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I&M II > III. CO Monitoring > Flashcards

III. CO Monitoring Flashcards

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1
Q

The Fick principle is used to measure what?

A

Cardiac Output

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2
Q

Which method, according to the Fick principle, is considered the scientific gold standard of cardiac output measurement?

A

The Direct Method

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3
Q

For practical purposes, which method of cardiac measurement do we prefer (direct/indirect)?

A

Indirect

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4
Q

Fick’s Law states, the total uptake of a substance by the peripheral tissues, is equal to what two things?

A
  1. The product of the blood flow to the peripheral tissues
  2. Arterial-Venous concentration difference
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5
Q

General cardiac output (CO) equation according to Fick’s Law:

A

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

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6
Q

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

A

VO2 = (COxCa) - (COxCv)

oxygen consumption is equal to the amount of oxygen delivered (COxCa) minus the amount of oxygen taken away/absorbed (COxCv)

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7
Q

What is the equation to determine arterial concentration of oxygen?

A

Ca=SaO2 x Hgb x 1.34

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8
Q

What is the equation to determine the amount of oxygen remaining in venous blood?

A

Cv = SvO2 x Hgb x 1.34

same as arterial equation

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9
Q

How do we get the most accurate measure of Venus oxygen content?

A

PA catheter placed in pulmonary artery

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10
Q

What three pieces of information do we need in order to calculate a patient’s cardiac output (using scientific “Direct” method)?

A
  1. OxygenConsumption (VO2): direct method would require spirometry measurement via “Douglas Bag method + Analyzer” {V=volume}
  2. Arterial oxygen concentration (Ca): direct method would require LA measurement
  3. Venous oxygen concentration (Cv): direct method would require PAC measurement
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11
Q

Practical Indirect Fick Method (equation) of calculating Cardiac Output (CO):

the method most likely used in the OR

A

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)
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12
Q

What pieces of information do we need to derive cardiac output using the practical Fick method?

A
  1. Height (m)
  2. Weight (kg)
  3. Hgb (CBC or H&H)
  4. SaO2 (ABG)
  5. ScvO2/SvO2

….also remember the necessary constants

Height and weight gives us BSA in m^2

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13
Q

DIRECT FICK METHOD:

What is the normal “resting” mL/kilogram/min VO2 measurement?

Normal mL/min measurement?

A

3.5 mL/kg/min (relative rate)

~250 mL/min (absolute rate)

These are not “VO2 Max” figures

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14
Q

DIRECT FICK METHOD:

Normal CvO2 measurement from PA catheter?

A

~150 mL/L

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15
Q

DIRECT FICK METHOD:

Normal CaO2 measurement from ABG?

A

~200 mL/L

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16
Q

List the features of the Douglas Bag used for DIRECT measurement of oxygen consumption (VO2):

A
  • 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

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17
Q

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.

A
  • CO2 Elimination
  • End-Tidal CO2
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18
Q

Rebreathing measurements are taken how often?

A

Every 3 minutes for 35 seconds

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19
Q

Fick CO2 rebreathing machines offer the following:

  • continual ____ monitoring
  • breath-by-breath measurements of ____.
A
  • Cardiac output
  • CO2 elimination
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20
Q

Inaccuracies may occur with the Fick method when?

A

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)

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21
Q

What is the method of CO measurement that employs temperature measurement via a PAC?

A

Thermodilution (TDCO/ICO)

this is the practical & clinical gold standard for CO measurement

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22
Q

Describe steps of thermodilution measurement:

A

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

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23
Q

Materials needed for Thermodilution:

A
  1. 10cc syringe
  2. 5-10cc injectate (5 or 10 cc D5W or 0.9% NS)
  3. Connections (Proximal Hub (RA), Thermistor, CO CPU)
  4. Computer & Monitor
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24
Q

