Cardiovascular%20Monitoring%20during%20Anesthesia

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Cardiovascular Monitoring during Anesthesia

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Electrocardiogram (EKG)

• One of the standardized monitors during any form
  of anesthesia.
• For detection and diagnosis of
• dysrhythmias
• conduction defects
• cardiac ischemia
• electrolyte disturbance

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Types of Monitoring

• Three-electrode system right arm, left arm, left
  leg white is always right, black is on the left,
  red is even lower.
• (Racial discrimination!!)

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Types of Monitoring

• Five-electrode system one on each lead and one
  precordial lead (V5, along the anterior axillary
  line in the fifth intercostal space ? for
  detection of anterior ischemia).

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Electrocardiogram (EKG)

• Kaplan et al. (Anesthesiology, 1976)
• 90 of intraoperative cardiac ischemia will be
  detected by multiple EKG, especially V5. At least
  two leads should be simultaneously showed on the
  monitor.

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Position of the Leads

• The four limb leads should be placed on the back
  of shoulders and hips, where they will disturb
  the operative field the least.
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• Every lead should be fixed and protected with
  tape to prevent dislodgement of leads during
  operation.

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Artifact Source of EKG

• loss of insulation
• motion artifacts
• crossing cables (especially the pulse oximeter
  cable, which transmits an amplified signal.)
• Electrocauterization

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Electronic Filtering System

• 1. Monitoring mode 0.540 Hz, eliminates high
  and low frequency artifacts, but distorts the
  height of QRS and the degree of ST depression.
• 2. Diagnostic mode 0.05100 Hz, does not filter
  high frequency artifacts.

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Non-invasive Blood Pressure (NIBP) Monitoring

• Drawbacks inaccuracy, intermittent data,
  requirement of a pulsatile flow.
• Common methods of detection of change in flow
• 1) Auscultation of Korotkoff sounds
• 2) Microprocessor-assisted
  interpretation of
• the oscillations.

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(from Essential Noninvasive Monitoring in
Anesthesia. New York Grune and Stratton, 1980)
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Non-invasive Blood Pressure (NIBP) Monitoring

• Familiarity with various type of the automated
  monitors is of prime importance.

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Cuff Size

• Too small cuff will result in high blood pressure
  reading.
• A loosely applied cuff will also produce a
  reading higher than it should be.
• Too large cuff will severely distorted the
  reading obtained.

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Cuff Size

• from Barbara Bates A Guide to Physical
  Examination

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Intravascular Pressure Measurement

• Components include intravascular catheter,
  fluid-filled connector tubing, transducer,
  electronic analyzer, display system.
• Rapid establishment of pressure-transducer system
  is essential in emergent conditions.

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Definitions of Terms

• Frequency Response (Amplitude ratio) Amplitude
  of input vs. output. Ideally 1.
• Natural frequency (fn, or Resonant frequency)
  the frequency at which the monitor system itself
  resonates and amplifies the signal.
• Common natural frequency of transducer system is
  1020 Hz.

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Intravascular Monitoring

• The natural frequency of the measuring system
  should be at least 10 times of the fundamental
  frequency (HR).
• When heart rate is fast (more close to natural
  frequency of the system), wave can be abnormally
  amplified
• ?Damping is necessary.

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• D diameter L length of tubing
• ? density of the fluid ?P/?V compliance

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Damping Coefficient

• Damping coefficient the rate of dissipation of
  the energy of a pressure wave. It can correct the
  erroneous amplification of under-damped system.

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Flush Test

• The damping coefficient can be evaluated by
  flush test(pop test).
• After a high-pressure flush, an under-damping
  system will continue to oscillate for a long
  period of time.
• ? Overestimation of SBP and under-estimation of
  DBP.

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Flush Test

• An over-damped system will not oscillate after a
  flush but will return to baseline slowly.
• An optimally (or critically) damped system will
  oscillate one or two times only and will
  reproduce BP accurately.

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Sources of Errors

• 1)Low-frequency responses Air in line or failure
  in flush device with formation of partial clot in
  catheter. ? Over-damping.
• 2)Catheter whip Motion of catheter tip itself
  produces a noticeable pressure swing not common
  in A-line but common in PA catheter.

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Source of Errors

• 3)Resonance in peripheral vessels The systolic
  pressure measured in a radial artery may be up to
  2050 mmHg higher than in the central aorta.
• 4)Change in electronic balance electronic
  zeroing should be done periodically to preclude
  baseline drift (for example due to change in
  room temperature).

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Source of Errors

• 5)Transducer position error ideally at right
  atrium. (Midaxillary line in supine patients.)
  Changes may be less significant in blood pressure
  but significant in CVP or PA pressure/wedge
  pressure.

