May 11, 2025 • 45 mins
Continue your journey to mastering anaesthesia—one chapter at a time.
In this episode, Dr. J.R. Decker reads and discusses Chapter 5 (Part 4) of Morgan & Mikhail’s Clinical Anesthesiology (7th Edition).
Follow as you read along to strengthen your foundations in anaesthesia, one clear and engaging session at a time.
Perfect for trainees, revision, or daily listening.
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Transcript
Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
(00:01):
Morgan and Michael's Clinical Anesthesiology, 7th Edition,
Part 4. Pulse pressure variation is the
change in pulse pressure that occurs throughout the
respiratory cycle in patients supported by positive pressure
(00:26):
ventilation. As volume is administered, pulse
pressure variation decreases. Variation greater than 12% to 13
percent is suggestive of fluid responsiveness.
(00:51):
Dynamic measures such as pulse pressure variation and stroke
volume variation become less reliable when arrhythmias are
present. Unfortunately, many of the
variation studies using these dynamic measures were performed
(01:14):
prior to the routine use of low tidal volume, that is 6 mils per
kilogramme long. Protection ventilation
strategies during positive pressure ventilation.
B Dye dilution If indocyanine green dye or another indicator
(01:44):
such as lithium is in injected through a central venous
catheter, its appearance in the systemic arterial circulation
can be measured by analysing arterial samples with an
appropriate detector, for example, a densitometer for
(02:07):
indocyanine green. The area under the resulting dye
indicator curve is related to cardiac output by analysing
arterial blood pressure and integrating it with cardiac
(02:29):
output. Systems that use lithium, that
is, Lidco, also calculate bit tobit stroke volume.
In the Lidco system, a small bolus of lithium chloride is
(02:50):
injected into the circulation. A lithium sensitive electrode in
an arterial catheter measures the decay in lithium
concentration over time. Integrating the concentration
over a time graph permits the machine to calculate the cardiac
(03:15):
output. The Lydco device, like the Pico
thermodilution device, employs pulse contour analysis of the
arterial waveform to provide ongoing bit to bit
(03:36):
determinations of cardiac outputand other calculated parameters.
Lithium dilution determinations can be made in patients who have
only peripheral venous access. Lithium should not be
(03:58):
administered to patients in the first trimester of pregnancy.
The dye dilution technique, however, introduces the problems
of indicator recirculation, arterial blood sampling, and
(04:19):
background tracer buildup, potentially limiting the use of
such approaches perioperatively.Non depolarizing neuromuscular
blockers may affect the lithium sensor.
(04:40):
C Pulse contour devices. Pulse contour devices use
arterial pressure tracing to estimate the cardiac output and
other dynamic parameters such aspulse pressure and stroke.
(05:03):
Very stroke volume variation with mechanical ventilation.
These indices are used to help determine if hypotension is
likely to respond to fluid therapy.
(05:24):
Pulse counter 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.
(05:46):
The devices then incorporate a calibration factor for the
patient's vascular compliance, which is dynamic and not static.
Some pulse control devices rely first on transpulmonary
thermodilution or lithium thermodilution to calibrate the
(06:11):
machine for subsequent pulse contour measurements.
The flow track sensor from Edwards Life Sciences does not
require calibration with anothermeasure and relies upon a
(06:31):
statistical analysis of his algorithm to account for changes
in vascular compliance occurringas a consequence of changed
vascular tone. D Esophagal Doppler Esophagal
(06:57):
Doppler relies upon the Doppler principle to measure the
velocity of blood flow in the descending thoracic aorta.
The Doppler principle is integral in perioperative
echocardiography. The Doppler effect has been
(07:23):
described previously in this chapter.
Blood in the aorta is in relative motion compared with
the Doppler probe in the oesophagus.
As red blood cells travel, they reflect a frequency shift
(07:44):
depending upon both the direction and velocity of their
movement. When blood flows toward the
transducer, it's reflected frequency is higher than that
which was transmitted by the probe.
(08:04):
When blood cells move away from the transducer, the frequency is
lower than that which was initially sent by the probe.
By using the Doppler equation, it is possible to determine the
velocity of blood flow in the alter.
(08:26):
The equation is velocity of blood flow is equal to frequency
change divided by cosine of angle of incidence between
Doppler beam and blood flow multiplied by speed of sound in
(08:50):
tissue divided by two times source frequency.
For Doppler to provide a reliable estimate of velocity,
the angle of incidence should beas close to 0 as possible.
(09:13):
Since the cosine of 0 is 1. As the angle approaches 90°, the
Doppler measure is unreliable asthe cosine of 90° is 0.
(09:34):
The esophageal Doppler device calculates the velocity of flow
in the iota. As the velocities of the cells
in the iota travel at different speeds over the cardiac cycle,
the much, the machine obtains a measure of all the of the
(09:57):
velocities of the cells moving over time.
Mathematically integrating the velocities represents the
distance that the blood travels.Next, using nomograms, the
(10:19):
monitor approximates the area ofthe descending aorta.
The monitor thus calculates boththe distance the blood travels
as well as the area. Area times length is equal to
(10:40):
volume. Consequently, the stroke volume
of blood in the descending utteris calculated.
Knowing the heart rate allows calculation of that portion of
the cardiac output flowing through the descending thoracic
(11:04):
aorta, which is approximately 70% of total cardiac output.
