This happens when there is clot in the
catheter tip, or an air bubble in the tubing.
The under-damped arterial line
waveform
• The under-damped trace will overestimate
the systolic, and there will be many post-flush
oscillations.
• The MAP remains the same in spite of
damping.

11. Effect of small air
bubbles within arterial
pressure monitoring
systems:

12. The arterial line pressure transducer setup

13. The Wheatstone
Bridge pressure
transducer
• Wheatstone bridge = electrical
circuit with one unknown
resistor
• Used to measure an unknown
electrical resistance.
• Resistance of the unknown
resistor is determined by
pressure
• Thus, the resistor becomes a
pressure gauge
• This pressure gauge is coupled
to the fluid-filled
compartment

14. Zeroing and levelling the ART line
• "Zeroing" can be defined as "the use of atmospheric pressure as a reference standard against
which all other pressures are measured". The canonical college definition is "a process which
confirms that atmospheric pressure results in a zero reading by the measurement system".
• The device is zeroed when the air-fluid interface is opened to atmospheric pressure.
• Strictly speaking the zeroing of an arterial line can take place with the transducer lying anywhere.
• "Leveling" can be defined as "the selection of a position of interest at which the reference
standard (zero ) is set".
• The system is conventionally "levelled" at the phlebostatic axis, which corresponds roughly to
with the position of the right atrium and aortic root.
For every 10cm below the phlebostatic axis, the art line will add 7.4 mm Hg of pressure.

15. The arterial pulse
waveform
• The systolic phase:
characterized by a rapid
increase in pressure to a peak.
This phase begins with the
opening of the aortic valve and
corresponds to the left
ventricular ejection.
• The dicrotic notch: it
represents the closure of the
aortic valve (?)
• The diastolic phase: represents
the run-off of blood into the
peripheral circulation.
• The peak correlates with the
systolic blood pressure as
measured by a normal non-
invasive cuff.
• The trough (i.e. the lowest
reading before the next
pressure wave) is the diastolic
pressure.
• The mean arterial pressure
(MAP) is calculated from the
area under the pressure curve.
• The systolic upstroke starts
120 to 180 ms after beginning
of the R wave.

16. Interpretation of abnormal arterial line waveforms
Arterial waveform in
hypertension and peripheral
vascular disease
Arterial waveform in
aortic stenosis

17. Arterial waveform in aortic
regurgitation
Arterial pressure waveform in
hypertrophic obstructive
cardiomyopathy

18. Central Venous Pressure Monitoring
CENTRAL VENOUS CANNULATION

19. Techniques & Complications
• The optimal location of the catheter tip is just superior to or at the junction of the superior vena
cava and the right atrium.
• Compared with other sites, the subclavian vein is associated with a greater risk of pneumothorax
during insertion, but a reduced risk of other complications during prolonged cannulations (eg, in
critically ill patients).
• The right internal jugular vein provides a combination of accessibility and safety.
• Left-sided internal jugular vein catheterization has an increased risk of pleural effusion and
chylothorax.
• The external jugular veins can also be used as entry sites, but due to the acute angle at which
they join the great veins of the chest, are associated with a slightly increased likelihood of failure
to gain access.
• Femoral veins can also be cannulated, but are associated with an increased risk of line-related
sepsis.

22. INTERPRETATION OF
CENTRAL VENOUS
PRESSURE
WAVEFORMS
• Checking the typical CVP
waveform on the monitor
screen is the confirmatory sign
of the catheter placement.
• The right atrial contraction
generates an average pressure
of 6 mm Hg.
• The normal CVP waveform has
five waves, three upward
waves namely “a”, “c” and “v”
waves and two downward
descents (“x” and “y”
descents).

24. PULMONARY ARTERY CATHETERIZATION
• The pulmonary artery (PA) catheter (or Swan-Ganz catheter) was introduced in the 1970s.
• The catheter provides measurements of both CO and PA occlusion pressures and was used to
guide hemodynamic therapy.
Contraindications
• Relative contraindications to pulmonary artery catheterization include left bundle-branch block
(because of the concern about complete heart block) and
• Conditions associated with a greatly increased risk of arrhythmias.

