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Monitoring > Cradiac Output Monitoring > Flashcards

Cradiac Output Monitoring Flashcards

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)
  • blood volume ejected with each cardiac contraction (stroke volume, SV) times the number of contractions per minute (heart rate, HR)
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2
Q

What are the determinants of MAP?

A

CO and SVR

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3
Q

What are the determinants of CO?

A

HR + Stroke Volume

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4
Q

What are the determinants of stroke volume?

A
  • Contracility
  • Preload
  • Afterload
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5
Q

What are the determinants of HR?

A

Sympathetic vs. parasympathetic NS

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6
Q

What are the local and systemic determinants of SVR?

A

Local:
- CO2
- PGs
- NO
- Histamine

Systemic:
- Vasopressin
- Angiotensin II
- Sympathetic NS

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7
Q

What are the determinants of oxygen delivery (DO2)?

A

CO and CaO2

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8
Q

Name the three determinants of CaO2?

A

ml of O2 per dl of blood:
- Hb
- SaO2
- PaO2

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9
Q

How is DO2 defined?

A

Oxygen delivery in ml per minute

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10
Q

Draw the “tree of life”?

A
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11
Q

Name 6 factors affecting preload?

A
  • circulating volume
  • venous tone
  • body position
  • intrathoracic pressure
  • pericardial pressure
  • RAP
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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

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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)

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14
Q

What are the sequelae of increased afterload?

A
  • decrease in velocity of cardiac muscle fibre shortening
  • greater pressures needed to open pulmonic/aortic valves
  • reduction in stroke volume
  • greater residual end-systolic ventricular volume
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15
Q

How is the relationship beetween stroke volume and afterload?

A
  • inverse
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16
Q

Name 3 factors affecting preload?

A
  • pulmonic and SVR (for the right and left ventricle, respectively)
  • function and integrity of cardiac valves
  • ventricular chamber size
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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 5 factors influencing contracility (independent of preload and afterload?

A
  • body temperature
  • HR
  • ischaemia
  • balance between SNA and PNS activation
20
Q

Name 9 causes if preload reduction?

A

Hypovolemia:
- Haemorrhage
- Severe Dehydration
- Edema/Cavitary effusions

Obstructive:
- Pericardial effusion
- GDV
- Mesenteric volvulus
- Caval/portal venous occlusion
- Severe pleural space disease
- Pulmonary thromboembolism

21
Q

Name 7 causes of reduction in cardiac function?

A

Primary:
- Cardiomyopathy
- Valvular disease
- Tachy- or bradyarrythmias

Secondary:
- SIRS/Sepsis
- Electrolyte abnormalities
- Severe hypoxia
- Severe acidosis/alkalosis

22
Q

Name 4 causes of increased afterload?

A
  • Sytemic hypertension
  • Aortic stenosis
  • Aortic regurgitation
  • Peripheral vasoconstrictions
23
Q

Name one disease process where CO monitoring might be beneficial and why?

A
  • Sepsis
  • can have both high CO and low CO hypotensive states, measurement can help guide therapy regarding use of fluids or positive inotropes
24
Q

What is the formula of SVR?

A

SVR = (MAP-CVP)/CO

25
Q

What is the Cardiac Index?

A

CI = CO referenced against bodyweight (ml/min/kg) or body surface area (ml/min/m2)

26
Q

What are normal CI for dogs and cats?

A

dogs: 125-200 ml/kg/min
cats: 120 ml/kg/min

27
Q

Name 6 techniques of CO monitoring?

A
  • Fick method (Oxygen consumption or CO2 rebreathing)
  • Indicator dilution (thermodilution, lithium dilution)
  • pulse contour analysis
  • echocardiography
  • transthoracic Doppler
  • Pulse wave transit time
28
Q

Desribe the technique of Fick Oxygen Consumptino for CO monitoring (original gold standard)? What are the downsides? How does it compare to dilution techniques?

A

based on the notion that tissue oxygen consumption (VO2) will be dictated by the product of CO and the difference between arterial (CaO2) and venous oxygen (CvO2) content.

CO=VO2 /(CaO2 xCvO2)

VO2: measuring oxygen concentration difference between inhaled and exhaled air in the amount of oxygen inhaled over a period of time (typically 3 minutes)

Downsides:
- Patient needs to be intubated
- arterial sampling (ideally from the pulmonary artery, but cranial VC also acceptable)
- no real-time assessment of CO
- major intracardiac or intrapulmonary shunting of blood will result in changes to the measured variables

compares well to indicator dilution techniques in dogs and cats

29
Q

What is the formula for oxygen content in the blood (venous or arterial)?

A

CxO2 =1.36 x [Hb] x SO2 + 0.003 x PO2

30
Q

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?

A
  • based on CO2 production
  • amount of CO2 expired is a function of cellular metabolism and CO driving blood from the tissues to the lungs
  • ETCO2 reflects changes in perfusion (CO) relative to changes in inspired CO2
  • also considers pulmonary shunt fraction by comparing inspired oxygen to arterial oxygen saturation

CO=Difference in CO2 elimination and end-tidal CO2 Difference in ETCO2 between rebreathing and non-rebreathing

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
Q

Desribe the indicator dilution method for CO monitoring?

A
  • 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 detec- tion downstream in the arterial circuit

32
Q

Describe thermodilution method for CO monitoring?

A

Swan Ganz catheter is placed through the jugular vein and has a therm- istor 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
Q

Name two methods for confirmation of the right location in pulmonary artery catheterisation?

A
  1. fluoroscopy
  2. detection of pulmonary artery pressure waveform
34
Q

Name 3 complications of pulmonary artery catheter placement?

A
  • pulmonary thromboembolism
  • pneumothorax
  • blood- stream infections
35
Q

What is transpulmonary thermodilution?

A
  • 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
Q

Describe the method of lithium dilution for CO monitoring? What are lmitations of this technique?

A
  • 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 hemody- namic states

Limitations:
- cost of equipment
- lithium accumulation (especially in smaller patients)
- amount of blood needed to be withdrawn across the lithium sensor

37
Q

Describe the method of Pulse Contour/Pulse Pressure Analysis for CO monitoring? What are the current limitations? How does it correlate to thermodilution?

A
  • beat-to-beat CO assessment
  • utilize area under the pressure waveform and mathematical models to account for differences in vascular compliance to calculate CO
  • some sytems require repeated calibration with lithium dilution (PulseCO) or transpulmonary thermodilution (PiCCO)
  • reasonable correlation between thermodilution and PiCCO
  • 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 (tendency to overestimate CO in low output states + underestimate in high output states - algorithms are based on people)
38
Q

Describe the method of transthoracic ultrasound for CO monitoring? How does it compare to thermodilution?

A
  • 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
Q

Name 2 possibilities to monitor CO through echocardiography? How does it correlate to thermodilution or cardiac MRI? What are the limitations?

A
  1. measurement of flow velocity in the RV outflow track and aortic diameter –> product of these two = 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
Q

Describe the method of pulse wave transit time for CO monitoring?

A
  • based on notion that the time from cardiac contraction to the generation of a pulse is inversely related to CO (the longer the time, the smaller the CO)
  • PWTT can be measured as the time from the electrocardiogram R-wave peak to the rise point of the pulse oximeter waveform (the point at which 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

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