Correcting for this 30% allows the monitor to estimate the
patient's total cardiac output. Esophageal Doppler is dependent
(11:29):
upon many assumptions and nomograms, which may hinder its
ability to accurately reflect cardiac output in a variety of
clinical situations. E Thoracic bio impedance changes
(11:55):
in thoracic volume 'cause changes in thoracic resistance,
that is, bio impedance to low amplitude, high frequency
currents. If thoracic changes in bio
impedance are measured followingventricular depolarization,
(12:17):
stroke volume can be continuously determined.
These non invasive technique requires 6 electrodes to inject
microcurrents and to sense bio impedance on both sides of the
chest. Increasing fluid in the chest
(12:42):
results in less electrical bio impedance.
Mathematical assumptions and correlations are then used to
calculate the cardiac output from changes in bio impedance.
Disadvantages of thoracic bio impedance include susceptibility
(13:07):
to electrical interference and motion artefacts.
F thick principle, the amount ofoxygen consumed by an
individual, that is VO2, equals the difference between arterial
(13:32):
and venous, that is, AV oxygen content, that is, C talking
about Cao 2 and CVO 2 multipliedby cardiac output.
Therefore, cardiac output is equal to oxygen consumption
(13:55):
divided by a minus VO2 content difference, which is also equal
to VO2 divided by CEO 2 minus CVO 2.
Mixed venous and arterial oxygencontent is easily determined if
(14:17):
APA 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.
Variations of the Feek principleare the basis of all indicator
(14:42):
dilution methods of determining cardiac output.
G Echocardiography. There are no more powerful tools
to diagnose and access and assess cardiac function
(15:05):
perioperatively than transthoracic, that is TTE, and
trans esophagal ecography, that is TEE.
Both TTE and TEE can be employedpreoperatively and
postoperatively. TTE has the advantage of being
(15:32):
completely non invasive, howeveracquiring the windows to view
the heart can be difficult in the operating room.
Limited access to the chest makes TEE an ideal option to
(15:53):
visualise the heart. Disposable TEE probes are now
available that can remain in position in critically I'll
patients for days during which intermittent TEE examinations
(16:15):
can be performed. Echocardiography can be employed
by anaesthesia staff in two ways, depending upon the degrees
of training and certification. Basic or hemodynamic TEE permits
(16:40):
the anesthesiologist to discern the primary source of a
patient's hemodynamic instability.
Whereas in past decades the pulmonary artery flotation
catheter would be used to determine why the patient might
(17:01):
be hypotensive, the anaesthetistperforming TEE is attempting to
determine if the heart is adequately filled, contracting
appropriately, not externally compressed, and devoid of any
(17:22):
grossly obvious structural defects.
At all times, information obtained from TEE must be
correlated with other information as to the patient's
general condition. Anesthesiologists performing
(17:44):
advanced diagnostic TEE make therapeutic and surgical
recommendations based upon theirTEE interpretations.
Various organisations and boardshave been established worldwide
to certify individuals in all levels of perioperative
(18:08):
echocardiography. More importantly, individuals
who perform echocardiography should be aware of the
credentialing requirements of their respective institutions.
(18:29):
Echocardiography has many uses, including diagnosis of the
source of hemodynamic instability, including
myocardial leiskaemia, systolic and diastolic heart failure,
valvular abnormalities, hypovolemia, and pericardial
(18:56):
tamponade. Estimation of hemodynamic
parameters such as stroke volume, cardiac output, and
intracavatory pressures. Diagnosis of structural diseases
(19:16):
of the heart such as valvular heart disease.
Schoen's aortic diseases. Guiding surgical interventions
such as mitral valve repair. Various echocardiographic
(19:39):
modalities are employed perioperatively by
anesthesiologists including TTETEE, EPI, aortic and
epicardial ultrasound and three-dimensional
echocardiography. Some advantages and
(20:04):
disadvantages of the modalities are as follows.
TTE has the advantage of being non invasive and essentially
risk free. Limited scope TTE examinations
(20:25):
are now increasingly common in the intensive care unit.
Bedside TTE exams such as the FATE Does focus assisted trans
thoracic echocardiography or FAST, that is, focus assessment
with sonography in trauma protocols can readily assist in
(20:51):
hemodynamic diagnosis. It is possible to identify
various common cardiac pathologies perioperatively
using pattern recognition. We get to Figure 5-26,
(21:14):
describing the normal apical 4 chamber view.
Next we get to Figure 5-27, explaining the fate examination.
Can you take some time to go through this?
(21:40):
Next we get to Figure 5-28, explaining important
pathological conditions identified with the FATE
examination. It's important to pause this
recording and go through this. Also unlike TTET, EE is an
(22:09):
invasive procedure with the potential for life threatening
complications, that is, esophageal rupture and
mediastinitis. The close proximity of the
oesophagus to the left atrium eliminates the problem of
(22:29):
obtaining windows to view the heart and permits and permits
great detail. TEE has been used frequently in
the cardiac surgical operating room over the past decades.
It's used to guide therapy in general cases has been limited
(22:54):
by both the cost of the equipment and the learning
necessary to correctly interpretthe image.
The images both TTE and TEE generate 2 dimensional images of
the three-dimensional heart. Consequently, it is necessary to
(23:20):
view the heart through many two-dimensional image planes and
windows to mentally recreate thethree-dimensional anatomy.
The ability to interpret these images at the advanced
certification level requires much training.
(23:48):
We get to Figure 5-29 that explains the structures of the
heart as seen on the mid esophageal 4 chamber view.
