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Mechanical Ventilation

HemodynamicMonitoring

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Cardiac Output

• Methods of measurement/calculation

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–

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–

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Dye Dilution

• Need– Catheter in central vein or Swan-Ganz– Arterial catheter– Cardiac output computer– Densitometer

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Dye Dilution

• Technique– Bolus of dye (Cardiogreen) injected while

arterial blood withdrawn by a “syringewithdrawal pump” at steady rate throughdensitometer cuvette

– Densitometer sends a light through bloodto a photocell

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Dye Dilution

• Technique– When dye bolus crosses light source -

more light passes through sample– Densitometer records arrival time of dye

bolus– Computer calculates cardiac output

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Fick Equation

• Estimation

• Assume VO2 stable at 250 ml/min

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Thermodilution

• Most common• Need

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–

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Thermodilution• Set-up

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Thermodilution

• Procedure– Room temperature saline injected fast

(< 3 sec.) through proximal port (RA)– Arrival time of temperature change

detected by thermistor bead near cath tip– Computer calculates cardiac output– Do x 3 then average

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Thermodilution

• Continuous measurement– Special swan-Ganz with thermistor– Heating filament on cath in RV– 1 to 4 sec. bursts of heat (44°C.)– Thermistor detects temp change– Computer calculates– Updates every 30 sec.– Display is average of previous 3-6 min.

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Complications of BTFDC

• Pulmonary artery perforation– Rare– Can hemorrhage

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Complications of BTFDC

• Pulmonary infarction– Cause

•••

– Precautions••••

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Complications of BTFDC

• Air, blood embolus– Cause

•– Precautions

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•

•

•

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Complications of BTFDC

• Dysrhythmias– Cause

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•

– Precautions•

•

•

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Complications of BTFDC

• Pneumothorax during insertion• Valve damage• Infection, sepsis• Endocarditis• Microelectric shock

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Care of the Patient

• Limit patient to supine, < 45°, leftlateral

• Do not use arms, axilla, shoulders tomove patient

• Insertion site inspected & dressingchanged daily

• Never flush catheter in wedge position

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Care of the Patient

• Never advance catheter in PA withballoon deflated

• Change catheter or DC after 72 hrs.• Transducer is very fragile• All readings taken at end-expiration

when on vent• All readings taken with transducer at

RA level

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Blood Gases

• measurement can beintermittent (co-oximeter) orcontinuous (in vivo oximetry)

• Both method use spectrophotometry

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Spectrophotometry

Measurement of light intensities ina specific portion of the light

spectrum

2 methods of operation:Transmission spectrophotometry

Reflection spectrophotometry

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TransmissionSpectrophotometry

• Reduced Hgb absorbs more light than oxyHgb• Photodetector senses amount of light• Transmitted to processor which converts value to

mixed venous saturation

• Blood samplebetween light source& photodetector

• Light passes through

• Different wavelengthsabsorbed

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ReflectionSpectrophotometry

• Same principle astransmission spectr.

• Photodetector &light source onsame side of bloodsample

• Uses fiberopticBTFDC catheter orforehead probes

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ReflectionSpectrophotometry

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Fiberoptic Catheter

• 5 lumens– Distal port– Proximal port– Balloon lumen– Thermistor– Fiberoptic

module

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O2 Transport Studies

• Various measurements & calculationscan serve as excellent indicators ofcardiopulmonary function

• We will look at– Total oxygen delivery– Arterial-mixed venous O2 content– Oxygen consumption– Mixed venous saturation– Oxygen extraction ratio

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Total Oxygen Delivery

• Total amount available for tissueoxygenation

CaO2 = (1.34 x Hgb x SaO2) + (PaO2 x .003) combined with Hgb dissolved

• ml O2/100 ml blood =• CaO2 depends on

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Total Oxygen Delivery

DO2 = CaO2 x QT x 10

• Can see that total DO2 also dependson cardiac output

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C(a-v)O2

• What is between & ? = 20 vol% = 15 vol% C(a-v)O2 = 5 vol% = 5 ml O2 extracted by

tissues from each 100 ml blood

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Oxygen Consumption

QT x C(a-v)O2 x 10

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Point #1

• How much oxygen was delivered in 1 minute?

