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553 - Monitoring & CV Patient > Exam 8 - Monitoring CO & Blood Flow > Flashcards

Exam 8 - Monitoring CO & Blood Flow Flashcards

1
Q

CO needed to calculate:

A
  • Stroke Volume
  • Blood O2 transport
  • Intrapulmonary shunting
  • SVR
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2
Q

Normal CO

A

4-8 L/min

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3
Q

What can change CO

A
  • Decrease in contractility
    - MI / Drugs / Acidosis / Hypoxia
  • Decrease in preload
  • Changes in SVR
    - Increase: arteriosclerosis / hypertension
    - Decrease: septic shock
  • Decreased ventricular flow (valve disease)
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4
Q

CO calculation

A

CO = SV x HR

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5
Q

Normal SV

A

60-100 ml/beat

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6
Q

Factors affecting SV

A
  • Preload
  • Afterload
  • Contractility
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7
Q

Normal CI

A

2.5-4 L/min/m^2

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8
Q

Normal HR

A

60-100 bpm

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9
Q

Normal ejection fraction

A

40-60%

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10
Q

CI formula

A

CI = CO/BSA

BSA = body surface area
- Does not account for: 
       Personal build (fat vs muscle)
       Diseases that alter metabolism
       Edema/Diuresis/Ascites (fluid in peritoneal cavity)
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11
Q

SV formula

A

SV = EDV - ESV

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12
Q

Variables affecting CO

A
  • Metabolic rate / O2 demand -> BIGGEST
  • Gender
  • Body size (more CO if bigger)
  • Age (highest in childhood and diminishes with age)
  • Posture
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13
Q

Factors increasing metabolism

A
  • Sepsis
  • Strong emotion
  • Major trauma
  • Surgery
  • Exercise
  • Fever
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14
Q

Female vs Male

A
  • Females 10% less CO than males in similar body mass

- Up to 45% higher if pregnant

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15
Q

Posture and CO

A
  • CO decreases by 20% when standing vs supine
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16
Q

BSA

A

BSA = sqrt of [(cm x kg) / 3600]

17
Q

CO equilibrium

A
  • Pulmonary flow = Systemic flow
  • Measurement from any point in CV system is representative
  • ONLY if free of shunts/disease
18
Q

PFO frequency

A
  • 20-30%

- Hagen et all at Mayo

19
Q

L to R shunting

A
  • Overloads R ventricle
  • Pulmonary flow > Systemic flow
  • In ASD / VSD / PFO / acyanotic congenital anomalies
20
Q

R to L shunting

A
  • Systemic flow > Pulmonary flow

- In Tetralogy of Fallot (TOF) / Cyanotic congenital defects

21
Q

Shunts and CO

A
  • Shunts render all CO measurements invalid

- CO measurements assume equal flow in systemic/pulmonary

22
Q

Regurgitant Heart Lesions

A
  • Goes unmeasured
  • Tricuspid/Pulmonary: recirculation of blood in R heart
  • Mitral regurgitation: jetting contaminates blood at PA sample site
23
Q

Most important hemodynamic measurement

A
  • CO….BP not enough
  • CO may decrease 33% with same measured BP
  • CO < 50% of normal…… life threatening
  • CO < 1 L/min/m2…..Death
24
Q

Fick O2 consumption method

A
  • Invasive
  • CO = VO2 / A-V O2 difference
  • Measures A-V sats and Oxygen uptake by lungs (3.5 ml/kg/min)
  • Advantages: Most accurate when done right
    Most accurate if CO is low
    Good for regurgitant tricuspid/pulmonary valves
  • Disadvantages: Time consuming and meticulous
    Multiple people
    Stable patient
    Hard to be repeatable
    NOT VALID if shunts
    Long wait for results
    Least accurate if high CO
25
Q

Dye-Dilution method

A
  • Invasive
  • Indicators must mix well/non-toxic/stable/not retained
    -O2 / indocyanine dye (green) / iodated albumin / temp
  • inject dye to PA and continuously draw from systemic artery
    -plot on graph…measure area under curve
  • done more in research…not clinically
  • can use bolus or continuous injection…open or closed system
  • Advantages: most accurate with high CO
  • Disadvantages: NOT VALID w/ shunts / regurg / shock
    Dye unstable
    Risk of allergy
    Requires calibration
    One shot estimate
    Time consuming
    Least accurate if low CO
26
Q

Thermodilution

A
  • Invasive
  • Uses Swan catheter
  • cold injectate into R side of heart via PA catheter
    - mixes with blood in RV….thermistor measures temp downstream
  • results averaged over three trials within 10% of each other
  • high CO will have quick dissipating curve and visa versa
  • Patient errors if: arrhythmias / low CO / shunts / regurg
  • Technique errors: wrong injectate / temp / volume / too slow / thermistor defect / thrombus formation / CPB rewarming
  • Advantages: No blood withdrawal
    Easy and quick
    Continuous information can be available
    Quick results
  • Disadvantages: NOT VALID if regurg / shunts
    Least accurate if low CO
    Carrying results in respiratory cycle
27
Q

Flotrac System

A
  • Invasive
  • attaches to Art catheter and uses algorithm
  • calculates SV based on BP/age/gender/BSA/ pulse rate
  • gives us CO / CI / SV / SVI / SVV / SVR
  • tells us if we need more/less volume to patient
    • good for patient outcome / decrease morbidity / less LOS
  • Advantages: easy connection
    Clinically valid
    Automatic
    No experience needed
  • Disadvantages: Needs accurate arterial tracing
    NOT VALID in VADs or TAHs
    Possible bad if IABP
    Arrhythmias cause errors
    Adults only
28
Q

Preload responsiveness

A
  • How likely an increase in preload will help CO
  • SVV: ventilated patients only / normal is 10%
  • PLR: raise legs and see if increase in CO…if not…no fluid add
  • SV fluid challeng: only if other two don’t work / give small vol of fluid and see what happens
29
Q

Doppler and Echo

A
  • Non-invasive
  • Doppler: assess flow velocity / signal and receiver transducer
    - flow of blood scatters waves and measure the feedback
    - used in valve cases for LV function/EF%/valve status
  • Echo: assess aortic diameter
  • results used to get CO
  • Disadvantages: time consuming / bulky equipment / need operator
    Bad for anemia / tachy/ thick walls / sternal incisions
    Tracheostomy / emphysema
30
Q

Thoracic electrical bioimpedence (TEB)

A
  • non-invasive
  • more impedance = poor conductor = air/bone
  • less impedance = good conductor = blood
  • systole = more blood = less impedance and visa versa
  • gives us HR / BP / MAP / fluid content / CO / CI / systolic time ratio /
    SVR / LV ejection time / velocity index / acceleration index
  • Advantages: continuous and non-invasive
    Cost effective
    Quick and versatile
    Wide application
  • Disadvantages: poor accuracy w/
    Sepsis / arrhythmias/ L to R shunt / regurg
    More for critical care…not OR
31
Q

Flow probes

A
  • Electromagnetic induction:
    - calculates flow / mean velocity of flow
    - Flow perpendicular to magnetic field
  • Ultrasonic meter:
    - used on our pumps
    - velocity of fluid to calculate volume flow
32
Q

In summary

A
  • No gold standard…each has its good/bad
  • Never 100% accurate
  • gives us a piece of puzzle….not whole solution
  • must look at total picture

553 - Monitoring & CV Patient (10 decks)

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