EPI. Aortic and epicardiac ultrasound
(24:10):
imaging techniques employ an echo probe wrapped in a sterile
sheath and manipulated by thoracic surgeons
intraoperatively to obtain viewsof the aorta and the heart.
The airfield trachea prevents TEE imaging of the ascending
(24:35):
aorta because the aorta is manipulated during cardiac
surgery. Detection of atherosclerotic
plaques permits the surgeon to potentially minimise the
incidence of embolic stroke. Imaging of the heart with
(24:59):
epicardial ultrasound permits intraoperative echocardiography
when TEE is contraindicated because of esophageal or gastric
pathology. 3 dimensional echocardiography, that is, TTE
(25:21):
and T EE has become available inrecent years.
These techniques provide a three-dimensional view of the
heart's structure. In particular, 3 dimensional
images can better quantify the heart's volumes and can generate
(25:43):
a surgeon's view of the mitral valve to aid in guiding valve
repair. Next, we get to Figure 5-30,
explaining 3 dimensional echocardiography of the mitral
valve. Kindly take time to go through
(26:04):
this. Echocardiography employs
ultrasound that is sound at frequencies greater than normal
hearing from 2 to 10 megahertz. A piezoelectric sensor in the
(26:27):
probe transducer converts electrical energy delivered to
the probe into ultrasound waves.These waves then travel through
the tissues, encountering the blood, the heart, and other
structures. Sound waves pass readily through
(26:52):
tissues of similar acoustic impedance.
However, when they encounter different tissues, they are
scattered, refracted, or reflected back towards the
ultrasound probe. The echo wave then interacts
(27:14):
with the ultrasound probe, generating an electrical signal
that can be reconstructed as an image.
The machine knows the time delaybetween the transmitted and the
reflected sound wave. By knowing the time delay, the
(27:36):
location of the source of the reflected wave can be determined
and the image generated. The TEE probe contains mirrored
crystals generating and processing waves, which can then
create the echo image. The TEE probe can generate
(28:03):
images through multiple planes and can be physically
manipulated in the stomach and oesophagus, permitting
visualisation of heart structures.
These views can be used to determine if the walls of the
heart are receiving an adequate blood supply.
(28:30):
In the healthy heart, the walls thicken and move inwardly with
each beat wall motion. Abnormalities in which the heart
walls fail to thicken during systo or move in a disc kinetic
(28:50):
fashion can be associated with myocardial ischemia.
Next, we get to Figure 5-31, describing the echo probe, that
the echo probe is manipulated bythe examiner in multiple ways to
(29:14):
create the standard images that constitute the comprehensive
perioperative TEE examination. Can you take a little while to
go through this? Next we get to Figure 5-32,
(29:37):
explaining the typical distributions of the right
coronary artery, left anterior descending coronary artery, and
the second flex coronary artery from the transisophageal views
of the left ventricle. Pause the recording to go
(29:57):
through this. Also, the Doppler effect is
routinely used in echocardiographic examinations
to determine both the direction and the velocity of blood flow
and tissue movement. Blood flow in the heart follows
(30:22):
the law of the conservation of mass.
Therefore, the volume of blood that flows through one point,
for example the left ventricularoutflow tract, must be the same
volume that passes through the aortic valve.
(30:44):
When the pathway through which the blood flows become narrowed,
for example aortic stenosis, theblood velocity must increase to
permit the volume to pass. The increase in velocity as
blood moves towards an esophageal echo probe is
(31:07):
detected. The Bernoulli equation, that is
pressure change equals 4 * v ^2,allows echocardiographers to
determine the pressure gradient between areas of different
velocities, where V represents the area of maximal velocity.
(31:37):
Using continuous wave Doppler, it is possible to determine the
maximal velocity as blood accelerates through a
pathological heart structure. For example, a blood flow of
four metres per seconds reflectsa pressure gradient of 64
(32:05):
millimetres of heck of mercury between an area of slow flow
that is the left ventricular outflow tract and a region of
high flow that is a stenotic aortic valve.
(32:25):
Next we get to figure 5-33. Explain that the time velocity
interval of the aortic valve is calculated using continuous wave
Doppler. While pulse wave Doppler is
useful for measurements at lowerblood velocities.
(32:49):
Kindly pause this recording to go through this figure.
The Bernoulli equation permits echocardiographers to estimate
PA and other intracavitary pressures.
(33:11):
Assume P1 is greater than P2. Blood flow proceeds from an area
of high pressure, that is P1 to an area of low pressure, that is
P2. The pulse gradient is equals to
(33:34):
four v ^2, where V is the maximal velocity measured in
metres per second. Thus 4V squared is equals to P1
minus P2. Thus, assuming that there is a
(33:59):
jet of regurgitant blood flow from the left ventricle into the
left atrium and that left ventricular systolic pressure,
that is P1 is the same as systemic blood pressure, for
example, no aortic stenosis, it is possible to calculate left
(34:22):
atrial pressure, that is P2. In this manner,
echocardiographers can estimate intracavatory pressures when
there are pressure gradients, measurable flow velocities
between areas of high and low pressure, and knowledge of
(34:45):
either P1 or P2. Next we get to Figure 5-34,
explaining that intracavatory pressures can be calculated
using known pressures and the Bernoulli equation when
regurgitant jets are present. Kindly pause this recording to
(35:11):
go through this figure. Colour flow Doppler is used by
echocardiographers to identify areas of abnormal flow.
