Cradiac Output Monitoring Flashcards
(42 cards)
1
Q
How is cardiac output defined?
A
- amount of blood delivered from the left ventricle to systemic circulation on a per minute basis (ml/min)
CO = SV x HR
2
Q
What are the determinants of MAP?
A
CO and SVR
3
Q
What are the determinants of CO?
A
HR + Stroke Volume
4
Q
What are the determinants of stroke volume?
A
- Contracility
- Preload
- Afterload
5
Q
What are the determinants of HR?
A
Sympathetic vs. parasympathetic NS
6
Q
What are the local and systemic determinants of SVR?
A
Local:
- CO2
- PGs
- NO
- Histamine
Systemic:
- Vasopressin
- Angiotensin II
- Sympathetic NS
7
Q
What are the determinants of oxygen delivery (DO2)?
A
CO and CaO2
8
Q
Name the three determinants of CaO2?
A
ml of O2 per dl of blood:
- Hb
- SaO2
- PaO2
9
Q
How is DO2 defined?
A
Oxygen delivery in ml per minute
10
Q
Draw the “tree of life”?
A
11
Q
Name 6 factors affecting preload?
A
- circulating volume
- venous tone
- body position
- intrathoracic pressure
- pericardial pressure
- RAP
12
Q
How is preload defined? What law is important for it?
A
- stretching of the ventricle prior to contraction (systoly)
As end-diastolic volume increases, there is increased stretching of the ventricular muscle fibers (loading) that then enhances contractile force (at least up to a certain point)
- Frank-Starling law
13
Q
What is afterload?
A
force (pressure) needed to achieve ventricular out-flow
(amount of work the heart must do in order to move blood forward during systolic ejection)
14
Q
What is the effect of increased afterload on the heart?
A
- decreased velocity of cardiac muscle fibre shortening
- greater pressures needed to open pulmonic/aortic valves
- decreased SV
- increased ESV
15
Q
How is the relationship beetween SV and afterload?
A
- inverse
16
Q
Name 3 factors affecting afterload?
A
- PVR/SVR
- function + integrity of cardiac valves
- ventricular chamber size
17
Q
How is contracility defined?
A
ability of cardiac muscle fibers to develop tension at a given preload and afterload
–> impacts the force of ventricular contraction (inotropy)
Stronger contraction –> mroe significant reduction in ventricular volume during systole –> increase in SV
18
Q
How is the relationship beetween contracility and CO?
A
direct
19
Q
Name 4 factors influencing contracility (independent of preload and afterload?
A
- body temperature
- HR
- ischaemia
- balance between SNS and PNS activation
20
Q
Name 9 causes of preload reduction?
A
21
Q
Name 7 causes of reduction in cardiac function?
A
22
Q
Name 4 causes of increased afterload?
A
23
Q
Name one disease process where CO monitoring might be beneficial and why?
A
- Sepsis
- high CO and low CO possible in hypotensive states
- guide therapy for use of fluids or positive inotropes
24
Q
What is the formula for calculation of SVR?
A
SVR = (MAP-CVP)/CO
25
What is the Cardiac Index?
CI = CO referenced against bodyweight (ml/min/kg) or body surface area (ml/min/m2)
26
What are normal CI for dogs and cats?
dogs: 125-200 ml/kg/min
cats: 120 ml/kg/min
27
Name 6 categories of technique used for CO monitoring?
- Fick method (Oxygen consumption or CO2 rebreathing)
- Indicator dilution (thermodilution, lithium dilution)
- pulse contour analysis
- echocardiography
- transthoracic Doppler
- Pulse wave transit time
28
Desribe the technique of Fick Oxygen Consumption for CO monitoring? What are the cons? How does it compare to dilution techniques?
= original gold standard
--> tissue oxygen consumption (VO2) depends on product of CO and the difference between arterial (CaO2) and venous oxygen (CvO2) content.
VO2 = COx(CaO2-CvO2) --> CO=VO2 /(CaO2 xCvO2)
VO2: measuring O2 concentration difference between inhaled and exhaled air in the amount of O2 inhaled over a period of time (3min)
Assumptions and considerations:
* Steady state oxygen consumption is assumed
* No intracardiac shunts (no abnormal blood flow bypassing lungs) present
* Accurate VO2 measurement is critical
Cons:
- Patient needs to be intubated
- arterial sampling
- mixed-venous: ideally from PA, but cranial VC also acceptable
- no real-time assessment of CO
- major intracardiac or intrapulmonary shunting will affect measured variables
compares well to indicator dilution techniques in dogs and cats
29
What is the formula for oxygen content in the blood (venous or arterial)?
CxO2 (mlO2/L) =1.36 x [Hb] x SO2 + 0.03 x PO2
0.003 of mlO2/dl
30
Desribe the technique of Fick's based carbon dioxide rebreathing methods for CO monitoring? What are the downsides? How does it compare to dilution techniques?
- based on CO2 production
Principle:
--> applies Fick principle to CO2, where CO is calculated by dividing the CO2 production (VCO2) by the difference in CO2 content between mixed venous + arterial blood:
CO=VCO2/(CvCO2−CaCO2)
Rebreathing maneuver:
--> The patient breathes into a closed or semi-closed circuit containing a known volume of gas enriched with CO2 where partial rebreathing occurs. This causes changes in partial pressure of CO2 (PCO2) in the lungs and blood over a short period.
Measurement of CO2 content:
--> expired CO2 concentration is continuously measured by capnography, allowing estimation of CO2 elimination (VCO2). The venous CO2 partial pressure (PvCO2) is estimated using mathematical models like the exponential rise or equilibrium method by analyzing the increase in end-tidal PCO2 during rebreathing.