25. Techniques & Complications:
• Although various PA catheters are available, the
most popular design integrates five lumens into
a 7.5 FR catheter, 110-cm long, with a
polyvinylchloride body.

27. Clinical Considerations:
• PA catheters allow more precise estimation of left ventricular preload than either CVP or physical
examination (but not as precise as TEE), as well as the sampling of mixed venous blood.
• Catheters with self-contained thermistors can be used to measure CO, from which a multitude of
hemodynamic values can be derived.

29. CARDIAC OUTPUT MONITORING
• Cardiac output is the total blood flow generated by the heart.
• In a normal adult at rest, CO ranges from 4.0 to 6.5 L/min.
Measurement of cardiac output provides a global assessment of the circulation.
WHY?
1. Low cardiac output leads to significant morbidity and mortality.
2. Clinical assessment of cardiac output is often inaccurate.
3. Newer techniques for cardiac output measurement are becoming less invasive.

30. A. THERMODILUTION CARDIAC OUTPUT MONITORING
• The thermodilution technique is considered the gold standard for measuring cardiac output.
• It is a variant of the indicator dilution method.
METHOD
• Injection of a quantity (2.5, 5, or 10 mL) of fluid that is below body temperature (usually room
temperature or iced) into the right atrium changes the temperature of blood in contact with the
thermistor at the tip of the PA catheter.
• After injection, one can plot the temperature as a function of time to produce a thermodilution
curve.
• CO is determined by a computer program that integrates the area under the curve.

31. • Thermodilution technique can be modified to
measure CO continuously.
• A special catheter contains a thermal filament
that introduces small pulses of heat into the
blood proximal to the pulmonic valve and a
thermistor measures changes in PA blood
temperature.
• A computer in the monitor determines CO by
cross-correlating the amount of heat input with
the changes in blood temperature.

32. Transpulmonary thermodilution (PiCCO® system):
• It relies upon the same principles of thermodilution, but does not require PA catheterization.
• A central line and a thermistor-equipped arterial catheter (usually placed in the femoral artery)
are necessary to perform transpulmonary thermodilution.
• Cold indicator is injected into the superior vena cava via a central line while a thermistor notes
the change in temperature in the arterial system following the cold indicator’s transit through the
heart and lungs and estimates the CO.
• Transpulmonary thermodilution also permits the calculation of both the
• Global end-diastolic volume (GEDV) and
• Extravascular lung water (EVLW).

34. • Moreover, the PiCCO® system calculates SV
variation and pulse pressure variation through
pulse contour analysis, both of which can be
used to determine fluid responsiveness.
• Both SV and pulse pressure are decreased
during positive-pressure ventilation.
• The greater the variations over the course of
positive-pressure inspiration and expiration,
the more likely the patient is to improve
hemodynamic measures following volume
administration.
Patients located on the steeper portion of the
curve will be more responsive to volume
administration compared with those whose
volume status is already adequate.

35. • Pulse pressure variation is the change in pulse
pressure that occurs throughout the respiratory
cycle in patients supported by positive-pressure
ventilation.
• As volume is administered, pulse pressure
variation decreases.
• Variation greater than 12% to 13% is
suggestive of fluid responsiveness.
• Dynamic measures such as pulse pressure
variation and stroke volume variation become
less reliable when arrhythmias are present.

36. B. Dye Dilution
• In the LiDCOTM system, a small bolus of lithium chloride is injected into the circulation.
• A lithium-sensitive electrode in an arterial catheter measures the decay in lithium concentration
over time.
• Integrating the concentration over time graph permits the machine to calculate the CO.
• The LiDCOTM device, like the PiCCO® thermodilution device, employs pulse contour analysis of the
arterial wave form to provide ongoing beat-to-beat determinations of CO.
DRAWBACKS:
• Lithium dilution determinations can be made in patients who have only peripheral venous access.
• Lithium should not be administered to patients in the first trimester of pregnancy.
• The dye dilution technique, however, introduces the problems of indicator recirculation, arterial
blood sampling, and background tracer buildup, potentially limiting the use of such approaches
perioperatively.
• Nondepolarizing neuromuscular blockers may affect the lithium sensor.