Colour flow Doppler creates a visual picture by assigning A
(35:33):
colour code to the blood velocities of the heart.
Blood flow directed away from the echocardiographic transducer
is blue, whereas that which is moving towards the probe is red.
(35:56):
The higher the velocity of flow,the lighter the colour hue.
When the velocity of blood flow becomes greater than that which
the machine can measure, flow toward the probe is
misinterpreted as flow away fromthe probe, creating images of
(36:18):
turbulent flow and aliasing the of the image.
Such changes in flow pattern areused by echocardiographers to
identify areas of pathology. Next we get to Figure 5-35,
(36:42):
explaining that the colour flow Doppler image of the mid
esophageal aortic valve long axis view demonstrates
measurements of the vernal contractor of aortic
regurgitation. Kindly pause this recording to
go through this figure. Doppler can also be used to
(37:08):
provide an estimate of stroke volume and cardiac output.
Similar to the esophageal Doppler probes previously
described. TTE and TEE can be used to
estimate cardiac output. Assuming that the left
(37:31):
ventricular outflow tract is a cylinder, it is possible to
measure its diameter. Knowing this, it is possible to
calculate the area through whichthe blood flows using the
following equation. Area is equals to π R-squared
(38:00):
which is equal to 0.785 times diameter squared.
We get to Figure 5-36 explainingthat the mid esophageal long
axis view is employed in this image to measure the diameter of
(38:20):
the left ventricular outflow tract.
Kindly pause to go through this figure.
Next, the time velocity integralis determined, a Doppler beam is
(38:41):
aligned in parallel with the left ventricular outflow tract.
The velocities passing through the left ventricular outflow
tract are recorded and the machine integrates the velocity
stroke time curve to determine the distance the blood
(39:04):
travelled. Next we get to 5 Figure 5 having
37 talking about pulse wave Doppler is employed in this deep
transgastric view interrogation of the left ventricular outflow
tract. So explaining that the machine
(39:28):
integrates the velocity stroke time curve to determine the
distance the blood travelled. We get to the equation area
times length is equals to volumein this instance.
The stroke volume is calculated as stroke volume times heart
rate is equals to cardiac output.
(39:54):
Lastly, Doppler can be used to examine the movement of the
myocardial tissue. Tissue velocity is normally 8 to
15 centimetres per second, that is much less than that of blood,
which is 100 centimetres per second.
(40:18):
It is possible to discern both the directionality and velocity
of the heart's movement. Using the tissue Doppler
function of the echo machine, during diastolic filling, the
lateral annulus myocardium will move towards the TEE probe.
(40:44):
Reduced myocardial velocities that is less than 8 CM per
second are associated with impaired diastolic function and
higher left ventricular end diastolic pressures.
Ultimately, echocardiography canprovide comprehensive
(41:08):
cardiovascular monitoring. Its routine use outside of the
cardiac operating room has been hindered by both the cost of the
equipment and the training required to correctly interpret
the images. It is likely that anaesthesia
(41:30):
staff will perform an increasingnumber of echocardiographic
examinations perioperatively. All anaesthesiology trainees
should acquire basic echocardiography skills.
When questions arise beyond those related to hemodynamic
(41:52):
guidance, interpretation by an individual credentialed in
diagnostic echocardiography is warranted.
Case discussion. Hemodynamic monitoring and
management of a complicated patients.
(42:19):
A 68 year old patient presents with a perforated colon
secondary to diverticulitis. Vital signs are as follows.
Heart rate 120 beats per minute.Blood pressure 800 millimetres
(42:41):
of mercury. Stroke 55 millimetres of mercury
Over 55 millimetres of mercury Respiratory rate 28 breaths per
minute Body temperature 38°C. The patient is scheduled for an
(43:05):
emergency exploratory laparatomy.
The patient's history includes placement of a drug eluting
stent in the left anterior descending artery 2 weeks
earlier. The patient's medications
(43:27):
include metoprolol and clopidogrel.
What HEMO question? What hemodynamic monitors should
be employed? Answer This patient presents
with multiple medical issues that could lead to perioperative
(43:51):
hemodynamic instability. The patient has a history of
coronary artery disease treated with stents.
Any previous and current EC GS should be reviewed for signs of
low of new St and T wave changesheralding ischemia.
(44:18):
The patient is both tachycardic and febrile, and those may be
concurrently ischemic, vasodilated, and he hypovolemic.
All of these conditions could complicate perioperative
management. Arterial cannulation and
(44:42):
monitoring will provide beat to beat blood pressure
determinations intraoperatively and will also provide for blood
gas measurements. In a patient likely to be
acidotic and hemodynamically unstable, central venous access
(45:03):
is obtained to permit volume resuscitation and to provide a
port for the delivery of fluids for trans pulmonary measurements
of cardiac output and stroke volume variation.
Alternatively, Paul's contour analysis can be employed from an
(45:30):
arterial trace to determine volume responsiveness should the
patient become hemodynamically unstable.
Echocardiography can be used to determine ventricular function,
feeling pressures and cardiac outputs and provide surveillance
(45:52):
for the development of ischemia induced wall motion
abnormalities. A pulmonary artery catheter
could also be placed to measure cardiac outputs and pulmonary
capillary occlusion pressure. However, we could use TEE if we
(46:16):
were unable to manage the patient well with an arterial
line, a central venous pressure catheter, and a monitor for
cardiac output. For example, pulse contour
analysis, transpulmonary thermaldilution, the choice of
(46:38):
hemodynamic monitors remains with the individual physician
and the availability of various monitoring techniques.
