III. CO Monitoring Flashcards
The Fick principle is used to measure what?
Cardiac Output
Which method, according to the Fick principle, is considered the scientific gold standard of cardiac output measurement?
The Direct Method
For practical purposes, which method of cardiac measurement do we prefer (direct/indirect)?
Indirect
Fick’s Law states, the total uptake of a substance by the peripheral tissues, is equal to what two things?
- The product of the blood flow to the peripheral tissues
- Arterial-Venous concentration difference
General cardiac output (CO) equation according to Fick’s Law:
CO = (VO2)/(Ca-Cv)
Cardiac Output is equal to oxygen consumption divided by the arteriovenous oxygen content difference
this equation is later expanded so that it may be used more practically in the clinical setting
How do we calculate oxygen consumption?
uncertain of practicality of this equation; how do we derive CO; avg VO2 constant is provided later essentially nullifying this equation
VO2 = (COxCa) - (COxCv)
oxygen consumption is equal to the amount of oxygen delivered (COxCa) minus the amount of oxygen taken away/absorbed (COxCv)
What is the equation to determine arterial concentration of oxygen?
Ca=SaO2 x Hgb x 1.34
What is the equation to determine the amount of oxygen remaining in venous blood?
Cv = SvO2 x Hgb x 1.34
same as arterial equation
How do we get the most accurate measure of Venus oxygen content?
PA catheter placed in pulmonary artery
What three pieces of information do we need in order to calculate a patient’s cardiac output (using scientific “Direct” method)?
- OxygenConsumption (VO2): direct method would require spirometry measurement via “Douglas Bag method + Analyzer” {V=volume}
- Arterial oxygen concentration (Ca): direct method would require LA measurement
- Venous oxygen concentration (Cv): direct method would require PAC measurement
Practical Indirect Fick Method (equation) of calculating Cardiac Output (CO):
the method most likely used in the OR
CO = (125 x BSA)/[(SaO2 - SvO2) x Hgb x 1.34 /10]
dont forget to divide denominator by 10 IOT convert answer from dL to L
- Avg VO2 Constant: 125 mL O2/min (>70: use 110)
- Body Surface Area (BSA): will be provided
- Arterial Oxygen Saturation (SaO2): derived from ABG
- Venous Oxygen Saturation (SvO2): derived from PAC (can substitute ScvO2 derived from CVC)
- Constant: 1.34 (ratio of oxygen bound per gram of Hgb)
What pieces of information do we need to derive cardiac output using the practical Fick method?
- Height (m)
- Weight (kg)
- Hgb (CBC or H&H)
- SaO2 (ABG)
- ScvO2/SvO2
….also remember the necessary constants
Height and weight gives us BSA in m^2
DIRECT FICK METHOD:
What is the normal “resting” mL/kilogram/min VO2 measurement?
Normal mL/min measurement?
3.5 mL/kg/min (relative rate)
~250 mL/min (absolute rate)
These are not “VO2 Max” figures
DIRECT FICK METHOD:
Normal CvO2 measurement from PA catheter?
~150 mL/L
DIRECT FICK METHOD:
Normal CaO2 measurement from ABG?
~200 mL/L
List the features of the Douglas Bag used for DIRECT measurement of oxygen consumption (VO2):
- One way intake valve
- Gas collection bag
- gas analyzer
sample taken from gas collection bag and measured by analyzer, compares difference in inspired vs expired oxygen content
Fick Principle applied to CO2 rebreathing:
Cardiac output is proportional to the change in ____ divided by the change in ____ resulting from a brief rebreathing period.
- CO2 Elimination
- End-Tidal CO2
Rebreathing measurements are taken how often?
Every 3 minutes for 35 seconds
Fick CO2 rebreathing machines offer the following:
- continual ____ monitoring
- breath-by-breath measurements of ____.
- Cardiac output
- CO2 elimination
Inaccuracies may occur with the Fick method when?
Inaccurate:
- using indirect values
- hemodynamic changes
- P. HTN
- HF
- Narrow arteriovenous oxygen content differences (high output states)
- Intracardiac shunts( (mixing of blood)
- Hyperdynamic consumption (febrile, tachycardia, pneumonia, sepsis, burns)
- Hypodynamic consumption (hypothermia, paralysis)
What is the method of CO measurement that employs temperature measurement via a PAC?
