Mod1: Monitoring for Cardiac Surgery - RIGHT HEART CARDIAC OUTPUT MONITORING

Question 1

_{MEASURING CARDIAC OUTPUT}

What was historically considered the “Gold standard” for calculating Cardiac Output (CO)?

Answer 1

The Fick method

Question 2

_{MEASURING CARDIAC OUTPUT - Fick method}

What does the Fick Method indicates? How is it calculated?

Answer 2

Indicates O2 consumption

“The total uptake (or release) of a substance is equal to the product of the blood flow to the peripheral tissues and the arterial concentration difference of the substance

CO = VO2/ (Ca-Cv)

VO2 = CO x (Ca-Cv)

VO2: Consumption of Oxygen (uptake or release of O2)

CO: Cardiact Output

Ca-Cv: Arterial concentration difference of O2

Question 3

_{MEASURING CARDIAC OUTPUT - Fick method}

Why is the Fick method rarely used in clinical practice?

Answer 3

Difficulty in collecting and analyzing the different gas concentrations

Measurement of oxygen uptake is technically demanding

Question 4

_{CARDIAC OUTPUT MONITORING}

Cardiac Output is defined as:

Answer 4

The total blood flow generated by the heart in one minute

Question 5

_{CARDIAC OUTPUT MONITORING}

How is CO calculated?

Answer 5

CO = SV x HR

Also know how SV is calculated

Question 6

_{CARDIAC OUTPUT MONITORING}

What are normal CO values in a normal adult at rest?

Answer 6

Range 4 - 6.₅ L/min

Question 7

_{CARDIAC OUTPUT MONITORING}

T/F: CO provides global assessment of circulation

Answer 7

True

Question 8

_{CARDIAC OUTPUT MONITORING}

CO can be used with other variables to compute additional hemodynamic values, such as:

Answer 8

SVR, PVR

Question 9

_{CARDIAC OUTPUT MONITORING}

T/F: CO must be considered within clinical context of the patient

Answer 9

True

Question 10

_{CARDIAC OUTPUT MONITORING}

Why is CO often expressed as Cardiac Index? How is Cardiac Index (CI) calculated?

Answer 10

To compensate for variations in body size

CI = CO/BSA

Question 11

_{CARDIAC OUTPUT MONITORING}

What are the Four determinants of cardiac output?

Answer 11

Heart rate - Preload - Afterload - Contractility

Which is logically CO = SV x HR

Question 12

_{MEASURING CARDIAC OUTPUT}

What’s the most widely used CO measurement in the OR?

Answer 12

Thermodilution

If done carefully, the results are within 5-10% of other methods

Question 13

_{MEASURING CARDIAC OUTPUT}

Explain the mechanics of Thermodilution

Answer 13

Room temperatue indicator (Dextrose or NS, iced or room air saline) is injected into RA of the PA catheter

Fluid is mixed with blood in the heart

Thermistor at the tip of PA catheter measures temperature of fluid that mixes with blood in the pulmonary artery

Cardiac output is obtained by plotting the change in temperature over time

Timing with respiratory cycle

Question 14

_{MEASURING CARDIAC OUTPUT}

Why is it important to time Thermodilution with respiratory cycle?

Answer 14

As much as 10% difference

Due to changes in pulmonary blood flow during respiration

Question 15

_{MEASURING CARDIAC OUTPUT}

T/F: The cardiac output is INVERSELY related to the area under the thermodilution curve

Answer 15

True

High CO = small area under curve due to rapid blood flow washout

Low CO = large area under the curve due to slow passage of blood flow through heart

Question 16

_{MEASURING CARDIAC OUTPUT}

Why is a High CO associated with a small area under curve?

Answer 16

Due to rapid blood flow washout

Question 17

_{MEASURING CARDIAC OUTPUT}

Why is a Low CO associated with a large area under the curve?

Answer 17

Due to slow passage of blood flow through heart

Question 18

_{MEASURING CARDIAC OUTPUT}

What are the different ways CO can be measured?

Answer 18

Continuous Mixed venous Oximetry Pulmonary Artery Catheter (SvO2 catheter)

Bioimpedance Cardiac Output Monitoring

Ultrasound Based Cardiac Output Monitoring

Lithium Dilution Cardiac Output Monitoring

Pulse Contour Cardiac Output Monitoring

Question 19

_{MEASURING CARDIAC OUTPUT}

Which method of measuring CO uses a catheter that offers a continuous display of mixed venous O2 saturation while also monitoring thermodilution and CO?

Answer 19

Continuous Mixed venous Oximetry Pulmonary Artery Catheter (SvO2 catheter)

Question 20

_{MEASURING CARDIAC OUTPUT}

Which method of measuring CO analyzes the arterial pulse pressure waveform and estimates Stroke volume from the area under the arterial pressure waveform?

Answer 20

Pulse Contour Cardiac Output Monitoring

Uses a beat-to-beat parameter obtained by the shape of the arterial waveform

The area under the curve during systole minus the bacground diastolic area are assumed to be proportional to the stroke volume

CO is derived from the SV and the Heart rate (CO=SVxHR)

Potential for noninvasive CO monitoring

Question 21

_{Sources of errors in CO determination}

T/F: With Thermodilution CO monitoring, the computer bases calculation of CO on a specific volume

Answer 21

True

Volume that is less than what the computer is set to compute will result in a falsely elevated CO, and vice versa

Question 22

_{Sources of errors in CO determination}

An error of 0.5 ml out of 10ml of injectate volume alter CO by what percentage?

Answer 22

5%

Question 23

_{Sources of errors in CO determination}

Volume that is less than which the computer is set result in a CO value that is:

Answer 23

Falsely high

_{(Smaller area under the curve)}

Question 24

_{Sources of errors in CO determination}

Volume that is more than which the computer is set result in a CO value that is:

Answer 24

Falsely low

_{(Larger area under the curve)}

Question 25

_{Sources of errors in CO determination}

How fast and over what period of time should the bolus be injected

Answer 25

Rapidly and smoothly over 4 seconds

Question 26

_{Sources of errors in CO determination}

How could injection of room temperature into a severely hypothermic pt affect CO reading?

Answer 26

Could result in inaccurate reading

Question 27

_{Sources of errors in CO determination}

T/F: Rapid infusion of other fluids does not affect CO reading

Answer 27

False

Rapid infusion of other fluids may cause inaccurate reading

Question 28

_{Sources of errors in CO determination}

How could intrathoracic shunts, tricuspid regurgitation, and pulmonic regurgitation affect CO measurement?

Answer 28

Will decrease accuracy of CO measurement

Question 29

_{Sources of errors in CO determination}

Why would cyclic changes in CO occur in patients on mechanical ventilation?

Answer 29

Because of changes in venous return and thoracic pressure during ventilation cycles

Question 30

_{Sources of errors in CO determination}

How many CO samples should be obtained and averaged for more accuracy?

Answer 30

Three

Question 31

_{Sources of errors in CO determination}

T/F

The full patient picture as well as ensuring that the proper technique is used while obtaining CO measurement are equally important.

Answer 31

True