It is important to also considerwhich monitors can be used post
operatively to ensure the continuation of goal directed
(47:00):
therapy. We've come to the end of Chapter
5.
Morgan and Michael's Clinical Anesthesiology, 7th Edition,
Part 4. Pulse pressure variation is the
change in pulse pressure that occurs throughout the
respiratory cycle in patients supported by positive pressure
(00:26):
ventilation. As volume is administered, pulse
pressure variation decreases. Variation greater than 12% to 13
percent is suggestive of fluid responsiveness.
(00:51):
Dynamic measures such as pulse pressure variation and stroke
volume variation become less reliable when arrhythmias are
present. Unfortunately, many of the
variation studies using these dynamic measures were performed
(01:14):
prior to the routine use of low tidal volume, that is 6 mils per
kilogramme long. Protection ventilation
strategies during positive pressure ventilation.
B Dye dilution If indocyanine green dye or another indicator
(01:44):
such as lithium is in injected through a central venous
catheter, its appearance in the systemic arterial circulation
can be measured by analysing arterial samples with an
appropriate detector, for example, a densitometer for
(02:07):
indocyanine green. The area under the resulting dye
indicator curve is related to cardiac output by analysing
arterial blood pressure and integrating it with cardiac
(02:29):
output. Systems that use lithium, that
is, Lidco, also calculate bit tobit stroke volume.
In the Lidco system, a small bolus of lithium chloride is
(02:50):
injected into the circulation. A lithium sensitive electrode in
an arterial catheter measures the decay in lithium
concentration over time. Integrating the concentration
over a time graph permits the machine to calculate the cardiac
(03:15):
output. The Lydco device, like the Pico
thermodilution device, employs pulse contour analysis of the
arterial waveform to provide ongoing bit to bit
(03:36):
determinations of cardiac outputand other calculated parameters.
Lithium dilution determinations can be made in patients who have
only peripheral venous access. Lithium should not be
(03:58):
administered to patients in the first trimester of pregnancy.
The dye dilution technique, however, introduces the problems
of indicator recirculation, arterial blood sampling, and
(04:19):
background tracer buildup, potentially limiting the use of
such approaches perioperatively.Non depolarizing neuromuscular
blockers may affect the lithium sensor.
(04:40):
C Pulse contour devices. Pulse contour devices use
arterial pressure tracing to estimate the cardiac output and
other dynamic parameters such aspulse pressure and stroke.
(05:03):
Very stroke volume variation with mechanical ventilation.
These indices are used to help determine if hypotension is
likely to respond to fluid therapy.
(05:24):
Pulse counter 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.
(05:46):
The devices then incorporate a calibration factor for the
patient's vascular compliance, which is dynamic and not static.
Some pulse control devices rely first on transpulmonary
thermodilution or lithium thermodilution to calibrate the
(06:11):
machine for subsequent pulse contour measurements.
The flow track sensor from Edwards Life Sciences does not
require calibration with anothermeasure and relies upon a
(06:31):
statistical analysis of his algorithm to account for changes
in vascular compliance occurringas a consequence of changed
vascular tone. D Esophagal Doppler Esophagal
(06:57):
Doppler relies upon the Doppler principle to measure the
velocity of blood flow in the descending thoracic aorta.
The Doppler principle is integral in perioperative
echocardiography. The Doppler effect has been
(07:23):
described previously in this chapter.
Blood in the aorta is in relative motion compared with
the Doppler probe in the oesophagus.
As red blood cells travel, they reflect a frequency shift
(07:44):
depending upon both the direction and velocity of their
movement. When blood flows toward the
transducer, it's reflected frequency is higher than that
which was transmitted by the probe.
(08:04):
When blood cells move away from the transducer, the frequency is
lower than that which was initially sent by the probe.
By using the Doppler equation, it is possible to determine the
velocity of blood flow in the alter.
(08:26):
The equation is velocity of blood flow is equal to frequency
change divided by cosine of angle of incidence between
Doppler beam and blood flow multiplied by speed of sound in
(08:50):
tissue divided by two times source frequency.
For Doppler to provide a reliable estimate of velocity,
the angle of incidence should beas close to 0 as possible.
(09:13):
Since the cosine of 0 is 1. As the angle approaches 90°, the
Doppler measure is unreliable asthe cosine of 90° is 0.
(09:34):
The esophageal Doppler device calculates the velocity of flow
in the iota. As the velocities of the cells
in the iota travel at different speeds over the cardiac cycle,
the much, the machine obtains a measure of all the of the
(09:57):
velocities of the cells moving over time.
Mathematically integrating the velocities represents the
distance that the blood travels.Next, using nomograms, the
(10:19):
monitor approximates the area ofthe descending aorta.
The monitor thus calculates boththe distance the blood travels
as well as the area. Area times length is equal to
(10:40):
volume. Consequently, the stroke volume
of blood in the descending utteris calculated.
Knowing the heart rate allows calculation of that portion of
the cardiac output flowing through the descending thoracic
(11:04):
aorta, which is approximately 70% of total cardiac output.
Correcting for this 30% allows the monitor to estimate the
patient's total cardiac output. Esophageal Doppler is dependent
(11:29):
upon many assumptions and nomograms, which may hinder its
ability to accurately reflect cardiac output in a variety of
clinical situations. E Thoracic bio impedance changes
(11:55):
in thoracic volume 'cause changes in thoracic resistance,
that is, bio impedance to low amplitude, high frequency
currents. If thoracic changes in bio
impedance are measured followingventricular depolarization,
(12:17):
stroke volume can be continuously determined.