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Air Bubbles in Line

• Air bubbles can result in a lower frequency
  response and greater resonance response.
• Small amount may augment systolic pressure
  reading while large amount cause an over-damped
  system.

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Site for Arterial Cannulation

• Radial artery Modified Allens test
• Apply pressure over both radial and ulnar
  arteries simultaneously and ask the patient to
  squeeze his or her hand several times to promote
  exsanguination. Then release the pressure on the
  ulnar side and measure the time for refill of the
  nailbed of the capillary. If refill time is
  greater than 15 sec, it is a positive test,
  indicating inadequate collateral flow.

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Site for Arterial Cannulation

• Femoral artery excellent access to central
  arterial system. Insertion with a Seldinger
  method.
• Brachial artery medial in antecubital fossa, but
  since it is an end artery, its cannulation is
  relatively contraindicated. However the incidence
  of thromboembolism is low.

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Site for Arterial Cannulation

• Dorsalis pedis and posterior tibialis artery
  distortion of the artery wave.
• External temporary artery rarely used

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Choice of Cannulation Site Special Considerations

• Blalock-Taussig shunt contralateral to the shunt
• Coarctation of Aorta right radial/brachial is
  preferred
• Thoracic aortic aneurysm right radial
• Ascending aorta surgery left radial
• Liver transplantation two cannulations are
  required

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Complications of Arterial Catheterization

• Ischemia incidence is reportedly low.
• Thrombosis incidence may be high but no adverse
  sequelae were reported.
• Infection incidence is higher in femoral
  cannulation.
• Bleeding

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Complications of Arterial Catheterization

• False lowering of radial artery pressure
  immediately after cardio-pulmonary bypass up to
  72 immediately after cardiopulmonary bypass the
  radial artery pressure is significantly lower
  than the aortic pressure. Mechanism
  Vasodilatation? Hypovolemia? AV shunting?? If an
  arterial trace is damped after cardiopulmonary
  bypass, a direct pressure measurement should be
  obtained from central site.

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Central Venous Pressure (CVP)

• measures right atrial pressure
• A wave with P wave, atrial contraction
• C wave QRS complex, tricuspid bulging into RA
• X descent when tricuspid valve is pulling down
  during the latter stage of ventricular systole
  indicating emptying of blood from ventricle.

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Central Venous Pressure (CVP)

• V wave after T wave, RA filling before tricuspid
  opening.
• Y descent when tricuspid valve opens and atrium
  begins to empty.
• TR giant V wave replacing C wave
• af absence of A wave

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Central Venous Pressure (CVP)

• AV dissociation frequent cannon A wave (atrial
  contraction over a closed tricuspid valve)
• Rapid and exaggerated x, y descent in
  constrictive pericarditis.

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CVP values

• a direct measurement of RV filling pressure, CVP
  is good measurement of LV filing pressure only in
  the absence of pulmonary hypertension or mitral
  disease.

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Site of Insertion

• Internal jugular vein, external jugular vein,
  subclavian vein, femoral vein
• PICC peripheral inserted central catheter,
  inserted from antecubital vein (or basilic,
  cephalic vein).

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• Measurement should be done at end-expiration
  phase.

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CVP and PEEP

• The effect of PEEP is rarely significant when
  PEEP is less than 7.5 cmH2O.
• PEEP may cause increased CVP value while
  decreases cardiac output.
• Discontinuation of PEEP for measurement of CVP is
  not recommended.

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Pulmonary Artery Catheter

• It can measure
• PA pressure
• Pulmonary capillary wedged pressure (PCWP) a
  balloon at catheter tip (volume 1.5 ml), when the
  balloon is inflated and the vessel is wedged, a
  valveless hydrostatic column exists between the
  distal port and LA.

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Pulmonary Artery Catheter

• CVP a port for CVP measurement is located at 30
  cm from the tip
• Cardiac output measurement of RV output
• Blood temperature
• Derived hemodynamic data
• Mixed Venous O2 saturation (SvO2)

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Pulmonary Artery Catheter

• PA Port YELLOW
• CVP Port BLUE
• PA balloon Port PINK

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Waveform during Insertion
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Length of Insertion

• Usual conditions (just for ease to memorize)
• 35 cm RV
• 45cm PA
• 55 cm wedge
• But the actual length may vary greatly between
  patients!

