Mod1: Monitoring for Cardiac Surgery - RIGHT HEART CARDIAC OUTPUT MONITORING Flashcards
MEASURING CARDIAC OUTPUT
What was historically considered the “Gold standard” for calculating Cardiac Output (CO)?
The Fick method
MEASURING CARDIAC OUTPUT - Fick method
What does the Fick Method indicates? How is it calculated?
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
MEASURING CARDIAC OUTPUT - Fick method
Why is the Fick method rarely used in clinical practice?
Difficulty in collecting and analyzing the different gas concentrations
Measurement of oxygen uptake is technically demanding
CARDIAC OUTPUT MONITORING
Cardiac Output is defined as:
The total blood flow generated by the heart in one minute
CARDIAC OUTPUT MONITORING
How is CO calculated?
CO = SV x HR
Also know how SV is calculated
CARDIAC OUTPUT MONITORING
What are normal CO values in a normal adult at rest?
Range 4 - 6.5 L/min
CARDIAC OUTPUT MONITORING
T/F: CO provides global assessment of circulation
True
CARDIAC OUTPUT MONITORING
CO can be used with other variables to compute additional hemodynamic values, such as:
SVR, PVR
CARDIAC OUTPUT MONITORING
T/F: CO must be considered within clinical context of the patient
True
CARDIAC OUTPUT MONITORING
Why is CO often expressed as Cardiac Index? How is Cardiac Index (CI) calculated?
To compensate for variations in body size
CI = CO/BSA
CARDIAC OUTPUT MONITORING
What are the Four determinants of cardiac output?
Heart rate - Preload - Afterload - Contractility
Which is logically CO = SV x HR
MEASURING CARDIAC OUTPUT
What’s the most widely used CO measurement in the OR?
Thermodilution
If done carefully, the results are within 5-10% of other methods
MEASURING CARDIAC OUTPUT
Explain the mechanics of Thermodilution
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
MEASURING CARDIAC OUTPUT
Why is it important to time Thermodilution with respiratory cycle?
As much as 10% difference
Due to changes in pulmonary blood flow during respiration
MEASURING CARDIAC OUTPUT
T/F: The cardiac output is INVERSELY related to the area under the thermodilution curve
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
MEASURING CARDIAC OUTPUT
Why is a High CO associated with a small area under curve?
Due to rapid blood flow washout
MEASURING CARDIAC OUTPUT
Why is a Low CO associated with a large area under the curve?
Due to slow passage of blood flow through heart
MEASURING CARDIAC OUTPUT
What are the different ways CO can be measured?
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
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?
Continuous Mixed venous Oximetry Pulmonary Artery Catheter (SvO2 catheter)
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?
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
Sources of errors in CO determination
T/F: With Thermodilution CO monitoring, the computer bases calculation of CO on a specific volume
True
Volume that is less than what the computer is set to compute will result in a falsely elevated CO, and vice versa
Sources of errors in CO determination
An error of 0.5 ml out of 10ml of injectate volume alter CO by what percentage?
5%
Sources of errors in CO determination
Volume that is less than which the computer is set result in a CO value that is:
Falsely high
(Smaller area under the curve)
Sources of errors in CO determination
Volume that is more than which the computer is set result in a CO value that is:
Falsely low
(Larger area under the curve)
Sources of errors in CO determination
How fast and over what period of time should the bolus be injected
Rapidly and smoothly over 4 seconds
Sources of errors in CO determination
How could injection of room temperature into a severely hypothermic pt affect CO reading?
Could result in inaccurate reading
Sources of errors in CO determination
T/F: Rapid infusion of other fluids does not affect CO reading
False
Rapid infusion of other fluids may cause inaccurate reading
Sources of errors in CO determination
How could intrathoracic shunts, tricuspid regurgitation, and pulmonic regurgitation affect CO measurement?
Will decrease accuracy of CO measurement
Sources of errors in CO determination
Why would cyclic changes in CO occur in patients on mechanical ventilation?
Because of changes in venous return and thoracic pressure during ventilation cycles
Sources of errors in CO determination
How many CO samples should be obtained and averaged for more accuracy?
Three
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.
True
