Exam 8 - Monitoring CO & Blood Flow Flashcards
1
Q
CO needed to calculate:
A
- Stroke Volume
- Blood O2 transport
- Intrapulmonary shunting
- SVR
2
Q
Normal CO
A
4-8 L/min
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)
4
Q
CO calculation
A
CO = SV x HR
5
Q
Normal SV
A
60-100 ml/beat
6
Q
Factors affecting SV
A
- Preload
- Afterload
- Contractility
7
Q
Normal CI
A
2.5-4 L/min/m^2
8
Q
Normal HR
A
60-100 bpm
9
Q
Normal ejection fraction
A
40-60%
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)
11
Q
SV formula
A
SV = EDV - ESV
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
13
Q
Factors increasing metabolism
A
- Sepsis
- Strong emotion
- Major trauma
- Surgery
- Exercise
- Fever
14
Q
Female vs Male
A
- Females 10% less CO than males in similar body mass
- Up to 45% higher if pregnant
15
Q
Posture and CO
A
- CO decreases by 20% when standing vs supine
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