Calculation:
--> Using measured VCO2 and estimated arterial + venous CO2 content difference, CO is derived.
Downsides:
- need to be intubated
- more accureacte if on MV
- volume of the rebreathing circuit limits the size of patient on which it can be used
Gunkel et al (JVECC 2004) ound good agreement and correlation using this method when compared with an indicator dilution technique
Yamashita et al (J Vet Med Sci 2007) found significant bias
31
Desribe the indicator dilution method for CO monitoring?
- injection of a known quantity of a marker (cold saline, lithium) at one location and subsequent measurement at a remote location
- curve is generated reflecting the change in concentration over time
- area under that curve is inversely proportional to CO, as a higher CO state will result in faster dilution of the indicator and a smaller curve
2 possibilites:
- measurement in the pulmonary artery after injection into the RA
- transpulmonary: injection in venous circulation with detection downstream in the arterial circuit
32
Describe thermodilution method for CO monitoring?
Swan Ganz catheter is placed through the jugular vein and has a thermistor tip that terminates in the pulmonary artery
fixed amount of cold saline is injected through the proximal port that will mix in the RA and eventually pass through the PA to be detected by the thermistor
conflicting evidence whether the use of PACs in clinical decision making has any beneficial impact on patient outcome
33
Name two methods for confirmation of the right location in pulmonary artery catheterisation?
1. fluoroscopy
2. detection of pulmonary artery pressure waveform
34
Name 3 complications of pulmonary artery catheter placement?
- pulmonary thromboembolism
- pneumothorax
- blood- stream infections
35
What is transpulmonary thermodilution?
- indicator: temperature
- administering cold saline into venous circulation, with detection by a thermistor-tipped arterial catheter (femoral artery)
- comparable CO determination compared with PAC in humans and lithium dilution in dogs
36
Describe the method of lithium dilution for CO monitoring? What are lmitations of this technique?
- indiator: lithium
- administering lithium into a central or peripheral vein and then measuring arterial lithium levels (e.g., dorsal metatarsal) and using a peristaltic pump to draw blood across the lithium sensor
- good correlation between lithium dilution and thermodilution, even in circumstances of varying hemodynamic states
Limitations:
- cost of equipment
- lithium accumulation (especially in smaller patients)
- amount of blood needed to be withdrawn across the lithium sensor
37
Describe the method of Pulse Contour/Pulse Pressure Analysis for CO monitoring? What are the current limitations? How does it correlate to thermodilution?
- beat-to-beat CO assessment
Basic principle:
* arterial blood pressure waveform is a result of SV and dynamic properties of the arterial vascular tree (compliance, resistance)
* Pulse contour analysis converts shape and characteristics of this pressure waveform into a SV estimate --> x HR = CO
* involves continuous high-frequency sampling of the arterial pressure waveform (e.g., 100-1000 Hz) to calculate the area under the systolic portion of the curve or related parameters like PPV
Calibration:
Some pulse contour systems require initial calibration with an independent CO measurement (e.g., thermodilution or lithium dilution) to estimate patient-specific arterial compliance and resistance
Others use patient demographic data (age, height, weight) + mathematical models (internal nomograms) for uncalibrated estimation
- reasonable correlation between thermodilution and PiCCO (Pulse Contour Cardiac Output)
- femoral arterial catheter necesssary for PiCCO
- other studies failed to show good correlation or trending between CO measured by thermodilution or lithium dilution and any of these systems
- algorithms are based on people
38
Describe the method of transthoracic ultrasound for CO monitoring? How does it compare to thermodilution?
- blind assessment of aortic or pulmonic flow velocity waveforms across the chest via Doppler ultrasound --> in conjunction with the vessel cross-sectional area --> determination of SV --> multiplied by HR = CO
USCOM:
continuous-wave spectral Doppler probe is placed over the thoracic inlet (for aortic flow) or below the xyphoid (for pul- monary artery flow)
device has an algorithm (based on people) to provide vessel cross-sectional area relative to body surface area
animals: direct determination of this value must be made using echocardiography + manually entered
- CO measurements exceeded the limits of agreement, but overall trended with hemodynamic changes when compared to thermodilution
38
Name 2 possibilities to monitor CO through echocardiography? How does it correlate to thermodilution or cardiac MRI? What are the limitations?
1. measuring the cross-sectional area (CSA) of the left ventricular outflow tract (LVOT) + the velocity-time integral (VTI) of blood flow through the LVOT = SV --> multiplied by HR = CO
2. determination of LVEDV and LVESV --> difference between these two values = SV --> multiplied by HR = CO
- strong correlation when compared with CO determined by thermodilution or cardiac MRI
Limitations:
- extensive training
- no real-time assessment
39
Describe the method of pulse wave transit time for CO monitoring?
--> time from cardiac contraction to generation of pulse = inversely related to CO (the longer the time, the smaller the CO)
- measured as the time from the ECG R-wave peak to the rise point of the pulse oximeter waveform (30% of the peak height is achieved)
- proprietary software necessary
- needs to be calibrated against another CO measurement (e.g. lithium or thermodilution)
- PWTT has shown the ability to detect changes in CO, though limits of agreement in comparison to reference CO measurement were beyond acceptable range
40
What is DO2?
Oxygen delivery to tissues = ml of O2 delivered per minute
41
Explain the expected changes in CO, contractility and SCR in hypovolemic, obstructive, cardiogenic and maldistributive shock.
