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Cardiovascular Monitoring Cardiovascular Monitoring during Anesthesiaduring Anesthesia

台大醫院麻醉部詹偉弘

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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.

• 顏色 : 白綠黑棕紅• Every lead should be fixed and protected wi

th 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: 0.5~40 Hz, eliminates high and low frequency artifacts, but distorts the height of QRS and the degree of ST depression.

2. Diagnostic mode: 0.05~100 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 10~20 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 20~50 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 Allen’s 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: 2~6 mmHg• RV pressure: systolic 15~25 mmHg; diastolic 0~4

mmHg• PA pressure: systolic 15~25 mmHg; diastolic

8~16 mmHg• Mean PAP: 10~20 mmHg• Pulmonary Capillary Wedge Pressure (PCWP):

6~12 mmHg

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Derived Hemodynamic Profiles

• Systemic Vascular Resistance (SVR): 80 x (MAP-CVP)/CO; 800~1200 dyne-sec-cm-5

• Pulmonary Vascular Resistance (PVR): 80 x (PAP-PCWP)/CO; 20~130 dyne-sec-cm-5

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Derived Hemodynamic Profiles

• Cardiac Output: thermodilution method; 4~8 L/min

• Cardiac Index: CO/BSA; 2.5~4.2 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

SvO2=SaO2 - (VO2/Q x Hb x 13)

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SvO2=SaO2 - (VO2/Q x Hb x 13)

Causes for decreasing SvO2:

• Hypoxemia

• Increased Metabolic Rate

• Anemia (Blood loss)

• Low Cardiac Output

當前三者不變時 , SvO2便成為 CO的指標 .

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Blood PressureIntravascular

Volume

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 RBC’s 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 (0.18%~0.5%).

• 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 10~30%

• Severe hypokinesia: less than 10%

• Akinesia: absence of wall motion

• Dyskinesia: paradoxical movement

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Regional Wall Motion Abnormality (RWMA)

83Duomo, 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