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 ____%)
A
  • 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%**)
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25
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
26
Thermodilution curve: CO is ____ to area under the curve (temperature over time).
Inversely proportional
27
Thermodilution Curve: Small area under curve = ____ CO
High *cold solution is very quickly rewarmed = takes less time to return to baseline Tº*
28
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*
29
Describe appearance of normal Thermodilution curve
Rapid peak, then decays
30
During CPB, PA temperature usually ____.
Decreases *this will create an abnormal thermodilution curve, where the end baseline is elevated (colder)*
31
Errors in ICO estimation:
1. Temperature 2. Volume 3. Inadvertent rewarming 4. Timing of Injection w/ respiration 5. Speed & mode of injection 6. IVF administration through CVC 7. Hypothermia 8. Catheter Dysfunction/malposition 9. Cardio Factors 10. Abnormal respiratory patterns 11. Pediatric patients 12. Abnormal HCT (will affect K1 value) = ANEMIC patients 13. Pathological conditions
32
0.5 mL variation of 5mL injectate will cause ____% error
10
33
Too large injectate volume will ____ CO Too small injectate volume will ____ CO
- underestimate - overestimate
34
Inadvertent hand rewarming of cold solution by 1ºC will cause ____ error.
3% increase
35
Ventilation can alter PA blood temp by:
0.01 to 0.2ºC
36
Too slow of injection will ____ CO
Underestimate
37
Even under ideal circumstances, TDCO measurements have ____ % error rate.
~10
38
Continuous Cardiac Output (CCO) monitoring is described as ____ ____.
Continuously Intermittent *Nearly Continuous*
39
With CCO, the value displayed is not a “live” number, rather it is the **average** of the measurements over the past ____ minutes.
3-6
40
T/F: CCO is the same principle as thermodilution, but is **automatic**, **continual**, with **no injectate**.
TRUE
41
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)
42
CCO: The thermal filament is cycled on and off every ____ seconds IOT take new dilution measurement.
30-60
43
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*
44
Flaws of CCO:
- response to acute changes in CO is VERY SLOW - **noticeable changes may take 5-15 min**
45
Describe the use of Trans-pulmonary Thermodilution:
1. Cold saline injected via **CVC** (not a PAC, like TDCO) 2. Temperature measured at **peripheral artery (femoral, auxiliary, brachial,etc) via A-line thermistor** 3. Measurement over several cardiac cycles (not affected by respirations)
46
whatever are two additional values derived from using Transpulmonary Thermodilution?
1. Extravascular Lung Volume (Pulmonary Edema) 2. Intrathoracic Blood Volume
47
Describe the process of using Pulse Dye Densitometry?
1. IV bolus injection of Indocyanine Green (ICG) (passes through pulmonary circulation) 2. Fingertip sensor estimates the arterial concentration of ICG 3. Relative ratio of ICG concentration is used to calculate CO *uses transpulmonary thermodilution*
48
Why is ICG dye preferred
1. Nontoxic 2. Rarely causes allergy 3. Exclusive HEPATIC clearance
49
Drawback to ICG
It hangs around a long time before being cleared, so there’s a **20 min delay** between tests
50
Describe CO measurement using Lithium Dilution:
1. Small amount of LiCl injected into **CVC** or *Peripheral IV** 2. Measured using **ion selective electrode** 3. Measurement location is peripheral arterial catheter (A-Line)
51
Advantages to Lithium Dilution:
- can be injected peripherally - blood can be sampled from peripherally placed A-Line
52
Limitations to Lithium Dilution:
- Cannot use on patients undergoing Lithium therapy, pregnant, recent NDMR - the need to sample blood and it’s disposability
53
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
54
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
55
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** -
56
Ultrasound Doppler assumes the descending aorta receives how much cardiac output?
70%
57
What four pieces of information does ultrasound Doppler use to quantify stroke volume?
1. Blood velocity. 2. Stroke distance. 3. Cross-sectional area of the aorta. 4. Ejection time.
58
What are some limitations of ultrasound Doppler? 1. Inaccurate in ____ patients and those with pathologies 2. Inaccurate measurement of the ____ will cause an error 3. ____ dependent. 4. Probe misalignment ____ results in an error.
1. Inaccurate in **hemodynamically unstable patients** and those with pathologies 2. Inaccurate measurement of the **aorta** will cause an error 3. **Operator** dependent. (skilled operator) 4. Probe misalignment **greater than 20°** results in an error.
