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7. Cardiac catheterization > CO > Flashcards

CO Flashcards

1
Q

CO

A

qty of blood delivered to systemic circulation/unit of time → L/min

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2
Q

Factors influencing CO

A

 Body’s O2 consumption/metabolic rate → correlated with BSA
 Age: ↓CO with aging
 Posture: ↓ by 10% when lying → sitting and by 20% when sitting → standing
 T, anxiety, heat/humidity

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3
Q

Extraction reserve depend on

A

o Nutrient extraction from blood: depend on
 Delivery rate
 Ability of tissue to extract from circulation

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4
Q

How does extraction reserve is expressed

A

o Expressed in arteriovenous difference across tissue
 Arterial blood: 95% O2 saturation (on 1L of blood that can carry 200mL of O2) = 190ml O2
 Venous blood: 75% O2 saturation = 150ml O2
* Normal arteriovenous difference is 40ml/L of O2
 Extraction reserve: ↑ arteriovenous difference with stable blood flow
* ↑ tissue metabolic demand
* Normal extraction reserve = 3 → can extract up to 120ml of O2/L

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5
Q

CO limits

A

 Lower limit: in cardiac dz → CO can fall to 1/3 of normal until tissue hypoxia, acidosis
 Upper limit: largest ↑ → athletes up to 600% of resting CO

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6
Q

Techniques to determine CO in cath lab

A

o Fick O2 technique
o Dilution technique

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7
Q

Fick’s principle

A

Total uptake release of a substance = Bloodflow to organ x arteriovenous [difference] of substance

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8
Q

Determination of O2 content

A

vol%, ml/dL, ml/L
Related to Hb content:
Numerator: measured O2 content
Denominator: theorical O2 carrying capacity of Hb
Volume %: expression of solution concentration
= (Volume of solute)/(Volume of solution) x 100 (ml of O2/100ml blood
Normal Arteriovenous O2 difference = 3-5ml O2/100ml of blood = 3-5vol%

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9
Q

O2 sat equation

A

(O2 content)/([Hb]x 1.34)

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10
Q

Fick O2 method

A

Pulm blood flow: determined by measuring
o Arteriovenous difference of O2 across lungs
o Rate of O2 uptake from lungs

Pulmonary = systemic blood flow in absence of intracardiac shunt
CO = (O2 consumption)/((Arterial - venous O2 saturation)(1.36)(10)[Hb])
O2 consumption → uptake of O2 from room air if measured for lungs O2 uptake
Arteriovenous difference → PA blood (arterial) + LV or arterial (venous) blood sampled
Bronchial and Thebesian venous drainage → ↓O2 content of 2-5ml/L
Calculate O2 content of blood samples and arteriovenous O2 difference with spectrophotometric method (see image)
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11
Q

Limitations of Fick O2

A

o Assume steady state → constant CO and O2 consumption during measures
 Most accurate in low CO with wide arteriovenous O2 difference
 Less accurate with irregular rhythms
o Spectrophotometric method: assume normal Hb for blood O2 saturation
o Improper collection of mixed venous samples (air bubbles)
o Calculation average error: 6% for O2 consumption, 5% for arteriovenous O2 difference, total 10%

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12
Q

Indications for shunting during KT

A

o R to L intracardiac shunt: unexplained arterial desaturation <95% → alveolar hypoventilation
o Le to R intracardiac shunt: ↑O2 content in PA >80%

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13
Q

how to detect L to R intracardiac shunt

A

Oximetry run
Qp/Qs

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14
Q

Oximetry run

A

o Blood O2 saturation/content in R heart: blood samples in PA → RV → RA → CrVC → CaVC
 Shunt detected + localized if ↑O2 content in specific chamber
* Normal max variation in O2 content is <1vol%, PA<0.5vol%
 RA has variable O2 content → receive blood from CrVC, CaVC and CS
* Could vary up to 2vol%
 Depend on [Hb]
o Simplest method: sample CrVC and PA → if O2 saturation difference >8% → shunt may be present
o Step up >7-9%
 CrVC → anomalous PV connection (partial or total)
 Atria → ASD, LV → RA, VSD with TR, anomalous PV connection
 Ventricle → VSD, ruptured sinus of valsalva, PDA with PI, primum ASD
 PA → PDA, AP window, subpulmonary VSD, aberrant CA

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15
Q

Qp/Qs calc

A

o L → R shunt = Qp – Qs (L/min)
o Qp: systemic arterial O2 content can be used if >95%
 If <95%, suspect R to L shunt
 Use 98% for Qp calculcation
o Qs: mixed venous sample should be measured in chamber just proximal to flow

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16
Q

Qp equation

A

(O2 consumption (mL/min))/([PV O2 content (mL/L)]- [PA O2 content (mL/L)] )

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17
Q

Qs equation

A

(O2 consumption (mL/min))/([SA O2 content (mL/L)]- [MV O2 content (mL/L)] )

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18
Q

Where is shunt: O2 step up in PA

A

PDA

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19
Q

Where is shunt: O2 step up in RV

A

VSD

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20
Q

Where is shunt: O2 step up in RA

A

ASD

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21
Q

Flow ratio Qp/Qs

A

: information about degree of shunt
o <1 → R to L shunt
o <1.5 → small L to R shunt
o 1.5-2.0 → moderate L to R shunt
o >2.0 → large L to R, >3 = massive

Qp/Qs= ((SA O2-MV O2))/((PV O2-PA O2))