Thermodilution (TDCO/ICO)
this is the practical & clinical gold standard for CO measurement
Describe steps of thermodilution measurement:
1. Cold saline bolus into PAC proximal port (RA)
2. Blood pushes cold saline distal through RV into PA
3. Blood temperature is measured at distal PA port
4. Temperature change (warm, cold back to warm) over time is measured
5. Computer plots temperature vs time (Stewart-Hamilton Equation)
6. Area under curve is inversely proportional to CO
Materials needed for Thermodilution:
- 10cc syringe
- 5-10cc injectate (5 or 10 cc D5W or 0.9% NS)
- Connections (Proximal Hub (RA), Thermistor, CO CPU)
- Computer & Monitor
How to perform ICO accurately:
- must have both an accurate ____ temperature and ____ temperature
- Stop other ____
- Injectate usually ____ or ____
- Iced, 0ºC: ____ syringe ok
- Room Tº: ____ syringe
- Inject quickly ____ at ____
- take ____ measurements (avg results within ____%)
- must have both an accurate injectate temperature and patient temperature
- Stop other CVC/PAC infusions
- Injectate usually D5W or 0.9% NS
- Iced, 0ºC: **5 **or 10cc ok
- Room Tº: 10cc
- Inject quickly <4sec at end exhalation
- take 3+ measurements (avg results within** 10%**)
Thermodilution Equation variables:
K1:
K2:
Q:
Tb(t)dt:
K1: density factor
K2: Computation constant
Q: Cardiac Output
Tb(t)dt: change in blood temperature over time
Thermodilution curve:
CO is ____ to area under the curve (temperature over time).
Inversely proportional
Thermodilution Curve:
Small area under curve = ____ CO
High
cold solution is very quickly rewarmed = takes less time to return to baseline Tº
Thermodilution curve:
Large area under curve = ____ CO
Low
Cold solution takes longer to rewarm due to less CO/BF, larger area under curve = takes longer to return to baseline blood Tº
Describe appearance of normal Thermodilution curve
Rapid peak, then decays
During CPB, PA temperature usually ____.
Decreases
this will create an abnormal thermodilution curve, where the end baseline is elevated (colder)
Errors in ICO estimation:
- Temperature
- Volume
- Inadvertent rewarming
- Timing of Injection w/ respiration
- Speed & mode of injection
- IVF administration through CVC
- Hypothermia
- Catheter Dysfunction/malposition
- Cardio Factors
- Abnormal respiratory patterns
- Pediatric patients
- Abnormal HCT (will affect K1 value) = ANEMIC patients
- Pathological conditions
0.5 mL variation of 5mL injectate will cause ____% error
10
Too large injectate volume will ____ CO
Too small injectate volume will ____ CO
- underestimate
- overestimate
Inadvertent hand rewarming of cold solution by 1ºC will cause ____ error.
3% increase
Ventilation can alter PA blood temp by:
0.01 to 0.2ºC
Too slow of injection will ____ CO
Underestimate
Even under ideal circumstances, TDCO measurements have ____ % error rate.
~10
Continuous Cardiac Output (CCO) monitoring is described as ____ ____.
Continuously Intermittent
Nearly Continuous
With CCO, the value displayed is not a “live” number, rather it is the average of the measurements over the past ____ minutes.
3-6
T/F: CCO is the same principle as thermodilution, but is automatic, continual, with no injectate.
TRUE
With regard to CCO, what is responsible for the temperature change of blood, thereby allowing necessary fluctuating temperature measurements to be taken?
Thermal filament placed in the RV portion of PA catheter (measured 15-25 cm downstream)
CCO:
The thermal filament is cycled on and off every ____ seconds IOT take new dilution measurement.
30-60
CCO benefits:
- Excellent correlation to injected TDCO
- Accurate from 1.6-10.6 L/min CO
- Accurate from core temp 33.2º-39.8ºC
- Respirations are accounted for automatically
slower response time vs accuracy of measurement
Flaws of CCO:
- response to acute changes in CO is VERY SLOW
- noticeable changes may take 5-15 min
Describe the use of Trans-pulmonary Thermodilution:
- Cold saline injected via CVC (not a PAC, like TDCO)
- Temperature measured at peripheral artery (femoral, auxiliary, brachial,etc) via A-line thermistor
- Measurement over several cardiac cycles (not affected by respirations)
whatever are two additional values derived from using Transpulmonary Thermodilution?
- Extravascular Lung Volume (Pulmonary Edema)
- Intrathoracic Blood Volume
Describe the process of using Pulse Dye Densitometry?