37. C. Pulse Contour Devices
• Pulse contour devices use the arterial pressure tracing to estimate the CO and other dynamic
parameters, such as pulse pressure and SV variation with mechanical ventilation.
• Pulse contour devices rely upon algorithms that measure the area of the systolic portion of the
arterial pressure trace from end diastole to the end of ventricular ejection.
• The devices then incorporate a calibration factor for the patient’s vascular compliance, which is
dynamic and not static.
• The FloTrac (Edwards Life Sciences) does not require calibration with another measure and relies
upon a statistical analysis of its algorithm to account for changes in vascular compliance.

38. D. Esophageal Doppler
• Esophageal Doppler relies upon the Doppler
principle to measure the velocity of blood flow
in the descending thoracic aorta.
• As red blood cells travel, they reflect a
frequency shift, depending upon both the
direction and velocity of their movement.
• By using the Doppler equation, it is possible to
determine the velocity of blood flow in the
aorta. The equation is:
• As the velocities of the cells in the aorta travel
at different speeds over the cardiac cycle, the
machine obtains a measure of all of the
velocities of the cells moving over time.
• Mathematically integrating the velocities
represents the distance that the blood travels.
• Next, using normograms, the monitor
approximates the area of the descending aorta.
• The monitor thus calculates: area × length =
volume.

39. E. Thoracic Bioimpedance
• Changes in thoracic volume cause changes in thoracic resistance (bioimpedance) to low
amplitude, high frequency currents.
• If thoracic changes in bioimpedance are measured following ventricular depolarization, SV can be
continuously determined.
• This noninvasive technique requires six electrodes to inject microcurrents and to sense
bioimpedance on both sides of the chest.
• Increasing fluid in the chest results in less electrical bioimpedance.
• Mathematical assumptions and correlations are then made to calculate CO from changes in
bioimpedance.
Disadvantages of thoracic bioimpedance:
• Susceptibility to electrical interference and reliance upon correct electrode positioning.
• The accuracy of this technique is questionable in several groups of patients, including those with
aortic valve disease, previous heart surgery, or acute changes in thoracic sympathetic nervous
function (eg, those undergoing spinal anesthesia).

40. F. Fick Principle
• The amount of oxygen consumed by an individual (VO2) equals the difference between arterial
and venous (a–v) oxygen content (C) (CaO2 and CvO2) multiplied by CO. Therefore
• Mixed venous and arterial oxygen content are easily determined if a PA catheter and an arterial
line are in place.
• Oxygen consumption can also be calculated from the difference between the oxygen content in
inspired and expired gas.

41. G. Echocardiography
• Both TTE and TEE can be employed preoperatively and postoperatively.
• TTE has the advantage of being completely noninvasive; however, acquiring the “windows” to
view the heart can be difficult.
Echocardiography has many uses:
• Diagnosis of the source of hemodynamic instability, including myocardial ischemia, systolic and
diastolic heart failure, valvular abnormalities, hypovolemia, and pericardial tamponade.
• Estimation of hemodynamic parameters, such as SV, CO, and intracavitary pressures.
• Diagnosis of structural diseases of the heart, such as valvular heart disease, shunts, aortic
diseases.
• Guiding surgical interventions, such as mitral valve repair.

46. REFERENCES
• Miller’s Anesthesia - NINTH EDITION
• Clinical Anesthesiology by Morgan and Mikhail - 6th edition
• Understanding Anesthetic Equipment & Procedures A Practical Approach - Dwarkadas K Baheti
MD, Vandana V Laheri DA MD
• Principles of invasive cardiovascular monitoring | Musculoskeletal Key
• home | Deranged Physiology

47. (end of presentation..)