22
Q

Effective blood flow calc

A

bidirectional shunts
o Flow that would exist in absence of shunting
 Recirculated pulmonary flow: L to R shunt = Qp – Qeff
 Recirculated systemic flow: R to L shunt = Qs – Qeff
 Net shunt = (L → R) – (R → L)

Qeff= (O2 consumption (mL/min))/([PV O2 content (mL/L)]- [MV O2 content (mL/L)] )

23
Q

Limitations of shunt calc

A

o Assume steady state
o O2 step up method: do not consistently detect small shunts
o Depend on O2 [Hb]

24
Q

What is the oxygen content of blood w/ a Hb 15g/dL & pO2 96

A

O2 saturation= (O2 content)/([Hb]x 1.34)

O2 content= O2 saturation x [Hb] x 1.34

O2 content= 0.96 x 15g/dL x 1.34ml O2⁄g Hb
=19.296 ml O2⁄dL of blood

25
Q

What is the principle of the indicator dilution technique

A
  • Adaptation of Fick principle: known amount of indicator
    o Indicator substance injected upstream
    o Average [indicator] through passage of sampling site determined by downstream measure
    o Rate of blood flow calculated
  • Usually: injection of indication into RA → continuous sampling into PA or peripheral artery
    o Flow is calculated by injecting an indicator and measuring its concentration over time
    o Fick O2 method: uses O2 as indicator
    o 2 types: bolus or CRI
26
Q

Indicators used for dilution technique

A

indocyanine green or thermodilution
 Non toxic, mixes completely w blood
 Concentration can be measured accurately/easy
 Cannot be added/subtracted from blood
 Majority must pass sampling site
 Must pass through central circulation (mixing

27
Q

Stewart-Hamilton equation

A

o Integral function = [mean] x time = area under the curve
o Blood flow (Q): determined from amount of indicator injected and area under the curve

Q = I/integral of indicator concentration over time

28
Q

Normal indicator curve

A

Injection of indocyanine green into RA + continuous blood draw from femoral artery
* A: Appearance time → delay prior to initial appearance of dye
o Early appearance of indicator → R to L shunt
* U: Rapid upstroke
* PC: Peak concentration
* D: exponential downslope interrupted by recirculation
o E: extrapolated continued curve if no recirculation
* R: recirculation

29
Q

What does AUC relate to

A

indicate [indicator] over time
o iα to CO → smaller area = ↑CO

30
Q

Indocyanine green can…

A

cause allergic rx and turn patient greenétoxic

31
Q

Conditions causing alteration of peak or distortion of recirculation curve

A
  • L to R shunt: ↓ peak with gradual downslope
    o Early recirculation
  • R to L shunt: early peak prior to primary curve
    o Normal delay is 3-5s after any right chamber injection
  • ↓CO: low, delayed peak + ↑ area under curve
  • ↑CO: early peak + ↓ area under curve
  • Valvular regurgitation: low, delayed peak + ↑ area under curve
32
Q

effect of location of indicator injection relative to sensor

A
  • Farther location of sensor:
    o ↑appearance time and delay peak
    o No effect on area under curve
  • Shunt localization: series of curves w successively more distal injection sites (RA, RV inflow, RV outflow, MPA, PA) until dye no longer appear prematurely
33
Q

Indicator dilution curves for TOF

A
  • Depend on level of PS (changes in CO) and direction of VSD shunting
34
Q

Indicator dilution curves for L to R VSD

A

dye appears after normal appearance time but have prolonged gradual downslope w/o separate recirculation phase after RA
o B-D: sampling in PA → premature appearance of dye with LA and LV injection, but not in ascending Ao
 Localize shunt at ventricular level

35
Q

Indicator dilution curves for R to L VSD

A

dye appears prematurely prior to primary curve (P) after RA and RV injection, but not after PA or LV
o Localize shunt to ventricular level
o Normal and quick rise after ventricular injection

36
Q

Indicator dilution curves for TR

A
  • Attenuated curve with prolonged upstroke and downstroke
  • ↓ CO
  • ↑time of appearance at sampling site
37
Q

Steps for measure of CO w/ thermodilution

A
  • KT in R heart with 2 thermistor located at site of
    o Injection: in CrVC or RA
    o Sampling: in MPA or distal PA
  • Measure known T in bowl before injection → use correction factor
    o Sometimes only 1 thermistor at distal site and injection T is assumed
  • Cold saline injection of known volume and T into venous site through proximal port
  • Sample in PA
  • Curve generated based on T over time
38
Q

Advantages of thermodilution

A
  • No recirculation
  • No arterial puncture
  • Cheap indicator
39
Q

Limitations of thermodilution

A
  • Inaccurate in several situations
  • T fluctuation with respiration
  • Loss of cold btwn KT and measurement site
40
Q

Situations where thermodil is inaccurate

A

o Severe Tr with falsely ↓CO and ↑ area under curve
o ↑CO → overestimate in patient with low CO
o Intracardiac shunt
o Low flow or slow push
o If tip of KT against PA wall
o Correction factor → warming in syringe, KT

41
Q

Hb units

A

g/dL

42
Q

PCV units

A

% volume

43
Q

O2 content units

A

ml/L

44
Q

SV units

A

L

45
Q

CO units

A

L/min

46
Q

cardiac index unit

A

L/min/O2

47
Q

Vascular resistance units

A

dynes-sec-cm-5

48
Q

Woods or Hybrid units

A

mmHg/L/min

49
Q

Plasma volume units

A

ml/kg

50
Q

Intracardiac P units

A

mmHg

51
Q

Central venous pressure units

A

cm of H2O

52
Q

1mmHg =

A

1.36 cm of H2O

7. Cardiac catheterization (11 decks)

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