- IV bolus injection of Indocyanine Green (ICG) (passes through pulmonary circulation)
- Fingertip sensor estimates the arterial concentration of ICG
- Relative ratio of ICG concentration is used to calculate CO
uses transpulmonary thermodilution
Why is ICG dye preferred
- Nontoxic
- Rarely causes allergy
- Exclusive HEPATIC clearance
Drawback to ICG
It hangs around a long time before being cleared, so there’s a 20 min delay between tests
Describe CO measurement using Lithium Dilution:
- Small amount of LiCl injected into CVC or *Peripheral IV**
- Measured using ion selective electrode
- Measurement location is peripheral arterial catheter (A-Line)
Advantages to Lithium Dilution:
- can be injected peripherally
- blood can be sampled from peripherally placed A-Line
Limitations to Lithium Dilution:
- Cannot use on patients undergoing Lithium therapy, pregnant, recent NDMR
- the need to sample blood and it’s disposability
Transthoracic electric bioimpedance method of calculating cardiac output.:
- cardiac output is calculated through changes and ____ during ____.
- Greatly affected by ____ and ____.
- Up to ____% error compared to TDCO
B- cardiac output is calculated through changes and impedance during cardiac cycle.
- Greatly affected by pathologies and motion artifact.
- Up to 43% error compared to TDCO
Gastric tonometry method of acquiring cardiac output:
- balloon is inserted into stomach
- Equilibrates with gastric CO2
- Content is aspirated and compared to arterial CO2 sample
Ultrasound Doppler method of calculating cardiac output:
- Can be performed either____ or ____
- Doppler is aimed at ____
- calculates ____
- Noninvasive/Invasive
- Can be performed either **trans thoracic **or esophageal
- Doppler is aimed at descending aorta
- calculates stroke volume
- ## Noninvasive
Ultrasound Doppler assumes the descending aorta receives how much cardiac output?
70%
What four pieces of information does ultrasound Doppler use to quantify stroke volume?
- Blood velocity.
- Stroke distance.
- Cross-sectional area of the aorta.
- Ejection time.
What are some limitations of ultrasound Doppler?
- Inaccurate in ____ patients and those with pathologies
- Inaccurate measurement of the ____ will cause an error
- ____ dependent.
- Probe misalignment ____ results in an error.
- Inaccurate in hemodynamically unstable patients and those with pathologies
- Inaccurate measurement of the aorta will cause an error
- Operator dependent. (skilled operator)
- Probe misalignment greater than 20° results in an error.
What method of calculating cardiac output will we most likely use clinically?
Pulse contour analysis
Describe how pulse contour cardiac output analysis works:
- Computer generated analysis of ____.
- Does not require a PAC but does require a ____.
- Requires calibration by ____ or ____ measurement
- Computer generated analysis of arterial pressure waveform
- Does not require a PAC but does require a special transducer
- Requires calibration by thermal dilution or indicator dilution measurement
Measured data from pulse contour analysis:
- Stroke volume.
- Stroke volume index
- Cardiac Output
- Cardiac Index
- HR
- SBP, DBP, MAP
7.Max LV contractility - SVV (important for fluid resuscitation)
The PiCCO (Pulse Index Continuous Cardiac Output) uses a combo of what two methods?
- Transpulmonary Dilution (measures CO intermittently to calibrate)
calibrates every hour - Arterial Pulse contour analysis
Describe how PiCCO works:
- PiCCO utilizes a proprietary cannula to monitor ____ and temperature via ____.
- A reference ____ is used to calibrate the ____. (Recalibration should be performed at least every ____ [time].)
- Pulse contour-derived Cardiac output is displayed as the main value of the previous ____ (time).
- Produces new data with every beat of the heart using ____.
- PiCCO utilizes a proprietary cannula to monitor arterial pressure (special A-Line) and temperature via thermistor.
- A reference, cardiac output is used to calibrate the pulse contour data. (Recalibration should be performed at least every eight hours.)
- Pulse contour-derived Cardiac output is displayed as the main value of the previous 12 seconds.
- Produces new data with every beat of the heart using Transpulmonary Thermodilution
Describe LiDCO (Lithium Dilution Cardiac Output):
- incorporates ____ dilution cardiac output to intermittently calibrate its pulse contour analysis based ____ measurement.
- Requires a ____ + ____
- Contraindicated in chronic ____, recent, ____, and ____
- Has been shown to have ____ correlation with the PAC TDCO
- incorporates lithium dilution cardiac output to intermittently calibrate its pulse contour analysis based continuous, cardiac output measurement.
