Cardiac Output and Blood Flow Flashcards
What are techniques for measuring CO and blood velocity? (7)
Fluid velocity
Flow probes– ultrasonic, electromagnetic
Balistocardiography
Fick determination (indicator dilution)
Indicator dilution
- Dye (Indocyanine green (ICG) or cardio green)
- Thermal
- Lithium
Bioimpedance
Airway gases
Rebreathing methods
How does velocity relate to frequency when using doppler or ultrasonic method?
the change in frequency is directly proportional to velocity
The frequency of the doppler/ultrasonic beam is generally in _____.
MHz
Doppler and ultrasonic velocity measurement is often used in the operating room to determine what?
venous air embolism
cardiac output
blood velocity in peripheral vessels during vasc surgery
return-to-flow systolic BP
locating arteries (ultrasound)
How does a transtracheal doppler measure cardiac output?
flow = velocity * area
Continuous wave doppler measures velocity of blood flow in the PA or aortic root
Gated doppler doppler determines the diameter of the pulmonary artery or the aortic root.
Why would espohageal doppler cardiac output be slightly off with respect to total CO?
- Estimate of CO is based only on descending thoracic aorta, which does not include the portion of CO in the ascending aorta.
- Not accurate when flow is turbulent with tachycardia and aortic stenosis
When is an esophageal Doppler contraindicated?
esophageal disease
severe coagulopathy
poorly tolerated in awake pts
Why do we use transcranial doppler?
Useful for detecting emboli during carotid surgery and CPB
Useful for detecting brain death
Where does the transcranial doppler transmit sound waves anatomically?
temporal bone
basilar arteries
What is balistocardiography?
It is quantitative seismocardiography.
Seismocardiography is non-invasive measurement of the accelerations in the chest wall produced by myocardial movement to determine CO.
Uses a marble slab and mercury.
What is the Dagmar CHM system?
What is this schematic circuit comprised of?
Contactless Heart Monitoring
Band pass active filter, amplifier, oscilloscope, display
What is the Fick determination of CO?
Flow (Q dot) = O2 consumption
(CaO2 - CvO2) /100ml blood
What does this information allow you to calculate?
Fick determination of CO
When determining CO using the Fick principle, how are the following values collected?
oxygen consumption (VO2)
CvO2
CaO2
Exhaled air is collected to measure O2 consumption per min.
Blood is withdrawn from the PA through a catheter into a cuvette oximeter
Arterial oxygen content is measure from any systemic artery.
What is the Stewart-Hamilton method? (4)
Dye dilution CO
Bolus injection in RA
Continual withdrawal of arterial blood from brachial/radial artery through a densitometer to get concentration of indicator as a function of time
Volume = mass of indicator / concentration
What indicators are used in Stewart-Hamilton method?
Indocyanine Green (ICG)
Cardio Green
What do the arrows indicate when using the Stewart-Hamilton method of determining CO?
Exponential curve– below the curve (area) is primary circulation.
Then, recirculation curve appears.
Where does the injectate disperse from the Swan-Ganz catheter?
proximal port, 30 cm from distal end
How do you expect the thermodilution curve to appear?
Exponential curve reaches a peak then exponential decay.
Peak of curve indicates max. temp change.
What does the textbook say regarding thermodilution?
Take 3 thermodilutions then take the average in succession.
What is the equation for CO?
RT injectate can be within ___% accuracy instead of icing injectate.
20
What situation can result in an erroneous CO reading?
Warm room with a cold patient
Identify the following thermodilution curves
A. Normal
D. Interrupted Injection
C. Low CO
F. Baseline temp shift following CPB
B. High CO
E. Tricuspid regurgitation – result in underestimation of CO
What is the Stewart-Hamilton equation of CO?
What happens to CO calculations when the Swan is placed in the femoral artery?
Altered CO calculation due to fluid warming in the line.
If we inject 5 ml of injectate when the computer expects 10ml, what occurs the CO value?
erroneously increased CO is calculated
What is the most accurate method for measuring injectate temperature?
Thermistor at injection port as well as thermistor at distal end.
Factors that influence the accuracy of thermodilution of CO
- Intracardiac shunts
- Tricuspid or pulmonic valve regurge
- Inadequate delivery of indicator
- Thermistor malfunction from fibrin or clot
- PA temperature fluctuations from CPB
- Respiratory cycle influence–turn ventilator off or perform at end exhalation to correct
The difference getween the injectate tempt and the pt’s temp should mbe more than ___ºC for optimum repeatability.
10
What should you not do relating to IV flow when calculating CO?
Do not change the flow rate after injection or it will produce falsely lower CO because the curve appears larger than that just related to the real injectate volume.
Turn off IV by clamping while measuring.
How will ventilator cycling change CO?
May change the CO by altering venous return (preload)
What effect can the bouvie have on CO readings?
Electrocautery may produce bizarre curves that may interfere in calculating CO.
What is the accuracy of CO readings using thermal dilution?
Typically ranges from at least 15-25% depending upon the operator. Ideal repeatability is in the range of 5% for the most meticulous operators.
Extremely operator dependent
What effect on CO readings can rapid infusion of IV fluids cause?
The measured CO is significantly less than CO determined under control conditions.
Think of greater change in temperature results in lower CO reading.
Describe the continuous thermodilution method of determining CO.
Thermal filament on catheter that turns on/off every 30-60 secs.
The balloon is rarely up at this time.
The cross correlator matches the input signal to the output signal in the PA.
Does NOT respond to rapid blood loss.
Where should the proximal injectate port and thermal filament be located?
Proximal injectate should be located in RA
Thermal filament should be located in RV
How does the transpulmonary thermodilution method work?
Normally used in ICUs
Necessary to have a central venous catheter and a near-centrally placed (femoral, axillary, or brachial) arterial catheter. It is still relatively invasive, but less than PAC
What is impedance cardiography?
High frequency to prevent shock
Low voltage to prevent burn
As blood is injected into thorax, CO measured
Very noisy, not really used in practice–respirations and blood volume changes produce noisy output.
How is impedance cardiography based upon?
Pt height and weight
What are problems with impedance cardiography?
Motion artifact, electrical noise (ESU)
Electrode placement precludes many procedures
Pleural or pericardial effusions
Hematomas
Pulmonary edema
Metallic osteosynthesis material
Pregnancy
Chest tubes
Obesity
Myocardial valvular insufficiency and shunts
What is NICO?
Partial rebreathing of CO2 to determine CO
Applies Fick equation
What is the pulse contour method of determining CO?
attach to art line
area under systolic portion of art waveform
related by means of characteristic impedance of the aorta
How does pulse contour calibrate?
Patient-specific calibration factor (determined by thermodilution)
Basically need accurate CO from Swan Ganz first.
What is the name of the pulse contour system?
FloTrac
What is the name of the lithium dilution method
LiDCO Plus