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Hemodynamic Measurements--Normal Range

• RA pressure 26 mmHg
• RV pressure systolic 1525 mmHg diastolic 04
  mmHg
• PA pressure systolic 1525 mmHg diastolic 816
  mmHg
• Mean PAP 1020 mmHg
• Pulmonary Capillary Wedge Pressure (PCWP) 612
  mmHg

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Derived Hemodynamic Profiles

• Systemic Vascular Resistance (SVR) 80 x
  (MAP-CVP)/CO 8001200 dyne-sec-cm-5
• Pulmonary Vascular Resistance (PVR) 80 x
  (PAP-PCWP)/CO 20130 dyne-sec-cm-5

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Derived Hemodynamic Profiles

• Cardiac Output thermodilution method 48 L/min
• Cardiac Index CO/BSA 2.54.2 L/min/m2

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Guidelines for Injection

• Injection port CVP
• Solution Normal Saline
• Volume 5 or 10 ml, usually 10 ml, set up in the
  machine before injection
• Injection time better within 4 sec. Prolonged
  injection will cause low measurement.
• Consecutive 3 measurements are required.

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Continuous Cardiac Output

• Continuous Cardiac Output (CCO) measurement can
  be achieved by a electric coil attached on the
  tip of PA catheter. It automatically measures CO
  every 3 min.

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Mixed Venous Oxygen Saturation (SvO2)

• Mixed by blood from both SVC and IVC, sampled at
  PA
• O2 consumption SaO2-SvO2
• ?SvO2SaO2 - (VO2/Q x Hb x 13)

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SvO2SaO2 - (VO2/Q x Hb x 13)

• Causes for decreasing SvO2
• Hypoxemia
• Increased Metabolic Rate
• Anemia (Blood loss)
• Low Cardiac Output
• ????????, SvO2???CO???.

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Intravascular Volume
Blood Pressure
Vascular Compliance
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TEE (Transesophageal Echocardiography)

• A vibrating piezoelectric crystal at the probe
  tip both produces and receives the ultrasound
  wave. The time required for the wave to travel
  through biological structures, together with the
  intensity of reflected waves, provides
  information about the size and the intensity of
  the structures.

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TEE (Transesophageal Echocardiography)

• Waves can be processed to analyze the frequency
  shift (Doppler effect) between the emitted and
  reflected waves to provide the direction and the
  velocity of blood flow.

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Modes of Imaging

• M-mode one-dimensional view
• 2D mode multiplanar view
• Doppler echocardiography

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Doppler Echocardiography

• Pulse-wave (PW) Doppler repetitive bursts of
  ultrasound focused at a precise location,
  drawback limitation for high-velocity flow
• Continuous-wave (CW) Doppler two transducers,
  one emits one receives. It measures velocity
  accurately but sampling location is unknown.

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Doppler Echocardiography

• A frequency shift is produced when sound waves
  are reflected by a moving target.
• V ?fc/2f0 x cos ?
• It can detect the velocity of blood flow,
  producing both visual and audible signals

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Doppler Echocardiography

• Color flow mapping
• Flow toward the probe red
• Flow away from the probe blue

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Doppler Echocardiography

• Turbulent flow contains RBCs of different
  velocities. Doppler flow showed a shaggy pattern,
  known as spectral broadening.

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TEE Contraindications

• Absolute
• Esophageal disease
• Active upper GI bleeding
• Severe C-spine instability

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Pressure Gradient

• Peak pressure gradient can be calculated by a
  modified Bernoulli equation
• ?P 4 x V2

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Pressure Half Time

• The degree of mitral stenosis can be assessed by
  pressure half time (T 1/2).
• Mitral Area 220/ T 1/2

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TEE Contraindications

• Relative
• Recent gastroesophageal operation
• Esophageal varices
• Severe cervical arthritis
• Dysphagia or odynophagia

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Complications and Risks

• Major complications are unusual (0.180.5).
• Esophageal tear/hemorrhage
• Transient vocal cord paralysis
• Sore throat with pharyngitis

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Basic Views of TEE
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Basic Views of TEE

• Mid-papillary view

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Basic Views of TEE

• Aortic short-axis view

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Regional Wall Motion Abnormality (RWMA)

• A more sensitive indicator of myocardial ischemia
  than ECG changes.
• A transient RWMA is consistent with ischemia a
  persistent change is consistent with infarction.

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Regional Wall Motion Abnormality (RWMA)

• Normal contraction greater than 30 of
  shortening of the radius from the center of the
  ventricle to the endocardial border.
• Mild hypokinesia shortening 1030
• Severe hypokinesia less than 10
• Akinesia absence of wall motion
• Dyskinesia paradoxical movement

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Regional Wall Motion Abnormality (RWMA)
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Duomo, Milan, Italy
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Suggested Reading

• Paul L. Marino The ICU book
• Anesthesia Secrets, J. Duke and ST Rosenberg,
  Mosby
• A Practical Approach to Cardiac Anesthesia, FA
  Hensley Jr., DE Martin, Little Brown