These non invasive technique requires 6 electrodes to inject
microcurrents and to sense bio impedance on both sides of the
chest. Increasing fluid in the chest
(12:42):
results in less electrical bio impedance.
Mathematical assumptions and correlations are then used to
calculate the cardiac output from changes in bio impedance.
Disadvantages of thoracic bio impedance include susceptibility
(13:07):
to electrical interference and motion artefacts.
F thick principle, the amount ofoxygen consumed by an
individual, that is VO2, equals the difference between arterial
(13:32):
and venous, that is, AV oxygen content, that is, C talking
about Cao 2 and CVO 2 multipliedby cardiac output.
Therefore, cardiac output is equal to oxygen consumption
(13:55):
divided by a minus VO2 content difference, which is also equal
to VO2 divided by CEO 2 minus CVO 2.
Mixed venous and arterial oxygencontent is easily determined if
(14:17):
APA 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.
Variations of the Feek principleare the basis of all indicator
(14:42):
dilution methods of determining cardiac output.
G Echocardiography. There are no more powerful tools
to diagnose and access and assess cardiac function
(15:05):
perioperatively than transthoracic, that is TTE, and
trans esophagal ecography, that is TEE.
Both TTE and TEE can be employedpreoperatively and
postoperatively. TTE has the advantage of being
(15:32):
completely non invasive, howeveracquiring the windows to view
the heart can be difficult in the operating room.
Limited access to the chest makes TEE an ideal option to
(15:53):
visualise the heart. Disposable TEE probes are now
available that can remain in position in critically I'll
patients for days during which intermittent TEE examinations
(16:15):
can be performed. Echocardiography can be employed
by anaesthesia staff in two ways, depending upon the degrees
of training and certification. Basic or hemodynamic TEE permits
(16:40):
the anesthesiologist to discern the primary source of a
patient's hemodynamic instability.
Whereas in past decades the pulmonary artery flotation
catheter would be used to determine why the patient might
(17:01):
be hypotensive, the anaesthetistperforming TEE is attempting to
determine if the heart is adequately filled, contracting
appropriately, not externally compressed, and devoid of any
(17:22):
grossly obvious structural defects.
At all times, information obtained from TEE must be
correlated with other information as to the patient's
general condition. Anesthesiologists performing
(17:44):
advanced diagnostic TEE make therapeutic and surgical
recommendations based upon theirTEE interpretations.
Various organisations and boardshave been established worldwide
to certify individuals in all levels of perioperative
(18:08):
echocardiography. More importantly, individuals
who perform echocardiography should be aware of the
credentialing requirements of their respective institutions.
(18:29):
Echocardiography has many uses, including diagnosis of the
source of hemodynamic instability, including
myocardial leiskaemia, systolic and diastolic heart failure,
valvular abnormalities, hypovolemia, and pericardial
(18:56):
tamponade. Estimation of hemodynamic
parameters such as stroke volume, cardiac output, and
intracavatory pressures. Diagnosis of structural diseases
(19:16):
of the heart such as valvular heart disease.
Schoen's aortic diseases. Guiding surgical interventions
such as mitral valve repair. Various echocardiographic
(19:39):
modalities are employed perioperatively by
anesthesiologists including TTETEE, EPI, aortic and
epicardial ultrasound and three-dimensional
echocardiography. Some advantages and
(20:04):
disadvantages of the modalities are as follows.
TTE has the advantage of being non invasive and essentially
risk free. Limited scope TTE examinations
(20:25):
are now increasingly common in the intensive care unit.
Bedside TTE exams such as the FATE Does focus assisted trans
thoracic echocardiography or FAST, that is, focus assessment
with sonography in trauma protocols can readily assist in
(20:51):
hemodynamic diagnosis. It is possible to identify
various common cardiac pathologies perioperatively
using pattern recognition. We get to Figure 5-26,
(21:14):
describing the normal apical 4 chamber view.
Next we get to Figure 5-27, explaining the fate examination.
Can you take some time to go through this?
(21:40):
Next we get to Figure 5-28, explaining important
pathological conditions identified with the FATE
examination. It's important to pause this
recording and go through this. Also unlike TTET, EE is an
(22:09):
invasive procedure with the potential for life threatening
complications, that is, esophageal rupture and
mediastinitis. The close proximity of the
oesophagus to the left atrium eliminates the problem of
(22:29):
obtaining windows to view the heart and permits and permits
great detail. TEE has been used frequently in
the cardiac surgical operating room over the past decades.
It's used to guide therapy in general cases has been limited
(22:54):
by both the cost of the equipment and the learning
necessary to correctly interpretthe image.
The images both TTE and TEE generate 2 dimensional images of
the three-dimensional heart. Consequently, it is necessary to
(23:20):
view the heart through many two-dimensional image planes and
windows to mentally recreate thethree-dimensional anatomy.
The ability to interpret these images at the advanced
certification level requires much training.
(23:48):
We get to Figure 5-29 that explains the structures of the
heart as seen on the mid esophageal 4 chamber view.
EPI. Aortic and epicardiac ultrasound
(24:10):
imaging techniques employ an echo probe wrapped in a sterile
sheath and manipulated by thoracic surgeons
intraoperatively to obtain viewsof the aorta and the heart.