59
What method of calculating cardiac output will we most likely use clinically?
Pulse contour analysis
60
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
61
Measured data from pulse contour analysis:
1. Stroke volume. 2. Stroke volume index 3. Cardiac Output 4. Cardiac Index 5. HR 6. SBP, DBP, MAP 7.Max LV contractility 8. **SVV** (important for fluid resuscitation)
62
The PiCCO (Pulse Index Continuous Cardiac Output) uses a combo of what two methods?
1. Transpulmonary Dilution (measures CO intermittently to calibrate) *calibrates every hour* 2. Arterial Pulse contour analysis
63
Describe how PiCCO works: 1. PiCCO utilizes a proprietary cannula to monitor ____ and temperature via ____. 2. A reference ____ is used to calibrate the ____. (Recalibration should be performed at least every ____ [time].) 3. Pulse contour-derived Cardiac output is displayed as the main value of the previous ____ (time). 4. *Produces new data with every beat of the heart using ____.*
1. PiCCO utilizes a proprietary cannula to monitor **arterial pressure** **(*special A-Line*)** and temperature via **thermistor**. 2. A reference, **cardiac output** is used to calibrate the **pulse contour data.** (Recalibration should be performed at least every **eight** hours.) 3. Pulse contour-derived Cardiac output is displayed as the main value of the previous **12 seconds**. 4. *Produces new data with every beat of the heart using **Transpulmonary Thermodilution***
64
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
65
How does the LiDCO work: 1. A bolus of lithium is flushed through a ____ or ____ 2. A lithium, sensitive sensor, attached to a ____, detect the concentration of lithium ions in the arterial blood. 3. The lithium indicator dilution washout curve on the ‘LiDCOplus’ provides an accurate absolute ____value 4. This value is then used to calibrate the ‘LiDCOplus’ to give ____ and derived variables from ____ analysis.
1. A bolus of lithium is flushed through a **central** or **venous line** 2. A lithium, sensitive sensor, attached to a **peripheral arterial line,** detect the concentration of lithium ions in the arterial blood. 3. The lithium indicator dilution washout curve on the ‘LiDCOplus’ provides an accurate absolute **cardiac output** value 4. This value is then used to calibrate the ‘LiDCOplus’ to give **continuous cardiac output** and derived variables from **arterial wave form** analysis.
66
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**
67
EV1000 parameters:
1. CO 2. SV 3. SVV 4. **SVR** 5. MAP 6. **Global End-Diastolic Volume (GEDV)**
68
T/F: FloTrac & ClearSight (finger-cuff) modes do NOT use thermodilution to estimate CO.
TRUE *input patient’s size and uses estimate CO*
69
T/F: the VolumeView system does not use Thermodilution to calculate CO.
FALSE
70
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
71
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*
72
ClearSight
- noninvasive real time finger pressure waveform - Continuous advanced hemodynamics
73
What are a couple clinical applications for the ClearSight
1. Helps determine the cause of intraoperative hypotension. 2. Helps guide individualized fluid management and goal directed therapy.
74
Limitation of the ClearSight
- Limited use impatience with PVD or poor peripheral perfusion (reynaud’s dz) cold patients
75
Use of SPV or PPV can determine ____, which represents the normal interaction between heart and lungs.
Stroke volume variability (SVV)
76
Normal SVV
7-10 mmHg
77
SVV > ____% = hypovolemia (fluid responsiveness)
12 *pt may respond to **250**-500cc fluid challenge*
78
SVV only accurate when following criteria met:
1. NSR 2. MV greater than or equal to 8mL/kg 3. Not open chest (heart/lungs must be interacting) 4. Accurate IABP waveform
79
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
80
Pulse contour analysis specifically allows for ____, even in hemodynamically unstable patients, less invasive and ____ than PAC methods.
- continuous monitoring a cardiac output - Faster
81
What are two factors that control heart rate?
1. Nerves 2. Hormones
82
2 factors that control stroke volume
1. Blood volume 2. Vascular resistance
83
Fick Principle Picture
84
Practical Fick Method Equation Picture
85
Thermodilution CO Curve picture
86
Thermodilution Curves Comparison Picture
87
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.
88
Transpulmonary Thermodilution Picture
89
Measured Data from Pulse Contour Analysis Picture
90
Comparison Chart Advantages/Disadvantages of Various CO Devices

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