2330 Module 2: Cardiac Output (CO) (Work in Progress)

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Afterload - Resistance to ejection of blood from ventricles

-Diastolic number on B/P cuff

Atrial Systole -

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Isovolumetric Contraction - Contraction against closed AV and SL valves (AV valves are closed) until afterload is overcome

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Anacrotic notch - Period in AO and Pulmonary wave indicating opening of SL valves and Start of Systole

Ventricular Systole - Begins w/ the A-V valve closure (S-1)

-3 Events: Isovolumetric contraction, Rapid ejection, Slow vent ejection

Atrial Diastole -

Dicrotic notch - Period in AO and Pulmonary wave indicating closure of SL valves and start of Isovolumetric contraction

Isovolumetric Relaxation - After SL valve closure (before AV valve closure) when ventricular muscle fibers relax, and ventricles fill

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- Subphase occurs after the T wave

Ventricular Diastole - Begins w/ SL valve closure (S-2)

- 3 Events: Isovolumetric relaxation, Rapid filling, Late filling phases

Preload - End-diastolic volume: "filling pressure" (LV-EDP)

Concepts of Cardiac Output (CO) (CO = VO2 / A- VdO2)

Stroke Volume (SV) (SV x HR =CO)

The amount the heart pumps out in 1 beat

Greater EDV (End-Diastolic Volume) means greater SV and CO.

Greater time is Diastole results in more blood in ventricles and greater SV

Arteriovenous Difference (A - VdO2)

Difference between arterial and venous oxygen content, and indicates how much blood is removed in the capillaries.

O2 Consumption (VO2)

Amount of oxygen taken up and used by the body per minute

Extraction reserve

Systemic Blood Flow (SBF)

Pulmonary Blood Flow (PBF)

Under normal conditions SBP will equal PBF. With intracardiac shunt, they will not.

Fick and Thermodilution (Indicator Dilution Technique) CO measure the amount of O2 used in body (Uptake by cells)

Factors Influencing CO:

Body size

Age

Posture - CO decreases approx 10% when rising from supine to sitting position

Body Temp - CO Increases secondary to Increased chronotropic state

Anxiety

Environmental Heat and Humidity

Cardiac Output (CO) (CO = VO2 / A- VdO2)

Stroke Volume (SV) (SV x HR =CO)

Arteriovenous Difference (A - VdO2

O2 Consumption (VO2)

Advantages and Disadvantages

Fick CO

Advantages: More accurate in low output states.

Disadvantages: Requires patient to be at steady state.

No O2 administration before MRM procedure

Requires both arterial and venous catheterization

Requires both arterial and venous catheterization

No as accurate in high output states

Measurements are invalid in presence of intracardiac or intrapulmonary shunts

Thermodilution

Advantages: More rapidly performed, requires one person/catheter, no blood needed

Disadvantages: Wires may pose shock hazard, not accurate in presence of shunts

Fick Cardiac Output Calculations:

Fick CO - Amount of O2 used in body (Uptake of O2 by cells)

Arterial O2 content minus mixed venous O2 content

CO = VO2 / A - VdO2

1. Arterial and mixed venous gases are obtained simultaneously at halfway points (2.5 minutes) and then analyzed

2. Arterial oxygen content minus mixed venous oxygen content

A - VdO2 = CaO2 - CvO2

Must be drawn simultaneously from both arterial and venous sites

3. O2 content = (Hgb x 1.36 x %Sat) + (PO2 x 0.0031) in Vol%

Amount of O2 in ml attached to Hgb + Amount of O2 (in ml's) dissolved in plasma

Each gram of Hgb carries 1.36 ml of O2 when full saturated

Normal A - VdO2 range is 3.0 - 5.5 Vol%

A - VdO2 - Varies inversely with CO - (Greater A - VdO2 = Less CO) (Less A - VdO2 = Greater CO)

Greater the flow, the less O2 is removed per unit of blood and the smaller the A - VdO2

(Increased CO = Decrease A - VdO2)

(Decrease CO = Increased A - VdO2)

As blood flow decreases, O2 extraction by tissues will increase and venous blood returning to the heart will be less saturated with O2.

A wide A - VdO2 of greater than 5.5 vol% reflects a low cardiac output

3. Estimated O2 consumption presumed to be relatively constant (Estimated with the following)

BSA x 125ml/min = Estimated O2 consumption in ml/min

Calculate A - VdO2

Divide estimated O2 consumption by A - VdO2 (x100) = CO ml/min

Convert from ml/min to L/min

A - VdO2 Calculation: CaO2 - CvO2

CaO2 = (Hb x 1.36 x SaO2) + (0.003 x PaO2)

CvO2 = (Hb x 1.36 x SvO2) + (0.003 x PvO2)

Examples of O2 content: Slide #39

Examples of CO: Slide #39

Fick (Long Method)

Wt: 185lbs

Ht: 5'8"

Hgb: 15

SaO2: 92%

SvO2: 75%

PaO2: 85

PvO2: 65

HR: 75bpm

BP: 135/85

1st Step: BSA BSA = .00184 x Wt (kg).425 X Ht (cm).725 (numbers after kg and cm are exponents) 1kg = 2.2 lbs 1in = 2.54cm

Convert if needed.

Wt: 185lbs

185 lbs X 1kg / 2.2 lbs = 185/2.2 = 84.09 Wt: 84.09kg

Ht: 5'8"

5'8" = 68in

68in X 2.54cm / 1in = 172.72 Ht: 172.72

BSA = .007184 X (84.09) .425 X (172.2) .725

BSA = .007184 X (6.58) X (41.79)

BSA = 1.97m2 (Shouldn't it be 1.98 since rounded up from 1.975m2 ?)

2nd Step: VO2 VO2 = BSA x 125

VO2 = 1.97 X 125

VO2 = 246.25ml

3rd Step: FCO FCO = VO2/A - VdO2 A - VdO2 = 3.53 vol% (A - VdO2 is )

FCO = 246.25ml / 3.53

FCO = 69.84ml

FCO = 69.84ml X 10 (Multiply by 10 to convert from deciliters to liters) (Deciliters are 1/10 of a liter 1 L = 10 dL)

FCO = 6.9L/min

FCO = 7.0 L/min (Rounded up) (Must be this number to get credit)

(In class they 7.1L/min. Why?)

Fick (Short Method)

Wt: 185lbs

Ht: 5'8"

Hgb: 15

SaO2: 92%

SvO2: 75%

PaO2: 85

PvO2: 65

HR: 75bpm

BP: 135/85

Step 1:

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Swan Ganz

Indications:

-CO (Thermodilution)

-Atrioventricular valvular function

-Venous system function, Volume status

-Venous blood sampling for shunt determination

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Finish slides 59 -76

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Thermodilution

Normal Curve will have

Sharp increaseas after an appearacne time to a peak temperature

Abnormal Curves

Low CO

Slow UPstoke and downslope

Large area beneath curve

Small afea beneth curve

Lower Output than expected may be due to: Higher Output than expected may be due to:

Cardiac Index ()

Stroke Volume ()

Calc: CO/HR

Unit: cc/beat

Normal Value: 30

Stroke Volume Index (SVI)

Vascular Resistance:

Poiseuille's Law