The airfield trachea prevents TEE imaging of the ascending
(24:35):
aorta because the aorta is manipulated during cardiac
surgery. Detection of atherosclerotic
plaques permits the surgeon to potentially minimise the
incidence of embolic stroke. Imaging of the heart with
(24:59):
epicardial ultrasound permits intraoperative echocardiography
when TEE is contraindicated because of esophageal or gastric
pathology. 3 dimensional echocardiography, that is, TTE
(25:21):
and T EE has become available inrecent years.
These techniques provide a three-dimensional view of the
heart's structure. In particular, 3 dimensional
images can better quantify the heart's volumes and can generate
(25:43):
a surgeon's view of the mitral valve to aid in guiding valve
repair. Next, we get to Figure 5-30,
explaining 3 dimensional echocardiography of the mitral
valve. Kindly take time to go through
(26:04):
this. Echocardiography employs
ultrasound that is sound at frequencies greater than normal
hearing from 2 to 10 megahertz. A piezoelectric sensor in the
(26:27):
probe transducer converts electrical energy delivered to
the probe into ultrasound waves.These waves then travel through
the tissues, encountering the blood, the heart, and other
structures. Sound waves pass readily through
(26:52):
tissues of similar acoustic impedance.
However, when they encounter different tissues, they are
scattered, refracted, or reflected back towards the
ultrasound probe. The echo wave then interacts
(27:14):
with the ultrasound probe, generating an electrical signal
that can be reconstructed as an image.
The machine knows the time delaybetween the transmitted and the
reflected sound wave. By knowing the time delay, the
(27:36):
location of the source of the reflected wave can be determined
and the image generated. The TEE probe contains mirrored
crystals generating and processing waves, which can then
create the echo image. The TEE probe can generate
(28:03):
images through multiple planes and can be physically
manipulated in the stomach and oesophagus, permitting
visualisation of heart structures.
These views can be used to determine if the walls of the
heart are receiving an adequate blood supply.
(28:30):
In the healthy heart, the walls thicken and move inwardly with
each beat wall motion. Abnormalities in which the heart
walls fail to thicken during systo or move in a disc kinetic
(28:50):
fashion can be associated with myocardial ischemia.
Next, we get to Figure 5-31, describing the echo probe, that
the echo probe is manipulated bythe examiner in multiple ways to
(29:14):
create the standard images that constitute the comprehensive
perioperative TEE examination. Can you take a little while to
go through this? Next we get to Figure 5-32,
(29:37):
explaining the typical distributions of the right
coronary artery, left anterior descending coronary artery, and
the second flex coronary artery from the transisophageal views
of the left ventricle. Pause the recording to go
(29:57):
through this. Also, the Doppler effect is
routinely used in echocardiographic examinations
to determine both the direction and the velocity of blood flow
and tissue movement. Blood flow in the heart follows
(30:22):
the law of the conservation of mass.
Therefore, the volume of blood that flows through one point,
for example the left ventricularoutflow tract, must be the same
volume that passes through the aortic valve.
(30:44):
When the pathway through which the blood flows become narrowed,
for example aortic stenosis, theblood velocity must increase to
permit the volume to pass. The increase in velocity as
blood moves towards an esophageal echo probe is
(31:07):
detected. The Bernoulli equation, that is
pressure change equals 4 * v ^2,allows echocardiographers to
determine the pressure gradient between areas of different
velocities, where V represents the area of maximal velocity.
(31:37):
Using continuous wave Doppler, it is possible to determine the
maximal velocity as blood accelerates through a
pathological heart structure. For example, a blood flow of
four metres per seconds reflectsa pressure gradient of 64
(32:05):
millimetres of heck of mercury between an area of slow flow
that is the left ventricular outflow tract and a region of
high flow that is a stenotic aortic valve.
(32:25):
Next we get to figure 5-33. Explain that the time velocity
interval of the aortic valve is calculated using continuous wave
Doppler. While pulse wave Doppler is
useful for measurements at lowerblood velocities.
(32:49):
Kindly pause this recording to go through this figure.
The Bernoulli equation permits echocardiographers to estimate
PA and other intracavitary pressures.
(33:11):
Assume P1 is greater than P2. Blood flow proceeds from an area
of high pressure, that is P1 to an area of low pressure, that is
P2. The pulse gradient is equals to
(33:34):
four v ^2, where V is the maximal velocity measured in
metres per second. Thus 4V squared is equals to P1
minus P2. Thus, assuming that there is a
(33:59):
jet of regurgitant blood flow from the left ventricle into the
left atrium and that left ventricular systolic pressure,
that is P1 is the same as systemic blood pressure, for
example, no aortic stenosis, it is possible to calculate left
(34:22):
atrial pressure, that is P2. In this manner,
echocardiographers can estimate intracavatory pressures when
there are pressure gradients, measurable flow velocities
between areas of high and low pressure, and knowledge of
(34:45):
either P1 or P2. Next we get to Figure 5-34,
explaining that intracavatory pressures can be calculated
using known pressures and the Bernoulli equation when
regurgitant jets are present. Kindly pause this recording to
(35:11):
go through this figure. Colour flow Doppler is used by
echocardiographers to identify areas of abnormal flow.
Colour flow Doppler creates a visual picture by assigning A
(35:33):
colour code to the blood velocities of the heart.
Blood flow directed away from the echocardiographic transducer
is blue, whereas that which is moving towards the probe is red.
(35:56):
The higher the velocity of flow,the lighter the colour hue.