• How much oxygen was consumed in 1minute?

Normally - O2 delivered > O2 consumed

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Point #2

• Can see that if VO2 is constant,as QT ↓, C(a-v)O2 ↑

=

Fick Equation

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• Normally, if:met. need for O2 ↑Hgb ↓SaO2 ↓PaO2 ↓

• Body will compensate by•↑ QT &/or•↑ O2 extraction from blood → SvO2 ↓ →

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• Healthy body can– ↑ QT up to x– ↑ O2 extraction → SvO2 toand still maintain normal amount O2 totissues (providing cardiac function is OK andtissue O2 extraction mechanisms are OK)

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However -

• If cardiac function is impaired orpatient is critically ill

⇓

Only mechanism now available tomaintain tissue oxygenation is to . . .

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So . . . ..

• If SvO2 monitored & it is ↓, it meansthat:– at least 1 of the O2 transport components

has been impaired (Hgb, SaO2, PaO2,QT) or

– VO2 has ↑

• Must determine which for proper Rx

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Assess . . . .

• Hgb, ABGs• If

– Hgb OK– SaO2 OK– PaO2 OK– VO2 constant

• A drop in SvO2 may be 1st clinical sign!!

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Mixed VenousSaturation

• Normal -

– < 60% = onset of cardiacdecompensation

– < 50% = onset of anaerobic metabolism– < 30% = loss of consciousness, death is

imminent

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Mixed VenousSaturation

• Uses– Assessment of QT

QT ↓⇓

O2 extraction ↑⇓

PvO2, SvO2 ↓⇓

C(a-v)O2 ↑

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Mixed VenousSaturation

• Uses– Management of sepsis (septicemia)

massive vasodilation⇓

regional pooling of blood⇓

↓ venous return, QT, VO2 ↑⇓

SvO2 ↓

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Mixed VenousSaturation

• Uses–

–

–

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O2 Extraction Ratio

• = amount O2 extracted by tissues ÷amount O2 delivered (per 100 ml blood)

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O2 Extraction Ratio

What if? →

⇓Looks OK

1 2

O2ER = 50%

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O2 Extraction Ratio

• = O2 coefficient ratio

• = O2 utilization ratio

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Worksheet

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Intra-Aortic Balloon Pump

• = circulatory assistance• Valuable for patients with severe

cardiogenic shock which occurs whenLV cannot maintain cardiac output

• Happens when > 40% of contractingmuscle mass is lost

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Intra-Aortic Balloon Pump

• IAB catheterthreaded throughfemoral artery intothoracic aorta untiltip is at level of leftsubclavian artery

• IAB inflated &deflated by externalpump with helium

Left subclavianartery

Left renalartery

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IAB Pumping

• Balloon inflated duringdiastole

• Aortic valve is closed• Inflation of balloon causes

blood to be forced– Up into coronary arteries– Into upper extremities– Down into renal arteries– Down into lower extremities

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Effect #1

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IAB Pumping

• Balloon deflated just priorto systole

• Aortic valve snaps open• Aorta contains deflated

balloon & very little blood• As LV contracts → pumps

against low volume, lowpressure

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Effect #2

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Care & Complications

• Anticoagulation therapy to ↓ clotformation around balloon & catheter

• Requires competent aortic valve• Risk of ↓ circulation to lower

extremities if arteriosclerosis• Pressure exerted by balloon may

enlarge existing aortic aneurysm

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Weaning

• Balloon may be set to inflate withevery heartbeat (1:1), every other beat(1:2), 1:3, 1:4, 1:6, 1:8