- Requires a standard A-Line + peripheral IV or CVL
- Contraindicated in chronic lithium use, recent, non-depolarizer neuromuscular blocker, and early pregnancy
- Has been shown to have good correlation with the PAC TDCO
How does the LiDCO work:
- A bolus of lithium is flushed through a ____ or ____
- A lithium, sensitive sensor, attached to a ____, detect the concentration of lithium ions in the arterial blood.
- The lithium indicator dilution washout curve on the ‘LiDCOplus’ provides an accurate absolute ____value
- This value is then used to calibrate the ‘LiDCOplus’ to give ____ and derived variables from ____ analysis.
- A bolus of lithium is flushed through a central or venous line
- A lithium, sensitive sensor, attached to a peripheral arterial line, detect the concentration of lithium ions in the arterial blood.
- The lithium indicator dilution washout curve on the ‘LiDCOplus’ provides an accurate absolute cardiac output value
- This value is then used to calibrate the ‘LiDCOplus’ to give continuous cardiac output and derived variables from arterial wave form analysis.
Describe the EV1000
- uses ____ to derive, continuous real time, cardiac output.
- Uses ____ for intermittent calibrations (____ ONLY)
- 3 setups: ____,____, ____.
- uses pulse contour analysis to derive, continuous real time, cardiac output.
- Uses transpulmonary thermodilution for intermittent calibrations (VolumeView ONLY)
- 3 setups: VolumeView System, FloTrac, ClearSight
EV1000 parameters:
- CO
- SV
- SVV
- SVR
- MAP
- Global End-Diastolic Volume (GEDV)
T/F: FloTrac & ClearSight (finger-cuff) modes do NOT use thermodilution to estimate CO.
TRUE
input patient’s size and uses estimate CO
T/F: the VolumeView system does not use Thermodilution to calculate CO.
FALSE
VolumeView System requires what pieces of equipment:
- PAC or CVC (IOT derive CO via Transpulmonary Thermodilution)
- Specialized Arterial Line (femoral or radial) used for distal temperature measurements & pulse contour analysis
FloTrac requirements:
- Input: age, sex , height, weight to calculate BSA & estimate SVR (via aortic impedance)
- pulse waveform = SVI
- SVI x HR = CI (CO indexed to BSA)
- records 2,000 samples of the A-line waveform over 20 seconds and averages them to get a mean BP
no Thermodilution
ClearSight
- noninvasive real time finger pressure waveform
- Continuous advanced hemodynamics
What are a couple clinical applications for the ClearSight
- Helps determine the cause of intraoperative hypotension.
- Helps guide individualized fluid management and goal directed therapy.
Limitation of the ClearSight
- Limited use impatience with PVD or poor peripheral perfusion (reynaud’s dz) cold patients
Use of SPV or PPV can determine ____, which represents the normal interaction between heart and lungs.
Stroke volume variability (SVV)
Normal SVV
7-10 mmHg
SVV > ____% = hypovolemia (fluid responsiveness)
12
pt may respond to 250-500cc fluid challenge
SVV only accurate when following criteria met:
- NSR
- MV greater than or equal to 8mL/kg
- Not open chest (heart/lungs must be interacting)
- Accurate IABP waveform
T/F: Aortic regurgitation (pulses bisferens) causes inaccuracy with Pulse Contour CO.
TRUE
double pea confuses diacritic notch location in computer
ALSO: arrhythmias, algorithm based estimations, high-dose V/D or V/C, intra arterial balloon pumps (IABP), and open chest wounds (intrathoracic pressure) interfere with Pulse Contour CO accuracy
Pulse contour analysis specifically allows for ____, even in hemodynamically unstable patients, less invasive and ____ than PAC methods.
- continuous monitoring a cardiac output
- Faster
What are two factors that control heart rate?
- Nerves
- Hormones
2 factors that control stroke volume
- Blood volume
- Vascular resistance
Fick Principle Picture
Practical Fick Method Equation Picture
Thermodilution CO Curve picture
Thermodilution Curves Comparison Picture
Abnormal Thermodilution Curves Picture
Tricuspid Regurgitation: Blood initially warm, becomes cold after injectate, but because there is regurge, the cold fluid takes longer to advance through RV. This causes the delayed return to baseline warm temperature.
Transpulmonary Thermodilution Picture
Measured Data from Pulse Contour Analysis Picture
Comparison Chart Advantages/Disadvantages of Various CO Devices