When the velocity of blood flow becomes greater than that which
the machine can measure, flow toward the probe is
misinterpreted as flow away fromthe probe, creating images of
(36:18):
turbulent flow and aliasing the of the image.
Such changes in flow pattern areused by echocardiographers to
identify areas of pathology. Next we get to Figure 5-35,
(36:42):
explaining that the colour flow Doppler image of the mid
esophageal aortic valve long axis view demonstrates
measurements of the vernal contractor of aortic
regurgitation. Kindly pause this recording to
go through this figure. Doppler can also be used to
(37:08):
provide an estimate of stroke volume and cardiac output.
Similar to the esophageal Doppler probes previously
described. TTE and TEE can be used to
estimate cardiac output. Assuming that the left
(37:31):
ventricular outflow tract is a cylinder, it is possible to
measure its diameter. Knowing this, it is possible to
calculate the area through whichthe blood flows using the
following equation. Area is equals to π R-squared
(38:00):
which is equal to 0.785 times diameter squared.
We get to Figure 5-36 explainingthat the mid esophageal long
axis view is employed in this image to measure the diameter of
(38:20):
the left ventricular outflow tract.
Kindly pause to go through this figure.
Next, the time velocity integralis determined, a Doppler beam is
(38:41):
aligned in parallel with the left ventricular outflow tract.
The velocities passing through the left ventricular outflow
tract are recorded and the machine integrates the velocity
stroke time curve to determine the distance the blood
(39:04):
travelled. Next we get to 5 Figure 5 having
37 talking about pulse wave Doppler is employed in this deep
transgastric view interrogation of the left ventricular outflow
tract. So explaining that the machine
(39:28):
integrates the velocity stroke time curve to determine the
distance the blood travelled. We get to the equation area
times length is equals to volumein this instance.
The stroke volume is calculated as stroke volume times heart
rate is equals to cardiac output.
(39:54):
Lastly, Doppler can be used to examine the movement of the
myocardial tissue. Tissue velocity is normally 8 to
15 centimetres per second, that is much less than that of blood,
which is 100 centimetres per second.
(40:18):
It is possible to discern both the directionality and velocity
of the heart's movement. Using the tissue Doppler
function of the echo machine, during diastolic filling, the
lateral annulus myocardium will move towards the TEE probe.
(40:44):
Reduced myocardial velocities that is less than 8 CM per
second are associated with impaired diastolic function and
higher left ventricular end diastolic pressures.
Ultimately, echocardiography canprovide comprehensive
(41:08):
cardiovascular monitoring. Its routine use outside of the
cardiac operating room has been hindered by both the cost of the
equipment and the training required to correctly interpret
the images. It is likely that anaesthesia
(41:30):
staff will perform an increasingnumber of echocardiographic
examinations perioperatively. All anaesthesiology trainees
should acquire basic echocardiography skills.
When questions arise beyond those related to hemodynamic
(41:52):
guidance, interpretation by an individual credentialed in
diagnostic echocardiography is warranted.
Case discussion. Hemodynamic monitoring and
management of a complicated patients.
(42:19):
A 68 year old patient presents with a perforated colon
secondary to diverticulitis. Vital signs are as follows.
Heart rate 120 beats per minute.Blood pressure 800 millimetres
(42:41):
of mercury. Stroke 55 millimetres of mercury
Over 55 millimetres of mercury Respiratory rate 28 breaths per
minute Body temperature 38°C. The patient is scheduled for an
(43:05):
emergency exploratory laparatomy.
The patient's history includes placement of a drug eluting
stent in the left anterior descending artery 2 weeks
earlier. The patient's medications
(43:27):
include metoprolol and clopidogrel.
What HEMO question? What hemodynamic monitors should
be employed? Answer This patient presents
with multiple medical issues that could lead to perioperative
(43:51):
hemodynamic instability. The patient has a history of
coronary artery disease treated with stents.
Any previous and current EC GS should be reviewed for signs of
low of new St and T wave changesheralding ischemia.
(44:18):
The patient is both tachycardic and febrile, and those may be
concurrently ischemic, vasodilated, and he hypovolemic.
All of these conditions could complicate perioperative
management. Arterial cannulation and
(44:42):
monitoring will provide beat to beat blood pressure
determinations intraoperatively and will also provide for blood
gas measurements. In a patient likely to be
acidotic and hemodynamically unstable, central venous access
(45:03):
is obtained to permit volume resuscitation and to provide a
port for the delivery of fluids for trans pulmonary measurements
of cardiac output and stroke volume variation.
Alternatively, Paul's contour analysis can be employed from an
(45:30):
arterial trace to determine volume responsiveness should the
patient become hemodynamically unstable.
Echocardiography can be used to determine ventricular function,
feeling pressures and cardiac outputs and provide surveillance
(45:52):
for the development of ischemia induced wall motion
abnormalities. A pulmonary artery catheter
could also be placed to measure cardiac outputs and pulmonary
capillary occlusion pressure. However, we could use TEE if we
(46:16):
were unable to manage the patient well with an arterial
line, a central venous pressure catheter, and a monitor for
cardiac output. For example, pulse contour
analysis, transpulmonary thermaldilution, the choice of
(46:38):
hemodynamic monitors remains with the individual physician
and the availability of various monitoring techniques.
It is important to also considerwhich monitors can be used post
operatively to ensure the continuation of goal directed
(47:00):
therapy. We've come to the end of Chapter
5.
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